IAEA-215

PLANT BREEDING FOR RESISTANC INSECO T E T PESTS: CONSIDERATIONF O SE ADOUUS E TTH INDUCED MUTATIONS

PROCEEDING ADVISORN A F SO Y GROUP MEETING ON THE USE OF INDUCED MUTATIONS FOR RESISTANCE OF TO ORGANIZEE TH Y DB JOINT FAO/IAEA DIVISION OF ATOMIC ENERGY FOON I AGRICULTURD DAN E AND HEL DAKART DA , SENEGAL, 17-21 OCTOBER 1977

A TECHNICAL DOCUMENT ISSUED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1978 ADDENDUM TO LIST OP PARTICIPANTS

Dr. P. Anglade I.N.R.A. Centre de Recherches de Bordeaux Station de Zoologie Agricole F-33140 Pont-de-la-Maye France

PLANT BREEDING FOR RESISTANCE TO PESTS: CONSIDERATIONS ABOUT THE USE OF INDUCED MUTATIONS IAEA, VIENNA, 19?8 Printee IAEth n y AustriAi d"b a October 19?8 PLEASE BE AWARE THAT ALL OF THE MISSING PAGES IN THIS DOCUMENT WERE ORIGINALLY BLANK The IAEA does not maintain stocks of reports in this series. However, microfiche copies of these reports can be obtained from INIS Microfiche Clearinghouse International Atomic Energy Agency Kärntner Rin1 g1 0 59 P.Ox Bo . A-1011 Vienna, Austria on prepayment of US $0.65 or against one IAEA microfiche service coupon. CONTENTS

Introduction ...... 1 A.Mick Moor. I d eean Breeding for insect resistance in cotton .....•**...... »...... 5 H. Khalifa Insect resistance in cotton ...... 17 T.P. Leigh Breeding for resistance to insect pests...... 27 Prem Nath crop resistanc insecto et e th n si : An example of induced mutation...... 49 K.J. Starks and E.E. Sebesta Host plant resistanc majoo et r insect Sorghum...... f so 3 6 . N.G.P. Rao, B.S. Rana, M.G. Jotwani La resistance des graminées aux lépidoptères foreurs...... 79 P* Anglade La resistance variétale de la luzerne (Medicago sativa L.) insectesx au . Intérê conceptiot e t programmes nde s relatifs aux aphides...... 5 .8 R. Bournoville Possible advantages of small differences in resistance to aphids...... 91 H.J.B. Lowe In tracing insect resistant plant si n treated technically and economically feasible...... 101 O.M.B, de Ponti Conclusion recommendations...... d san 7 .10

Annex...... 117 List of participants...... 123 INTRODUCTION

A. Micke and I. Moore Joint FAO/IAEA Division, Vienna

To further increase agricultural productio declaree th s ni d first priority objective of national and international efforts in most developing countries. Nevertheless, the means to achieve this objective are disputed among agricultural advisors. There are those who "believe, that existing knowledge only needs to "be transferre necessarfarmere e th th d o dt san y materia financiad lan l inpute sb provided in order to "boost up production "by 50 or 100$. As true as this may Toe for certain areas and for certain farming systems, there are other points to consider and we want to mention a few: 1. Even under primitive farming conditions, the economy of production gains importance as soon as the level of subsistance farming is surpassed. Yield level costd san productio f so n elsewhere determine the product market pric decidd ean e whethe farmee r th affor n rca d inputs for increasing his production or not. The most efficient use of fertilizers, water, energy, under specific cropp- conditiong in determinee havy "b so ma et researchy db , evea t na stag developmenf eo t where these input utilizee sar d onla y yb fraction of the farmers and at levels far below those recommended as optimal. 2. At whatever level of productivity farmers are working, crops will always suffer from damag environmentay eb l stres pathogensd san . It appears to be a general phenomenon that with increased product- ion levels potential hazards increase too, but often one observes a change in pathogen pattern or the development of new pathogenic problems which require researc their hfo r solution. 3. Recent years have seen a tremendous demonstration of the potential to increase agricultural production by genetic improvement of . Many cultivars are being introduced from abroad, and if they turn out to be higher yielding than local ones they will replace them rather quickly. Such introduced havy sma e wida e geographical adaptation insurancethero t n , bu s ei , that unusual stress condition particulaa n si r are yea r causay o rma e greater harm to them than to those cultivars that evolved locally during many generations. Again research will hav tacklo et e eth problems arising. widespreae Th higf o . 4 he yieldindus wideld gan y adapted cultivars introduces another risk, hitherto unknow moso nt t developing countries rise ,whaf th k o calles ti d "genetic vulnerability". remembey ma u leae Yo rth f rust susceptibilit Mexicaf yo n in the Near East and the tungro problems in Asia associated witearle hth y rice cultivar Internationae th f so l Rice Research Institute forgeo t catastrophie t t,th no c Helmine effecth f to - thosporium epidemic on in the USA facilitated by the in- considerat onl f source o yon e malef us eo e sterility asseso T . s the nee genetif do c diversit supplo t d yan appropriate germ plasm is a must. It is obvious that some disease and pest problems are man-made in the sense that they either arise or are aggravated with man's successful efforts to ste p productivitpu y whethe supplyiny r"b g irrigation, increasing mineral fertilizatio usinr n o cultivars w gne . Extensio existinf no g knowledgo et fanners must be intensified, "but cannot be an alternative for agricultural research, the need of which I have tried to illustrate with a few examples.

In this context, one will have to see the activity of the Joint Division d IAEan A O oconcernefFA d witapplicatioe hth f so-calleno d nuclear techniques in agricultural research. This organization is responsible for determining areas of research that could benefit from the application of such techniques, and

FAO/IAEe meane th Th f so A programm manifolde ear provide W . e training through course fellowshipsr so sene W .d expert d supplsan y equipmente W . organize study tours and seminars. We also give financial research support to scientific institutes and help to increase efficiency of research by establish- ing coordinated research programmes. In these, from developing and developed countries cooperate towards achieving objectives which have been agreed upon at research coordination meetings convened at certain intervals (1-2 years).

Of course, we cannot rely upon our own restricted wisdom in determining objective prioritied an s work r ou d therefor ,r an fo s e seekinear advice gth f o e experts and specialists. This also is the frame and the purpose of the present meeting: PAO and IAEA are seeking your advice on a difficult and complex subject. We expect, that by the end of this week we have reached jointly convincing con- clusions, not only about the value of and the need for crop cultivars with im- proved insect resistance or tolerance, but also the available or missing tools for developing such cultivars, the kind of work to be done, the priorities of such work, the organization of such work, the financial support that might be required r reachinfo objectivee gth d eventuallan s e scientistyth d institutionsan s that shoul askee db becomo t d e engage plannea n i d d project. VJhat type of research may be considered? Concerning plant protection against insect pests, the most common and con- ventiona insecticidesf o e l us measure th s e.i Breedin insecr gfo t resistance receives ha d relatively little attentio mosn ni t plant breeding programmese Th . reasons are primarily that the must give priority to yielding capacity d producan t quality. Resistanc microbiao t e l pathogen takes si n into account rather frequently, perhaps because of their more dangerous role in most parts of the world, or may be because of the relative easiness of selecting and manipulat- diseasg in e resistance factors. Insect resistanc coursf eo bees eha n attempted to for, where serious insect problems occurre wile w ld certainlan d y hear more about such programmes during this week. But it appears that in most pro- grammes progress has been hampered by difficulties to identify plant with better resistance or tolerance. In other words, selection using insects in nursera difficuls yi variour fo t s host/pathogee reasonth d san n interactione sar not sufficiently understood to select indirectly, e.g. by chemical tests or micro- scopical examination. Only when adequate selection technique handt a e e ,on sar n looca k deeper intmattee oth d fin whethet rwhao an dt ou td extenran d usable resistance trait e availablsar cron ei p plant germ plasm collection neer so o t d be created by genetic techniques such as mutation induction, alien transfer, chromosomal translocation etc. Here entomological research will be required. Identificatio usablf no e resistance traits, however, requires alsdefine oth - ition of breeding objectives and these cannot be defined without taking into con- sideration other means of pest control. Crop rotation, , crop diver- sification for instance are means to reduce the impact of insect pests and "by this the level of resistance to be aimed at "by the "breeder. Growing cultivars with different developmental patterns often helps to interrupt the insect pest cycle, rathea e b certairn y an i eas dma y ywa n instance plane th tr breedesfo cono rt - tribute to insect pest control. However, this has to be planned in coorperation with agronomists. Another point we should not forget is that resistance to in- sects may be caused by chemical compounds noxious also to man. It would seem obvious in such cases that the breeder should aim at the lowest antibiosis levels that are still effective against insects, rather than higher ones which may be easie recognizo rt handld ean genetin ei c experiments. Otherwise release ,th f eo a resistant cultivar might be prevented by national health authorities. Geneticists today know quite well the extent to which genetic variability createe b n mutagen y ca methode db th d useo s.t san Once told which characters are in need, they could set up appropriate experiments for producing the desired . However generaln ,i knoe ,littlo w wto e abou genetice th t insecf so t resistance. Here woul anothee db r important basic fiel researchf o d mutantd ,an s could provide good experimental tools in such research. On the other hand, ento- mologists have studied quite well the , and epidemiology insectsf o besidet ,bu mentionee sth d insufficient knowledg host/parasitf eo e interaction knot no w y enougma e shon abou potentiae tth l co-evolutio hostf no ? and parasites, once resistant cultivar introducee sar larga t a de scal farmersy eb . Thi anothes si r field that certainly deserves investigation.

This list of topics open for research can be extended and we look forward to your suggestion recommendationsd san active ar u e mosyo s researchersA .f to , there neeo n streso t de b importance y sth ma agriculturaf eo l researc futurr hfo e agri- cultural development. However, at the international scene too often you find that short-term programmes with immediate benefits only receive attention and longer term projects involving technology developmen neglectede tar wane W streso .t s that you should not limit your scope at this meeting towards immediate needs, but include future problem d lonsan g term solution wels sa youn li r deliberations.

The task before us is certainly not an easy one and it may be that soon we realiz inabilitr eou perhapd yan s incompetenc questione answeo th t e l ral s arising frodiscussioe th m mako t ed sufficientlnan y sound recommendations t eve, Bu .nso we expec mako t essentian ea l step forward towards initiating action. The country where we are having this meeting will certainly give the adequate background for our discussion so that we do not get lost in theoretical and purely academic argument keet minsn bu p i d tha tneen i morf ther d o e peopl e ear e ar o ewh . BREEDING ffOE INSECT SBSISTANCE IN COTTON

HASSAN KKALIPA AGRICULTURAL HSSEARCH CORPORATION, COTTON BEADING SLCÎDIQN, SHAMBAT, P.O.Bo KHARTOU, x30 M NOET SUDANH- .

Abstract The importance of cultivated cottons as fibre food an d crop discusseds swa . Llore pest control researc bees hha n conducten do cotton than in any other crop plant. Hie different control measures such as use of chemicals, agronomic and cultural operations and utilization of parasite predatord san s were discusse detailsn di . breedinr Fo g resistant cultivar cooperatioe sth f no the entomologise breedeth d ran essentias ti successfua r lfo l breeding programme. Plant resistance shoul lookee db de upoth s na degre interactiof eo n betwee hoss insece it t nth d plantan t under certain physiological, genetical and environmental conditions affecting both the insect and its host plant. Therefore more studies insece onth plant- t e relationshith carriee y b b o t t dou e par and the entomologists. Breedin jassir g fo bollwor d dan m resistance th n ei Sudan was discussed in details. The characters frego-bract, glabrous plant body, nectariless flower and leaf together with high gossypol conten confey tma r resistanc man, eto y insect cottonn si . The possibilities of utilizing induced mutations in insec hosd tan t plants were discussed.

Cultivated cottons are still competing well with other synthetic fibres and are becoming one of the important crop plant sourca s sa higcookind f eo an h l qualitgoi y protei animar nfo l and consumption. More tha specie0 n3 Soss.ypiuf so m have been identified aroun Worlde dth mainl t ,bu y fou thef undee ro mar r cultivation namely: Gr.hirsutu (mediu. mL staplm- e cottons), G.barbadens (long—stapl. eL e cottons) and the two Old World species, G.herbaceum L. and G.arboreum L. Most of the commercial cultivars throughout the World are selections from Gr.hirsutum. AI most about 35 million ha of cotton are being cultivate ove l Worlde dal rth yieldin d ,an g abou millio8 t5 n balef so fibre aboud milliosan 0 t15 n tons (long cottonseedsf )o e th n I . Sudan the crop makes about 90 percent of the value of all export income. Cotto serious nha s insect problem producinl al n si g countries, and due to crop's economic importance more pest control researc bees hha n conducte cotton o d nothey thaan rn no cro p plant. Therefore, such insect pests losses in yield and damage to fibre quality substantiate the urgent need to solve this problem. A lis 1J2f to 6 specie cottof so n insect publishes swa d (1), and only 15 per cent of them were considered as pests and less than hal thesf fo e wer f economio e c importance distributioe Th , thesf no e insects vary frolocalite mon anothero yt , som thef e considereo e mar d destructive tob mosn ei t World e partth attacd f ,so an k different parts of the cotton plant in varying degrees and at different stages of plant growth. Example thesf so e insects are: American bollworm Heliothis armiaera (Hh). Spiny bollworm lurias insulana (Boisd.) P-ink bollworm Pectinophora~oas.ypilla (Saud.) Cotton jassid Kmpoasca lybica De Berg Cotton Whitefly 3emisiä~tabaci (Genn.) Cotton leaf thrips Galiothrips impurus (Pr.) Lygus Taylorilykua vosseleri (Popp.) Boll weevil Anthomonus grandisSon Cotton leafworm Heliothis virescens (Fab.) Egyptian Cotton leafworm SpodopteraTittoraJLis Boisd. Cotton aphid Aphis gossypii (Glover)« Spider mite vetranychus urticae (Koch.) American lygug sbu Lygus hesperus Knight Cotton Shedder bug Gréontjades pallidus (Hamb.) Flea beetle Podogrica puncticoliis Weise. Stainer bugs Dysdercus spp. Cotton soil termite Microtermes thoracalis sjost. Ihe economic crop loss of these insects depends not only populatioe onth pesf no t attacplane alsth t tn kbu o reactioo nt infestation, stage of plant growth, and duration of the attack» It is also worth mentioning that these insects are naturally regulated by abioti biotid can c factors. 'The abiotic factor uncontrollablee sar , while the biotic factors are affected by the excessive application of . Such complex situation will not allow to produce cotton crop economically. 2. COHTSOL MkASUEES 2ol Chemical controls Chemica insecticidef o e lus adoptes si ovel Worle al d r considereth d dan d co be an essential part of crop protection» Although it is considered as most effective, dependabl adaptabld an e user millionefo t ,bu f so dollars are spent annually in such a practice. In addition to this, excessive use of insecticides has its harmful effect e.g. residues on the harvested crop, hazards to , animals, pollinating insects, increases environmentan i l pollutio killind nan parastif go predaceoud can s insects. Sometimes insects may develop resistance to chemicals and in some cases the appropriate chemical is scarae» 2.2 Agronomic and cultural practices Certain agronomic practices in cotton agroecosystem may chang characteristice eth croe th p f planso d crotan p environment, thus reducing insect pest levels. Such practice includy sma e planting date, crop rotation, plant density, eradication of alternate host plants and other sanitary measures. Examples are the successful contro pinf lo k bollwor Texan mi s (U.S.A adoptiny )b g certain cultural practices, and the increase of mortality rate of leafworm in iugypt by irrigatint no g clover afte (2)y firse Ma r th . f to 'ihe presencr o e alternate host plants near cotton fieldharmfue b y beneficialsr ma lo , because it was found that lygus bugs were attracted to and remained in alfalf strip) a(3 s interplante cotton di n fields, wherea ïanzanin si a growing maize (Ze.a maize) with cotton apparently increased Heliothis damage to cotton (~4). In the Sudan, large areas of dura (Sorghum vulgäre) and groundnuts (Arachis hypogae) grown before cotton supported the populations of Heliothis• It was also found that lubia (Dolichos lablab) was very attractive to moths and "breeding of Whitefly (5)»£a southern U.S.A., prior to 1900, cotton cultivars were susceptible to boll Weevil and the breeders found that rapid fruiting and early matur- ing cultivars could circumvent Weevil attack (4). 2.3 Biological control by parasites and predators» Cotton agroecosyste variea s compled mha dan x predatod ran parasite funa. These predator parasited san s hav beet eno n studied very carefully time theif Th .eo r occuranc appearance th e d th ean f o e associated priminsecf o e et ar importance wels i lt I know. n thae tth preservation of an effective local of such natuiri. enemies can reduc insece eth t pest levels example n parasiteg a eg s A .e ,th , Trichogramm abundans i desere . th asp n tti part southerf so n California. During the growing season this parasite may destroy an average of from 40 to 50 per cent of bollworm eggs,(4). 3. BREEDING EESISTANT CULTIVAES Breeding crop plants resistant to insects is a complex problem, and in most cases the knowledge of the mechanisms underlying plant resistanc inadequatee ear . More information abou interactioe tth n betwee hos e insecd nth t an require e tar bettealloo a dt r wfo r knowledge botr fo h breeder entomologistd san enablo st e the cooperato mt d ean carr effecient you t breeding programmes. wels i lt I known that plant resistanc insecto et s si the more economica highld lan y effective mean reducinf so g damago t e crop plants minimizind ,an g hazard humanso st , animal naturad san l predator». In breeding for resistant cultivars the breeder should take into consideratio life-cycle nth insecte th infestinf e eo , th g stage, the relationships between the insect and the crop plant together with the morphology, physiology and the genetic make up of the plant, and the insect« It is also worth mentioning that resistance developed tparticulaoa permanenbeneficiae e b b r y t insecma no r y to o tl t ma other insects. Example of this is the hairy cotton cultivar synthesized Sudae jassidr th nfo n i , resistanc harbourinfoune d b an o dt ) e(6 g Whitefly (?). Criteria to screen effeciently the breeding material and the knowledge concerning the complex interactions between insects and their host plants are important for a successful breeding programme. Plant resistance is the collective heritable characteristics by which a plant species, race, cj.one or individual may reduc probabilite eth successfuf yo l utilizatio thaf no t plans ta a host by an insect pest (8). I believe that resistance should also be looke ddegree upoth inter-actiof s neo a n betwee s insece it nth d tan host plant under certain physiological, genetical and environmental conditions affecting bothos s insece it ht th d planttan mechanism e Th . s of resistance include oviposition, feeding habit of insect, morphological biochemicad an l characteristic hose th t f plantso « However, such characteristics wil utilizee l b breede e th y dsurveyinn b ri gers ghi m plasm for insect resistance« * Breedin3*1 jassir gfo d resistanc cottonn ei . Breeding resistant cotton cultivars to Jassid attack had started Shamban i t (CBS) sinc earle eth y forties bees ha n t knowI . n that sus- ceptibilit 3assio yt d infestation depende greaa o dt t extene th n to degree of hariness on the leaf (9). It has been demonstrated that hairs of sufficient -length (1.1 mm) and density (6.6 per sq.m) on the leaf lamina confer immunity to jassid attack (9»10). The cotton germ plasm was surveyed for hairiness (6,11,12,13,14), A number of confering hairiness on different parts of the plant "body have "been isolated (Hi» factoy ke a rs showe necessarb wa gene o _ nSh t eH] . yHg d an H/j., J Hz HC , , % developmen e Worlw te Ne r d e founfo s th tetraploi wa hai n f td i o ran d dan the Old World diploid cottons (11). The gene Eg was identified in the wild tetraploid fl.tomentosum (11)» The genes 13 and H^ were also isolate utilized dan "breedinn di g hairy cottons (12)s wa gene . z Th eH necessary for stem and petiole hairs, and H^. for the development of hairs on the upper surface of the leaf lamina. The genes H5 and He were also identified, and isolated from the diploid wild species G.barbadense and G.raimondii respectively (13). The major hairiness genes HI, H2 and HO when present with suitable minor genes backgrounds all produce hairs which will provide virtual immunit jassio yt d attack(lj;. Such typf eo resistanc alsy effectivee ma o b e against other piercin suckind gan g insects. These genes have been successfully transferred n singli d yan combinations to the susceptible glabrous G.barbadense cultivars using the classical backcross method. BAJ 5/57~"and BàJ 7/57 used to be the most promising strains. Unfortunately these strains proved to be below the standard of yield and fibre quality. In addition to this, they were foun harbouo dt r whitefly. Such strain usefue b y localitien sli ma s free from whitefly infestation. The "tough leaf" character which was investigated for possible mechanisa uss ea resistancf mo e against absencJassie th n leaf di eo f hairs was not promising. Some of these lines were tested in a replicated trial and no differences in response to jassid infestation were found(16). 2 BreedinJ. bollworr gfo m resistance. Work on transferring bollworm resistance from G.thurberi and Gr.armourianu susceptible th o mt e cotton cultivar startes swa Shamban di t in194ÏIGr.thurberi resistance was supposed to be due to the hard leathery pe"ricar bolle th G-.armourignmd ,f an o p aromatin a s nha c repell- (15)t en « Families selected from these materials were tested dan no significant differences were found as compared to the controls (16). A long term breeding programme is now being under-taken writee bth y Shamban ri t (CBS transfeo )t characterse rth : frego-bract fg)g (f ---•--'', nectariless flowe lowed ran r -lea f- lamina- (ne» ) ip neine - ? ,ne •• - •>- "T and - —_..__ _ _ _.,__...- _ -.___...._. ..__.. __. objectiv f reducino e g bollworm othed san r insects infestatio alloo n t economir wfo c chemical control. îïectariless; glaadless; nectariless + high gossypol; frego-bract + ^landless frego-bracd ;an higt+ h gossypol isogenic lines together with Acala 4—4 contros 2a l were teste replicaten di d trials their ,fo r performanc bollwormo t s ea s oviposition, larval infestation, shedding of fruiting bodies and damage to seedcotton. The experiment was carried seasono tw r oustfo 1974-7 1975-7d 5an plantd 6an s were subjecteo dt natural infestation. The results indicated that the genotypes homozygous for the genes controlling one or two of the following characters frego-bract; nectariless flower and high gossypol showed significantly lower numbers of deposited eggs (Table 1). It is then apparant that the characters nectariless flowers and frego-bract were less attractive to the adult moths than flowers with nectaries and normal bracts. Usin numbee gth entrf ro y hole givo st indirecn a e t estimate of infesting larvae, it was evident from Table 1 that Acala 4-42 and glandless strai significantld nha y higher numbe entrf ro y holes than the other strains heave Th .y glandlesattace th n ko s strain suggested that gossypol rendered the pericarp of the boll unpalatable to larvae. The distribution of larvae throughout the fruiting period seasono tw e sth respectivelyr ifo s t showI d Figsn ni an e a Th ,l , curves depict that the peak of infestation was in late December and early January. The strain with i'rego—bract and high gossypol showed consistently lower levels of infestation in the two seasons. Acala 4-42 and glandless strains showe highese dth t level infestationf so . The amount of shedding of fruiting bodies coincided with the peak of infestation (Figs. 2a and 2b). Acala 4-42 and glandless strain showed agai highese nth t amoun infestef to sheddind de bu th n gi two seasons. Strains with frego-bract showed the least amount of shedding. The dat seedcotton ao n confirme significane dth t role played by frego-bract and nectariless characters in reducing the damage caused by bollworms infestation. Glandless strains and Acala 4-42 showed the highest percentage of infested locules and damaged seeds ('fable 2). However frego-brac,a t cotton cultiva beed rha n developed that provided an extremely high leve resistancf lo bole th l o weeviet l (21) thit ,bu s variet susceptibls ywa otheo t e r insects suc lygus ha s bug. Another nectariless cultiva developes rwa showed dan d moderate resistanco et fleahopper slightld san y resistan Heliothio tt s spp. (22). Therefore it was possible that nectariless and frego-bract characters may be combined to confer resistance to boll weevil, fleahopper, lygus bug and Heliothis. Such resistant cultivar will also havgreatese eth t utility in cultural, chemical and biological insect suppression techniques« These encouraging preliminary results will direct us to investigate more carefully the problem of bollworms and other similar insect basie th manipulatin f so n s o physiologicale gth , biochemical and morphological characteristics of the cotton plant in rendeo t s unattractiva t ri y sucwa hadule a unfavourabld th tan o et e for the development of any stage of the life-cycle of the insect pest. Isogenic lines with nectariless flowe leafd ran , frego-bract, glabrous plant bodhigd an yh gossypol have been synthesized. These linee sar backcrossed to the commercial cultivars to transfer these characters and restore the genotype of non-recurrent parents.

4. UTILIZATION OP INDUCED MUTATIONS There is no cotton plant, whether wild or cultivated whic completels hi y resistan insecl al o tt pests infestation. Induced mutations, whether gene and/or chromosomal aberrations, on both insect and plant can be utilized for the eradication of crop plant insects and breeding for insect resistance in plants. Through irradation at specific doses one can induce sterility or lethality either to the female or male insectfouns wa dt I .tha t chromosomal translocations coul utilizee db d as dominant lethals for the eradication of boll weevil through a care- fully designed breeding programme (23). If homozygous lines for a number of translocations were mated when the offspring heterozygous for numbea translocationf ro theif o t r en gametec sr ovepe s8 r 9 woul e dh lethal. Therefore, lethal gametes woul producee db d throughout their entire life span. Eradication programmes including genetic manipulation are being directed against bot bole hth l pin e weevith k d bollworlan m (24, 25), Such methods require tha targee tth t insect populatios ni relatively low in number and confined in a specific locality and isolated by geographical barriers naturao therd n ,an s ei l selection. plane Onth t side induced mutation manifesy sma t physiological, biochemical and biophysical characteristics which may rende plane rth t resistan certaio tt n insects difficultiee Th . s encount- deteco t w tho ere these dar e characteristic methode useth e b d do st an in screening the irradiated plant material. RLFERSIJiCES

) Hargreaves(1 "Lis. ,H Recordef to d Cotton Insect -unf so e World". London: Commonwealth Institut Entomologyf eo , (1948. pp 0 )5 (2) Hafez, M. Methods of integrated insect control in cotton. Doc.8. Int. Cotton Advisory Comm. (1972) pp.30-58. (3) Stern, U.M. Interplanting alfalfa in cotton to control lygus bug d othesan r insect pests Procn I . . l'ail Timbers Gongn ,o Scol. Anim. Control by Habitat Manage, ïallahassee, Fia«, Vol.1 1969.pp.55-69. (4) Louis, A.I1., Smith, A.P., "Guidelines for integrated control of cotton insect pests" PaneO PA .Expertf lo Integraten so d Fest Control. (First Session, Rome, 19&7). (1973) PP.69 (5) Ripper, W.E., George L., "Cotton Pests of the Sudan", Their Habits and Control. Oxford: Blackwell Scientific Publ., (1965) 34. 5PP ) Saunders(6 , J.H mechanise .Th hairinesf o m Goss.ypiun si m G.barbadens. 2 inheritance th e- stef o e m hair, .amp. Gott. .Gr Hev. 40 (19&3) 104-116. ) Mound(7 , L.A., Effec leaf to f hai cotton ro n whitefly populations in the Sudan Gezira. Emp. Cott. Gr. Rev. 42 (1965; 33-39. (8) Beck, S.D. Resistance of plants to insects. Ann. Rev. int. 10 — (1965) 207-232. ) Parnell(9 , *.R., Kmp. Cott Corp.. .Gr , Rep. exp. Sta., South Africa (1926/27). (10) Peat, JoE„, Emp. Cott. Gr„ Corp., Rep. exo. Sta., South Africa (1926/27). (11) Knight, R.L., The of jassid resistance in cotton, ïhe Genet.. J . (19521 H2 ,5 d genean ) I 47-66sH . (12) Knight, H.L. ,genetice SaddTh , jassif ,J. o s d resistancn ei cotton. Ill The Kapas Purao, Kawanda punctatum and Phillippines Eerguson group, J.Genet. 5.2 (1954) 186-198. (13) baunders, J.H., Genetic hairinesf so s transferred from G.raimondii to G.hirsutum. Euphytica, 14 (1965) 276-282. (14) Saunders, J.H. mechanise ,Th hairinesf o m Goss.ypiun si m G.barbadens. 3 inheritance th e- uppef o e r leaf lamina hair, Emp. Cott. Gr. Kev. 1 (1965) 15-32. (15) Dark, S.O.S., Emp. Cott Corp. .Gr . Prog. Rep. exp. Sta. Sudan (1952-57). (16) Khalifa Cott, ,Corp.H. . .Gr , Prog. Rep.exp. Sta, Sudan, (1970/71). (17) Brazzel, J.R., Resistance of cotton to pink bollworm damage, Rev. appl. Ent. (1958)6 ,4 . 490. (18) Lukefahr, M.J., Effect of nectariless cottons on populations of three Lepidopterous insects, 5J> (I960) 242. (19) Cross. J.li. Gossypol conten cottof to n seed, Emp. Cott Corp.. .Gr , 19. (1962) 136. (20) Shaver, T.N., Gracia,. J.2L., Gossypol conten cottof to n flower buds, J.econ. Ent. 66 (1973) 327-329. (21) Jenkins, J.H., Parrott, W.L., Effectivenes frego-bracf so s ta a boll weevil resistance characte Cotton ri n Crop SeiI .I (1971) 159. (22) Schuster, M.F., Maxwell, P.G. impace ,Th nectarilesf to s cotton on plant bugs, bollworm, and beneficial insects, Proc. Beltwide Cotton Res. Conf., (1974)«

10 (23) Smith, R.t'., Falcon, L.A., Insect Contro cottor lfo n ni California, Cott. Gr. Rev., £0 (1973) 15-27. (24) Cross, W.H., Biology, contro eradicatiod lan bole th l f nweevilo , r Ann. Rev. Entomol. 18 (1973) 17-46.

(25) Enipling, E0F., Boll weevil and pink bollworm eradication: Progress and plans. Ginner's J. Yearbook,0971)» 23-32.

. I ÏÏUIûBhiH 01»' EGG ENTRD SAN Y HOLLS PRODUCED THROUGHOUT THE: SEASONS, 1974/7 51975/7- 6

No. of eggs Mof Entro . y holes Genotype 1974/75 1975/76 1974/75 1975/76

Acala 4-42 (control) 17 34 72 77 Glandless 12 22 76 77 ITectariles hig+ s h gossypol 8 21 56 59 ITectariless 8 19 46 57 ïrego-brac glandles+ t s 11 18 57 54 i'rego-brac hig+ t h gossypol 9 17 45 45 ±2.4 ±3.7 ±7.1 ±7.4

TABLE II. PLiiObJNTAGU OS IlfiiSOSD LOCUIiS AND DAMAGED Si-EDS AT HAUVLST TII/L x-OR SEASONS, 1974/7 5- 1975/7 6

Infested locules Damaged seeds Genotype % % 1974/75 1975/76 1974/75 1975/76

Glandless 23 25 89 90 Acala 4-42 (control) 22 24 86 87 1'rego-bract + glandless 18 17 85 89 Nectariless 16 19 83 82 1'rego—bract + high gossypol 16 12 71 83 Nectariles higs+ h gossypol 11 13 75 67

11 —————' Glandless strain • -----, Acala 4-42(control) .._._._, Nectariless strain .—_ - ,. - Nectanless* h'igh gossypol strain -••--•—'Frego-bracts* glandless strain gossypol

Dec- Jan. Feb. a Fig. 1- Distribution of larvae weeklyat intervals throughoutthe growing period- season 1974/75

-"Acala-— 42(controt) - 4- strain . __.^ gossypol strain —•—•'Nectariless stra'm

glandless strain _ 5 _.._..,, Frego-bracts +high I gossypol strain *< I

2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 13th 14th

Dec. Jan. Feb. b Fig. J- Distribution larvaeof weeklyat intervals throughout growingthe period , season 7975/76

12 Acalo 4- 42(control ) Glandless strain Nectçriless+high gossypol Nectariless strain Frego-bracts*high gossypol Strain g10 Frego-bracts * glandtess I» strain

IL -C

S

Dec. Jan, Feb. Mar. a Fig. 2- Infested sheddingbud fortnightat intervals throughoutthe growing period.seasons 1974 / 75 (266 plants sample)

Acala 4-42 (control ) Glandless strain Nectariless+high gossypol strain Nectariless strain Frego-bracts+high gossypol strain Frego -brae ts + glandless, s train

23 Dec. Jan.b Fe Mar. Fig. 2-b Infested bud shedding at fortnight intervals throughout the growing period,season 7975/7 5 plants33 ( 6 sample)

13 ïig.J« thres Floweha e) nectarie(A r "base th e u sarouno d the pedicel, and flower (B) is nectariless. Leaf (C) is nectariless and (D) has nectary on the main lowee veith rf no lamin a

Fig.4. Boll (E) has frego-bract and dark glands containing gossypol .glandless i Bol) (F l s

14 Fig.5. Shows healthy seecotton (I) and damaged seedcotton health(J)e Ih . s yha bol; l(G frego-brac higd tan h gossypol, while boll whic) (H glandlesss hi damages ,ha d locales and seedcotton.

15 INSECT RESISTANC COTTON I E N Thoma . LeigsF h Department of Entomology University of California - Davis Davis, California 95616 United States of America Abstract An abundance of cotton germplasm is available to breeders through world collections. This germpoo s beeha ln utilize a limite o t d d extent for disease resistance and agronomic improvement. Insect resistance researc s beeha hn limited althoug receives ha t i h d stronger emphasin i s recent years. Several plant conditions offer resistance to boll weevils, plant bug d lepidopterousan s pests through nonpreferenc d antibiosisean . The most noteworthy resistance characters are extrafloral nectariless, frego bract, glabrous foliag stemd ean , okra leaf, plant gossypol content and other natural chemicals, and other, yet unidentified, characters. The cotton germpool is extensive and of diverse genetic makeup. Some germplass presen it usee b n i dn e tsearc ca mth for r n i mhfo insect resistance. Full utilization of the wild and primitive cottons will require genetic manipulation. The potential value of genetic manipulation is evident in some of the highly improved cultivars used in current production which carry germplasm from triple species hybridization. The valu f inseceo t resistanc s immeasurablei e presen vieth n i ef wo t high rate of use on cotton and the resistance situation.

A wealth of cotton germplasm is available throughout tropical and near tropical regions of the world. Collections have been gathered at centers of research and efforts have been made toward their utilization. Fryxell [1] has reviewed cotton germpool utilization for development of disease resistance and more productive cultivars. He further suggests this germpool remain f immensso e potential valu r futurefo e breeding endeavors. Development of insect resistant cotton cultivars has become a matter of most serious importance in view of the present insecticidal control dilema e lis Th f insect.to mited san s that have become resistano t pesticide extensives i s . Most noteabl f theseo complea s i e f He!iothio x s bollworms that occur aroun worlde th d . Member f thiso s insect genue sar uncontrollabl somn i e e area Australif so Mexicd an a o where their severity has caused termination of cotton production. Areas of the United States as well as other countries are now similarly threatened. Cotton is only one of several endangered crops. Host resistance to insect attack is well recognized in , rice, alfalfa, corn and a of other crops where its utilization is an integral part of production programs. Insect resistance in cotton has received little attention until recent years. Progres developinn si g resistant cotto bees nha n summarize Maxwel d Maxwely b an d J al.t e l[2 l , [3], Durinyear5 e sth g sinc lattee eth r review much progres bees sha n madn i e locating new characters of resistance and in development of methods for utilizatio f knowno n resistant character production si n programs. purpose th r f thieo Fo s report resistanc defines e ei th s a d consequence of heritable plant qualities that result in the plant being relatively less infested or damaged than a susceptible plant without these qualities. Insect resistanc expresses ei severan i d l ways. Painter

17 [4] elected to categorize plant resistance into what he defines as three "mechanism f resistance"o s : antibiosis, nonpreferenc d toleranceean s Hi . approximate definitions are: 1. Antibiosi - Resistancs e that adversely affect e biologth s f o y an insect. 2. Non-Preference - Resistance that adversely affects the behavior of an insect for food, oviposition, and/or shelter. . 3 Toleranc Resistanc- e whicn i e a planh abls i to withstan t e d damage or recover from damage caused by an insect population approximately equa o that l t damagin a susceptiblg e host. My intention is to review the recognized mechanisms of resistance in cottonn theca ne W conside. r their rol programn i e f pesso t managmend tan area f researcso h emphasis neede brino t d g about greater utilization. CHARACTERS OF RESISTANCE Several character recognize w f cottosno o e nar d tha associatee tar d with resistanc type8 o f pestset so . Thes e summarizeear tabln i d . 1 e Som f theseo e characters function against onle pestyon , others against several pests. In a few cases a character that confers resistance to one pest may be associated with greater susceptibility to yet another. Plant characters most commonly recognized as confering resistance in cotton to morr o e majoon r insect pest e fregsar o bract, high gossypol, nectariless, and plant hair condition. Nectariless Cotton normally develops nectar producing glands within the bloom, inside the bracts, at the base of the bracts, and on one or more of the major leaf veins. Nectariless cottons are devoid of the glands that occur on the outside of fruiting structures and on abaxial leaf veins, but produce nectar within the flower. The extrafloral nectaries have been removed by crossing Gossypi urn hi rsutum L. with the naturally nectariless G. tomentosum Nutt. Lukefan Rhyned ran , severa[5]d an ,] TSchuste[6 . al t e r other researchers have reported significant reduction numbern i s f so plant bugd lepidopterouan s s pests through remova f thio l s carbohydrate n researchsourceow r Ou . , utilizing cages s show,ha n reductionn i s oviposition, survival d growt,an h rat y Lygub e s hesperus Knightn I . field experiment e havsw e measured significant reduction lygun i sg bu s number e nectarilesth n i s s plantings compare o isogenit d c nectaried types. This reductio pesn i n t number s beeha sn accompanie y increaseb d yieldn i s . Nectaries e nectarilese remaibloomth th n f i nso s plants. However, since cotton blossoms open only during daylight hour e availabilitth s y f thio s remaining sourc f nectaeo limites i r a tim o t ed perio f eaco d h day whew moth nfe activee e confiden sar ar e W . t that wide f scalo e us e this character could greatly reduce lepidopterous pest number fieldsn i s . This trait should be particularly effective in regions where there are few other sources of nectar or free water. Nectariless cottons have been sufficiently effective against plant bug d lepidopterousan s insect o stimulatt s e interes developmenn i t f o t commercial cultivars. This w includetraino s i t n severai d l privatd ean public Unitee th n i sd State f Americaso . Plant hairs Occurance of hairs on foliar and stem surfaces is common to many crop plants. Their type, length and density is often variable between

18 cultivars. Webster [7] has developed an annotated bibliography on the relationshi f plano p t hair o insecst t resistance cotton I .e pilos th n e conditio bees ha nn user resistancfo d o jassidet s (Empoasca spp.n )i part Africaf so , AsiAustraliad aan contrasty B . , several lepidopterous (Heliothis spp d Trichoplusi.an d hemipterouan ) ni a s (Pseudatomoscelis sériatus (Ruter) and Lygus spp.) pests demonstrate strong oviposition preferenc r pilosefo e cultivars. Brazze Martid an l n [8],. Davial t e s Schusted an ] [9 r [10] have found tha glabroue tth smootr so h condition causes a reduction in pink bollworm, plant bug and boll worm numbers through oviposition nonpreference. While equal number f planso t buge ar s reported by Schuster and Frazier [10] to be more destructive to glabrous tha o pilost n e cotton, oviposition nonpreference reduce e probabilitth d y for development of a resident infestation. The glabrous or near glabrous condition is now included in most U.S. cotton breeding programs. The initial goal was elimination of trash since pilose leaves contribute more trash to mechanically harvested lint. We are now utilizing the near glabrous condition for ovipositional nonpreference by plant bugs, boll worms and budworms. In breeding a glabrous cotton acknowledge ,w e sacrific f resistanco e e on o t e pest in order to gain resistance for another. Breeders and entomologists y nee mako ma t d e suc choica h e and/o o loor additionat r fo k l characters that will provide supplemental resistance to the pest complex. For example, nectari s cottoles y serv charactea nma s ea r that will function against a multitude of pests without increasing susceptibility to others. It may then serve to supplement characters such as glabrous. Otherwise, we must select combinations of characters that complement one another in a particular pest complex situation. The pilose cottons which were formerly utilized for jassid resistance in some parts of the world have been abandoned for more productive, near glabrous types. This change is accompanied by intensive pesticide use. Such changes shoul viewee b d d with alarrate th viet whicn ea i m f wo h pesticide resistanc developings i e . Frego bract Freg a conditio s i o cotton i n n which produce sfloraa l bract thas i t narrowed, strap lik d turneean d away fror bollflorae o th md .bu l This expose fruitine sth g structur deprived ean s insect f desireso d seclusion r thigomotropiso m while feedin r ovipositingo g . Boll weevils, Anthonomis grandis Boh. reportee ,ar Huntery b [11d. al exhibio ]t t ,e t be ha v i oraï nonpreference for cotton with this character through reduced feeding and oviposition and through greater mobility. Leigh, et al [12] report indications of resistance to the pink bollworm, Pectinophora gossypjella Saunders. The frego condition should also enable more effective insecticidal control of insect pests that feed on the squares and bolls through more efficient deposit of insecticides at that site. Parrott et al. [13] and Schuste Andersod an r n [14] obtained more effective contro f bolo l l weevil fregn so o tha norman no l cotton cultivars. They credit improved control to greater insecticide deposit and greater probability of the boll weevil coming into contact with an insecticide through its increased mobility. There are no reports as yet that clearly indicate an influence by this character on beneficial insects and their efficacy. There are, however, reports of greater susceptibility to plant bug injury. The latter is not believed to be related to the frego condition, but rather o somt e gustatory factor tha frege linkes i tth oo t dcharacter . This possibilit undes i y r intensive study needeeffore n b A . y o breat dtma k

19 such a linkage in order to reduce plant bug susceptibility, and thereby, increas e utilitth e f thio y s character. Okra Leaf The okra leaf character of cotton is widespread in wild germplasm. It has not been reported as contributing directly to insect resistance. However ,[15. Joneal ]t se report resistanc bandedwine th o et g white fly, Trialeurodes abutilonea (Haldeman) in two okra leaf varieties bred for an open plant canopy to provide boll rot resistance. The white fly resistance mechanism is not known. This same trait has been suggested s resultina greaten i g r boll weevil mortalit earln i y y summer through exposure of infested squares to the sun after they have fallen from the plant. Okra leaf should also permit better distributio f insecticideo n s to all parts of the plant. Biochemical resistance Cotton plants contai r produco n arran ea f substanceyo s that influence th ee toxiactivit ar o insec t cr o mitd f tan yo e pests. Gossypo amons wa l g the first so recognized by Cook [16], Recently Stipanovic, et al. [17] have prepared an extensive review of research on the pigment glands of cotton with which this terpenoid compoun associateds i d r morFo .e than a decade a group of scientists at Mississippi State University and the U.S. Boll Weevil Research have sought to isolate and identify a number of chemicals that regulate boll weevil behavior on cotton. McKibben, et al. [18] report such compounds may confer nonpreference and/or antibiosis addition I . n t severasa l location e attemptinsar g o isolatt d identifan e y additional chemical agents, generally referred to as X-factors, that cause antibiosis to one or more of the cotton pests. Gossypol: Gossypo cotton's i l s best recognized natural resistanc o insecet d an t mite pests. While this compound has long been known for its toxicity to insect d highesan r animals, discover f glandlesyo s plant McMichaey b s l [19] drew renewe glandee th d f emphasio d e characterus o st . Lukefahr et al. [20] and Seaman et al., [21] have achieved noteable success in breedin o increast g e gossypol conten orden i t o providt r e greater resistance in cotton to bollworms and other cotton pests. The high ossypol cotton f Lukefahso r have provided effective suppressioa ze . H_ f o n ?Boddie) and H_. virescens (F.). Since seed gossypol content greatly limits utilizatio f cottonseeo n s livestoca d k feed, grower acceptancf eo cultivars with this type of resistance is questionable. Discovery of the glandless condition by McMichael brought forth the mucd possibilitan hw needene a df o y sourc f vegetableo e n proteima r fo n and animals to which the glanded seed is toxic. Several commercial or near commercial glandless availablecottonw no e s. Anguar Dr . s Hyef o r our breeding program has moved the glandless character into Acala cottons with agronomic backgrounds competitive with commercial varieties. However, [22Tinge. othed al ]an t ye r entomologists have shown thaglandlese tth s character increases susceptibilit o somt y e common insect pestsn I . addition, Brader, [23], Jenkins et al., [24], Leigh and Hyer [25] report cottons carrying the glandless character are damaged by insects and other animal previouslt no s y peste knowb f o cottonso t n . This greater susceptibilit o somt y e overcom e b pest y sma y breedin b e g glabrous-glandless- nectariless cotton which should provide reduced probabilit f attaco y y b k bollworms and lygus bugs in the San Joaquin Valley of California. Similar

20 efforts may utilize other resistance character combinations in glandless cottons. Of even greater value would be development of glanded cotton plants bearing glandless seed. This would greatly increase the value and utility of the crop without seriously affecting the natural insect resistance provide gossypoly b d . Thipossibilita s i s y since wild cottons exist in Australia (6. sturtianum var. sturtianum and G. sturtianum var. nandewarenis) which posses these characters. FryxeTl [21], reports that while gland e presen e seesar th dn i tcotyledon f thesso e plants, gossypo t depositeno s i l d until they germinate. Since this condition occurs in 26 diploid Gossypium of very wild type it would certainly require complex genetic manipulation for use in any program of commercial breeding. There is a possibility of locating the glandless seeded-glanded plant conditio geneticalln i n y more advanced cottona f i s diligent search were made. While breeding efforts of this type will not be easy, success would be highly rewarding. X-factors: What appeabiochemicae b o rt l compounds that provide resistanco et one or more insect pests are reported by several scientists. These have sometimes been referred to as X-factors. Several have been isolated, tedioue th n otheri s e processar f isolatios o majorit e t th ye d e an ny ar to be chemically defined. Mckibben and others in the research team at Mississippi [18] have identified an array of behavior modifying chemicals from cotton that elicit responses frobole mth l weevil. Non f theseo e t beeye hav ns ea utilize a hos n i td plant resistance program. Similar studies of this magnitude have not been carried out for other cotton pests nor for other crop-pest groups. Their future value is not known. Lukefah [27. al ] t have r e isolated unidentified chemical fractions occuring within cotton squares tha e toxit ar o Helipthit c s boll wormd san to pink bollworms, Pectinophora gossypiella Saund~They have elected to name some of these "Heliocides" in recognition of their toxic action on bollworms. There are some indications that these compounds are terpenoids and tannin or tannin related compounds. Wilson and Wilson [28] have obtained extracts from both the boll wall and the combined seed-lint fraction of cotton bolls that are toxic to the pink bollworm. They have not yet isolated the toxic components. Dr. Anthony Waiss (personal communication extractes )ha d tannins from cotton tha e highltar y toxic to lygus bugs. BREEDIN R RESISTANCFO G E Complexity of the inheritance involved in the several insect resistant characters of cotton is expectedly variable. Schuster and Frazier [10] have proposed as few as one gene for bract type (frego vs normal) throug r gossypofo 3 h lr pilosity fo conten man5 s a s ya o . t Transfe f somro e characters appeara simpl e b o est task. However, some desirable resistant characters may be linked to undesirable traits. This appear true b f freg eo o st o wherein plants with this characte more rar e attractiv o lygut e s bugsoccurance Th . f appareneo t linkages muse tb confirmed. Where linkages of desirable and undesirable traits occur an effort should be made to sever them to make the desirable traits available to breeder useabln si e form. Glandless seeds would greatly enhanc cottoe value th eth f neo crop and provide hungry peoples with much needed proteine samth e t timA . e ew can not tolerate use of the glandless plant if it will surely require intensive insecticide use to be productive. Transfer of the primitive gossypol free seed conditio commerciao t n l cotton n interestina s si f i g

21 complex challenge. Since commercia hirsutu. G_ l m cottons have been developed through complex interspecific genetic manipulation, further utilizatio f theso n e methods shoul givee b d n serious consideration. Small increments of resistance may individually be of little value. However, several small increments may have significant impact on a pest. While small increment resistance is difficult to locate and evaluate, it e neglecteshoulb t no d breedinn i d g programs. PLANT RESISTANC PESN I E T MANAGEMENT Plant resistanc o insectt e uniqus i s full s n i thai et i ty compatible with other methods of insect pest management. Resistance may slow the rat f populatioeo n increas a particula r efo r pest, providing better synchrony between the pest and its parasites or predators. It may also resul greaten i t r exposur a pes o naturaf et o l enemies sorghumn I . , r examplefo , resistance will caus greenbuge th e , Schizaphis graminumo t , locate in a more exposed position on the plant which leads to greater parasitism. Studie f hosso t plant resistance-beneficial insect inter- actions in cotton are few, particularly with respect to cause and effect. Schuster, et al. [29] and others report reductions in numbers of some beneficial insects in response to selected resistant characters. They have not reported reductions in effective parasitism or prédation. In n researcow r ou e havhw e found significant reductio e numbeth f n o i rn big-eye predatorg bu d s associated witnectarilese th h s characte f cottonro . We have not determined whether this is related to the nectariless condition o reducet r o d abundanc f preyo e . There a reductiodoe appeat e b sno o t r n in big-eye g efficiencbu d fieln i y d plot f nectarileso s s cotton. Wherein resistance result reducen i s d pest number t shouli s d enhance e impacth f culturao t l controls suc wintes a h r crop destruction. Some form f antibiosiso e recognizesar s resultina d greaten i g r sensitivity n inseca f o t specie o insecticidesst e fregTh . o bract conditio alss ha no been associated with more effective use of insecticides against boll weevil d bolan sl worms. Host plant resistanc a recognize s i e d effective tool in pest management. It has been used intensively in some field crops. Current pesticide resistance in insects indicates the need for strong focus on this element of pest management for cotton. DISCUSSION Plant characters that convey resistanc cotton i e o insect n t pests are recognized and are being bred into commercial varieties. We now have useable resistanc majoo t e r insect pests e glabrouTh . r smooto s h leaf character offers resistance to plant bugs, bollworms, and pink boll worms because the adult females find a smooth leaf undesirable for egg laying. e nectarilesTh s condition reduces number f lyguso s bug wels a ss a l lepidopterous pests by depriving them of a source of food. High gossypol cotton presents resistance to pests through its toxic action. Germplasm with as yet unidentified characters of resistance has been located. The g resultlayineg e g sar nonpreference , form f antibiosiso r varioufo s s pest othed san r form f pesso t suppression e naturTh . f theseo e sources mus e identifiedb t . Identification of resistance mechanisms is helpful to the breeder and the entomologist in their research programs and in development of resistant cultivars. However, to the farmer the mechanisms of resistance are of little significance if they work. Progress in development of useable resistanc e sak th f identificationeo r e fo e helshoul b p u dt no d e Th . massive available cotton germpool contains a wealth of . This relatively unused material mus e screeneb t d evaluatedan d . When

22 necessary genetic manipulatio d complean n x program f breedinso g shoule b d utilize mako t d e resistant germplasm availabl o productiot e n programs. Progress in developing resistant cotton needs careful coordination betwee e scienceth n s along with educatio f scientistso n , politicians and farmervalue th f thio eo st s too programn i l f managemento s . Plant resistance needs teams of researchers to place resistance in the position of first line of defense in pest management. It also needs the unique individual wit n understandina h f genetio g c manipulatio o brint n g desired traits into useable form. Plant resistance research is tedious and labor intensive e resultth t e highl,bu sar y rewardin durabilitn i g y of pest control.

REFERENCES ] FRYXELL[1 , PAU . GermpooLA l utilization: Gossypium ,casa e history. U. S. Dep. Agric., Agric. Res. Serv. ARS-S-137 (1976). [2] MAXWELL, FOWDEN G., Plant resistance to cotton insects, Bulletin Entomol. Soc. Amer 3 (1977).2 , 199-203. [3] MAXWELL, FOWDEN G., JENKINS, JOHNIE N., PARROTT, WILLIAM L., Resistanc plantf eo insectso st Advance^ Jj . Agronomyn i s (1972)^ ,24 , 187-265. (Academic Press, NY). ] PAINTER[4 Insec, H. . t,R resistanc cron i e p plants, Univ. Presf so Kansas, (1951). ] LUKEFAHR[5 , MAURIC RHYNE, EJ. , CLAUDE, Effect nectarilesf so s cottons on populations of three lepidopterous insects, J. Econ. Entomol, 53 (1960) 242-44. [6] SCHUSTER, M. F., HOLDER, D. G., CHERRY, E. T., MAXWELL, F. G., Plant bugs and natural enemy insect populations on frego bract and smooth- leaf cottons, Tech. Bull. 75, Miss. Agric. and Forestry Expt. Sta., (1976). [7] WEBSTER, JAMES A., Association of plant hairs and insect resistance: An annotated bibliography, USDA, ARS, Misc. Publ. 1297 (1975). [8] BRAZZEL, J., MARTIN, D. F., Pink boll worm resistance in cotton, J. Econ. Entomol, 52_ (1959), 385-90. [9] DAVIS, D. D., ELLINGTON, J. J., BROWN, J. C., Mortality factors affecting cotton insects . ResistancI : f smooteo nectarilesd han s character Acaln si a cotto o Heligthint s zea, Pectinophora gossypiella and Trichoplusia ni.. J. Environ. Quality, £ (1973), 530-3?; [10] SCHUSTER, MICHAEL F., FRAZIER, JAMES L., Mechanisms of resistance to Lygus spp. in Gossypium hirsutum L., Proceedings: Conference on Host Plant Resistance to Insects and Mites, EUCARPIA/OLIB, Wageningen, Holland, (1976), 129-35. [11] HUNTER, ROBER , LEIGHTC. , THOMA LINCOLN, SF. , CHARLES, WADDLE, A. . ,B BARIOLA, LOUI , EvaluatioSA. selectea f o n d cross sectio cottof no n r resistancfo e bolth l o weevilet , Arkansas Agric. Expt. Stn. Bull 700 (1965). [12] LEIGH, T. F., HYER, A. H., RICE, R. E., Frego bract condition of cotton in relation to insect populations, Environ. Entomol., 1_ (1972) 390-91. [13] PARROTT, W. L., JENKINS, J. N., SMITH, D. B., Frego bract cotton and normal bract cotton; how morphology affects control of boll weevils by insecticides Econ. ,J . Entomol. 6 (1973),6 , 222-25. [14] SCHUSTER, MICHAE ANDERSON, F. LInsecticida , E. . ,R l efficacn yo insect resistant cottons, J. Econ. Entomol., 69 (1976), 691-92.

23 [15] JONES, J. E., GLOWER, D. F., MILAM, M. R., CALDWELL, W. D., MELVILLE, D. R., Resistance in upland cotton to the banded-wing whitefly, Trialeurodes abutilonea (Haldeman), Proceedings, Beltwide Cotton Product. Res. Conf., National Cotton Council, Memphis, TN, (1975), 98. [16] Weevi, COOKF. . l,0 resisting adaptation cottoe th f nso plant. S . ,U Dept. Agric. Bur. Plant Indust, Bul 8 (1906)8 l . [17] STIPANOVIC, ROBERT D., BELL, ALOIS A., LUKEFAHR, MAURICE J., Natural insecticides from cotton (Gossypium) In ACS Symposium Series, No. 62, Host plant resistance to pests, (19777^97-214. [18] MCKIBBEN, G. H., MITCHELL, E. B., SCOTT, W. P., HEDIN, P. A., Boll weevils are attracted to volatile oils from cotton plants, Environ. Entomol (1977S I . ) 804-06. [19] MCMICHAEL, SCOT Hop, TC. i cotton ,a sourc f cottoeo n seed fref eo gossypol pigments, Agronom (1959)_ 51 . yJ , 630. [20] LUKEFAHR, M. J., HOUGHTALING, J. E., CRUHM, D. G., Suppression of Heliothis spp. with cottons containing combination f resistanso t characters Econ. ,J . Entomol. 8 (1975)6 , , 743-46. [21] SEAMAN, FRED, LUKEFAHR, M. J., MÏÏBRY, T. J., The chemical basis of the natural resistance of Gossypium hirsutum L. to Heliothis, Proc. Beltwide Cotton Production Res. Conf., (1977), 102-03. [22] TINGEY Glandles, LEIGHHYER, , H. F. M. . . ,. A ,W T s cotton: susceptibility to Lygus hesperus Knight., Crop Sei 1_5_ (1975), 251-53. [23] BRADER, L., La faune des cottonniers sans glandes dans la partie méridionale du Tchad, II.-Les chenilles de la capsule. Coton et Fibres Tropicales, 24_ (1969), 333-36. [24] JENKINS MAXWELL, e comparativ N. , LAFEVERTh . G. , ,J . N. ,F . H , e preference of insects for glanded and glandless cottons. J. Econ. Entomol. 9 (1966),5 , 352-56. [25] LEIGH, THOWTS F., HYER, ANGUS H., Susceptibility of glandless cotton to attack by Diabrotica beetles, J. Econ. Entomol. 64_ (1971), 319. [26] FRYXELL, P. A., A revision of the Australian species of Gossypium with observations on the occurence of Thespesia in Australia (Malvaceae), Australian J. Bot. 13, (1965) 71-102. [27] LUKEFAHR, M. J. STIPANOVIC, R. D., BELL, A. A., GRAY, J. R., Biological activity of new terpenoid compounds from Gossypium hirsutum agains e tobaccth t o budwor d pinan m k bollworm. Proc. Beltwide Cotton Production Res. Conf. (1977), 97-100. [28] WILSON, R. L., WILSON, F. D., Laboratory diets for screening cotton r resistancfo o pint e k boll worm, Cotton Grow. Rev (1974)_ 5J . , 302-08. [29] SCHUSTER, M. F., LUKEFAHR, M. J., MAXWELL, F. G., Impact of nectariless cotto n planno t bugd naturaan s l enemies . Econ,J . Entomol. (1976)9 ,6 , 400-02.

24 Table 1. Some recognized genetic forms of resistance in cotton to insect and mite pests. Mechanism of resis- tance and potential percentage pest population suppression is indicated where known. Insec d Spidean t r Mite Pests Resistance Anthonomis Heliothis Lygus Spp. Pseud, Tetranychus Empoasca Trialeurodes Pectinophora Character grandis spp. Keurocolpus seriatus spp. spp. spp. gossypiella

Freg% 90 oo t brac 0 6 t insect- non- icide preference coverage susceptible susciptible Nectariless % 50 o t 0 2 33 to 60% 35% 35% 40% antibiosis antibiosis antibiosis antibiosis antibiosis Glabrous 60% 35-50% unknown 20% non- non- antibiosis resistance non- preference preference preference Pilose preferred preferred preferred variable antibiosis High gossypol 50% 35!« antibiosis antibiosis antibiosis unknown antibiosis X-factors antibiosis antibiosis antibiosis antibiosis Okra leaf insect- insect- icide icide coverage coverage unknown Red color non- preference Oviposition 40% suppression unknown Plant bug suppression unknown unknown

25 BREEDING VEGETABLE CROPS FOR RESISTANCE TO INSECT PESTS Dr.. Prem Nath FooAgriculturad dan l Organizatio Unitee th f dno Nations o Nationac/ l Horticultural Research Institute, Ibadan, Nigeria

ABSTRACT Breeding Vegetable Crops for Resistance to Insact Pests. The paper reviews the work done on resistance of various vegetable crops (excluding and sweet corn) to common insect pests (excluding mites differenn )i t countries. Result n sourcso resistancf eo o meloet n aphid, striped an d spotted cucumber beetles, squash bug, squash borer, pickleworm, red pumpkin beetle, fruit tly in different cucurbits; to maggot and aphid in cabbage; to aphid in spinach; to fruit and shoot borer and stem borer in brinjal; to jassids in okra o jassid;t , bean weevil, mexican bean beetle, potato leaf hopper, melon fly in different beans; to aphid, pea weevil o lean peat i fd ;an miners , flea beetle, fruitworm, Drosophila in tomato have been high-lighted. Genetic basis of insect resistance has been reported to be monogenically dominan n muskmeloi t o melot n nn i aphi d an d pumpki watermelod an n o fruit n t fly, whereas, additive gene action have been reported for resistance to both striped and spotted cucumber beetles and squash bug in squash. In interspecific crosses of muskmelon with wild melon 2 pairs of complimentary gene e reporte sar involvee b o t dr resistanc fo d e fruio t t fly. Maternal influenc s alseha o been indicaten i d intervarietal crosse f squasso r resistancfo h spotteo et d cucumber beetle. Breeding methods involving conventiona wels a ls la induced mutations have been discussed.

INTRODUCTION During recent years interes vegetabln i t e productios nha increased rapidl resula s a yf greate o t r appreciatioe th f no food value of and of the place of vegetables in /horticultur developinn i e g e countriesth f o e On . serious problems facing modern vegetable cultivatioe th s i n

27 attac f insecto k diseasesd an s e importancTh . f inseceo t pests in relation to this group of crops which demands intensive culture cannot be ignored* It is difficult to estimate the losses e serioucauseth y b ss insect pest n differeno s t vegetable crops, but enormous losses have been indicated in various reports while information e completelsar y lacking from many developing countries. During 1951-60 in the United States alone insects caused an average annual loss of over $185 million to vegetables and an additional $100 millio controe morr th o ns spen er wa lfo t (8). cenr pe t I0 nlos 10 Indiay fruisb o t t0 , 6 fly, Dacus cucurbitae Coq. alon s beeha en estimate differenn i d t cucurbit d coulan s d e controlleb t no d satisfactoril y othean e ry b yth mean d an s efforts were directed towards breeding resistant varietie, ?70( 71 s, 73, 74). With insecticidal use a group of trops like vegetables, which demand very frequent harvests and consumed raw or cooked within a relatively shorter period unlike grains, pose problems of residual toxicity. Furthermore, the resistance of some common insect pest o somt s e insecticide s addeha s de proble th mor o t em of insect control. Under these circumstances insect pest resistant varieties offer satisfactory control, avoi cose th dt f insecticideo e growerth d o furthet san s r avoid residual toxicity hazardconsumerse th o t s . Relatively more contributions have been made in plant breeding r diseasfo e resistanc s comparea e o breedint d r insecfo g t resistance which has received relatively less attention of the plant breeders. Ther e occasionar e s where plant breedinr fo g insect resistance takes priority over breeding for yield or quality characters. Painter (80) gav n accouna e f plano t t resistanco t e insects as applied to breeding vegetable crops. REVIE F LITERATURO W E Work done on resistance of vegetable crops to insect pests seem havo t s histora e f abou o yx decades si t e presenTh . t review on evaluation, genetics and breeding for insect resistance would limit itself to common vegetables excluding, potato and sweet corn. Earlier, Bailey ('9), Nath (66 Stoned )an r (100) have reviewee th d work don breedinn eo g vegetable crop resistancr sfo inseco et t attac Natd an kh (71 ) agai,73 n reviewe wore th dk donn o e cucurbitaceous crops.

28 Oacurbitaoeous crops. AB early as in 1944t Ivanoff (39) reported that the P. to P cantaloupe lines had different shipping qualities with varying resistance downey,mildewo st , powdery tnildew melod ,an n apnid larvae alsth d ,Diaphane an o f o efurthet s o Hi . rasp report s) indicate (4042 , ,41 d aphid resistant rouskmelon varietie gives sa n ni Table 1. and the techniques of evaluation. Another tea workersf o m , Hall, associatePaintee th d ran Kansat sa s State University, Manhattan worked on the resistance of cucurbits to striped and spotted cucumber beetle squasd san h bug. Sources, mechanism, biochemical basid san genetics of resistance in squash, muskmelon, cucumber and were studied 1T$, 86 , .81 Othe , 80 r , researc79 , 78 h, centre Unite34 (10e , th ,33 n dsi States have also reported resistanc cantaloupef e o 104) » 51 ,, squas 30 aphio st , (6 dh

to stem borer (13), cucurbits to squash borer (2), watermelon to aphid &2) ; pumpki squaso nt (^08)g h bu squasd ,an pickleworo ht m (15). Chamblis Joned san s (l?) gav accounn ea chemicaf to genetid lan c basi insecr sfo t resistanc cucurbitsn ei . Indian I authoe ,th r initiate wore resistancn dth ko cucurbitf eo d re o st pumpki IARIe n Delhth bettlw ,t Ne a fruid i ey an durin ifl g 1962 sourcee .Th f so resistance were isolated and utilized in bottlegourd, spongegourd, ridgegourd and squash as given in Table 1 (61, 63, 64, 65, 68, 69,84). During 1967, the author initiate differenda t scheme, 'Evaluatio cucurbitf no resistancr sfo inseco et t pests' at the University of Udaipur and financed by the Indian Council of Agricultural Research. The results are indicated in Table 1 (82). At the Indian Institute of Horticultural Besearch, Bangalore, another project on 'Breeding for insect resistance in cucurbitaceous crops was started during 1969 (85) as a follow up of the previous scheme and it continued up to 1975 when it was merged with the PL-480 Project No. A7-CB-455 £3.). During this period, hundreds of lines of muskmelon and its related sp., pumpkin, watermelon and bittergourd were evaluated for resistance to red pumpkin, beetle» These lines-wer« further screened for resistance to fruit fly (85). No appreciable source of resistance to fruit fly obtaines wa rauskraelon di relativ s it t nbu e CucumiG africanu fairls swa y resistant

29 to this pest highlA . y resistant sourc obtaines wa fruio et y pumpkin fl tdi n (2.3), which was profitably utilized, in breeding a resistant variety, Arka Suryamukhi (76) and genetic basi resistancr sfo e studied (77) .pumpkie Somth f eo n lines were fairly resistan pumpkid re o t n beetle (^5). authoe Th r observed that more tha percen0 n6 t commercial cro locaf po l melon,

j^itrullus colocynthis was damaged by fruit flyf- Bacus sp. in Nigeria.

Tomato thin I .s crop studies were mad resistancn eo leao et f miner, Liriomyza

munda. Frick (48,107,1.12) fleo ;t a beetle (.31, 132) fruitwormo ;t , Heliothis zea (Bod-die) (l6, 26, 27); and to Drosophila Q,01,IE). The interesting work by Pery and Cuthbert (27), who observed Lyeopersicon hirsutum Humb. & Bonpl. and L. jqrsutum f.glabratura C. H. Mull, as resistant to fruitworm, indicated that since these were crops-compatible with L. esculentum Hill, it was possible to

transfer the resistance factor in the cultivated varieties. It was further indicate thesy db e authors that sinc hirsutu. eJL glabratur. f m s alsnwa o resistant to tobacco flea beetle (ll.2) and carmine spider mite (99), it was possible to

incorporate resistarce to more than one insect species in one genotype.

Oniont More emphasis was laid on resistance to thrips. Sources of resistance were obtained, caus mechanisd ean m studie d suitablan d e varieties dveloped (11, U,35, 44, 45,46,52,53, 57,90,91,94,106, 103).

J3eans. An appreciable amount of work has ";iean reported in different bears. Literatures of interest on insect resistance are lima beans to jassid in Puerto Rico (4); Vici Lathyrud aan weevia pe Australin o sli t a (?)j dwarf bean beao st n weevil in Mew Zealand (l9)> beans to mexican bean beetle (2l); beans to

potato garded .leaan f) nhoppe 59 bea / melo o Unite9 ne t r£ (36y th nfl n d)i States; d beanan Agromyzo st a phaseolj Mauritiun .i s (60)« .Pea. Work on insect resistance in this crop was dealt with regard to pea aphid (2Çweevi a 97), pe , 55 o Etielll;o t t @-03 d an a ) ; zinckenella (20) mostly dealing with source of resistance and varietal differences.

30 Okra. Jassi reportes serioude wa th s da s pesokr* Inditoi n ai a (66). differencA e in varietal respone» to jassid attack was observed and fruit of the resistant line was found to have strong prickly hairs and was highly susceptible to tue most serious yellow vein mosaic virus (62). Spinach. The spinach variety Manchuria was reported as resistant to aphid as early as in 1920 (98). Cabbage thin I .s crop sourc resistancf eo isolates ewa resistand dan t varieties reporte cabbagr dfo e maggot, Hyluna brassica , 110)58 d , an e 56 (Bouche , 54 , )(3 for aphid 0.09). Turnip. The turnip variety Petrosky was reported to be resistant to root maggot (25),- Later resistanc aphio et alss dwa o observed (5). Brinjal. In India, fruit and shoot borer. Leucinodes orbonalis Guen and stem

borerf Euaophera perticella. Rag. were reported to be most serious pest of egg plant (66). Varietal difference with regard to its resistance T*as observed in cultivated Solanum melongena lines but appreciable source of resistance was indicative only in wild Solanum sp. (1GB). The variety Annamalai was reported to be resistant to aphid (95). . Thi beet s no ncro s takepha extensivelp nu y except that resistanco et fruit fly was reported (l). Amaranthusamaranthue th f o e sOn . line observes swa havo dt e high field resistanc grasshoppeo et Ibadat ra Nigerian ni .

GENETIC BASIS OF INSECT RESISTANCE Good evidence upon the genetic basis of resistance comes from studie f hybriso d populations between resistan d susceptiblan t e plants. According to the experimental results so far reported in vegetable crops genetie ,th c basi f inseco s t resistance b y ema classifie followss a d : Monoqenic control. The resistance of muskmelon, Cucumis mel meloo t o n aphid, Aphis qossypi s reporte wa ie governe b o t d d bsingla y e dominant gene (38» 41) e toleranc.Th f muskmeloeo o t n western biotypes of Aphis qossypii in breeding line LJ 90234 . 371391 (inbre . P 5 f froo d m India governes )wa singla y b d e

31 dominant gene (12). Inheritance studies of fruit fly, Dacus cucurbitae resistanc n pumpkini e , Cucurbita maxima cultivar Arka Suryamukhi showed that the resistance was controlled by a dominant gen r (77)F e . Similar studie n water-meloi s n indicated thae th t resistance to fruit fly was governed by a single dominant gene Fwr (49). Additive gene action. Nath and Hall (79, 81) reported that the Cucurbita pepo cultivars Royal Acorn and Early Golden Bush Scallop were resistant to Diabrotica undecimpunctata howardi Barber and that the inheritance of resistance was mainly due o additivt e gene effect n anotheI . r repor Acalymmn o t a vittat. F a Nath and Hall (8Q) observed that the inheritance of plant resistance to the beetle was mainly additive in and the resistanc s partiallwa e y dominant over susceptibility wore Th k . on Cucurbita pepp revealed thae resistancth t o squast e h bug, Anasa tristis was a genetic character controlled by at least 3 gene gend an se action appeare e additivb o t d n naturi e e (10). Complementary gene action. In an interspecific cross between resistant Cucumis callosu susceptibld an s e Cucumis s wa mel t i o revealed that the susceptibility to frui.t fly was governed by two pairs of complimentary genes (18, 96 >.

Pleiotropic effect wheae Th t . varieties resistan purpld o hessiat t ha y e nfl

colouration (89). Also, solid stra resistancd wan y werfl o steet w msa

correlated among segregating wheat populations (89).

Maternal influence. While studying inheritance of resistance to Diabrotica

undecimpunetajnowardi in C. pepo, it was concluded that the resistance was

mainly additive gene effect but a high degree of resistance was inherited when the maternal parent (in the cross between resistant and susceptible

varieties) was resistant, and the resistance was inherited to such a degree

tha t i coult utilizee db plana n di t breeding programme (81).

While working with tomato for resistance to fruitworm, Heliothis zea,

Pery and Cuthbert (27) reported that the antibiotics factor present in

Lycopersicon hirsutum Humb Bonpl& . . and_L. hirsutu . mf glabratu . MulH . mlC appeare inheritee b o t d d recessively.

32 SOURC INSECF EO T RESISTANCE. In view of relatively less occurrence of biological races and less marked host specificity in insects, a plant breeding programme for insect resistance has to be handled separately from that for disease resistance. It seems necessary to continue search for resistant strains until all available germplasm are carefully surveyed. genera o Thertw e lear source genef so resistancer sfo : ) thos(l e provide variabilite th y db y withi croe nth p species, ) varietie(i s from original hom insectf eo , (ii) varieties from centre greaf so t insect occurrence, (iii) varieties from area greatesf so t morphological diversity. centr) (a originf eo . (b) secondary centre of or?*"vn (iv) through induced mutations ) thos(2 pl'-nn ei d an t species closely relatecroe th p o dt species .

Som thesf eo e points woul illustratee db d further elsewher thin ei s paper. However, the studies made by Khandelwal and Nath (50) as shown in Figures 1 and 2 with regard to resistance of watermelon to fruit fly indicates that the resistance gen locates ewa d froaree greatesmth f ao t insect occurrenc possibld ean y froe mth secondary centr originf eo .

BREEDIN INSECB GFO T RESISTANCE. Incorporation of resistance genes into a commercial variety depends on the available knowledge of genetics of the crop and on the maintenance of an insect population with whic resistance hth testede b y casn e I ma beetle.f eo aphidsd san , plantseedlintestee e e b th th n t dsa ca g stag savo et e time. Pure line breeding. This method has been profitably used in self-pollinated crops lik cross-pollinaten e i okrd beansd an aan a ,pe d crops like muskmelon, watermelon, pumpkin, squash, bottlegourd or calabash, riugegourd, spongegourd, and longmelon without any depression observed 0^2). This breeding procedure has been well-illustrated in developing fruit fly resistant pumpkin variety, Arka Suryamukhi (76).

33 Hybridisation. With the genetic knowledge available on insect resistance in

vegetable crop s discussea s d previously t i woul, necessare "b d o employt y hybridization o transfet r single, multipl r additivo e e genes into commercial varietiee th n i s

advanced filial generations majoe Th r . achievemen s expectei t d through jnter specifie

hybridization where wild species are donors of genes for insect resistance. In musk-

melon Cucumis rnelc? where gene for resistance could not be obtained in the cultivated

species, Cucumis africanus was found to be fairly resistant to fruit fly (85).

Similarly, Cucumis heptadactylis was fairly resistant to red pumpkin beetle (85).

Evaluatio f Solanuno m melongena line s indicateha s d that resistanc o fruiet d an t

shoot borer was probably possible through related Solanum sp. (105).

Backcross method. With monogenic inheritance available for melon aphid in cantaloupe (41 ) , for fruit fly in pumpkin (77) and in watermelo t i woul ) e possibl9 b d (4 n o utilizt e e backcross method for incorporating resistant gene in commercial varieties. . In crops where resistance was dominant and the hybrids were being commercially grown, it was possible to use it for the best advantage. In watermelon, the F (between resistant and susceptible) showed pronounced resistanc o fruit e y (50)fl t . Multiple crosses. In order that fruit quality, yield ar.d resistanc o insect e t preferrably pesma t e incorporateb y e on n i d geno type, it may possibly involve number of parents to achieve desired results, . There have been many report t induceo s d mutation n vegetabli s e crop r characterfo s s other than insect resistance. Literatur mutation o e n breedin f vegetablo g e crops for resistance to insect attack is meagre. It seems to intensive effororganisen a n i t d progra mads o mexploiwa t e e possibilitth t y f achievino g insect resistance genes preliminare Th . y studiey b s the author and his associates at IIHR, Bangalore, have indicated varietal differences for resistance to jassids in the M.. and M~ population f okro s a (dry seed irradiate gammR K a0 6 d o t wit 5 5 h rays) e Mo aphit th ,_ population i d f muskmeloo n n (30-4 gammR K 0 a e Mo rays)aphit th Q d population i dan ; f watermeloo n n (dry seed irradiated wit 0 K5 hR gamma rays). This indicativwa s e that

34 there was a great potential in this approach for resistance genes. However, it was indicated that one needs an efficient screening method to isolate potential resistance genes. Another dimensio f thio n s approac e compulsioth s i h n i n particular cases where no useful resistance genes have been obtained so far. It is particularly applicable in case of muskmelo o fruit n t fly f brinjao , o fruit l t and. shoot borerf o , tomat o fruit o t borer (Heliothis artnigera) f locao , l melon (colocynthis o fruit )y fl t

and others where useful source of resistance has not been obtained. Further

in cases where one or two sources have been located in nature, it would be desirable

to obtain more sources of resistance through mutation breeding. There is no reason

to believe that increase in available sources of resistance could not be obtained,

by extende f induceo de researcus d e mutationsth n ho .

It is evident that very little experience has been gained in the use of

induced rnutations in resistance breeding against insect pests but the prospects

of this approach are great. Important improvements in horticultural crops can

be expected.

. VI CONCLUSION.

Since interest in insect resistance of vegetable crops started more than

hal a centurf somo yag e wors beeha kn don majon o e r insect s pestsbeyoni t I .d this paper to discuss the results of various experiments made by each group/

individua differenn i l t countries, however t i seem, s earl drao yt w reliable conclusions. A few thorough searches for resistance has been made and little is

known about its nature and inheritance. We need more informations on host-

pest interaction - causative factor and its mechanism so as to help inject resistance breeding programme« The knowledge of the genetics of resistance is insufficient for efficient

breeding programmes either by conventional methods or by . However,

studies have shown that the Mendelian segregation has led to the identification

35 of major gene d thaallelee san th t r resistancsfo e were dominant over thosr fo e susceptibility in number of instances except in some where it was found to "be additive or complementary gene action or recessive* Thus it is expected that majorit e induceth f type yo d th e mutation f o involvin e "b y sma g major genes identifiee b o t d radiatee easilth n yi d host populations. Further mutation breeding provides scop developinr efo g increased numbe sourcef ro innecf so t resistance.

Withi lase nth t decad concentrateo s r eo d efforts were mad develoo et p insect resistant vegetable varieties e succes th seemet i d f havo ,so an t d e

rested largely on the availability of enough of host germplasm, the development of efficient screening methods, the screening of huge gcrmplasm from various sources trainew followe fe interese e th dth y d b f plan o t t breederd san entomologists. However, most of these achievements are credited to individuals/ teams mor stata lesr o e n nationar so eo l leve d lacke lan assistance dth y an f eo international cooperative research programme to make a desired headway in this

field of research which is so vital to the vegetable crop production.

REFERENCES

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38 43. Jardine, J. T,, .et al.. A new cantaloupe, Texas Resistant No» 1, resistant to melon aphid. USDA Report on Expt. Stas. 1945 (1945) 39. 44 .Fromme d . ResistancJardineD an , . r T , . J ,onioo t e n thrips. USDA Rpts n Agro . . Expt. Stas. 1936 (1937. 55 ) t . al..e Jardine45 , . T. Resistanc . J , onioo t e n thrips. USDA Rpts. on Agr. Expt. Stas. 1943 (1944) 25, 26. Emswellerd . an , JonesBailey 46 . . A. L F Thrip. . . H ,S S ,, s resistanc e onionth n i e. Hilgardi 8 (1934a ) 213-32, . 47 Field studie f Thripo s s tabaci Lind, with special reference to resistance in onions. Jour. Econ. Ent. 28 (1935): 678-80. 48. Kelsheimer, E. G. Tomato varietal resistance to leaf minor attack. Proc. Fla. State. Hort. Soc. 76 (1963) 134-135. 49. Khandelwal, K. C. and Nath Prem. Inheritance of resistance to fruit fly in watermelon. Canadian J. Genet. Cytol. (1977) in press. 50. Khandelwal, R. C. and Nath Prem. Evaluation of the genetic stocks of watermelon for resistance to fruit fly. Sabrao Jour. (1977) Submitted. . d TobaH Resistanc . an . . 51 H Kishaba ,Bohn, W . N« G . ,o t eA , Aphis gossypii in muskmelon, Cucumis melo. J. Econ. Entomol. 64 (1971) 935-937. . Mcleod52 . F Som . G ^e example f varietao s l resistanc f planto e s o insect t attack . J Econ. . Ent (19336 .2 ) 62-67. 53. Macleod, G». F. Plant varietal resistance to insect injury, èornell University Agr. Expt. Sta. Ann. Kpt8 4 . (1935) 100. . Mahoney54 . Wha H e plan. th C t , t r d shoulbreedefo an o n d d ca r e vegetablth e growers. Breedin r insecfo g t resistance. Proc. Ohi. GrowVe o . Assoc9 1 . (1934) 57-59. . Maltais55 . ResistancB . J , f somo e e varietiee f th peao s o t s pea aphid, IIlinoi i Kalts i p a . Ontario Ent. Soc. Ann. Rept 7 (19366 . ) 40-45.

56« Mathewman, W. G. and Lyall, L. !!. Resistance in cabbage to the cabbage maggot, Hylema brass!cae (Bouche). Canad. Entomol. QQ (1966) : 59-69. 57. MsUghan, F. 2. and Macleod, G. F. Farther studies of onion varieties and onion thrips. Econ. . Eritomoï 9 (19362 . ) 335-39

58^ McColloch, J. W. The resistance of plants to insect injury. Kansas Sta. Hort. Soc. Bien. ÎJpt. JH (1924) 196-200.

59, McParlane, J. S. and Rieman, G. H. Leafhopper resistance among the bean varieties. Journ. Econ. Enbomol. 36 (1943) 639.

60« Moutia. A. Resistance of beans to Agromyza phaseoli Coq. Mauritius Dept. Agri., Div. Ent. Rpt. .1944 (1945) 14-19. Port Luis.

39 61.. Nath, Prem, Evaluation of cucurbits for resistance to the red pumpkin beetle, Ii963flalacpphor) n:a j'oyeicolli— : sQuart . Rot. (Hort) IARI, New Delhi

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63. Nath, Prem. Evaluation of cucurbits for resistance to fruit fly, Daeus cucurbitae. Quart, ïïpt. (Hort.) IARI, New-Delhi (1963. 12 )

64» Nath, Prem. Observations on resistance of cucurbits to the fruit fly. ) (1964. J HortInd(2 .1 2 ), 173-75.

. Nath65 , Prem. Resistanc pumpki d f cucurbitre o e e th n beetleo t s . Ind . HdrtJ . . 21 (1) (1964Î 77-78.

66. Nath, Prem. Breeding for insect resistance in vegetable crops. Ind. J. Hort. ) (19644 d an ) 3 206-212( 1 2 .

67» Nath, Prem. Varietal resictanc f cucumbereo , muskmelo watermelod an n e th o t n striped moumber beetle. Ind. J. Ent. 27 (3) (1965) 304-309.

68. Nath, Prem. Hultiple resistance to insect pests in G, pepo._ Rajasthan Agric (19666 . ) 27-30.

. Nath69 , Prem. Varietal resistanc f gourdfruie o e th to t s fly. Ind . HortJ . 3 2 . ) (l (1966) 69-78.

. Nath70 , Prem. Cucurbits: Problem remediesd an s . Agric. Agro.-Industr , BombayJ. . . 2 (6) (1969) 26-31.

. Nath71 , Prem. Breeding cucurbitaceous crop r resistancfo s o insect e t pests. SABRAO Newsletter, Japa 3 n(I97l ) 127-134.

72. Nath, Prem. Breeding techniques in cucurbitaceous crops. SABRAO Seci Congress. Ind. J. Genet. 34-A (1974) : 1228-31. 73. Nath, Prem. Breeding of cucurbitaceous crops for quality, j'ield and resistance o diseaset insecd an s t pests. Third Intn. Symp. Snb~trop. Trop. Hort. 1972. Vol . Improv1 . . Hort. Mecl. Plants (1976) -14-54. 74. Nath, Prem. Vegetables for the Tropical Region. Low-priced Book Series No. 2, Indian Council of Agricultural Research, New Delhi (1976).

75. Nath, Prem and Dutta, 0. P, A note on the improvement in roundmelon. Ind ) . (l97lHortJ (l . 8 2 .) 55"5C. 76. Nath, Prem, Dutta 0. P. and Velayudhan, S. Breeding pumpkin for resistance to fruit fly. SABRAO Jour.. 8 (1976) 29-33.

77. Nath, Prem, Dutta, 0. P., Velayudhan, S. and Swamy, K.R.ÎI. Inheritance of resistanc pumpkinn i o frui t ey fl t . SABRAO Jour (19768 . ) 117-19«

. Nath78 , PreHalld man , C.V. Resistanc f cucurbio e t seedling o cucumbet s r beetle feeding. ASHS Vege . Improv. News 3 (l96l) 34« 79. Nath, Prem ar;d Hall, C.V. Inheritance of resistance to the spotted cucumber "beetl n Onmrbiti e a pap . IndL o . J Genet. (19633 2 . ) 337-341.

40 90.» Hath, PreHalld man , C.V. Inheritanc f resistanco e e stripeth o t ed cucumber beetle in Cucurbita pepo L. Ind. J. Genet. 23 (1963) 341-345« » Nath81 , PreHalld man , C.V. Genetic basi r cucumbesfo r beetle resistancn ei Cucurbita £ep_o. Proc. Amer. Soc. Hort. Sei 6 (19658 . ) 442-45.

fi.2. Nath, Prem, Khandelwal, R.C Buttad . P Evaluatio.an . 0 , f cucurbitno r fo s resistance to insect pests. ICAR Scheme Ann. Kept. 1967-68. Univ. Udaipur, India (1968).

3.3- Nath d Prasad ,. an Pre G Breedin d Pal. . mB an V ,. ,A g cucurbitaceous vegetables for resistance to insect pest - PL 480. Project Ho. A7-CH-455. IIHR, Bangalore, India (1976.)

. Hath84 , PrerThakurd . an nEvaluatioR . IT d pumpki, re r nfo n beetle resistance n gourdsi ) (1965.4 d Indan ) . 3 330-39HortJ ( . 2 2 . «

8.5. Nath, Prem and Velayudhan, S. Breeding for insect resistance in cucurbitaceous crops. IIHR, Bangalore, India. Ann. Rpts (1971-75). 86. Novero, E. S. et al. Interactions of the squash bug, Ana&atritis, to six varieties of squash (Cucurbita sp). J. Econ.Entomol. 55 (1962): 912-19 . Painter87 . ResistancH . R , f planteo o insectsst . Ann. Rev. Entomol 3 (1958. ) 267-90

. Painter88 , R .

41 97. Searls, E. M. Resistance of to aphids. Wis. Agr. Expt. Sta. Bul. 425 (1933) 94-95. . Smith 98 Breedin. B . ,L g mosaic-resistant spinac noted an hn o s malnutrition Truca V . k Expt a Bul 1 .(1920)St 3 » . . Stoner99 . ResistancK . ,A f Lycopersicoeo n speciee th o t s caramine spider mite. USDA, ARS, Production Research Rpt. No. 102 (1968) 9. 100. Stoner, A. K. Breeding for insect resistance in vegetables. Hort. Sei. 5 (1970) : 76-79. 101. Masond . MethodC Stoneran . . ,H K f selectin. o s,A g tomatoe r Drosophilfo s a resistance Amer. J . . Soc. Hort. Sei. 94 (1969) 396-400. 102 .. Ottod ResistancE an Stoner . Mason B , . C K. . . H ,,A o t e Drosophila oviposition in field plots of two tomato breeding lines . AmerJ . . Soc. Hort. Sei. 97 (6) (1972) 795-796. 103. e possibilitUferTh . ,M breedinf o y g Bruchus resistant peas. Bodenkultu (19482 r ) 28-35 (P.B.A 22O1: 9 .1 ) Halternn 104Va . . ,F Cantaloupe s resistan mildeo t aphidsd an w . Ga Expt. Sta. Ann. R^pt 0 (1948.6 . )66 105. Vjjay, 0. P., Nath, Prem and Krishnaiah, K. Breeding brinjal for quality, yield and resistance to pests. IIHR, Bangalore, India Ann. Pepts. (1974 to 76). 106. Wakeland . ,C Resistanc y certaib e n onion varietie onioo t s n thrips. Idaho Agr. Expt. Sta. Bul 0 (1936.22 . )32 107. Webb, R. E., Stoner, A. K., Gentile, A. G. Resistance to Leaf Miner I.ycopersicon i s n Accessions . Amer.J . Soc. Hort. Sei (19716 .9 ) 65-67. 108. Webster, &. L., et_ al^. Resistance of pumpkin to squash bug. Wash. Agr. Expt. Sta. Bul. 435 (1943) 38-44. 109 .al. Resistanc Uebisteret L. cabbageR. of e, aphidsto s . Wash. Agr. Expt. Sta. Bul. 455 (1944) 36-42. (PoB.A. 16 : 1142).

lltX Whitcomb, T .'J. .ControD f cabbago l e maggot (cabbage resistan e cabbagth o t t e maggot). Mass. Agr. Expt. Sta. (Rpt. 1945-46) Bul (19466 43 . ) 33-43. I GL d Painter Uiseman . an . . InteractionH. R Hall V . . . R B ,C , , s among cucurbit varieties and feeding responses of the striped and spo^ted cucumber beetles. Proc. Amer. Soc. Hort. Sei 8 (196l.? ) 379-84»

11.2. Wolfenbarger . VariationA . D , n leai s f mino fled an ra beetle injurn i y tomato varieties . J Ecou. . Entonol (19669 5 . ) 65-68. 113. Wolfenbarger, D. A. and Sleesman, J. P. Resistance on common bean lines to the potato leaf hopper. Jour. Econ. Entomol. 54 (1961) 846-849.

42 TABLE 1. SOME DISECT RESISTANT VEGETABLE VARIETIES.

CROP RESISTANT VARIETIES INSECT RESISTED REFERENCES r Resistant Varieties 1. Squash Royal Acorn, Striped and spotted cucumber Hal Painted lan r (Cucurbita pepo L.) E, G. Bush Scallop beetles (Acalymfaa vittatd an . aP (1968), Natd han D. unde cjj.jpunctata howardii Barber) Hall (1963). Royal Acorn, Squas (Anaag hbu s tristis DeGeer) Hall and Painter Butt emut (1968), Nevero et aj (1962)

Butternut Squash vine borer Painter (1958)* (Melittia cucurbitae) White Bush Scallop, Summer Crookneck» E. P. Straightncck, u> Butternut Striped cucumber beetle , (l96lBreta] i ).s t Royal Acorn, Red pumpkin beetle E. G. Bush Scallop (Aulacophora foveicollis L.) lîath (1966)

Pumpkin Arka Suryamukhi Fruit fly (Cucurbita maxima (Dacus ^ucurbitae Coq) (1976) Dach}"

.Cucurbit0 ( a rooschata Green Str'ped Cushaw, Duch] Dickinson, Large Sweet Squash vine borer Howe (1949) Cheese, Sweet Potato , Kentucky Field Squasg hbu Eichmann (1945).

3. Cucumber Nappa 63 Striped and spotted cucumber (Cucuinis sativusL») beetles ITat Hald an h l (l96l) Ohio MR-1? - do - VJiseman et al (1961) TABLE 1 Contd.

CROP RESISTANT VARIETIES INSECT RESISTED REFERENCES

4. Muskmelon Smith's Perfect, Cuban Melon aphid (Aphie Ivanoff (1944) (Cucujnis rnelo L_.) Castillian, Rockey Dev;, gossvnii Glov.) Texas Resistant No. 1 Homegarden Gold Cup 55, No. 6 Stripe d spottean d d Nath and Hall (l96l) cucumber beetles Heart Gol

7. Ridgegourd (Luffa acutangula) Pusa Nasdar Red pumpkin bettle Nath (196/5)

8. Bottlegourd No. 28 Red pumpkin beetle Hath (1964) (Lagenaria siceraria No. 29 Red 'pumpkin beetle Nat h1966; )(1964 (iTol.) Standl.) and fruit fly. 9. Roundmelon (TincLa) Fruiy tfl (Praecitrullus vulgaris) Arlca Tinda (tolerant) Nath and Dutta (1971)

10. Okra (Abelmoschu.s Hairy resistant line Jassids esculentu Moench. sL ) (Ehipoasca devastans) Hath (1963) Tabl (contd.e1 )

CROP RESISTANT VARIETIES INSECT RESISTED REFERENCES 11« Onion (Allium cepa) Sweet Spanish Onion thrip (Thrips MacLeod (1933) tabaci JL. ) White Persian -do- Jonel (1934a t e_ s ) . Cabbag12 e Early Jersey Cabbage maggot Whitcomb (1946), ( Wakefield (Hylemya brassicae Matthewman and Lyall (1966) var. capitataj Red Dutch Bouche) McColloch (1924) and Cabbage root maggot Mahoney (1934) . Bea13 n Wade Mexican bean beetle Painter (1958)* (Phaseolus sp.) Kentucky Wonder Melon fly Holdaway (1940) Wild Lima Bean Pod borer Bailey (1938) . Turni14 p (Brassica campestris Petrosky Root Maggot Fairchild (1938) var. râpai . Spinac15 h Spinacea oleracea Manchuria Aphid Smith (1920) 16. Brinjal (Solanum melonqena) Annamalai Aphid Sambandan (1975)

Source7 /§ resistancf so e 17. Beans Potato Leaf hopper, McFarlane and Rieman (1943) Wolfonbarged an r Sleesman (1961) Bean thrip Gui (1945) 18. Pea Pea aphid Searles (1933) Maltais (1936) Gardiner (1946) 19. Celery Tarnished plant bug McLeod (1935) 20. Lettuce Lettuce root aphid Dünn (1960) Tabl 1 (contd.e )

CROP RESISTANT VARIETIES INSECT RESISTED REFERENCES 21. Solarium sp. Myzus persicae (Sulzer) Macrosiphum euphorbiae Radcliff d Lauean e r (Thomas), Empoasca f abae (1968) (Harris) 22. Tomato Leaf minor (Liriomyza Kelsheimer (1963) Lycopersico. sp n munda Frick) Webb et al (1971), Wolfenbarger (1966) Flea beetle Gentile and Stoner (1968) Wolfenbarger (1966) Fruitworm (Heliothis Canenday (1969), zea Boddie) Fery (1974) Fery and Cuthbert (1975) Drosophila Stone d Masoan r n (19692 «7 ;

Fig 1 .Worldwis e distributio f watermelono n germplasra evaluated dan e centrth f sourco e f resistanco e o fruit e t fly. Fig. 2 Distribution of indigerious watermelon germplasm evaluated and the centr f sourco e f resistanco e fruio t e t fly.

47 CEREAL CROP RESISTANCE TO INSECTS IN THE UNITED STATES: AN EXAMPL INDUCEF EO D MUTATION

Kenneth J. Starks and Emil E. Sebesta Scienc Educatiod ean n Administration, U.S. Departmen Agriculturf to e Departmen Entomologyf to , Oklahoma State University Stillwater, Oklahoma United State Americf so a

Abstract CEREAL CROP RESISTANCE TO INSECTS IN THE UNITED STATES In the United States, entomologists and plant scientists are coop- erating in the production of varieties of cereal crops (corn, wheat, and sorghum) that have commercially effective resistance to key pests. Active researc progresn i s hi plann so t resistanc Europeae th o et n corn borer, southwestern corn borer, corn earworm, corn rootworms, greenbug, sorghum midge, Hessian fly ceread ,an l leaf beetle. Plant resistance importann a had sha t rol wheareducine n ei th t d chinc e stean gth g mhbu sawfly to minor pests. There are deficiencies of programs in the U.S. For example, collections of cereal crop germplasm are large, and most have not been adequately evaluated. Induced mutation research could be highly usefu specifir lfo c objectives transfee Th . greenbuf ro g resistanc examplewheaen o a t fro s e ti m ry .

Until recentl Unitee th n dyi States plant resistanc insecto et s has not had as much emphasis as plant resistance to pathogens, largely because of highly effective insecticides. Also, the typical entomolo- gist, unlik plane eth t pathologist littls ,ha e exposur plano et t breed- ing durin academis ghi c understandabls trainini t i o gs e thae tth small amount of research that has been done with induced mutation for pest control has been directed mainly toward diseases, not insects.

49 In fact uniquU.St e no ,th .this n ei i s regard 197n I . 2repora n to research throughou worle tth d containe cro7 2 lisda pf to varietie s developed through induced mutations for disease resistance, none had been developed for insect resistance (1). Later, we will return to induced mutations and mention a recent success that gets insect resist- ance for cereal crops through the starting gate, but we entomologists must travel at a faster pace if we are to take better advantage of available techniques for a proven control method-plant resistance to insects. Luginbil 196n i l 9 stated that host plant resistanc "ideae th s lewa method of controlling insect pests", and estimated a return of $300 to producers for each $1 invested in research on plant resistance to insects (2). impressivn Thia s si e return. Other investigators have stressed the advantages of plant resistance in comparison with other methods of control. For example, plant resistance is generally compatible with other method controlf so . sharn Thii s psi contras situatioe th o tt n for two other methods, contact foliar insecticides and beneficial in- sects. Also, the built-in nature of plant resistance gives protection, whether needed or not, thereby, freeing growers from any concern rela- tiv technologicao et l aspects suc timins ha dosagd controgan a f eo l agen therdirecd o n t an s ei t cos growerso t e latteTh .considero rtw - ations make plant resistance important to both developed and developing countries shoult integran i a d e db ,an l parpesa f to management scheme but frequently is not. There is one aspect of plant resistance that should have special mention wito d .ho t foreseeablThi s sha e changes in agricultural practices due to the need to reduce energy consumption. totae th lAbouf o energ% t4 y consume U.Se th 197.n n i di uses 4wa o dt produce agricultural products and more than half of this was used to produce corn, wheat, cotton soybeand ,an s (3) .same Thesth e e ear four export crop importssl oi tha r tthed fo ,helan y y palspa o help

50 feeclothd dan e peopl mann ei y countries reduco T . amoun e eth f to energy use cron di p production, farmers will increaso likelt y ytr e yields on fewer cultivated acres and will turn more to minimum tillage. Bumann ti y cases this solution will increase insect problems, especi- ally with pests that shelte plann ri t residues morf I .e insecticides must then be applied, that would at least partly cancel the energy sav- ings from minimum tillage. Alternative methods of control such as plant resistance must therefor increaso t emphasize e ee b ar r eo e w f di even maintain present production. In fact, the yield potential of cereal crops in the U.S. cannot be realized unless the crops are protected from insects. Estimates of insect losses are by nature imprecise. However, on the basis of published surveys, technical advisors in the Science and Education Administration recently estimated that insect U.S e pestth .n si wer e responsible for an annual 12% production loss of corn (maize), a 5% loss of small grains, and a 9% loss of grain sorghum. The value of lost productio controd nan l costs would certainld di greatee yb e w f ri not already have some use of plant resistance in commercial crops. Corn, wheat, and sorghum, the crops that we are considering here, hav insecf mixeo ea t tdlo pests encompassing ovespecies0 r10 . For- tunately, mos localizede tar , secondar sporatir yo c pests onld ,an y about ten are generalized, key pests. We will discuss some of these pesty ke relation si commerciao nt l plant resistance. Although rice is an important cereal crop in the U.S., there has been relatively little effort to develop resistant varieties in the U.S. It will therefore not be discussed.

EXAMPLES OF PLANT RESISTANCE TO INSECTS resistance Th denn ei tEuropeae corth o nt n corn borer (Ostrinia nubilalus exampln a s ) i effectivf eo e resistance found localln a o yt

51 introduced pest. It is also an example of resistance that is present in the vegetative stage of the plant but not in the shedding and later stages factn I . , resistanc e leaf-feedinth o et g first generation larvae has been relatively easy to find in corn, but resistance to second-generation feedincollae th d sheatn gro an mors hi e elusive. somr Sfa oe hybrids sho degrewa tolerancf eo e (abilit stano yt da moderate infestation) to the second generation, but only inbred B52 has shown a high level of antibiosis (4). Efforts are now underway to simplify screening procedures so both first and second-generation resistance can be combined in the same plant population. Then since type resistancf so inheritee ear d quantitatively, some procedure such as recurrent selection wil usee lb accumulato dt e desirable genet sa numerous locations (5). Although closed pedigrees make estimates difficult Sprague. F . ,G ,worla d leade maizn ri e breedin geneticsd gan , calculated that even in 1969 corn borer resistant hybrids were grown on abou millio7 t8. n hectare U.S.,almos e acreagee th th n sf i o .3 t1/ southwestere Th n corn borer (Diatraea grandiosella imporn a s )i - tant pessouthere corth f t o n ni U.Sne lats parth It . e f tgeneratioo n lik eEuropeae thath f to n corn mosborere th t s damagin,i g since eth diapausing larvae girdl core eth n stalks. Again, resistanc thir efo s plant development stag bees eha n difficul locato tt transfed ean t rbu progres beins si g made (6). Othe pesty r ke cor f whicso r nfo h plant resistance researcs hi underway include the corn earworm (Heliothis zea) and the corn rootworm complex (Diabrotica spp)mose th t . e importanHeliothib y ma a tsze plant pest in the U.S. since it is widely distributed and has several agron- omic hosts including corn, cotton, tobacco, and sorghum. Also it attacks plants throughout most of the growing season and has multiple generation southers it n si n range thesr Fo .e reasons plucomplee th s x inheritance mechanism resistancf ,o developmene eth resistanf to t

52 hybrid bees sha n difficult (7,8) stile utilizint ar . l no e w Eve , nso g fully the resistance that is actually available in some dent corns. Development of resistance to corn rootworms has been hampered by an inadequate artificial rearing system. Also, larvae damage the roots, and this makes evaluations extremely laboriou variabled san . Resistance to rootworms is mainly tolerance expressed as the ability of the plant to regenerate roots (9). All these pests of corn are somewhat difficult to control with insecticides becaus timine th applicationf f geo o , pest resistanco et the available insecticides restrictione th r ,o pesticidn so e usage. In addition beneficial insects, though useful, cannot be relied upon for primary control. Obviously, we must continue with host plant resistance research. Turning to sorghum, the greenbug (Schizaphis graminum), an amazingly adaptable pest insect, extended its host range to sorghum in 1968. Unti resistanla t straiinsece th f nto became prevalents wa t ,i relatively eas controo yt l with insecticides thit ,bu s intensf o e eus chemicals probably caused mite becomo st e serious pests insteaf do incidental ones. Plant resistance to greenbugs in sorghum was quickly located in tunisgrass (Sorghum virgatum), and commerical resistant hybrids were availabl 197y eb 5 (10). This achievement demonstrated that breeders and entomologists in public and private agencies could cooperate effectivel develoo yt p effective resistanc hign ei h yielding cultivars in only a few years. However, the greenbug too most be given credi beinr tfo g eas manago yt rearina n ei screenind gan g program. Also, there are only a few dominant or incompletely dominant genes involved (11) resistance .Th disturbins ewa first ga o somtt e people because the plants were not greenbug free as they were when insecticides were used. Also, the resistance is specific for the greenbug so separate sources of resistance for other aphids such as Rhppalosiphum

53 maidis and Sipha flava must be separately developed. Greenbug resist- ance doereduct sno incidence eth maizf eo e dwarf mosaic virus even though the greenbug is one of the principle vector of this disease. (Fortunately, ther separate ear e source resistancf so disease.e th o et ) progresn i Researc w no develoo st s hi p alternative source resistf so - ance to greenbugs such as the type that is linked to bloomless. Several workers are trying to combine greenbug resistance with resistance to anothe pesty rke sorghue ,th m midge (Contarina sorghicola). The sorghum midge is a specific pest of the genus Sorghum and is found wherever sorghum is grown. In the past, the damage done by the insec bees tha n minimize uniformakinf y do b e gus m flowerin earld gan y planting, but early planting has disadvantages. The problem has been that the sources for resistance discovered had undesirable brown seed linkag werd ean e frequently talphotosensitivd lan e (12)cooperae Th . - tive sorghum conversion program in Puerto Rico has helped to overcome some of these problems. But there are others.We have no way of rearing this midge artificially, the adults live only a few hours and all larval development occurs hidden from view. This makes progress difficult. Resistance seems to be a combination of oviposition non- preference and larval antibiosis, and, unlike greenbug resistance is not simple . Also, there may be midge biotypes within the U.S. Young and Teetes give a comprehensive review of research on the sorghum midg othed ean r sorghum pests (13). No discussion of sorghum would be complete without mentioning the chinch bug, (Blissus leucopterus). pestThi y oncs ke d s wa ,e a an elaborate procedures suc creosots ha e barriers were use preveno dt e tth movement of chinch bugs from small grains or grasses to sorghum and corn. It is now usually difficult to find chinch bugs in a cereal crop. Whyanswee Th ?successfus ri l pest management with plant resistance playing an important role.

54 Upland small grain vere sar y suite planr dfo t resistance inputs becaus case eth h returns from expenditure d sucan hw croplo e r sar sfo pest control mus limitede tb . Also, some pest thesf so e graine sar active during cool weather when insecticides and natural enemies are ineffective Hessiae Th . y (Mayetiolnfl a destructor exampln a s )i f eo successful plant resistance in small grains. Conventional insecticides and cultural practices such as the destruction of stubble and volunteer wheat and delay in planting dates were not always practical for the contro thif lo s pest. Plant resistance othee th rn , o hand proves ,ha d to be highly effective and to have few disadvantages. Resistance in the form of antibiosis is usually conditioned by a single dominant or incompletely dominant gene, but there are exceptions such as Marquillo an9458I dP 7 resistance (14) 197n .I 4 there were abou millio1 t8. n hectares in the U.S. planted to wheats resistant to the Hessian fly. cereal Ofal l crop insect Hessiabees e sha th n y mosnfl t comprehensively investigated for biotypes. There are usually dominant genes for resist- ance in the plant and corresponding recessive genes for virulence in the y (15)fl . Sixteen biotype Hessiaf so identifiee b nw flieno n y dsb ca by usin gene-to-gene gth e theory. Another small grain pest with biotypes is the greenbug. Three major biotypes have bee nU.Se founth .n d i withi lase years5 nth t1 . These, like the Hessian fly, cannot be separated morphologically. They can only be distinguished by plant and insect reactions. However, Unitee inth d States greenbuge ,th , unlik Hessiae eth nt flyno s ,ha been demonstrated to reproduce sexually so no detailed genetic research is possible resistance Th . greenbue th bot f Hessiaed o e han th g y nfl woul classifiee db verticas da l Yet, feed barleys with greenbug resistance have been grown widely since 1965 withou breakdowta e th f no effectiveness. Conversely, resistanc whean ei loss twa t when biotype B of the greenbug became predominant and a search of the world collec-

55 tion faile reveao dt l alternative sources solutioe Th . n provee b o dt the cas successfuf eo l induced mutation referre earliero dt . Over the years, greenbug resistance had been found in only one line, Insav froA eF m Argentina junioe Th . r author starte lone dth g and arduous process of transferring the resistance from this rye to whea 196n ti usin6y b g X-rays firse H . t crosseo dt Insave ry A eF Chinese Spring whea thend tan usiny ,b g , doublee dth

chromosome complement in the primary F, hybrid in order to restore fertility. This produce greenbug-resistanda t named 'Gaucho,1 the first greenbug-resistant triticale availabl growerso et mort Bu e. importantl providet yi source th d e essentia transfee th r resisf lfo ro - tance to wheat (16). Next, Gaucho was backcrossed to , and X-rayed pollen of resistant hybrid derivatives was subsequently used to cross onto wheat. By using genetic tests in the X2 generations, several possible translocations were identified. After further cytogenetic analysis, one of these was shown to be a bonafide translocation havin pair1 2 g chromosomef so s (like wheat) with resis- tance controlled by a single dominant gene. This material, comprising abou families0 3 t s release,wa s 'Amigoda ' germplasm. Breedere th n si U.S., Sout Centrad han l America, Europe Australid ,an a have requested seed. This is the only example of practical insect resistance obtained from an intergeneric cross. The importance of this achievement, is evident from the fact that in 1975, in Oklahoma alone, the losses due to the greenbug and the cost of control efforts totaled an estimated $80 million. The cereal leaf bettle (Ouléma melanopus) an introduced pest in the U.S., was considered a serious potential threat to cereal crops. However, this sprea t insecno s d tha muc h beyon eastere dth n soft wheat area mentioe W . becaust ni e resistant varieties were foun havo t d e visuala , plant morphological characte thin i rs- case tricornee th n so

56 leave stemd san s (17). Another formerly serious pes wheatf to e ,th wheat stem sawfly (Cephus cinctus), can be controlled by using stem solidness trai,a adverstn a thas tha e effec oviposition to larvad nan l development. The suppression of the pest has been so successful that little researc bees hha n done withi lase yearn5 th t1 s (18).

DEFICIENCIE PLANF SO T RESISTANCE RESEARC U.SE TH .N HI Sinc have ew e emphasize successee dth s achieve developinn di g plant resistance to cereal pests in the U.S., it seems fair to mention areas where less progres bees sha n made. Excep morphologicar tfo l causes nature ,th resistancf eo largels eha y elude . Althougdus h ther mane ear y publications attributing resistanc nutritionao et l fac- tors or to allelochemicals, further investigations have revealed that some of these attributions, such as DIMBOA for corn borer resistance or benzyl alcohol for greenbug resistance, were oversimplifications. The searc singlr hfo e chemical compounds that migh causee tb resistancf so e therefore continues though the answers may be revealed by some other branch of science such as biophysics. Adequate methods of rearing some cereal crop pests have not been found. This lack is important because reliable, viable, and uniform infestations are essential to searches for resistance; otherwise there is proliferatio planf no t escapes coursef O . , natural infestationn sca be used, but in a temperate zone, field screening with natural infesta- tions can only take place during one part of the year. Specifically, better rearing technique needee sar insectr dfo corse sucth n s rootha - worm and the sorghum midge. Ther bees eha n little succes determininn si impace gth widelf to y grown resistant cultivars. Onc eresistana t cultiva growes rha r accept- ance, there tends to be little programmed follow-up unless trouble arises. Consequently, a pest decreases in importance, but the resist- ance is not adequately evaluated for its ecological impact.

57 Furthermore, ther onls ei y indirect concern wit potentiae hth l importance of introduced pests such as the sorghum shoot fly,Atherigona soccota or the Senn pest,Burygaster integriceps. Instead, the focus is on work on pests that offer quick solutions like the greenbug thoug realle hth y difficult problem those sar e involving borerr so subterranean pests. Also, screenin concernes i g d mainly with resistance to specific insects, which could mea release nth widelf eo y grown cul- tivars tha susceptable tar damago et e from formerly unimportant pests. Full advantag taket no germplasf ns o ei m resources usuae Th . l goal is the development of high levels of plant resistance usable as the sole control input. This approach ignores low levels of resistance that might be used to reduce injury or pest populations to a point at which insecticides or natural enemies would be more effective. Finally, there are still too many reports of lines with a deluge of undesirable genes. Even considering these suggested deficiencies, worker cerean so l crop resistanc insecto justifiable t b n sca y proud of their achievements.

NEE INDUCER DFO D MUTATIONS Most world collection cereaf so l crop germplas largeo s e ,mar that sufficient workers or funds are not available for full evaluation. For example Science ,Th Educatiod ean n Administratio USDe s th Aha f no about 35,000 accession wheaf so d 17,00tan sorghumf 0o ; CIMMY oves Tha r 12,000 selections of maize (19). However, these numbers are not so impressive if one realized that most of the collections have not been systematically assembled and that there is considerable duplication with many geographical gaps. Moreover, there has been genetic erosion varietiew asne CIMMYse th suc s Tha wheats have replaced primative iso- lates neee W continuo .dt systematie eth c collectio cereaf no l crop germplasm, especially among wild race related san d species. Also,

58 some such as millets have not had adequate attention. Induced mutation doeaffort sno substitutda collectinr efo g germplasm. How- ever, induced mutation coulimportann a e db t tool tha beins i t g inadequately use plann di t resistanc insectso et thin I .s regard, the following suggestions are offered. 1) Corn and sorghum grown commercially are mainly hybrids. This means there are reduced chances for selecting natural mutations. Could induced mutation usee sb recreato dt genetie parth f to c variablility? ) 2 Entomologis sometimee tar s pleased wit sourcha insecf eo t resistanc breedert ebu understandable sar y repelled because conven- tional breeding cannot separate the resistance from undesirable agronomic traits. An example is sorghum in which greenbug resistance is linked with bloomless, a character that is related to excess water loss from leaves and stems. Could induced mutations be used to break such linkages? ) 3 Morphological traits suc hairs h a plan d san t color could reduce insect damage without promoting new biotypes. Could induced mutatio usee n b obtaio dt n these advantage adapten si d cultivar- sin stea gettinf do traie gth t along with unwanted genes from wide crosses? greenbue Th ) g4 resistance tha induces twa whean di t suggests possibilities of using wide crosses if all else fails. What do related techniques hav offeo et r Tripsacu x froa mZe Saccharur mo mSorghux m crosses? In other words, induced mutation researc U.Se th .n h i shoule db resumed. However resultse ,th , like 1950' e thos th earl d f san eo y 1960's wil disappointine lb expece w f gi t miraculous results after subjecting see traio dt erro d lan r dosage gammf so a ray thed san n selfing the deformed plants. It should be seen as a highly usefultool to use with existing methods of obtaining insect resistance. The

59 ultimat eresistancy an goa f lo e program mus release tb acceptancd ean e of resistant cultivars that will benefit crop production. Tools that will hel reacs pu h thi sshortese th goa n i l t possible time mus usee tb d to the fullest extent if we are to feed and clothe the expanding world population.

REFERENCES

(1) SIGURBJORNSSON, B., Current status of mutation breeding -- philosophy and accomplishment Proc. Mutation Breeding Workshop, Knoxville, Tennessee (1972).

(2) LUGINBILL, P., JR., Developing resistant plants -- the ideal metho controllinf do g insects. U.S. Dept. Agr. Prod. Res. Rep. Ill (1969. p 4 )1

(3) FARM INDEX Trimming agriculture's energy appetite U.S. Dept. Agr. Econ. Res. Serv. 16 (9) (1977) 8.

(4) BRINDLEY, T.A., SPARKS, A.N., SHOWERS, W.B., GUTHRIE, W.D., Recent research advances on the European corn borer in North

America Ann. Rev. Entomol (19750 ._2 ) 221.

(5) RUSSELL, W.A., GUTHRIE, W.D., GRINDELAND, R.L., Breeding resist- ance in maize to first and second broods of the European corn borer. Crop Sei 4 (19741 . ) 725.

) (6 SCOTT, G.E., DAVIS, P.M. Effec southwesterf to n corn borer feed- ing on maize. Agron. J. 66 (1974) 773.

) WIDSTROM(7 , N.W., WISEMAN, B.R., MCMILLIAN, W.W., Evaluatiof no selection potentia earworr lfo m resistanc coro tw nn epopulationi s and their cross. Crop Sei _15 (1975) 183.

60 (8) ZUBER, M.S., FAIRCHIID, M.L., KEASTER, A.J., FERGUSON, V.L., KRAUSE, G.F., HILDERBRAND LOESCH, ,E. , P.J., JR., Evaluatiof no 10 generation masf so s selectio corr nfo n earworm resistance., (19711 1 CRO I . )PSC 16

) ORTMAN(9 , E.E., GERLOFF, E.D. Rootworm resistance: Problemn si measuring and its relationship to performance. Proc. Ann Corn Sorghum Res. Conf. 25. (1971) 161.

(10) SCHUSTER, K.J., STARKS Greenbugs, J. . ,K : Component hostf so - plant resistance in sorghum, J. Econ. Entomol. 66 (1973) 1131.

(11) HACKEROTT, H.L., HARVEY, ROSS, W.M., Greenbug resistancn ei sorghum. Crop Sei _9_ (1969) 656.

(12) JOHNSON, J.W., ROSENOW, D.T., TEETES, G.L., Resistance to the sorghum midge in converted exotic sorghum cultivars, Crop Sei 13 (1973) 754.

(13) YOUNG, W.R., TEETES, G.L., Sorghum entomology, Ann. Rev. Entomol. 22J1977) 193.

(14) GALLUN, R.L., STARKS, K.J., GUTHRIE, W.D., Plant resistanco et insects attacking cereals, Ann. Rev. Entomol. 2Q_ (1975) 337.

(15) GALLUN, R.L., Genetic interrelationships between host plants and insects, J. Environ. Qual. ^ (1972) 259.

(16) WOOD, E.A., JR., SEBESTA, E.E., STARKS, K.J., Resistancf eo 'Gaucho' Tritical Schizaphio et s graminum, Environ Entomol_ ,3 (1974) 720.

(17) WEBSTER, J.A., GAGE, S.H., SMITH, D.H. JR., Suppression of the cereal leaf bettle with resistant wheat, Environ Entomol. 2_ (1973) 1089.

61 (18) WALLACE, L.E., NfcNEAL, F.H., Senn sawflies of economic importance in grain crops in the United States, U.S. Dept. Agr. Tech. Bull.

1350 (1966) 50 pp.

(19) HARLAN, J.R. , STARKS, K.J., Germplasm resources and needs in "Breeding Resistance to Insects", Maxwell, F.G., Ed, John Wiley § press)n Sons(i Y ,N .

62 HOST PLANT RESISTANC MAJOO ET R INSECT PEST F SOHGHISO M

N.G.P. RAD, B.3 A« , R .M.G . JOTWJWI JEL1 India Coordinated Sorgho« Improveaent Project ZABI-Regional Station Rajaadrœagar, Hyderaba 0300 d50 , India

Abstract

HOST PL/HT HESISTJHC MAJOO ET R I»SECT PEST F SORGHISO M Crosses between tropica temperatd an l e sorghum e currentlar s y receiving increasing attentio o stabilisnt improvd ean e aorghOB productivity. Since insect problem f tropicso e g «sar a «rally «ore severe, ooabining productivity with insect résistance become primare tb s y objective. The sources, mechanism genetid an s c basi f resistancso e together with plant breeding implications have been examine r thredfo e major pest f airghuso m_ shoo flyt , stem bore rcasese anth dl , midge al non-preferenc n I * e th s ei prédominait mechanis f resistancemo inheritmnce Th « s equantitativi e with prédominanc f additiveo e gene action» Incorporating multiple resistanco et several of the pests and diseases of sorghum cultivars is feasible and necessary since sorghan cultur tropicn ei s largelsi y rainfed and less intensive* Induced m station s might be useful in enhancing the diversity of alleles conferring insect resistance. Selection of fbr attributes governing resistance may be rewarding» Mutation breeding might thus supplement conventional breeding methods*

Compared to temperate cones, insect problems in tropics are generally more severe and this is particularly so in case of sorghtat, the world's fourth important cereal. Sorghum cultur tropicn ei s still being largely traditionale anth f do subsistence type, chemical contro f inseco l t pests receives scant farmer attention although control schedules have been well worked eut. Current research efforts to enhance sorghum productivity all over the world involve hybridization between tropical and temperate sorghums. Since non-preference (l) appears to be the predominant component of resistance to most srghum pests, it becomes essentia o avoit l d developmen releasd an t f inseceo t preferred type o guarst d against accentuatio f insecno t problems (2)« Combining productivity with insect resistance, therefore, becomes the primary objective of sorghum breeding piegrammes»

63 MAJOR INSECT PESTS OF SDRGHIH

Abou 0 specie10 t f insectso e knosar o attacwt k sorghu t severambu f o l thee polyphagou»ar n detaileA . d accoune insecth f o tt pests attacking sorghvn s givei Tot»y b n g (5). The aorghun shootfly (AtherLgona varia aoc«ata e seedlinBond.th n i ) g stage, toe stem borers (Chilo part all us Swinh., Buaseola f usca Fuller, Sesania inférons WLk., aid Sesania cretica Led»), the sucking chinch bag (Blissus

leucopterus Say), green bug (Schizaphis gran in an Bond.) aid spider mites causing danage durin l stageal g f growthso , midg Gontarlni( e a sorghicola Goq.d earheaai ) d bugs (Galoooris aa gusLoth.s u t ta , Agnosceli d severaai » op sl other bugsd ai ) caterpillars after flowering may be considered as major pests which require priority attention. Sorghum shoo t fly is prevalent in Asia, Africa and Mediterranean Europe.

Anongst stem borers, Ghilo parteilo Sesanid san a inférai e distributear s e th n di Indiai Sob-continent, VesBasd an t Afric South-Basd ai a t Asia . CreticS ; n ai middle-eas partd ai t f Europso Busseold an e a fusc n Africai a . Sorghan nidga ei the most widely prevalent pest occurring almost throughout the world. Amongst r bugea s Calocoris aigustatu serioua s «i s pes Soutn i t h Indi Agnoscelid aai s sp., s considerei nationaa e b o dt l pes Sudann i t ; several other specie f bugso d ai s

earhead caterpillars have been reported fron various parts of India and Africa. The nymphs aid adults of the sucking chinch bug, widely distributed in the Ihited States, Canada, Mexico and Latin An erica attack sorghvn during all stages f growtho . Good level f resistancso gree d havo chincg et an nbu g e beehbu n builv t presene th U y n Si da toultivars . Severasoie th l f insectso l , foliage pests like grass hoppers, locusts, aray wo ans, sucking insects like mealaphid an dys bugd ai s earhead caterpillar e knowsar o attact n kconsideree b aorghu t no t they s bu nda yma specific pest f sorghoaso . The present paper attempts an analysis of the problem of insect resistaic n sorghoei n with emphasi n sorghaso n shootfly, stan borerd ai s midge. Since non-preferenc tolerancr eo hose to tmaie f plaieo th n a i t mechaiism of resistaace, geaetic diversity within these insect species as races, strains or blotypes «ay not pose any serious problems (4). The emphasis,

64 thereforetowarde b o t s s understandinha , capitalizind gan g variability withie nth host plaat cpeeies*

SHDOTÏLY.

Sorghos shootfLy (Atheriflona varia, soccata Brad.) is essentially a seedling pes f sorghuo t n «aosing damage darin e firsgth t three weeks it f so life cycle f conditionI . t conducivno e ar s satisfactoro et y early growth the t extendedamagge y e»a d beyond this period. Generally 1-10 egg laie ar sd r pint pe egge th ;s hatch after two days firse th ; t Instar larva travels from the leaf penetrating downward and destroys the growth point restating In deadheart fomatlon. The incidenc f shootfLeo s highli y y seasonal. Late plaited crops daring monsoon suffer heavy losses since the build ic> Increases after first plantings» Detailed studies en seasonal incidence of shootfly have been carried eat In different parts of India, Africa aid Southeast Asia and the best recommendation to avoid shootfly damage is early plaiting or at times when the incidence is at its lowest in the respective areas* Sburee f resistancso e First attempt screeo t s n sorghtn r fielsfo d résistanc shootflo et y attaëc were made by Ponnaiya (5) who observed that the winter (rabi) sorghon selectio f deccao ns n plateau were tolerant*

Systematic screening of the world aorghin collection for sources of shootfly resistance were carried eut m der the All India Coordinated Sbrghon Improvement Project (AIGSEP). Screenin dons t gwa severaa e l locations with progressive Improvement n techniquei s adjustmend san f sowino t g dateo s(k correspond with high level f infestationso . Selected lines that exhibited field resistance were screened in der artificial conditions of infestation in green hous t Hyderabaa e Delhid e detaildan th , f thesso e studies have been published by Singh et al. (6) aid To tug (7) and in successive annual progress report AICSIPe th f so . Selected resistant varieties viz« nosS I , . 1034,

1054, a46, 2269, 5962, 4567, 4776, 5383, 5470, 5483, 5604, 5613, 5655 and 5801

were also include Internationan dI l shootfly trial n Thailandsi , Israel,

65 Uganda and Nigeria during 1969-70. Based on studies ifl India and abroad, the following lines were observed to exhibit high levels of toleraicet

nosS I . 1034, 1054, 1061, 1082, 2122, 2125, 2146, 2265, 2269, 3902, 3962,

4522, 4545, 4553, 4567, 4607, 4646, 4664, 4776, 5072, 5251, 5285, 5383, 5469,

5470, 5480, 5483, 5490, 5566, 5604, 5613, 5615, 5622, 5633, 5636, 5658, 5801, 8315 aid a few others« These résistait neaavarietieo n y sb immtne y attackfl sar t o t e bu , exhibited consistenia.y lower levels of injury. Discussing about the available variability among sorghan r shootflfo s y resistance ) remarke(8 o Ea ,d thae th t identified résistait line sr dagad o belondal i naa d semi( o it g - compacd an t compact headed types respectively) type f Indiaso n winter (rabi) sorghunr o s (pou l pH sorghanse th ) types usually grown mixed with ma r ldagad o da i nd i types which consequently survive n smaldi l populations. Thu variabilite th s y available anon g résistait types was apparenia.y limited and largely confined to winter

sorghan f Indiaso .

Loggetd otheai ) r (9 Africat n workers selected types likr fo e a Ner a mt a

high tillering recovery ) felresistance(8 to thas e scopRa it t th tf eo bu , utility may be limited, particularly, aider moisture stress* Stability of resistaace Host iumtnit o shootflyt y attack being absent r cenpe , t deadhearts in susceptible aid resistant varieties vary with seasons, years aid degree of infestation. Ihder the circonstances, it would be useful if stable sources

of resistance could be distinguished from amongst the available pool of resistant sources« 1b accomplish this, fce stability analysis technique developed by

Eberhart and Russell (10) was suitably modified aid applied to Singh's (1977)

unpublished data* In place of environmental index in the original model a susceptibility inde obtaines xwa meas a d n deviatio knowa f no n sensitive variety. In this model, stabilit f resistancyo bees eha n defineabilite th genotypa s f a dyo e to resist deadheart formation mder varying degree f insecso t infestationD A . absolutely stable varietwite on h s zeryi o deadheart zerd ai so rat f changeo e (b « 0) to increased infestations. Ihe data obtained are sanmarised in Fig.l.

66 It is evident that IS Nos. 5469, 5490 and 1054, are relatively more stable anong résistait lines and aouLd be chosen as preferential parental stocks in programmes of incorporating shootfly resistance» Meohaniang of resistance ïhe primary mechanism of resistance to shootfly has been observed to be non-preferenc r ovipositio levefo ew f antibiosilo o la d larve an th n ao t s (11) * The non-preferred varieties «ill not, however, suppress ovipositioe th n ni absence of preferred varieties, Jotwarti et al. (12) observed, on an average, r plan lespe resistan n g o t seg thae non t varieties nosS I , . 1034, 5359, 5470, 5655 and 5801 aid a maximun of 5.73 eggs/plant on Swama a susceptible check* r cagliade e conditions, non-preferreWe ier d hos s preventedi t , ovipositios ni equa résistain o l susceptibld ai t e varieties differentiae th t bu , l survival rate, although low, indicates presence of low levels of antibiosis (13). Ponnaiya (14) found that shootfly resistant aid susceptible varieties differe occurrence th n i d f irregularleo y shapeh d7t silico t h a4t bodiee th n si leaf sheaths. Blun (15) observed that resistant varieties were characterized bdistincya t lignificatio thicknesd nai walle th f cellf so s o s enclosine gth vascular bundle sheaths within the central whorl of young leaves at the three leaf stage. The causal relationship between anatomical attributes and seedling resistance has not been established. Shootfly resistance has also been found to be associated with glossy and light green colour of seedlings characteristic wintee oth f rabi( r ) sorghtn varietie f Indiaso . Genetic basi f afrootflso y resistance Genetic analysis of ovipositional non-preference «iderlying résistai ce to sorghon shootfly aid its plant breeding implications have been investigated aider the ÄL1 India Coordinated Sorghum Improvement Project. . (l6analysisal Base± ¥ t ) e n indicatedo o Ra , d that hybrid e generallar s y superio parento t r s with respec shootflo t t y toleranc parentad em l performance was a good indicator of hybrid behaviour. Further studies by Balakotaiah et al. (17)

using large ?2 populations derived from a diallel Rating system revealed that the frequency distributio f differenno t mortality classes closely fitte nomae dth l curve and inherit aice of shootfly résistai ce is predominantly additive. Based advanced m S F d generatioon n progenies ,. (18al San £ )ae established

67 the heritability of shootfly resistance axemd 25% and indicated selection procedures for development of resistant lines*

Breeding for shootfly résistance

The superiorit f hybridyo s over parente additivth d an s e naturf eo inheritance of shootfly résistai ce could be advantageously capitalized in hybrid breeding as well as line development (16). The characteristic gradation with which the mortality percentages increased from 23-65$ in the groups, résistait (Indian parents), resistan résistaitx t , moderat résistaitex ,

susceptibl resistantex , susceptibl moderateex , susceptibl esusceptiblx d ean susceptible (exotic paraît s) indicates (TABLE I) that resistance is due to gradual

ace an ULat ion of desirable all ale s rather than due to presence of one or two major genes (17).

I. GHDUP COMPARISONS OF SHOOTFLY DAMAGE IN PARENTS AND F2 PHD GENIES

Average Per cent daaage plant Group popula- Actual values Transformed values tion(no.) Mean Range Mean Bange

Parents Exotics (susceptible) 1266 64.4 33.5-88.9 54.3 35.3-70.5 In sistai e diar ( i t) 1198 22.5 20.0-26.7 28. S 26.5-31.1 Derivatives 1212 22.9 25.3-51.5 34.8 30.1-45.8

Fg p ID génie s

Exotic x Exotic 1350 56.3 45.5-67.6 43.6 42.4-55.5 Exotic x Derivatives 1323 47.9 7-61. 11 .5 43.6 20.0-51.6 Exotic Indiax n 1269 37.7 24.9-56.8 37.7 29.9-48.9 Derivatives x Derivatives 1284 32.2 18.5-40.6 34.3 25.5-39.6 Derivatives x Indian 1257 25.0 12.2-34.4 29.8 20.4-35.9 Indian x Indian 1293 23.4 16.2-27.1 28.7 23.7-51.3 G.D. 0.05 10.4

The résistan résistaix t t crosset exhibino d di st improvement over parents

indicating that there is no diversity among resistant lines and absolute resistance is lacking, liider such circumstaices selection of résistait types may be confined

to families which exhibit mortalitie standare son d deviation belo populatioe wth n meai uader re«eonable level f infestatioso n (Fig.2). Whil mortalitieg eF s enable identification of potential cro sses, differences among susceptible and resistant

68 progenie t establishege s 3 generatioP y db selectiod an n n thereafter oould result in further improvement and stabilization of résistance. Since absolute resistance encomterede b o t t ye s , i selectio f resistanno t confinee lineb y spa»génie»a o t d s exhibiting 70% mortalities, when susceptible lines exhibit abou mortalit£ 67 t y »der field conditions. selectio* Wit10 a h n intensity 10a , % gain (TAO,) EII

was anticipated from Fg to F4 generation (18). Folio win g such procedures tolerant lines such as GSV-S (IS 3687 x Aispori). CSÏ-6 (IS 3922 x Aiapuri.). GSW.7R 295S (I 0 xM.35-1) have been isolated from exoti Indiacx n crosses. Continued screenin f resistango t types «der artificial infestation may eventually enable plane th o evolvt t inmmito ea y mechanism. 2 TABL . En HERHABn. HBHITABILITE I (o ) JND GAIN FROM SH,ECTION (as) IN F3 FAMILIES FOR 6HOOTFLY RESISTANCE

i - 10% i - 5% Method h2

OS EE4 >? GS EIP F4

(D 22.57 -3.40 31.16 -3.98 20.58 (2) 27.00 -2.10 32.46 -2.45 32.11

(1) h* - (T

E + H + D D/ - 2 (2h ) i « Intensity of selection

srai BORERS

majoe Alth l r borers . Busseolus l , el Chilt aar fuscaop . Sesamia inférons and Sesamia cretica hav wida e e host range attacking maize, , Eleusine ooracana, Pennisetaa typhoides and Sorghan helepense; Sesamia inferens also attacks whea riced an t . Early incidence result deadhearn si t fcmation, late incidence

in stem tunelling and even later incidence causes boring of the peduncle which may resul necn i t k breakag r ill-filleeo d grains. Sinc borere eth s have more than one generation each seaso attacd an ns kcontinuoui s throughou life th et cyclf o e the host plant biologicae th , l relationship betwee hose insece th th ntd planan t t may not be the same for each generation (19).

69 iburce f resistancso e Sporadic report f differentiaso l host plait reactio o stent m borers hare appeared bot a systematic pxograame of screening the world sorghum collection vas taken up under the ill India Coordinated Sorghin Improvement Project, the results

of which «ere pifcliabed by Singh et al« (6). This work was further continued by Jotwai co-workerd aa i totaa d f abouo lan s t 10,000 lines were screened «der field conditions at several locations (20). After subjecting the promising ones to

artificial infestation, 26 lines were identified as showing relatively less damage. These are nosS »I . 1044» 1056, 1115 , na ,3096 , 4424, 4552, 46a, 4689, 4747,

4764, 4776, 4782, 4827, 4841, 4875, 4954, 4894, 5030, 5021, 5470, 5837, 6041,

7273, 831 9136d 4ai . Mos f varietieo t f Indiao e ar sn origin wite exceptioth h n of IS 5096 from Georgia, USA, IS 7273 from Nigeria and IS 9136 from Kenya. Mechanian of resistance Informatio resisn o n ci tea mechanism s limitedi s . Jo wat ni (20) observed that toleraace aid antibiosis are operating in resistant varieties* Evidence for antibiosis was furnished by Kalode and Part (21). Jotwaai ejb aU (22) have

reported tha e developmenth t adversels l u ael wa f Gfallt o t ar p oy affecte thren o d e selected résistait varieties, IS Nos. lia, 4764 aid 4776. There was higher mortalit earln yi y larval stage larvae th , l perio longes percentagd dwa an r e p vp at ion was less on résistait varieties compared to the susceptible hybrid GSH-1. They also observed positive correlation between leaf danag d steai em tunnelling. Toughness of the stems is usually attributed as one of the causes for resistance. Genetic basis of resistance Rana aid Murty (23) attempting a genetic analysis of stem borer resistance reported polygenic inheritaice. The F^ hybrids were intermediate for primary damage (leaf feeding) but better thai mid-parental values for secondary damage (stem tunnelling). Résista o primart e ic y damag governes ewa d

by additiv additivd eai additivex e gene action while additiv non-additivd ean e type f genso e action were Importan r secondar & t y damage. They felt thae th t inheritance pattern f primarso secondard an y y damage were different.

70 Breedin r resistancfo g e The dwarf temperate types exhibit greater stem tunnelling compared to In dial varieties. Utilizin sourcee gth f resistanceso , tolerant derivatives have been developed from exotic x Indian crosses in the Indian prograane. &-502 fron Kafi BP-5x B r 5 cross, B-305 derived fro £95S mI BP-5. 4x e highl3ar y tolerant to stem borer. CSV-6 a high yielding variety derived from the cross IS 3922 x Aiapuri is also tolerant to borers. Several of ifae derivatives in the breeding nursery also exhibit high level f resistancso o steet m borers* Systematic work on breeding for stem borers resistance has been limited n Indii d abroaai a futur d dan ee line worth n f worso ko k don European o e m co n borer cotfLd yield valuable info natio materialsd nan .

MIDGE

SorghUB midg Gontarini( e a sorghioola Goqa rapidl s 0i ) y multiplying Cecidomiid fly completing its life cycle in 22-23 days end the larvae feed on the ovary preventing normal seed set. Ihe peak periods of midge incidence are know in most sorghum growing parts of the world end it is generally the late flowering or late planted types that are prone to nidge damage.

In India developmene th , releasd ai t f earleo y maturing hybridd di s bring out the yield advantage of hybrids in years of subnonnal rainfall, «hen late locals failedyearn i t normaf so bu , l rainfal t suffelocale no th ld rs di from moisture stress, but failed to make grain because of extensive midge damage. This is not becuase midge was a new introduction into India, but once midge appeared, the hybrids plante differenn do t dates provide continuoua d s perio f flowerindo y b d an g the time the locals flowered, an epiphyte tic situation arose. It is the scattered sprea f hybriddo s resultin situatioa n gi f alternatinno g fieldf so early hybrids and late locals which accentuated midge incidence. We now recommend maturita y oriented sprea f hybriddo varietied san enblocn a n so k basi groupd san s of hybrids and varieties of approximately similar maturity are distributed in an entire block. This has resulted in containing the midge problem to a considerable extent (24). This experience should provide a pointer to attempts of trensfonaing

traditional uncertain late sorghun belt f tropicso areao st f greateso r productivity througf earlo e yus h maturing hybrid varietiesd an s .

71 dp urces of real stance Although sporadic reports have appeared regarding midge tolerant varieties

earls a 1912s ya t muc,no h reliance coul placee db thesn do e observations since earlier screening methods wer t systematiceno *

Organized studie midgn so e were initiate Wisemas y colleaguedb hi d nan t sa Tifton, Georgia •onmenelng from 1968. Wiseman and McMUlaa (25) evaluated 216

sorghum lines at Tifton, USA, end found that nine lines were consistently less

damaged. Out of them, they have released SGLflL-Mft-1 developed from ODG-19 an unknown 3>uth African Hegari s mosa . t résistait (26). Thiisolates wa s d after seven generations of selection under highly infected conditions.

The Texas workers of USA operated a sorghum conversion pro g rame at Ghillicoth Peurtoriod een o involving tropica temperatd an l e sorghume th d ai s

converted lines viz., IS 12666C (zerazera), IS 2508C (Gaudatun kafir) were reporte résistaie b o dt midgo t t e (27). MttLtilocation trials on screening for midge damage uader the All India

Sorghum Improvement Project commenced during 1969. To date 22 lines have been

selecte promisings a d f whic o followine t th hou , g exhibited consistently less

danage nosS I t . 1151, 3472, 4307, 4308, 4411, 4477, 4832, 4870, 4876, 5230,

61759Cd 0an i (28). Further studies under AIGSIP also identified EC-92792, EC-92794, DJ-65L4 «id IS-12573 as résistait. Genetic breedind ai s r midggfo e resistance Midge resistance in SOQ.HL-MR-1 has been reported to be of the non-preference

type thad ai ,t susceptibilit dominais ywa t (29). WLdstrom, Wisana McMilliad ai a n (26) from analysi f generatioso n means

observed that both additiv epistatid ean c gene effects were importan additived an t

gene effect highle b o t sy significant. They felt that simple backcross techniques may not be sufficient to transfer midge resistance into breedin g lines. s beeAha sn pointe t earliedou re converte th som f eo d lines like IS-12666C IS-2508d ai C wer consciouslm e y selecte r midgdfo e resistance since midge populations prevailed during the period of selection (27).

Inder the All India Sorghum Project selections made from crosses involving SGLHL-KPr-1 have begu o yielt n d r resultscenpe e t midgTh . e damage n th somi e f eo

F line presentee sar n TABLdi I whicII E h indicate partial gain. s

72 TABLE III. MIDGE REACTIO 3DMF NO g PK)GENIE F E S

% »Lage damage to grate __ Entry Pedigree Parbhani Goimbatore Average

Fg-575.1 SŒLHL-M&.x 8 14 1 37.SE 52.5 34.8

Fg-575-2 x SGLHL-MÄ. 8 14 1 37.00 20.1 28.5

Fg-575-5 K. Local x SGLRL-KB.1 29.00 19.4 24.2

IS-12573 31.25 19.3 25.3

SGLBL-Ma-1 13.00 22.6 17.8

MULTIPLE RESISTÄJGE Tropical sorgbons of traditional subsistence faraing need to be transformed Into note productive types aid this is the task to which most aprghiai breeders in tropics are addressing themselves. Apart fro» the higher production potential of altered genotypes, the most decisive factors in making them acceptable would be resistance to the major pesta and disease f sorghunso . Current work on temperate x tropical (Exotic x In dial) crossing programm n aorghui e n lays considérable evphasi multipln so e resistanco et pest s welsa l diseases. Such crosses furnis l possiblal h e alternativen si recombination breeding. As examples nosS I , . lia, 4776, 5470, VZH-2548d an 0e résistan Bar t to both shoo t fly and stem borer. In general, several lines résistait to shootfiy also exhibit some resistance to stem borer« to. Indien variety Aispuri (IS-115L), extensively use n breedindi g programme s knoi , havo wt e aome resistanco et shootfiy, stem borer aid midge. Compared to exotics several of the derivatives extracted from exotic x Indioi crosses exhibited superior performance with respect to shootfiy aid stem borer reaction (TABLE IV). WLdstrom, Wlsama McMilliad an n n (26) reported combined resisttncr efo midge aid sorghoa web wot» (Gel en a aorghiella) and a similar pattern of inheritance releasem di fon I r e dbot th varieties hf o pests e On ., CSW.5 (IS-368 Aj.ap«ri7x ) exhibited some degre f résistaeo shootfiyo t e ic , stem ix>rer, downy mildew, striga,

aid several leafspot diseases and is now being extensively used for farther

73 TABLE IV. DERIVATIVES OF EXOTIC X INDIAN (TEMPERATE x THOPICAL) CROSSES RESISTAN O SSOOTSLT STED YAN M BORBH.

a. Si-try Pedigree aiootfLy Stas borer No. deadheart stem t inn ell ID g (« (V

1. CS^6 (604) IS-3922 x Aispuri 23.36 12.05 2. SPÏ-S (529) IS- 608 x Karad local 21. 78 12.34

3. SPV-13 (SB-803) Karad local x IS-84 36.96 4.86

4. SP1M.4 (141) 368- IS Aispur7x i 26.18 11.73

5. SPV-19 (669) IS-29SO xM.35-1 24.63 8.10

6. SP*-26 (E-3D2) BP-53 x Kafir 36.25 6.93

7. SP^-34 (SB-461) Mutaat derivativ f CM1-eo 5 29.49 9.61

8. SPMU70 (16) BP-5x 2- 4 9IS 5 3 31.72 5.97

9. CSH-7R 36A x 168 26.71 11.54

10. 15-5469 (Résistait check) 19.10 6.95

n. CSH-1 (Susceptible check) 60.20 32.66

iraprovement. Base availabln do e information t i appear, s feasibl o recombint e e productive genotype of sorghun with appropriate maturity, height, yield and midtLple resistance factors*

SOOP F INDUCEEO D MUTATION N BREEDINSI INSECR GK) T RESISTANCE Mutation breedin t receiveno s gha d attentio breedinn ni r insecgfo t resistanc n sorghunei . Non-preference bein mose gth t important componenf o t resist ai ce to major sorghun pests and its inheritance being polygenic, it vo

74 Compare tropicao t d l types e eaotith , c (temperate) sorghans being generally a»re susceptible to Insect pests, the derived lines generally tend towards susceptibility aid to date only intermediate levels of resistance have been built up into derivatives» If the tropical genotype is maintained with some redaction in duration and height, such genotypes could become more immediately adapte acceptedd dan . Some succesn si this directio bees nha n achieve n Indidi a where induced notants fro varieta m y Gidda maldaidi have reduced duration, height and a superior insect reaction» Such varietie S&.4SLe sar presentle SB-46d ar ai 1 d 1ai y undergoing advaiced field testing« Further effort thin i s s directio rewardinge b y nna . With special referenc o shootflyet , while susceptibl resistanex t crosses are superior to susceptible x susceptible crosses, the resistant x resistant crosses do not exhibit superiority over résistait parents» The sane could be the case with stem bore r nidgero , sinc majoe eth r component governing resistanc s largelei y non-preference in all oases. This imposes a limitation on building up lines with giei h r level f resistancso s apparentli d ai laceo t f diversite ko ydu r alleleyo s conferring resistaice» Consequently, resistan résistaix t t crosse r intematinso g n selectei d t resultintypeno s si furthen gi r improvement. Induced mutations in résistait lines could brig t greategou r diversity. That thi s possiblsi e has been brought out in studies of Jotwani, Sethi, and Baisal (Unpublished) where résistant line nosS sI . 5469, &-30549d an 0 2 subjecte o gt d ann a radiation and NMU treatment yielded progenies slightly superior to entreated controls with respect to shootfly and stem borer reaction» The studies are preliminary aiconclusiono dn s coul dratne d b t thee indicativbu ,ar y e thae diversitth t y for alleles governing resistance nay possibly be enhanced« It has been stated earlier that non-preference of certain genotypes to shootfly has been attributed to presence of silica bodies in the leaf sheaths or lignification of walls enclosing vascular bundle sheaths in seedling stage« Similarly, toughnes f possiblstes so mwa y responsibl r boreefo r resistance» Investigations on biochemical basis of non-prefermce will alas be worthwhile attempting. This infbzmatixm on aiatomicaL and biochemical basis of inheritance coul usee db n selectindi g whers mu t tai e such attributes coul furthee db r strengthene o enhaicdt levele eth f resistanceso . Mutation studies might, thuse b ,

75 usefU o furthet L r strengthen conventional breeding method n combinini s g stability, productivity and insect resistance in sorghoa, a predominantly rainf ed crop.

REFERES CES

*(1) PAINTER, R.H., Insect resistanc n croei p plants Maomillae Th , n Co., New Tork (195L).

) (2 RAD, N.G.?., SorghuB researc productiod han n Sudani n , Somalia, Yemen-Arab Republic and Peoples Democratic Republic of Yemen, FAD Report, Near East Regional Office, Cairo (1977).

) (5 YOUNG, W.R., "Sorghan insects'», Sorghan Productio utilizationd an n , (WÄLL, J.S. and ROSS, W.M., Eds.), Ohé AVI Publishing Co., Inc., (1970) 235-287. (4) GALUN, R.L., STARK, K.J., GÜTHRIE, W.D., «Plant resistance to insects attacking cereals", Ann. Rev. Ent., 20 (1975) 337-3S7.

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(7) YOUNG, W.R., "Sources of resistance to sorghum shootfLy, Atherigona varia 30 coa ta Rond.« , Contro f Sorghvo l » Shootfl ( yJOTWANI , M.G YOUNGd an . , V.R. Eds.), Oxford and IBH Co., New Delhi, (1972) 168-179. (8) RAD, N.G.P., "Discussion", Control of Sorghon Shootfly (JOTWANI, M.G. sod YOUNG, W.R., Eds.), Oxford & IßH Co., New Delhi, (1972) 222-224. (9) EOGGETT, H., "Breeding for resistance to sor^ion shootfLy in Uganda", Contro f Sorghoo l s Stootfly (JOTWANI, M.G d YÖUNG» . , W.R., Eds.), Oxford & IBH Co., New Delhi, (1972) 192-231.

(10) EBERHART, S.A.,and RUSSELL, W.A., Stability parameter r comparinfo s g varieties, Crop Sei. (1966,6 ) 36-40. (11) JDTO, P.E., «Mass raring of the sorghua shootfly and screening for host plant resistance aider green house conditions", Control of Sorghum Shootfly (JOTWANI, M.G. and YOIMG, W.R., Eds.), Oxfcrd & IBH Co., New Delhi, (1972) 137-146.

(12) JOTWÄJI, M.G., SHAEMA, G.G., SHLVASTAVA, B.G., MAHWAHA, K.K., "OvijBsitional response of shootfly, Atherigona varia so coat a Bondani on promising resistant line f sorghun"so , Investigation insecn so t peat f sDrghoso milletsd nan , (Tech. Rep*. Div. Bot., IAH., New Delhi) (1971) 119-122. (13) SDTO, P.jS., Ovipositional preferenc antibiosid an e relation si resistanco nt e to a sorghon shootfly, J.Econ. Ent., 67 (1974) 265.267.

(14) FONNAIYA, B.W.I., Studies in the genus sorghut II. The cause of resistanc insece th o et t pest, Atherigona indic . MadraaM s Univ. J . a (19a) ao3~a7.

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(18) RANA, B.S., TRIPATHI, D.P., BALAKDTAIAH , DAMODARK. , , RADR. , , N.G.P., Genetic analysis of some exotic x Indian crosses in Sorghan H. Selection for shootfly résistai ce, Indian J. Genet., 35 (1975) 350-355. (19) GUTHRIE, W.D., Entomological problems involved in developing host plant resistanc grannieso epr , Iowa State Res (19759 4 . ) 519-525. (a)) JOTWANI, M.G., Host plant resistance with special reference to sorghum. P roc, Nat. Acad. Sei. India, 46B (1976) 42-48. (21) KALODE, H.a., PANT, N.C., Effect f hoso s t plant survivaln so , development aid behaviour of Chilo zonellus (Swinhoe) «der laboratory conditions, India . Bat.J i 1(19679 ,2 ) 48-57. (22) JOTWANI, M.G., OHAUHAN , SINGHS. , , S.P., "Developmen f Chilo t o zonellus (Svdnhoe thren o ) e promising resistant varietie susceptibla d sai e hybrid of aorghu«", Investigations on insect pests of aorghun and millets, (Tech. fiept. Div. Bat., IAHE., New Delhi), (1976) 147-148. (23) RANA, B.3., MURTT, B.R., Genetic analysi f resistancso o steet m borer n sorghosi , India . J Genet.n (19711 3 , ) 521-529.

(24) RAO, N.G.P., JOTWANI, M.G., SarghuB midge-suitafcLe varietal policy and survillaice essential, Indiai Rng. (19744 2 , ) 9-11. (25) WI5SMAN, B.R., HdOLLIAN, W.W., Resistance in sorghun to the sorghun midge, Contarinia aorghioola (Coquilett) (Dipterat Cecidomyiidae) . BatomolGa . J , . Soc., 3 (1968) 147-153. (26) WIDSTROM, N«W., WISEMAN, B.R., McMttLIJB, W.W., Some gene effects conditioning resistanc o midget Webwazd an e m injur n »rghunyi Agroa G .n Abstracts 15 (1972) 1-2.

(27) JOHNSON, J.W., BDSBSOW, D.T., TESTES, G.L., Resistanc e sorghuth o et m midg converten i e d erotic sorghoa cultivars. Crop Sd. (19733 ,1 ) 754-755. (28) JOTWÄJI, M.G., SINGH, S.P., GHAUHAN , 5. «Relativ, e susceptibilit f yscno e aorghun lines to midge damage", Investigations on insect pests of sorghun aid millets (Tech. Rept. Div. Knt., IARI, New Delhi)

(29) WISBMJN, B.R., MdŒLLIAN, V.W., KEDSTROM, V.W., Registration of SG1RL-MR.1 sorghum geimplasm (Reg.No.GP19), Crop Sei. (19733 ,1 ) 398.

(30) JNJWTHARAMAN, P.V., AGHUTARAO , KANILIKARK. , , S.S., RAD, N.G.P., Genetic analysi f somso e ex>ti cIndiax n crosse n Sorghusi n XIX. Patteras mattey o nutriendr fd an r t accumulation, India . nJ Genet. (19788 3 ,press)n (i ) <

Tenninolog* y jrertainin naturo gt f résistanceo e use thin i d s papes i r according to Painter (1951).

77 i «u 16

0.9 - 65

K O.ö S S g 4 0 0.7 8 . GS

| 10 12 § 0.6 ^ 0 15 i » « 7 ?* * Z 0.5 *

14 » 0.4 6

H 1 17 GL * 0.3 G2 . «

6 „ 8.* . . « 1 M 0 8 0 6 0 4 ? '3 DEAD HEAR (Transfonne% T d values) Fig.l. Stabilit r ahootflyfo y resistance GHDUP- ISnoB.l1 I . 1054 . 54695 ,. 54908 , } GHDUP-I . 54766 . : I11 , 56215 GHOUP-II . 21232 : I . 3. 2129, 4. 4777, 7. 5433, 9. 5604, 10. S613,"5JTT553, 13. 5642, 14 . . 5801831515 ,} GKIUP-I7 17. Swam«; GHDUp-y > 16. Ca-1. SE(b) .t - 0.42 DH 3D - 9.9

28

p- .33.8 5 S.S » -KJ.9. 3 S.D " .~7.7 9 OBSERVED

ao

16

12

25 35 45 55 R OBIPE T DAMAGE (THANSTOI«BD VALUES)

HLg.2. Frequency distributio 3 familieF f no r shootflfo s y damage,

78 A RESISTANCL S GRAMINEEDE E X LEPIDOPTEREAU S S FOREURS

. ANGLADP E INRA Zoologie, 33140 Pont-de-la-Maye , France

Résumé

Les cultures vivriëres de diverses graminées : Maïs, Millet, Sorgho, Riz, sont très largement répandue t sone s t soumise attaquex au s nombreusee d s s espèces de Lépidoptères dont les chenilles ont des comportements de foreurs. Par suite de l'importance des dégâts sur le rendement de ces cultu- a difficultl e coû l u ret o te s é d'emplo s insecticidesde i l i import, rechere d e - cher pour leur protection des moyens de lutte biologique : emploi d'insectes entomophage t créatioe s variétée nd s résistantes. Des exemple e telled s s recherches peuvent être e donnéMaïl r s su s concernan a Pyrall t e Ostrinia nubilalisa Sésamil t e n e Hb Sesanria nonagrioî- des Lef. La présente communication insiste sur les points suivants : la recherch variétée d e s résistante e peun s t être développéa misl u r a e pa e qu e point de techniques d'élevage de masse de l'insecte pour les infestations arti- ficielles homogènes nécessaires au jugement du matériel végétal. La définition des matérietechniqueu d i tr le d sdoi t s'appuye s connaissancele r su r s écolo- giques des relations entre l'insecte et la plante-hôte. Dans un programme à moyen terme doin o , t vise à accumuler s gène de re résistanc d s t tenie r compte des phénomènes de tolérance en vue de l'obtention directe d'un matériel de haute productivit présencn e é ravageuru d e .

Les foreur graminéee d s s constituen groupn u t e écologique impor- tant rassemblan nombreusee d t s expêce Lépidoptère«appartenane d s familx au t - PyraUdaes s de Noctuidae.de s t le e espècess Ce , capables,pou a plupartl r , e développeds e s graminéede r su r s spontanées constituen s ravageurde t s majeur culturee d s s vivrière industrielleu so : sMais , Sorgho, Riz, Cannà e sucre. Le Mais (Zea mays) t soumies attaquex au sa Pyrall e d su Maï d e s (Ostrïnia nubilalis), des Diatraea et de plusieurs espèces de Sesanria. Le ravageur primaire permanent des cultures de Sorgho (Sorghwn bicolor) en Afrique et en Asie est le Pyralide Chilo partellus ; les espèces Eldana saocharina, Busseola fused, Sesamia oretioa et le genre Diatraea étant ses ravageurs occasionnels (1). Plusieurs espèces du genre chilo et notamment

Chilo suppressaUst d'autres Pyralides (Scirpophaga albinella, Tryporyza inaertulus, T. innotata, Maliarpha separate lia dans l'Ancien Monde, Diatraea saceharalis et D. lineolata en Amérique), sont les ravageurs les plus com- muns et les plus dangereux pour les culturesdu riz (Oryza satïva) qui subis-

79 sent également les attaques des Noctuelles polyphages du genre Sesamia, (2). Ces mêmes genres, Chilo t Sesamiae d'une par t Diatvaeae t d'autre part, sont répandus sur la canne à sucre (Sa.ccha.Twn off-icinarum) (3).

Les comportements alimentaires des chenilles de la plupart de ces espèces sont très similaires partiA . pontee d r s déposée a facl à se inférieure des feuilles ou directement sous les gaines, les jeunes chenilles se nourris- sent sur les feuilles enroulées en spirale dans le cornet des jeunes plantes, ou/et s'installent sous gaine le sfeuilles de s s développées, puis pénètrent dan a tigel s , creusan galeries de t s dan a moelll s s'alimentanu o e parois de t s interne tiges de s s creuses. Selo s conditionle n s écologiques (nombr génée d e - rations, coïncidenc cultures)s de e s dégâtle , s peuvent n'intervenir su e qu r des plantes jeune n phase s e s plantevégétativde r ssu u complètemeno e t déve- loppées après floraison. Sur les plantes" jeunes, les larves peuvent s'alimen- s plus feuillele le ss r graveca t su dane s r le ste elles atteignen e poinl t t végétatif provoquant la destruction du plant. Sur les plantes développées, la présence des foreurs peut se traduire par le dessèchement des panicules, par exemple s cassepou le s e chute rizl r tigee rle d s pa t , e ss d'épis commr su e façoe d e maïsl t ne générals baissede r rendemene d spa e t duemauvaisex au s s migrations vers les grains. Ces possibilités de dégâts sur des plantes à divers stades et l'installation des jeunes chenilles sur des organes différents rend complexe la recherche de variétés résistantes.

Des caractères généraux des variétés résistantes des graminées citées ci-dessus peuvent cependant être recherchés. Pou e rizl r connaîn ,o t des variété i induisenqu s taus survie croissance de d xd t t e e plus faibles des foreurs (2). Ces variétés résistantes seraient celles qui présentent un plus grand nombre de couches de tissu lignifié, une plus grande quantité de sclérenchyme, davantag silice d e , 5,)(4 e . Pou a cannl r sucreà e , MATHEt e S CHARPENTIER (6), cités par LONG et HENSLEY (3) relèvent un certain nombre de caractères défavorables à l'installation des Diatraea : dureté de la partie extern a tigel e d e, couleur clair t revêtemenee t cireu tigess de x , haute teneur en fibre, tiges fine grandà s s entre-noeuds, etc..

Parmi ces caractères, cités à titre d'exemple, certains peuvent avoir une valeur générale pour l'ensemble des graminées : ce sont ceux qui peuvent apporter à la plante une tolérance à la présence des foreurs, d'autres sont probablement plus spécifique t gouverneraiene s s réactionle t s d'antibio- e l'agressiod s vi à s jeune s nde vi ss chenillessi deus Ce x. type caractèrese d s , parfois liés, doivent être combinés en vue de l'obtention de variétés résis- tantes.

80 Des programme sélectioe d s graminéee nd s pou a résistancl r e vis- à-vis des foreurs sont en cours de développement dans de nombreux pays. Nous n'exposerons ici que l'exemple du maïs et des résistances vis-à-vis de la Pyrale (Ostrinia nubilalis]a Sésamil e d t ee (Sesam-ia nonagr-ioîdes). rechers Le - ches sur la Pyrale ont été développées aux Etats-Unis dans des Etats du Corn Belt et particulièrement à 1'European Corn Borer Laboratory de l'USDA à Ankeny, Iowa. Elles sont actuellement étendue a pluparl à s pays de st d'Europe grâce à l'actio Groupu nd Travaie d e l internationa r Ostrinia.su l (IWGO). Dana l s grande diversit situationss éde retrouvn o , s phénomènele e s différent- ré e d s sistanc évidencn e s Etats-Unix emi au e s selo s stadenle végétatione d s . La résistance à l'alimentation des jeunes chenilles dans le cornet des feuilles est polygénique, les différents gènes agissant sur le mode ad- ditif (7)corrélations De . é trouvéeét t on ss entr e degrel résistance d é à e l'alimentation sur feuille apprécié visuellement, lié au taux de survie larvaire et la teneur des tissus en 2,4- dihydroxy-7 methoxy-1,4 benzoxazine 3-one (DIMBOA) (8, 9). Mais d'autres facteurs entrent probablement en jeu. s agissenIl t tous comm dissuadants de e s alimentaires conduisan s jeunele t s chenilles à une recherche permanente de nouveaux sites de prise de nourriture réduisant ainsi le taux de survie. Sus plantele r a floraisonl à s s jeunele , s chenille nourrissene s t de pollen stock l'aissellà é feuilles ede t s'alimentense niveaue c à t , puis s sutissua gainl le r e d se foliaire avan a pénétratiol t n dan a tigel ss Le . mécanismes de résistance à ce niveau n'ont pas été totalement élucidés et matériee d trèu pe s l résistan êtru p ea t isolé. Le souci des sélectionneurs est de combiner dans une même variété s deule x type résistancee d s effetn E . a mêml , e plante peut être spumisx au e attaques successives des deux générations et, dans d'autres régions, 1'infes- génératioe un tatioà e nndu unique don a périodl t e d'activité s'éten r pludsu s d'un mois, peut aussi intervenir sur des stades différents de la plante. Cet objecti t difficiles f atteindreà trèr eca s corrélatiosouvena y l i t n inverse entre la résistance sur feuille et la résistance sur tige. Il ne faut pas non plus perdre de vue la nécessité d'obtention de variétés à bons caractères agronomique t tenie s r compt caractères de e tolérancee d s méthoda - L . sé e d e lection récurrent i permeequ t l'accumulatio gènee nombreue nd d à s x loci pour s caractèrele résistance d s e souhaités, tou gardann e t base un et génétique large pour les autres caractères a été recommandée (10, 11, 12).

Des variétés synthétiques utilisant notamment du matériel végétal européen sont en cours de préparation par IWGO. L'exécution de tels program-

81 mesélectioe d s n n'est possible qu'à deux condition : sréalise infestas de r - tions homogènes de l'insecte sur le matériel à tester et disposer d'une méthode rigoureuse de jugement. Pour la Pyrale du Maïs, les chercheurs amé- ricains pensen "Lese qu t progrès auraient nulsé ét sans a techniquel d'in- festation artifioielle" (12). La maitrise de l'élevage sur milieu artificiel (13> 14, 15, 16) a permis de multiplier les essais et de donner plus de souplesse à la technique d'infestation. L'adoption d'échelles précises de notation pou s différentle r s type dégâtse d s , admises internationalement, facilité grandement les observations et les échanges d'informations. On s'efforce d'adapter les systèmes de jugement établis aux Etats-Unis aux conditions locales de relations entre l'insecte et la plante-hôte.

Les travaux sur les Sésamie ont fait l'objet d'un bien moindre développement techniques De . s d'infestion artificiell t cependaneon é ét t proposées (17). Les possibilités d'élevage de l'insecte sur milieu artifi- cie démontréesé l ét (18 t )on . L'expérience acquis r Ostriniasu e nubilalis peut guider dans l'adoption de critères de discrimination. Des sélections pour la résistance aux stades jeunes ont été entreprises en Espagne (MONTE- AGUDO, communication personnelle) et des jugements de la sensibilité de lignée t d'hybridee s l'attaquà s lieu e Francn r tigut e su eeon e (19)s .De progrès pourraient certainement avoir lieu en étudiant le matériel végétal cultivé dans les zones habituellement très attaquées par ces insectes.

s quelquePace r s exemples n peuo , t remarque s programmele e qu r s de sélection en cours pour la résistance des graminées aux Lépidoptères fo- reurs sont encore relativement peu développés mais devraient, dans de nom- breux cas, faire l'objet d'une attention particulière. Une première phase est de définir, pour les différentes situations, la ou les espèces "clés" dont les populations retentissent lourdement et régulièrement sur la culture t d'envisagee a recherchl r variétée d e s résistante toléranteu o s i s nécess - sair à el'ensembl s espècesce e bonne d e Un . e connaissanc s situationde e s écologiques particulières des relations végétal-insecte permet d'orienter e programml t d'affinee e s méthodesle r incluann E . a recherchl t carace d e - tère de résistance à l'insecte dans les schémas classiques d'amélioration, des progrès doivent être immédiatement attendus de l'utilisation de la variabilité naturelle des espèces végétales. Néanmoins, dans certains cas, le recours aux mutations induites ne doit pas être a priori écarté. Plus facilement envisageable pour les espèces autogames, il suppose toutefois, étant donné les effectifs importants à observer, l'existence d'un crible fiable et facile à utiliser techniqua L . e d'élevag masse d el'insecte d e e doit être maitrisée pour réaliser moindru a , e coût s infestationle , s artificielles nécessaires

82 et les critères de discrimination doivent être simples et faciles à mettre en oeuvre. Il convient d'insister tout particulièrement sur ces conditions essentielles à la mise en oeuvre d'un programme d'utilisation des mutations. La disposition d'un moye criblage d n e efficace, intervenan i s possiblt r su e des stades jeunea plantl e d t sbie e n corrélé ave a situatiol c champu na , parait indispensable. En conclusion, les exemples de travaux de recherche de variétés de graminées résistantes aux lépidoptères foreurs permettent de tirer les enseignements suivant: s Les programme moyeà s n terme doivent cherche accumuleà r s de r gène résistance d s e apportan améliorations de t s partielles don a somml t e peut abouti haun u à tr nivea résistancee ud doin O .t combine s résisce r - tances avec les phénomènes de tolérance pour l'obtention d'un matériel végétal de haute productivité même en présence du ravageur. La définition des méthode jugemene d s t doit s'appuye s connaissancele r su r s écologiques locales des relations entre l'insecte et la plante-hôte. Enfin, la mise au poin techniquee d t s d'élevag masse d e l'insecte d e e pou s infestationle r s artificielles homogènes du matériel à étudier constitue la phase prélimi- naire indispensable.

Note : La terminologie (résistance, tolérance, antibiosis) se réfère aux définition e PAINTEd s . R

Remerciements : Nous remercions nos collègues CORNU, DOMMERGUES et MARIE pour leurs conseils concernant l'utilisation des mutations induites pour l'augmentatio niveaus nde résistance d x x eau insectes. Références

) (1 YOUNG, W.R., TEETES, 6.L., Ann. Rev. Ent (1977^ .22 3 )19 (2) PATHAK, M.D., Ann. Rev. Ent. ^3 (1968) 257 (3) LONG, H.W., HENSLEY, S.D., Ann. Rev. Ent. _17 (1972) 149 ) (4 DJAMIN PATHAK, ,A. , M.D. Econ. ,J . Ent 0 .6 (1967 7 )34 ) (5 PATANAKAMJORN PATHAK, S. , , M.D., Ann. Ent. Soc. Amer 0 (19676 . 7 )28 (6) MATHES, R., CHARPENTIER, L.J. in Pests of sugarcane. Elsevier, Ams- terdam (1969) 175

83 ) (7 JENNINGS, C.W., RUSSELL, W.A., GUTHRIE, W.D., GRINDENLAND, R.L. Crop Sei. ^4 (1974) 394 (8) KLUN, J.A., TIPTON, C.L., BRINDLEY, T.A., J. Econ. Ent. 60 (1967) 1259 ) (9 KLUN, J.A., GUTHRIE, W.D., HALLAUER, A.'R., RUSSELL, W.A. Crop. Sei 0 ^ .(1970 7 8 ) (10) PENNY, L.H., SCOTT, G.E., GUTHRIE, W.D. 7 (Î967,_ Croi 7 Se p) 40 (11) GUTHRIE, W.D., RUSSELL, W.A., JENNINGS, C.W. Ann. Corn Sorghum Conf. Proc 6 (19712 . 5 )16 (12) BRINDLEY, T.A., SPARKS, A.N., SHOWERS, W.B., GUTHRIE, W.D., Ann. Rev. Ent. 20 (1975) 221 (13) CHIPPENDALE, G.M., Proc Cent. N .. Ent Br .. Soc. Amer _ (197227 . 4 )11 (14) GUTHRIE, W.D., RAUN, E.S., DICKE, F.F., PESHO, G.R., CARTER, S.W. Iowa Stat Sei. 0 J e4 (1965 . 5 6 ) (15) REED, G.L., SHOWERS, W.B., HUGGANS.J.L., CARTER, S.W. J. Econ. Ent. 5 ^ (1972) 1472 (16) LEWIS, L.C., LYNCH, R.E., Iowa Stat Sei. 4 J e4 (1969 . )9 (17) ANGLADE , AnnP. , . Epiph 2 (19611 7 . 35 ) (18) POITOUT, S., BUES, R., Ann. !. Ecol. Anim. 2_ l (1970) 79 (19) ANGLADE , AnnP. , . Epiph 2 1 (1961.3 41 )

84 * LA RESISTANCE VARIETAL A LUZERNL E D E E (Medicago sativa) L. AUX INSECTES INTERET ET CONCEPTION DES PROGRAMMES RELATIFS AUX APHIDES . BOURNOVILLR E INRA Zoologie 86600 Lusignan, France Résumé

On présente l'intérêt des programmes relatifs à la résistance varié- tair l'exemplsu e s relationde e luzerna l e sd e Môdicago aphis de sativa-t e . L x Etats-UnisdesAu . , cette méthod utilisét ees e pour lutter contr s dégâtele s provenant de l'introduction accidentelle de pucerons. En Europe, l'intensifi- catioproductioa l e nd n fourragère justifi n emploso e i puisqu'elle évita l e pollution et limite le coût de la protection phytosanitaire pour les produc- teurs . Les diverses étapes de ce programme sont analysées. Le cas du Puce- Poiu d sn ro (Acyrthosiphon pistm HARRIS notamment es ) t discuté d'après le s éléments bibliographique notrt se e expérience premiee .L rmisa l poinn e t es t évidenc dégâts ede ravageuru d s l fau.I t ensuite dispose méthodee d r s d'élevage de cet insecte. On se méfiera du conditionnement réalisé par la Fève (Vicia fdba L.) comme hôte de remplacement dM. piswn. On doit de plus, disposer de tests fiables et répétitifs. Nous évaluons pour notre part le taux net de des pucerons. La sélection de variétés de luzerne au déterminisme génétiqu résistance d e e suffisamment large doit permettre d'évite problès le r - variabilita l e med s populations de é s d'aphides. Divers exemple modis ce -e d s fications de résistance sous l'effet de la sélection de nouveaux biotypes sont présentés A l'heur. e actuelle e disposprésomptionn e d n ,o e qu e s quanx tau causerésistanca l e d s e variétal a luzernl e Aphidesx ed eau s programme.Le s de sélection sont cependant favorisé. sativaa grandM l r e d epa s ca dan e l s variabilit l'espèce éd e végétale.

La première idée qui vient à l'esprit pour justifier les programmes de sélectio variétée nd luzerne d s e résistante s ravageur de quaa s à s t -es s lité de plante fourragère. Il n'est en effet pas question de prendre des risques avec l'emploi d'insecticides pou végétan u r l consomms animaude r xpa é domestiques, à brève échéance après d'éventuels traitements. En fait, il a fall événements ude s relativement fortuits pour imposer cette méthod luttee d e . En effet, la sélection de cultivars de luzerne résistants aux insectes a four- ni une solution élégante aux problèmes graves soulevés par l'introduction accidentell divere ed s ravageur x Etatau s s Unis. Dansle Sud-Oues payse c e d ,t l'implantatio Pucerou nd n tacheté Thevioaphis maculatan e Bucs n 195mi e k a 4 caus a culturl e a luzernel e ed 1957s a sélectioDè l ., a variétl e nd é Moapa, résistant . e poinmaculatal T déparé e ed à ét t a t d'un important programme de lutte intégrée qui a permis de limiter les dégâts de Taphide ( 1). En 1972,

terminologia L * e (résistance, tolérance, antibiosis réfère s défini)x eau - tions de PAINTER.

85 SORENSE l a signalaien t e N 5 variété 2 e plu e qu d ts e luzernd s e résistantee c à s puceron étaient disponibles pou s producteursle r succèe C . a d'ailleurs - en s train regain u é n d'attention pou s étudele r s concernan e pucerol t poiu d n s Acyrthosiphon piswn Harris, insecte à propos duquel l'intérêt de la résis- tance variétale avai é soulignét t s 1934dè é . For e cettd t e expérience- re n o , a lèverrécentl e qu a e introduction d'Acyrthosïphon Kondoï Shinj Etatx au i s Uni a rapidemens é suivi a ét recherchl t e d e e planted e s résistantes (2)n O . dispos à présen s dè ee lignée d t s expérimentale e luzernd s e présentan- ré e un t sistance multiple aux trois aphides A. Konâoi, A. pïswn et T. maculata (3). La situatio t différentes n n Europa e luzerneel ù o e , mêm i s ell et introes e - duite des confins de l'Asie, est implantée depuis le 16e siècle. Ce n'est que depuis quelque tempe l'intensificatioqu s a spécialisatiol t e n a l e d n culture ver a productiol s e fourragd n e déshydraté notamment, incit à surveile - ler les facteurs du rendement. Les pullulations de certains insectes ravageurs justifien à auss l investigatioe t un i a résistancl r su n e variétéd e s adaptées aux conditions européennes, d'autant que la luzerne est considérée comme une plante "pauvre" , mêm où n excluan, e e s risquele t e pollutiond s , l'emplos de i pesticides n'est pas économiquement justifiable. C'est ainsi que nous avons entrepris des études sur la résistance variétale de la luzerne au Puceron du Pois. Nous allons exposer, d'aprè s donnée le a sbibliographil e d s t notre e e propre expérience, la stratégie des programmes de sélection variétale sur le s précica s rapportde s a luzernel s aphide e de sd t e s. Le poin s e a déparétudemisl d ce tn évidenc t e e d es a st l e d e nuisanc ravageuru d e s rechercheLe . s portan a résistancl r su t s plantede e s son effen e t t relativemen t téviden es longue l l'intérêe i qu t t e s t économique s espècede n cause s e guid e choil e s programmesde x . C'est ainsi qu'en France, nous avons établ deue qu xi insecte e Phytonoml : s e Hypera variabilis Hbstt e . e Pucerol Poiu d n s justifiaien e telled t s recherches (4) transpositioa .L s de n méthodes des auteurs nord-américains ne permettent pas d'établir d'avantages décisifs dans testno s s réalisé n conditione s s contrôlée s rare de e l'ud ssn cultivars sélectionné pour sa résistance variétale envers le phytonome. Nos premiers résultats e acquiPucerol r su Poiu s d n s sont beaucoup plus satisfai- sants (5) choie .L e l'insectd x e réalisé l i convien, e disposed t r d'une métho- de d'élevag e massd e ravageuru d e . BARNE, reconnaissaienal t e S ) (6 n 197e t4 que parmi les insectes nuisibles à la luzerne, on ne disposait de telles tech- niques u laboratoir a s ,puceron de n s serree t ca e dane d'uu s o e nqu l ,s Hymé- noptère nuisibl semencex au e e luzernd s e Bruahophagus rodai Gus. Dans le s infestationx autreau é li s t cases s n naturelle,o à leur t e ss t aléases l I . certaia reproductiol e qu n n parthénogénétiqu s aphidede e s facilit e maintiel e n

86 et la multiplication des souches. Cependant, la luzerne ne constitue pas un matériel végétal facil manipuleeà peun o t t e rêtr e amen utiliseà é hôtn u e r d e remplacement Fèva L . e plante viciaun t e es fababie . L n accepté e pucerol r pa e n . piswn,A mais tout comm s auteurle e s américains, nous avons constaté dans certaines de nos expériences, un conditionnement à cet hôte de remplacement. Le retour de la souche d'insecte sur une variété sensible de luzerne parait sou- haitable, dans de tels cas avant le début du test. Sur l'exemple d'une même espèce d'insecte, on constate que les types de tests retenus par divers auteurs, varient. Certains s'intéressen l'insecteà t , d'autres retiennent l'effe- ra u d t vageua plantel r su r .

Au sujet du Puceron du Pois , les auteurs américains recommandent d'infester des plantules au stade cotylédonnaire avec de grandes quantités d'aphides (6). Lorsque la plupart des plantes sont mortes dans le témoin sensi- ble, on compte le pourcentage de survie des variétés évaluées. Nous avons adopté pour notre part comme indic comportemene ed t variéta a luzernl e d l e enver. A s pisim, le taux net de reproduction des aphides après deux semaines d'élevage de larves de 4e stade qui allie les deux critères de fécondité et de survie. Nous pesons de plus les pucerons au début du test et après 1 et 2 semaines. Cette pesée nous permet d'avoir notamment une appréciation sur l'état initial de nos insectes. On sait en effet que les aphides sont très sensibles aux facteurs du a surpopulationl milie à t ue . Leur poid t trèes s seffets altérce r s épa défavo - rables don s conséquencele t sone n s t effacées qu'après deux générations (7). Or, la fécondité est significativement corrélée avec le poids initial (r = + 0,71).

Les qualités des tests mentionnés par GUY (8) sont : la fidélité, a discriminatiol bonne un e t ne corrélatio passe s champu i na e qu ave e . c cSou - lignon propoa e variabilitl c e à s qu s végétau éd l peut implique notablee d r s modifications de résistance. C'est ainsi que sur un clone de luzerne, nous avons trouv variations éde a résistancl e d s e variétale selo a phénologil n u d e végétal reproductioe d tau e t L . ne x . e doublpisuml ndM t es e lor stadu d s e stadu a floraqu'ie c t e e es végétatild l stadu a u eo f fructifère. Nous testons donc nos luzernes au début de leur floraison.

La connaissanc a génétiqul e d ea résistancl e ed e variëtale un t ees étape importante d'un programm a résistancel e sélectioe d d e e vu coma n L n.e - plexité de ces études explique que des données contradictoires peuvent exister. Les auteurs ont parlé successivement à propos de la résistance de la luzerne au Puceron du Pois, de disjonction à caractère allopo^lyploïde avec deux gènes, un dominant récessifn u , , puis, danétude un s e plus récente, d'une disjonction de type autotétraploîde mettant en jeu un seul gène dominant (9). La recherche

87 d'un déterminisme génétiqu basà e e a meilleurl larg t ees e solution pour éviter les surpassements de la résistance occasionnés par l'existence de races d'in- sectes. Cela nous amène à parler de la variabilité des populations des aphides de la luzerne. Les travaux successifs de NIELSON (10) ont prouvé l'existence de biotype . maculataT e d s dans l'Oues s Etats-Unisde t . L'étud l'intere d e - action entre ces biotypes et la résistance de diverses variétés (11) montre que dans quelques cas nouveaue ,d x biotypes attaquent certaines variétéu (o s leur clones parentaux) spécialement sélectionnés pour leur résistance envers l'aphide relatioe Un . n gène pour gène entr a virulencl e biotypes de ea l t e s résistanc variétés de eparfoiu p a s s être mis évidencen e faitn E .a stabil , - lité de la résistance de la variété Lahontan, quel que soit le biotype auquel oa confrontel n système,s prouvde e qu es plus stables, sans doute polygéniques, existent également. Il est évident que l'efficacité de la sélection variétale repos r l'utilisatiosu e tele nd s déterminismes. D'ailleurs cettà , e variation dans le temps des populations d'insectes, est associée une variation dans l'espace. Nous obtenons des résultats souvent différents de ceux des auteurs nord-américains dans l'évaluatio a résistancl e nd variétéss de e , comme noue l s prouvent les données suivantes :

Variétés Résistance (R) ou Sensibilité (S) aun France x Etats-Unie s S R Apex Kanza R R R S Lahontan S R Team

Quelle est donc la meilleure voie pour trouver ces gènes de résis- tance ? Chez la luzerne, c'est la variabilité géographique du végétal. Trois raisons expliquent ce fait. Il s'agit d'une plante allogame, tétraploïde et relativemen sélectionnéu pe t e comparativemen certaineà t s céréales liéeà s l'agriculture humaine depui milliers de s s d'années mutations Le . s induitee n s permettron révélee d t caractères de r s utilisables pou a sélectiol r n variétale que dans les cas de mutations dominantes. De même, chez la luzerne, les mé- thode croisemente d s s interspécifiques s'avèrent délicate utiliserà s n O . trouve cependant leur mentio propo à na résistancl e d s phytonomu ea e (12)l I . est vrai que les facteurs de résistance trouvés jusqu'ici envers cet insecte relèvent de la tolérance de la luzerne cultivée (13).

On pourra être surpri trouvee d s dernièrn e r e mentios étapece e sd n d'un programme de sélection variétale l'étude des mécanismes de la résistance. En fait s relationle , s plante-insecte sont complexe t n'one s t trouvé d'expli- catio dan e nombrn u nqu s d'exempls epa limita y case - en' éd lu che l .I a l z t définai n composn zernu Vo i ù eo é responsabl a résistancl e d e e variétale. Les résultats de HORBER (14) indiquent cependant que la convenance de diverses variétés pour le puceron du pois pouvait être liée à leur teneur en certains glucoside s saponinesle : s . D'aprè auteurss ce s , c'es fractioe un t n bien spé- ciale de ces saponines : l'acide médicagënique qui serait à l'origine d'une actio type nd e "antibiosis e pucerol r a cicadelll poisu u " d nt e s e Harris. On sait par ailleurs que les saponines ont une action anti- croissance sur certains animaux. Une autre approche plus éthologique de la nature de la résistance variétale est fournie par NIELSON et DON (15) qui, au moyen d'une technique d'enregistrement du comportement alimentaire de T. maeulata ont prouvé que sur des clones résistants de luzerne, la pénétra- tion des tubes libériens et l'ingestion de sève par le puceron ne s'effectuent pas convenablement. Au term cette d e e rapide enumeratio s étapende s d'un programme d e sélection, on peut poser quelques questions. Le manque d'information sur les mécanisme a résistancl e d s e n'Impliqu ecertaine t-iqu s lspa tests d'étudu d e comportement variétal sont mal adaptés ? La logique voudrait qu'on parte da connaissancl e a natur l a résistancl e d ee ed e pour défini programmn u r e cohérent alors que dans la pratique, cette phase occupe bien souvent la dernière place raisonn e , , nous l'avons dita complexitl e ,d relations éde s insecte/plante-hôte. L'exempl saponines de e s nous incit corollairn e e ed cette première question à nous demander s'il n'existe pas de risques pour les autres critères de sélection lorsqu'on ne connait pas les causes de la résistance risques Ce . s sont sans doute très limités, mai doin s o sle t avoir présents à l'esprit. En second lieu, quelle importance doit-on accor- x biotypeau r de Certain? s s d'entrconstituent-ile n x eeu s supede s r pa s racedistinctioa L ? s biotypes nde s parait actuellement plus nette dans le s rapports d'une espèce d'aphide plusieure d t e s s espèces végétales qu'au nivea rapports de u s aves variétéle c s d'un seul végétal. C'est ainsi qu'àa l suit MULLEe ed R (16), nous avons montré danexpériences no s a séparatiol s n marquée des biotypes trouvés sur pois et sur luzerne (17). Nous concluerons cependan a variabilitl e qu t é naturell- lu a l e ed gagn u zern et suffisanes e réussite d t programmes de e s relatif a résisl sà - tance variétale enver s aphidesle s , sous réserv l'oe qu en prenn s précaule e - tions méthodologiques évitant les principales difficultés que nous venons d'énumérer. L'étroite dépendance des pucerons avec leur végétal-hôte est très certainemen élémenun t t important pour explique travaules que rx dance s domaine de sélection soient plus avancés que sur les autres groupes d'insectes.

89 Remerciement : sNou s remercion . GUM s Y (INRA, Amélioratio s Plantesnde ) des éléments de discussion très profitables qu'il nous a confiéi sonqu t e sinclu s dan e textl s cette ed e note.

Références

) (1 SMITH , n KILGOR n i BOSCHR.F.de , n ,R. EVa W.W. DOUTT, Academic Press New York (1967) 295 ) (2 NIELSON, M.H., LEHMAN, W.F., KODET, R.T. econ. J , . Ent 9 (1976.6 1 )47 ) (3 NIELSON, M.H., LEHMAN, W.F. econ. J , . Ent 0 7 (1977. 3 )1 ) (4 BOURNOVILLE , RapporR. , t Eucarpia, groupe Med-iaago sat-iva, Piestany, Tchécoslovaquie (19763 8 ) (5) BOURNOVILLE, R., COMTE, B., Bull. SROP-OILB "Amélioration des plantes pour la résistance aux insectes et acariens" 3__ (1977) 97 (6) BARNES, O.K., FROSHEISER, F.I., SORENSEN, E.L., NIELSON, M.W. LEHMAN, W.H., LEATH, K.T., RATCLIFFE, R.H., BUKER, R.J., USDA agric. Res. Serv. (1974) NC 19 ) MURDIE(7 , TransG. , Ent. .R . Soc. Lond 1 (196912 . ) 443. ) GUY(8 , Fourrage,P. 4 6 (1975s 9 )1 (9) BUSB1CE, T.H., HILL, R.R.Jr, CARNAHAN, H.L. Alfalfa Science and tech- nology. Amer. Soc. , Madison (1972) 283. (10) NIELSON, M.W., DON, H., SCHONHORST M.H., LEHMAN, W.F., MARBLE, V.L. J. econ. Ent. 63 (1970 1822 (11) NIELSON, M.W. econ. J , DON. , Ent, H. 7 .6 (1974 8 )36 (12) ELGIN, J.H., RATCLIFFE, R.H., GRAHAM J.H., Me MURTREY, O.E., 39th ann. Rep. Forage, Beltsville agric. Res. Cent. (1975) suppl5 . (13) BARNES O.K. HANSON, C.H., RATCLIFFE, R.H., BUSBICE, T.H., SCHILLINGER, J.A., BUSS, G.R., CAMPBELL, W.V., KEMKEN R.W., BLICKENSTAFF C.C., USDA agric. Res. Serv. (1970) 34 (14) HORBER LEATHE., , , K.T., BERRANG MARCARIANB., , HANSONV., , , C.H., Ent. exp. et appl. 17_ (1974) 410 (15) NIELSON, M.H., DON, H., Ent. exp. et appl. YJ_ (1974) 477 (16) MULLER, F.P., Zool 8 Syst. 9 (1971 Jb .d B .1 )13 (17) BOURNOVILLE, R., Ann. Zool. Ecol. anim. 9 (1977) 87

90 POSSIBLE ADVANTAGE SMALF SO L DIFFERENCE RESISTANCN SI E TO APHIDS

H.J.B. LOWE Plant Breeding Institute, Trumpington, Cambridge, UK.

Abstract

POSSIBLE ADVANTAGE SMALF SO L DIFFERENCE RESISTANCN SI APHIDO ET S Small differences in resistance are often available to plant breeders but their use presents practical difficulties, needing sensitive assessment techniques and careful evaluation in the field. Low levels of resistance to aphid sugan i s r beet, field bean d adulan s t cereal plants were observed glasshousee ith n . Field experiments with resistant beet showed reduction of aphid numbers and in some years of virus yellows infection. Breeding programme progresn si s with sugar bee d fieltan d bean . faba (V sbasee )ar d on selection amongst small differences of resistance to aphids. argues Ii t d that low-level resistanc n contributeca e significantlo yt the success of breeding for resistance, whether based on natural variation or on induced mutation. The time over which resistance remains useful in agriculture depends unpredictabl evolutionare th n yo y relationship between crop plants and their pests, but low levels of resistance should maintain their usefulness.

INTRODUCTION

The development of insect-resistant crop varieties has generally involved types of resistance where resistant and susceptible plants were clearly distinct. However, resistanc defines ea a Paintey s db i } {1 r relative phenomeno d collectionnan planf o s t genotypes often show numerous small difference resistancn si w largfe et edifferencesbu examplr ,fo e with resistance to aphids in Solanum {2, 3} or {4, 5}. Work on resistanc Plane aphido t eth tt a sBreedin g Institute (PBI), Cambridge, aims to exploi Ivelw lo tinheritef o s d resistanc s concernei t ebu d only with naturally occurring variation. The arguments set out below on the prospects of this approach would apply equallcase exploitinf th eo n i y g induced genetic variability. Varieties wit w levelhlo resistancf so unlikele ear repao t y y breeding effort in every situation. Where large populations of insect pests regularly cause severe damag r totaeo l los unprotectef o s d crops, effective contro likels li y only with high level resistancef so breedint ,bu g material or plant collection assessee b n ca s effectivenese d th fiele easil d th an dn i y s resistance oth f e judged directly. However, ther mane ear y crops, including sugar beet {6} and cereal crops {7, 8} in Britain, which suffer sporadic attack from pests which rarely cause total loss. The variability of pest population levels results from partial contro naturay lb l agentsw lo d ,an level resistancf so e shoul e consideredb elemenn a s a dintegratef to d control, taking advantag naturae th f eo l control presence Th . f eo effective predators of pests can, however, make breeding for resistance much more difficul assessmend tan t test wely sma l don e havb protecte n eo i t e d environments, especially if a quantitative approach is used to identify low levels of resistance.

91 Two problems are implicit in any consideration of low level resistance for plant breeding. First, can sufficiently sensitive methods of assessing resistance be developed to handle enough plants for an effective breeding programme? Second, are small differences in resistance likely to have sufficient impac pesn to t control, shor d lonan t gbreedine termth r ,fo g worthwhilee worb o t k ?

ASSESSMENT OF LOW LEVEL RESISTANCE

g advantagbi A s thai e t low-level resistanc y ofteema e founnb n i d advanced breeding material and therefore may be readily accessible to plant breeders with continuing programmes. However difficuls i t ,i develoo t p methods which are sufficiently sensitive to separate plants or stocks possessing small differenc resistancef eo , whilssame th e t ta tim e being both practical, when applied on a scale suitable for breeding, and compatible witothee th h rbreedine partth f o s g work methoA . d develope r sugafo d r bee , 10}{9 t , which satisfies thesa n ei requiremente us n i s i parn d i s an t plant breeding programme at the FBI, assesses resistance to the aphids Myzus persicae and Aphis fabae in glasshouse tests which emphasize the effect of aphid settling behaviour {ll}. Beet plants to be tested in the glasshouse are grown in pots set out in large replicated blocks with beet stocks randomise eachn youne i d Th .g plant eace ar sh infeste d w apterouwitfe a h s aphids taken from stock cultureaphide th e lef d roaar o s t an ss the ma y will. Number aphidf o s recordee ar s d w dayafte givo fe t sa r e assessmentf o s resistance differences amongs stocke th t s tested. Resistanc . fabaA o n t ei was observed by the same method {12}, which is now used for a small breeding programme at the FBI to increase levels of resistance in these beans.

It has proved more difficult to assess small differences in the resistance of adult cereal plants to Sitobion avenae and Metopolophium dirhodum A techniqu. rearinf eo g caged aphids separatel eacn o y h variety hala fo rd f an abouaphi e ton d generation s consistentlsha y given statistically significant (at 5 per cent) differences amongst varieties of wheat and barley {10, 13}, but the results have varied widely between experiments. The suit- ability for aphids of wheat and barley differs greatly amongst plants at various growth stagesalss i od muc,an h affecte y environmentadb l factors. A few varieties have been identified as having resistance in a number of experiments {13}, but no breeding programme for resistance to the two aphids is practicable as yet.

The expressio f resistancno aphido t e sugan i s r beet alss greatlowa y affected by environmental influences, and differences between beet stocks were often reduced both under conditions causing increased resistance of beet poog ,e r lightin exhaustior o g resourcee th f no planf o s t pots {9}, and under very good growing conditions when all beet tended to be more susceptible. Other environmental changes altered the resistance relation- ships amongst beet stocks. Sugar beet is an outbreeding crop and the breeding programme at the FBI aims to increase levels of aphid resistance by recurrent selection in beet populations, thus combining a wide range of genes each having small effects on the expression of resistance. This approac d beehha n followeanalogoue lighe th th f to n i d s wor Arnoldf ko , Inné Browd san bacterian no l bligh cottof Afric. o tE n i na {14, 15}, Quantitative techniques {14} demonstrated continuous variatio blighf no t lesion severit botn i y h resistant material n loca froSudai e th d ml n an cotton which had been wholly susceptible in the Sudan. Selection for resistance in the resistano lattet d le r t stocks which appeare havo t d e major-gene resistance when tested in the Sudan, demonstrating "that what could be treated as major- gene segregation in one set of environmental conditions could more usefully

92 be regarded as a problem of continuous variation in another" {l5}. The resistanc f cottoeo n bacterial blight e considereb cam o breedine t e th n i d g programme charactea s a s r with continuous variation like exampler ,fo , yield and co-workers Arnolhi d an d s concluded that "Instea relyinf e do th n go transferenc resistancf eo e genes from introduced varieties worr s ,ou kha repeatedly demonstrate importance th d examininf eo g locally-adapted material for relatively small amounts of variation under polygenic control...." {15}.

This approac resistanco t h e breeding relie a carefu n o s l assessmenf to small differences in resistance to build up the level of resistance by accumulation of minor genes, and is clearly more feasible with outbreeding crops than with inbreeding species e initiaTh . l observatio f low-leveno l resistance offers the possibility of developing effective high-level, polygenic resistance by repeated selection amongst the small differences observed. Breeding for resistance in this way is much easier to integrate wit generaa h l breeding programme sinc doet t involvi e sno disruptioe th e n often caused by the introduction of wild or agronomically unsuitable material which includes just one or two desirable resistance genes.

LOW LEVEL RESISTANCE AND PEST CONTROL

Breeding resistant crop varieties appears the most cost-effective metho pesf diseasd o an t e contro nationaa n lo l scalecerean i . ,eg l crops practicn i {16} t potentiae ,bu th e l benefi addinf to g further resistance characteristic plano st t breeders' aims mus establishee tb d before extensive breedin considerede b n ca g . Field experiment necessare ar s determino t y e whether available resistanc producn ca e e significant improvement controln i s , or what levels of resistance must be developed by breeding to achieve worth- while results. An evaluation may be made from relatively small field plots, where resistanc majoe th likels re i b factoo t y n controli r sorghun i . ,eg m {17}w levelLo . resistancf o s more ar ee likelvaluable b o t y e where natural mortality of the pest is important {18}, but field evaluation must then be base plotn o d s large enoug accommodato t h n insecea t community specifio ct the variety concerned, eg. investigation of the effect of two levels of pea- aphid resistance in alfalfa {19}. Large plots may be expected to detect effects such as that proposed by van Emden {20, 21} who argued from a model that control of aphid infestation may be achieved by combination of a low level of resistance with an appropriately synchronised attack by natural enemies, when neither effect would exert useful control alone.

The effect of resistance to aphids in sugar beet on field populations of M. persicae has been studied at the FBI in large plots (25 to 27m square) of susceptibl resistand an e t beet {22}, usin experimentas ga l varieties mixtures of seed available from the beet breeding programmes. This work coincided wit perioa h f severo d e infestatio . persicabeeM f n o y tb n i e Britain {Figure l}, but nevertheless aphids were released to supplement the natural population 1972n i s , 197 d 1975 3normae an Th . l coursf eo infestatio Cambridgt na s showewa 197n ni d 197 3an 4 when aphid populations botn o h resistan d susceptibltan e beet increased from mid-Jun peaa t o ka et the end of the month and then declined rapidly at the beginning of July. There were fewer aphids on the resistant than on the susceptible beet, but in these years virus yellow . persica mai(M se th n s vectorei ) spread rapidly and there was no reduction of virus incidence associated with the smaller aphid population resistane th n i s t plots 1972n I . , however usuae ,th l peak of aphid numbers occurre susceptible th n o d e plots only, whilst numberf so M. persicae on the resistant beet remained small. The observation of numerous Coccinellid larva t thiea s time appeare supporo t d Emden'n tva s predictio combinee th f no d effect f low-leveso l resistan naturad tan l enemies.

93 There was also much less virus yellows on the resistant than on the susceptible beet in 1972.

The contribution of natural enemies to aphid control in Britain is not clear, but polyphagous predators (Carabidae, Staphylinidae, Forficula, etc.) appear important in reducing aphid numbers {23,24}, Especially where aphid numbers are low as on beet, these predators which are commonly present in the crop befor aphide th e s appear e closel,ar y synchronised {20} witaphie th h d populatio therefore ar d nan e most effective 197n I . 4 when there were very w Coccinellidfe other o s r specialist aphid predators ver,a y simple model indicated mortalities on the beet of about 5 to 15% of the population per day in increasing populations and 30 to 40% per day in declining populations. Carbaryl suppresses natural enemies of aphids {25} and when applied to beet, has given substantial increase aphin i s d numbers {Figur . These2} e observations emphasiz potentiae th e l importanc naturaf eo l enemien i s integrated contro aphidf lo n sugao s r beet.

The British Sugar Corporation's advisory and spray warning services to growers provid backgrouna e r integratefo d d aphid controEnglise th n i lh suga possible r th beef beeo r te t fo evarietieus cro d an p s wit w levello h s of aphid resistance. In 1975 plots treated with aphicides, applied in accordance with the British Sugar Corporation spray warning scheme thresholds, were compared with unsprayed plots in the field experiment at the FBI, and the resistant beet suffered less virus yellows than the susceptible beet both with and without aphicide treatment {18}. Together these field experiments, 1972-75, indicated that level resistancf o s producee b n ca e d within available sugar beet breeding stocks which could make an important contribution to the integrated control of aphids and virus yellows on beet in England.

The number of years over which resistance is likely to remain effective if pest-resistant varietie widele ar s y grown should als e considereob n a t a d early stag breedinn i e resistancer fo g . Although durability cannoe tb predicted in any specific case, certain general arguments are relevant in assessing the likely value of resistance. The evolution of resistance- breaking (virulent) races or biotypes depends both on the selection pressure exerted by resistant cultivars and on the ability of pest populations to respon o that d t pressure. Clearly w leve lo resistanc f ,o la s lesi e s likely to exer dominatina t g selection pressur pesa n teo tha high-leves i n l resistance. This applies particularl f low-levei y l resistanc uses i es a d one componen pesa f tto management scheme wher selectioe th e n pressuren ca s be diversified with corresponding reduction of the chances of the evolution of pests able to overcome any single component of control. Also, if a resistant cultivar is protected by combination of low levels of several types of resistance, selection pressure should again be diversified and failure e cultivaoth f r less likely. The competence of a pest population to respond to selection by resistant cultivar predictee b n ca s d only rarely dependt ,bu availabilite s th bot n o h y of appropriat life th e e n cyclo gene d ean s which govern rate whicth st ea h w genotypene multiplyn ca s generan I . l virulent race f inseco s t pests have occurred less ofte d aftenan r resistanf longeo e us r t cultivars tha bees nha n the case with fungal pathogens. Aphids appear exceptional amongst insects in the number of virulent races reported, eg in greenbug and spotted alfalfa aphid {16, 26}, but it is noteworthy that they share certain life cycle characteristics with the more troublesome fungal pathogens, eg barley mildew, Erysiphe graminis f.sp. hordei. These features, rapid asexual reproduction on crops, widespread aerial dispersal and one sexual generation per annum,

94 favour rapid evolutionary respons environmentao et l changee us se th suc s a h resistanw ne oa f t cultivar.

Entomologists concerned with developing strategie future th r e fo s contro f inseclo t pest y considesma models ra experience th s e gained with pathogens such as E^. graminis which have responded rapidly to the use of resistant varieties and of . Control of barley mildew was sought over many year breediny sb g barley varieties wit successioha oligogenif no c high-level resistances, but these rapidly evoked new virulent races of the pathogen. frequence Studth f o y virulencf o y e gene milden si w populations in the UK {27}, rather than observation of the occurrence of virulent races, has given improved understandin evolutioe th pathogee s f th go ha f d no nan generated new strategies for exploiting current resistant barley varieties in the presence of the corresponding pathogen virulence gene. This further exploitatio f resistancno e depend disruption so genetie th f no c homogeneity of barley crops whic bees hha importann na t dominatine factoth n ri g selection pressure exertew resistanne y db t varietie pathogen so n populations. However, evolution of virulence can occur on the heterogeneous cultivars of outbreeding crops. Thus on cotton, virulence in the bacterial blight pathogen Africi. nE a increased slowly after releas resistana f eo t variety thao ,s t it was necessary at intervals to release new varieties in which further selection had restored the resistance to former levels, although the resistance never broke down completely {15: Arnold and Brown, personal comnunication}. Significantly, followin sloe th gw build-u polygenif po c resistance in cotton by selecting for small differences in the breeding programme, subsequent evolutio blighe th f tno bacteri fiele th dn i aresulte d in onl graduaa y l declin resistancn i e e unlik explosive eth e epidemicf o s fungal disease commo cerean no l crops afte evolutioe pathogew th rne a f no race.

In America, the Hessian fly (Mayetiola destructor) has been controlled by use of resistant wheat varieties together with cultural methods. Resistance-breaking race varietiesf o arose responsus n i ee sth wito t eh high-level, simply inherited resistance w displayno d san , amongst insects, the best documented gene-for-gene relationships between parasite raced san resistant plant varieties. However, Somse Oppenlanded nan r {29}, after studyin abundance gth hare winted th re dHessia f en o i r y wheanfl t zone of America, concluded "incorporating low resistance into all wheat grown is more important than developing a single variety with strong resistance ... {which} grown ove widra e area will increase more virulent Hessia racey nfl s by the mechanism of selective pressure". This low-level resistance, whose inheritance appears complex, in combination with cultural control practices has effectively controlled Hessian fly in the area studied over many years without evolutio resistancf no e breaking races. These arguments and observations of past events indicate that in future w levello resistancf o s exploitef ei d whethe n combinationi r resistancesf so , or as a component of integrated pest management are likely to remain useful for longer periods than simply inherited, high-level resistances. Nevertheless, although aphids appear specially well adapted to evolve virulent race biotype r resistanso f o e responsn us i se tth cultivarso et , the response of insect populations in general to crops with high-level resistance seems likely to be slower than that of many fungal pathogens; and plant breeders should be reassured therefore that the obvious advantages of exploiting sources of high-level inherited resistance are unlikely to be offset by rapid evolution of virulent pest races. Equally, breeders should not dissuadee b greatee th y db r difficultie workinf so g witw levello h f so resistance from exploiting this resource which offer routsa cultivaro et s with valuable resistance properties which shoulf long-lastino e b d g usefulness. 95 CONCLUSION

Low levels and small differences of resistance are more difficult to exploit than oligogenic high-level resistance because special assessment techniques are likely to be necessary, and although in outbreeding crops phenotypic variation exposed in each generation permits the build-up of polygenic resistanc y recombinationeb mor,e b thi ey sdifficulma achievo t e in inbreeders othee th rn O hand. , small difference resistancf o s e occur more commonl d constitutan y elarga d readilean y available resourcn i e breedin resistancer fo g .

maio Tw n possibilities appea e exploitatio th exiso t rr fo t f thino s typ resistancf o e e botachievee whicb f o hy hma sugan i d r beet: firstly, that small differences in resistance based on complex polygenic inheritance breedina builn e i b n p tu gca programm givo t e higea h leve f resistanceo l , capable of exerting effective control of pest populations: secondly, that with pest lest wito bu ss h funga bacteriar o l l pathogens, integrated control management provides the possibility of interaction between resistance in the crop, natural enemies of the pest and applied insecticides to give control on crop varieties with only moderate levels of resistance. In the latter case especially, field studie e necessarar s establiso t y e leveth hf o l resistanc e attaine b breedine o th t e n i d g programme.

Hitherto natural variability has appeared to provide sufficient small difference f resistanco s r thifo es approac resistanco t h e breeding» However, in any programme based on increasing variability by inducing mutations it would seem worthwhile to adopt procedures that would detect and utilise small change occasionae th wels a ss a l l highly resistant .

e durabilitTh f resistanco yw cultivane a f o er canno e predictetb d becaus e abilite pesth eth t f populatioo y o evolvt n e rapidl n responsi y o t e the resistance is unknown before the cultivar is widely grown. However, it may be postulated that by comparison with oligogenic high-level resistance, resistance conferred by many genes combined by continued selectio unlikels i n breakdowo t y n epidemii n c pest outbreaks because th e pest is unlikely to be competent to evolve rapidly. Further, if low or moderate level resistancf o s exploitee ear n integratei d d control systems thee selectioth n n pressure e pesth t n o populatios n wil diversifiee lb d an d a slower rate of evolution can be expected.

n futury expecI ma develoe o ew t w strategiene p exteno t s e th d exploitation of host-plant resistance in pest control, based on studies of responses to resistance by pest populations. It is likely that such strategies will require considerable flexibility of control methods to counter pest evolution. Further development, through plant breeding, of low level d smalan s l difference heritablf o s e resistance froy sourcan m e could provide an important method of increasing that flexibility.

REFERENCES

{1} PAINTER, R.H., "Insect Resistance in Crop Plants", Macmillan New York (1951) 520pp. } {2 RADCLIFFE, E.B., LAUER, F.I., "Resistanc Myzuo et s persicae (Sulzer). Macrosiphum euphorbiae (Thomas) Empoascd ,an a fabae (Harrise th n )i Wild Tuber-bearing Solanum (Tourn. Species". )L , Tech. Bull. Minn. Agr. Exp. Sta 9 (196825 . . )1

96 } {3 RADCLIFFE, E.B., LAUER, F.I. Appraisan ,"A Aphif lo d Resistant Tuber- bearing Solanum Germ Plasm", Tech. Bull. Minn. Agr. Exp. Sta6 .28 (1971) 1. —— } {4 HSU, S-J., ROBINSON, A.G., Resistanc barlef eo y varietie aphie th do t s Rhopalosiphum padi (L), Canad Plan. .J t Sei (1962^ .42 ) 247. {5} HSU, S-J., ROBINSON, A.G., Further studies on resistance of barley varieties to the aphid Rhopalosiphum padi (L), Canad. J. Plant Sei. 43 (1963) 343. {6} HEATHCOTE, G.D., BYFORD, W.J., Surveys of sugar beet seed crops, mangold clamps and weeds in England for aphids and , 1963-73. J. agric. Sei. (Camb. (1975_ )84 . )87 {7} DEAN, G.J., The four dimensions of cereal aphids, Ann. appl. Biol. 77 (1974. )74 } {8 GEORGE, K.S., Damage assessment aspect cereaf so l aphid attacn i k autumn spring-sowd -an n cereals, Ann. appl. Biol (19747 .7 . )67 {9} LÖWE, H.J.B., Testing sugar beet for aphid-resistance in the glasshouse: methoa somd an de limiting factors, Zeits. angew. Ent (19746 .7 ) 311. {10} LÖWE, H.J.B., Testing for resistance to aphids in cereals and sugar beet, IOBC/WPRS Bull. 1977/3. ,45 MARREWIJKN {11VA } , G.A.M. PONTIE ,D , O.M.B., Possibilitie limitationd an s s of breedin pesr gfo t resistance, Meded. Fac. Landbouw. Rijks. Univ. Gent (19750 .4 ) 229. {12} BOND, D.A. LÖWE, H.J.B., Test resistancr fo s Aphio et s faba fieln ei d beans (Vicia faba), Ann. appl. Biol. (1975) 21. {13} LÖWE, H.J.B., Detection of resistance to aphids in cereals, Ann. appl. Biol. (in press). {14} ARNOLD, M.H., BROWN, S.J., Variation in the host-parasite relationship ocroa f p disease agric. ,J . Sei. (Camb. 1 (1968)7 . )19 {15} ARNOLD, M.H., INNES, N.L., BROWN, S.J., "Resistance Breeding": In . Arnold, M.H. ed. Agricultural Research for Development, CUP. (1976) pp.175. {16} GALLUN, R.L., STARKS, K.J., GUTHRIE, W.D., Plant resistance to insects attacking cereals, Ann. Rev. Ent (1975£ .2 ) 337. {17} TEETES, G.L., JOHNSON, J.W., ROSENOW, D.T., Response of improved resistant sorghum hybrids to natural and artificial greenbug populations econ. ,J . Ent (1975^ .68 ) 546. {18} LÖWE, H.J.B., Crop Resistanc Pesto Componena et s a s Integratef to d Control Systems. Proc. 8th Brit. Insect. & Fung. Conf. (1975) _!_ 87. {19} PIMENTAL, D., WHEELER, A.G. Jr., Influence of alfalfa resistance on a pea aphid population and its associated parasites, predators and competitors, Environ. Ent. "L_ (1973. )1 {20} VAN EMDEN, H.F., "The effectiveness of aphidophagous insects in reducing aphid populations" HodekEcologn . I .ed . Aphidophagouf ,I o y s Insects Liblice 1965, Prague (1966) 227. EMDENN {21VA }, H.F., WEARING, aphie C.H. th role df Th , eo hos t plann i t delaying economic damage levels in crops, Ann. appl. Biol. 56 (1965) 323. {22} LÖWE, H.J.B., Infestation of aphid-resistant and susceptible sugar beet by Myzus persica fielde th n ,ei Zeits. angew. Ent (1975^ .79 ) 376. {23} DUNNING, R.A., BAKER, A.N., WINDLEY, R.F., Carabid sugan i s r beet crops and their possible role as aphid predators, Ann. appl. Biol. 80 (1975) 125. {2#} VICKERMAN, G.P., SUNDERLAND, K.D., Arthropod cerean i s l crops: Nocturnal activity, vertical distributio aphid nan d prédation appl. ,J . Ecol. 12^ (1975) 755. {25} RADCLIFFE, E.B., NANNE, H.W., Nature: man's ally against the aphid. Minn. Sei. 27(3) (1971) 4. {26} NIELSON, M.W.DON Interactio, ,H. n between biotype spottee th f so d alfalfa aphi resistancd an d alfalfa.n ei econ. ,J . Ent (19747 .6 ) 368.

97 {27} WOLFE, M.S., BARRAIT, J.A., Population genetics of powdery mildew epidemics, Ann. NY Acad. Sei. 287 (1977) 151. {28} HATCHETT, J.H., GALLUN, R.L., Genetics of the ability of the Hessian fly, Mayetiola destructor survivo ,t wheatn eo s having different genes for resistance, Ann. entom. Soc. Amer. 63^ (1970) 1400. {29} SOMSEN, H.W., OPPENLANDER, K.L., Hessian fly biotype distribution, resistant wheat varieties and control practices in hard red winter wheat, ARS, USDÂ. NC 34 (1975) 7. {30} LÖWE, H.J.B. role varietie,f Th eo controllinn i s g pest diseasesd an s . IIRB 5 (1972) 224.

10.0-

Aphids

per

5.0 H plant

2.5-

1958 1961 1965 1969 1973 1977

Figur 1 eGREE N APHIDS SUGAN *O R BEE BRITAINN TI , 1958-77, Maximum average aphids per plant before mid-July, from fieldsmen's beel countal t n i growins g areas (data supplie y G.Db d . Heathcote).

*mainly Myzus persicae, some Macrosiphum euphorbiae, Aulacorthum solani and other species.

98 1975 1976 1977

20- June

30-

July 10-

101 101 1 0 1 Log (n + 1) mean aphids per plant

WITH CARBARYL CONTROL= - SPRAYET , NO , D

Figure 2 Myzus persicae populations on sugar beet plots, treated and not treated with carbaryl to suppress predators.

99 IS TRACING INSECT RESISTANT PLANT MUTAGEN SI N TREATED POPULATIONS TECHNICALL ECONOMICALLD YAN Y FEASIBLE?

O.M.B. DE PONTI Institute for Horticultural Plant Breeding Wageningen, the Netherlands

Abstract e difficultieTh s connected wite detectioth h f raro n e mutants with resistance to insects in large mutagen treated populations are discussed. It appears advisable searchinn i , r sourcefo g f resistancso o insectst e o givt , e priority o screenint g germplasm collections rather than mutagen treated populations.

INTRODUCTION developmen e f insecTh o e tus resistand tan t varietien a s si important component of integrated control [ 1] , an insect control system which gains growing interes crof to p protectionists because of increasing drawbacks of chemical control. Ajoinsa t initiativd IAEmattee an Ath bees O rha FA n f eo developmene raiseth f i d f insecto t resistant varietiee b n sca promoted by mutation breeding; in other words if induction of insect resistant mutants is necessary (1), theoretically possible (2) and feasible (3). casew 1fe . sa Onl havn i y e large germplasm collectionf so existing source variabilitf so y been thoroughly screener fo d resistanc o insectset . Unles detectioe sth inducef no d insect resistant mutants appears equally efficient, screening of germplasm collections has priority. e introductioth n 2I .Manuae th Mutatioo n nlt o n Breeding Sigurbjörnsson [ 2] stated that "Mutations are the ultimate source of all variability in organisms. Variability caused by induced mutations is not essentially different from variability caused by spontaneous mutations during evolution." Many reports on resistance to insects [3, 4, 5, 6] prove that this trait is subject to genetic diversity and it is, therefore, very probable that genetic variability in the resistance of crop plants to insects can also be induced. 3. Every plant breeder will welcome any widening of genetic variability, but "any proposal to use induced mutations in plant improvement must conside e likelihooth r f succesdo s when compared with conventional techniques and the effort required to obtain the desired genotype" [ 7] . This las whole tth crue poinef th xo matter s i t , which will be discussed in this paper on the basis of the present knowledge of insect resistanc mutatiod ean n breeding disciplineo ,tw s rather far remote from each another.

OBJECTIVES OF BREEDING FOR RESISTANCE TO INSECTS Although it might be the wish-dream of every plant breeder to create varieties that remain completely unattacked knoe ,w w that immunity to insects seldom occurs. This sounds rather dis-

101 couraging t fortunatel,bu s repeatedlha t i y y been demonstrated that the effect of only a slight reduction in population increase n injuriouoa f s insec occurs a t- moderateln i s y resistant varieties - on the control by natural enemies or on integrated control is unexpectedly large [8, 9, 10, 11, 12, 13]. As long as nothin knows i g n abou e leveth t f resistanco l e expectedb o t e , e selectioth n techniques e attunedetectioe havb th o t eo t d f no relatively small difference n resistancei s , e accumub whic n ca h- late higo t d h level resistances e developmen.Th d applicatiotan n of such techniques doet facilitatsno e matters. In addition to host plant resistance1 attention should also be pai otheo t d r plant characters, which might promote pest management, like (1) tolerance1 , (2) characters which influence the predatory or parasiting activities of natural enemies and (3) properties by which insecticides are better retained [1]. As the characters of the last two categories are often of a morphological nature and may be simply inherited, they deserve extra attention of mutation breeders.

GENETICS OF RESISTANCE TO INSECTS Amongst many other factors mutation frequencies depend on the mod f inheritanceo e characteth e f inducedb eo o t r wils ,a e b l shown later. Therefore some attention is given to the genetics of resistance to insects. There is a large number of publications on the occurrence of resistance to insects, but only few on the genetic f thio s s character. Pathak [14 . [15d Gallu]al an ]t e n review but a few studies leading to clear hypotheses; several of these hypotheses concern monogenic inheritance.e Baseth n o d general experience that unclear or incomplete results are seldom published, this small number might suggest that in many cases the resistance is genetically rather complex (polygenic). This opinion is confirmed by a number of personal communications. The frequent breakthroug f instablo h e resistance- de s sha tracted froreliabilite th m usinf o y g resistanc r diseasefo d an e pest control. Based on a better knowledge of host-parasite rela- tionship strategiew sne s have recently been develope. ] 16 [ d Resistances which are relatively complex by nature are expected to be more stable [ 17, 18] , so that the development of biotypes might be at least retarded. Because biotypes have also shown up in resistanc o insectt e s [13 19], ,15 , modern plant breeding should creatioe focuth n so f compleno x resistances t shoulI . d be realized, however, that a practical breeder will try to commer- cializ y resistancan e e found, irrespectiv it f o e.

THE DETECTION OF MUTANTS RESISTANT TO INSECTS IN MUTAGEN TREATED POPULATIONS For general aspects of the induction and detection of mutants referenc relevane th mads i eo t e t literature (e.g Manuae .th n lo Mutation Breeding, 2nd ed., IAEA, Vienna, 1977). Hereafter the problems connected with the detection of quite a few mutants in very large populations wil emphasizede lb . For seed propagated crops there is generally little point in attemptin o detece first g th t, t M^ generatiomutant e th n i s n after

For definitions see [ 1] .

102 mutagenie th c treatment thin .I s generation, namely plante ,th s wit mutatioa h mostle ar n y heterozygou genee th sr sconcernedfo , sinc alleleo same etw th e t locusa s seldom mutate. BesideI M e sth contains many plants wit deviatina h g habit, mostly physiologic- ally determined, which disappears in the next generations. Insects are often sensitive to differences in the crop-canopy. Tinge Leigd ] demonstratean y20 h[ d that difference plann si t height may influence the degree of attack by insects to such an extent, that differences in resistance are totally overshadowed. Therefore, certainl insecr fo y t resistance, screenins ' ^ M f o g shoul dissuadede b d . Although it is difficult to generalize about mutation fre- quencies, the mutability of a character can roughly be predicted on the basis of its inheritance. According to the data of Brock 2 plantM 0 00 s t leas 0 a originatin 00 1 7 t5 t plantj M g0 00 sfro 0 m25 have to be screened to detect with a probability of 90% one mutant, if its mutant character is governed by a single dominant gene; analogousl plant2 M 0 plantI M 00 s 0 0 casfron 00 si y50 5 em2 of a single recessive gene. If several genes governing the same character are available the mutation frequencies increase by a facto thao s abouf ro t, 500010 t plant2 0M s from 250 plantI 0M s might suffice whe mutana n t governe singla y b d e recessive gene is looked for. Mutation frequencies of quantitatively inherited character difficule sar determineo t . Becauspolygenie th f eo c inheritance of such characters mutation frequencies for one gene are probably relatively high phenotypie .Th c genee effecon ,f to however generalls ,i y rather smal thereford lan e plants wita h mutatio onln gene no difficule on year detecto t . Plants with several mutated genes are indeed easier to detect because of the accumulated phenotypic effect, but the frequency of such plants is again very low. Raising the probability level of induction and detection of mutants from 90 to 99% requires the fourfold number of plants. alse Ion fo want knoo st w whethe mutane inducen a rth a s i tr o d spontaneous one, a non mutagen treated check-population of similar size should also be screened. e abovTh e figures demonstrat e largth e e number plantf so s involve mutation i d n breeding programs e implementatio.Th f no such programs mainly depends on the availability of labour, expe- rimental field glasshouser so efficiend san t screening techniques. In developing insect resistant made varietieb f eo n ca e sus different techniques laborator) (1 : y tests seedlin) (2 , g tests, (3) glasshous fiel) e (4 test d d detectioe testssan th r .Fo f no one mutant out of thousands of plants only labour saving techni- ques are appropriate. - Laboratory tests are mostly too laborious. Besides the correla- tion between resistanc e laborator th e fieln th ei dd an ymigh t be insufficient. - Seedling tests may prove very efficient, but if the seedling is normall t attackeyno correlatioe dth n with resistancf eo fully grown plants deserves further investigation. - Glasshouse tests can be used as "field test" for glasshouse crops and glasshouse pests. If, however, field crops are screened in glasshouses the correlation with field tests should be in- vestigated. - Altogether the field test seems to be the most suitable for a first screening unless reliable tests, such as described above, are available.

103 Unfortunately screenin s r resistanca gfo t e fielno th s i dn i e easy as would be expected. The following factors can complicate efficient selectio resistanf no t plants [19, 21]: 1. The natural population of insects fluctuates markedly, so that one canno certaie tb sufficiena f no t selection pressure; 2. As the insects spread unequally over the field, differences in selection pressure occur. e plant3Th . e attackear s differeny b d t insects. The firs o factortw t s will cause high percentage plantf so s which escape insect attack. This will hamper the detection of resistant plants, especially if they occur in low frequencies as in mutagen treated populations. The extent and significance of this problem can be illustrated by two examples from our own work. Since 1974 abou onio0 10 t n (Allium cep ) varietieaL. d san breeding material and about 100 accessions of the related species Allium fistulosum L. have been tested in the field for resistance to the onion fly, Hylemya antiqua Mg. Some of these were tested in several years. Table 1, containing only a few of the data collected, demonstrates large differences between years and between repetitions differencee .Th s between repetitions already necessitated extensio experimentae th f no l desig eigho t n t repe- titions. The differences between years are not random fluctuations, because the mean degree of attack increased every year. This was caused by the fact that the successive experiments were intention- ally carrieneighbourinn o t ou d g plots thao e ,s insec th t t popula- tion steadily increased. Although, by this cultural practice, the natural insect population coul markedle b d y enlarge ensuro t d a e high selection pressure, it is highly questionable whether this has not been pushed too far. It is also the experience of Nieuwhof testinn i ] 22 g[ carro resistancr fo t carroe th y (Psilo fl et a

TABLE I. PERCENTAGES OF Allium PLANTS ATTACKED BY THE ONION FLY (Hylemya AntiquN FIELI ) D Mg aTEST N DIFFERENI S T YEARS

t ions Material Test % attacked plants in different repeti Year 1 2 3 k 5 6 7 8 x 'Zittauer gelbe1 197^ 70 71 70 70 1975 100 92 100 100 86 100 82 100 95 'Grobol1 197* ^k 13 3^ 20 1975 70 87 90 83 80 95 50 80 79 1977 100 100 100 100 100 100 100 100 100 . fistulosuA m 1971* 0 7 13 7 (Welsh onion) 1975 22 29 20 **3 22 80 11» 22 32 1977 98 98 93 100 96 100 100 ^ 97

rosae F.), that very large insect populations are less suitable to distinguish relative difference resistancen i s wilt .I l always remain difficult to decide whether to use a low selection pressure permitting escape from attack (e.g. 'Grobol n 1974 i 'higa r ho ) selection pressure entailing loss of partially resistant plants (e.g. A. fistulosum in 1977). The detection of induced mutants with insect resistance in this and similar cases seems to be very complicated.

104 Ifirsa n t screenin r resistancfo g twospottee th o et d spider mite (Tetranychus urticae Koch cucumben )i r three plants eacf ho 395 varieties were inoculated with 20 adult female mites just after transplanting in a glasshouse [ 23] . Because in the Nether- lands cucumber growe sar n almost exclusivel glasshousen i y s such consideree b tesa n tca "fiela s a d d test" with controlled arti- ficial inoculation. Six weeks after inoculation the 29 least attacked varieties were selecte average basie th th f sn o eo d damage of the three plants. These varieties were judged again in a similar test, but with three repetitions of four plants. In this test only ten out of the 29 varieties were shown to be signifi- cantly different from the susceptible control. So in spite of an uniform inoculation and an uniform environment, which favours the pest concerned, in the first screening 19 from 395 varieties (5%) were wrongly selected insteaf .I thref o d e onlplane on yd tha been teste percentage th d escapf eo e would have been much higher. This indicates tha selectinn i t g individual mutants resistano t insects in this and similar cases an estimated escape percentage of 5 is rather too low than too high.

DISCUSSION foregoine Inth gprobleme th som f eo s connected wite hth detectio f insecno t resistant plants have been illustrated. Even if the insect population is controllable, it seems very difficult to determine the right selection pressure to detect partially resistant plants without causing many plant escapo st e attack. This especially applies to the detection of the few resistant plant n largi s e mutagen treated populations consequencee .Th e sar plant? M 0 00 s i 0 onle seriour example10 yon fo f o , t sif ,ou expected to be resistant, 5000 plants will remain unattacked in case of 5% escape. All these plants have to be propagated indivi- dually and retested in the M^, in which generation the chance of escape is much less because lines instead of single plants are tested. technicae Th l imperfection screeninn i s g large populations for insect resistance also hampe searce th rresistancr fo h o et insect existinn i s g source genetif so c variability, suc germs a h - plasm collections. The main difference is, however, that in that case rather homogeneous group plantf so comparede sar thao ,s t the selectio meae basee th b n n n o dperformanc nca e whic mucs i h h more reliable thaperformance nth f singleo e plants. Within the scope of this paper it was impossible to discuss all aspects of the field of study interdisciplinary between bree- ding for insect resistance and mutation breeding. Nevertheless some tentative conclusions migh drawne tb . Distinguishing resistant and especially partially resistant plants appears to be so complicated that in most cases priority in research must be given to screening genetically rather homo- geneous groups of plants over searching for single resistant plant largn i s e mutagen treated populations. During screeninf go germplasm collection knowledge s th factor e th f eo s which contri- efficienn buta o et t screening will certainly increase, .If contrar expectationo yt germplase th n ,i m collection sourceo sn s of resistanc founde ear , this knowledge will mak easiet i e o t r decide whether a mutation breeding program for insect resistance is technically and economically feasible.

105 REFERENCES ] 1 PON is [ s O.M.B , tancTRe I Cucumi, n i eDE . s satîvu o Tetranychut . L s s urticae Koch. 1. The role of plant breeding in integrated control, Euphytica 26 (1977) 633. [2] SIGURBJÖRNSSON, B., "Introduction : mutations in plant-breeding program- mes", Manua n Mutatioo l n Breeding d ed.2n , , IAEA, Vienna (1977. )1 ] PAINTER[3 , R.H., Insect Resistanc Cron i e p Plants t Ed.1s , , MacMillan, New York (1951). [y PAINTER, R.H., Resistance of plants to insects, Ann. Rev. Ent. _3_ (1958) 267. [5] BECK, S.D., Resistance of plants to insects, Ann. Rev. Ent. 10 (1965) 207- [6] MAXWELL, F.G., JENKINS, J.N., PARROTT, W.L., Resistance of plants to insects. Adv. in Agron. 2k_ (1972) 187. [7] BROCK, R.D., "When to use mutations in plant breeding", Manual on Muta- tion Breeding d ed.2n , , IAEA, Vienna (1977) 213. [8] PAINTER, R.H., Crops that resist insects provide a way to increase world food supply, Bull, agric. exp n Kansa St .. Univ St 0 s(1968) 52 . . [9] STARKS, K.J., MUNIAPPAN, R., EIKENBARY, R.D., Interaction between plant resistanc d parasitisan e m against greenbu n barleo g d sorghuman y , Ann. entom. Soc. Amer. 6_5 (1972) 650. [10] JENKINS, J.N., PARROTT, W.L., McCARTHY, J.C., Jr., The role of a boll weevil resistant cotton in pest management research, J. env. Qual. 2_ (1973) 337. t 11] LÖWE, H.J.B., Infestation of aphid resistant and susceptible sugar beet by Myzus persica e fieldth n . angewi Z e, . Ent 9 (19757 . ) 376. [12] LÖWE, H.J.B., 1978, Possible advantage f smalo s l difference n resisti s - ance to aphids, These Proceedings. [13] PATHAK, M.D., "Utilization of insect-plant interactions in pest control", Insects, Science & Society (PIMENTEL, D., Ed), Acad. Press, New York, London (1975) 121. lib] PATHAK, M.D., "Genetic f planto s pesn i s t management", Concept f Peso s t Management (RABB, R.L., GUTHRIE, F.E., Eds), North Carolin . UnivSt a . Press, Raleigh (1970) 138. [15] GALLUN, R.L., STARKS, K.J., GUTHRIE, W.D., Plant resistanc o insectt e s attacking cereals, Ann. Rev. Ent (1975^ 20 . ) 337. [161 PARLEVLIET, J.E., ZADOKS, J.C., The integrated concept of disease resist- ance; a new view including horizontal and vertical resistance in plants, Euphytica 26 (1977) 5. [17] EENINK, A.M., Genetics of host parasite relationships and uniform and differential resistance, Neth. J. PI. Path. 82 (1976) 133. [18] ROBINSON, R.A., Plant , Springer-Verlag, Berlin, Heidelberg, New York (1976). [19] MARREWIJK, G.A.M. VAN, PONTI, O.M.B. DE, Possibilities and limitations of breeding for pest resistance. Meded. Fac. Lanbouww. Rijksuniv. Gent jtO (19-75) 229. [20] TINGEY, W.M., LEIGH, T.F., Height preferenc f Lyguo e s bugs [Het., Miridae] for oviposîtio cagen o n d cotto nGossypiurn[ ] plants, Env. Ent .^ (1974) 350. [21] MARREWIJK, G.A.M. VAN, DIELEMAN, F.L., Screening techniques for the determinatio f aphio n d resistanc barleyn i e , SROP/WPRS Bull. 1977/3. ,37 [22] NIEUWHOF , SomM. , e preliminary dat n researco a h into carro y resistfl t - ance. SROP/WPRS Bull. 1977/3. 13 , [23] PONTI, O.M.B , ResistancDE . Cucumin i e s sativu o Tetranychut . L s s urticae Koch . Searc3 . sourcer fo h f resistanceo s , Euphytic 7 09782 a ) in press.

106 CONCLUSION RECOMMENDATIOND SAN S ===s=r=SÄ=:»=s=rsB=r=rs=:s:3:5S:z=r==:=S3=rÄ=r=5r:Ä:=:=

A. Introduction

vien I potentiaf wo l economi legad can l restrictione us e th n so of insecticides, their potentially detrimental effect upon the environ- ment, the risk of harmful residues in food and feed and the development of resistanc mann ei y major pest species, alternative method conf so - trolling insec othed tan r arthropod crop pest receivine sar g mord ean more attention. Breeding crop plant varieties with resistanc harmo et - insectl fu para pesf s to sa t management system promisina s si g method of insect control, and much success has been achieved by plant breeders with certain crop plants against certain insects. However, plant breed- ing for insect pest resistance has not always been successful for reasons such as lack of appropriate screening methods or absence of effective re- sistance traits in the particular host species.

Inducing genetic variability in host plants with ionizing radiation or chemical has proven to be an effective method of creating genotypes with improved resistance to pathogenic microorganisms. PAO and IAEA are stimulating and sponsoring research aiming at the produc- tion of useful resistant mutants as well as the development of the methods required. Therefore IAEd an Acomplyin - O ,FA g witrequeste hth s of some of its member states - convened a meeting of experts for assess- ing critically, whether and where induced mutations could also be used to furthe developmene rth improvef to d crop varieties with bette- rre sistanc inseco et t pests meetine Octobe1 2 Th . - hel s 7 gwa rd1 1977t a Dakar (Senegal considered )an followine dth g main topics:

1. Current control practices, their effectiveness, economics and environmental impact

controw Ne 2. l method futurr sfo e eus

3. Experiences with resistance of crop plants to insect pests

4. Feasibility of expanding and intensifying plant breeding for insect resistanc relation ei o nt

a) availability of resistant genotypes and need for additional genetic resources

107 ) b availabilit d effectivenesan y "breedinf so g a.nd screening techniques

) insect-planc t relationships

d) mechanisms of resistance

e) genetic basis of resistance

5- Potential role of induced nutations in producing resistant genotypes

. 6 Educatio d traininan n provido gt e scientific manpowe r planrfo t resistance

"any aspect thesf o s e topics have been considered alreade th n i y lectures presented "by the experts, others were brought up during the discussions. The discussions were very extensive and led to the follow- ing conclusions and recommendations:

. ConcluB s ions

1« When,.and where to breed for insect resistance? . a Chemical contro insecf o l t pests affecting crop subsistencf so e agri- culture receives little attention from farmers. On the other hand, cash crops receiving increasing applications of pesticides are now posing-problems of pollution, residues, increasing costs and evolution of pesticide-resistant insects. Improving host plant resistance to insects is, therefore, equally important for developed and developing countries, for subsistence as well as for commercialised farming.

The panel realize importance sth insecticidesf o e , natural ene- mies and cultural practices for plant protection, but wishes to see more attentio ne integratio th pai o dt planf no t resistancn a s ea insect control factor into pest management programmes. Integrated programme pesf so t management operate most effectively when basen o d productive, pest-resistant varieties.

. b Compare temperato dt e regions, insect problem tropice th e f so sar generally more severe. In the tropics, rainfed agriculture is still largely traditional and is much affected by vagaries of weather and

108 attack insecf so t pest diseasesd san . Here crops with resistanco et insects will havgreatese eth t impact.

Current plant "breeding efforts are aimed at increasing and stabilizing agricultural productivity. This will often involve hybrid- ization with non-adapted genotypes from temperate regions adequatf I . e attention is not paid to pest reactions, movement and utilization of germplasm across dissimilar zones could lead to accentuation of insect pest problems or may create new pest problems. All breeding methods, including mutation induction, should be exploited in combining prod- uctivity with insect and disease resistance.

2. What level of resistance is desirable? The developrincipao t s i pm varietielai s wit higha h - levere f lo

sistance, definee whicb y hma d approximatel varieties ya whicn so e hth pest problem disappear ceased san constraio st farmerse nth 1 workA . secondary, but often more realistic and immediate aim is to develop moderate levels of resistance in varieties which can be the foundation of good integrated pest-management systems.

The plant breeder will nee distinguiso dt h betwee concepte nth f so low-level resistanc smalf o d l ean difference resistancen si . Several small differences combined togethe givy r ma variete a y with moderate resistance. Accumulation of many small differences can lead to high levels of resistance.

Sensitive screening method needee sar d which wil onlt lno y show larger differences of resistance but will also detect small differences reliably.

. Wha3 t typ resistancf eo e shoul aimee db ? dat Resistance against insect bees sha n classifie sucy db h terms sa "non-preference", "antibiosis", "tolerance", etc. The breeder certainly mose th t wishee effectivus o st e type. However, above all choice ,th e will depend on the kind of resistance that is available. When resistance is recognized and preliminary studies made, decisions appropriate to the particular case must be made by the breeder in consultation with entomolo- gists familiar with the biology of the pest both in the field and in the environment of the testing method.

109 Insect resistance in harvested crops Post-harvest crop losses to insects are of major magnitude. Such losse mose sar t evident in,tu limitet tno cereao t d d feelan d grains, and dry peas and beans. Losses range from as low as 4 to 12 per cent in zones of temperate climate to more than 50 per cent in tropical zones. Such losses are tragic when we recognize they are most common in regions where greatesn peopli e ear t nee foodf do . Strong efforts shoul takee db n to develop storage systems that will preserve product qualit reducd yan e insect attack. Biophysical and biochemical forms of resistance are recognized that inhibit field and storage attack by insects.

We should actively seek and utilize heritable characters that will reduce post-harvest los insectso st . Such programmes must recognize the need to preserve the agronomic and utilization qualities of the particular crop.

Sources of insect resistance There are two general sources of genes for insect resistance; (i) those provided by variability within the plant species and (ii) those in plants closely relate croe th p o dt species e initiaTh . l searcr hfo resistance should be made preferentially within locally adapted genetic stocks in order to take advantage of existing adaptive qualities, follow- ed by screening of collections of germplasm from areas of greatest genetic diversity, although any available germplasm should be tested. The search for resistant plants should be continued until all available germplas bees mha n screened easd ,an y flo germplasf wo m acros worle sth d should facilitate success in breeding resistance.

Collections of germplasm for a great many crops are available at centers throughout the world. Lists of the centers and their crop emphasis are available through FAO, Rome, .

When available reservoir germplasf so m have faile yielo dt d satisfactory resistance, synthetic method genetif so c manipulation shoul triede db . Induced mutation usee b creat o dt n sca e further variabilit develoo t r yo p increasen a d numbe insecf ro t resistance sources.

110 6. How to screen, for insect resistance

In order to select for resistance by using the insect itselff one homogeneou a sur e f eo "b o t s sha infestatio sufficiena f no t leven lo the plants one is selecting. Such infestations may not be available in the field severat ,bu l method usee b favouo dt n increasd sca ran e wild insect populations. Artificial infestation can also be used. For obtaining sufficiently large quantitie insectf appropriatse o th f so e stage at a given moment, artificial rearing might be necessary. A prerequisite is the development of a good technique for mass production insectf o minimut sa m cosmaximud tan m reliability. This often implies the development of artificial diets. Other techniques such as diapause manipulatio field-collectef no d insects might als usee ob obtaio dt n adequate numbers of insects for screening. Care must be taken to maintain variability in the insect populations used for screening to avoid the developmen laboratora f to y stock different fronaturae mth l population.

Artificial infestations with the insect must be carried out on the stage of the host plant which is usually infested in the field. This is important because differences in susceptibility are known to exist between the different growt sometimehe planar stagee d th tan f s o s quite large particularly between seedlings vegetative ,th post-flowere th stag d ean - ing stage. However, small seedlings are often more easily tested in large numbers than adult plant thereford san e seedlings usedi e test b t I y .s ma important to ensure that the observation of resistance in such tests is closely correlated with the occurrence of resistance under normal field conditions.

Additionally, environmental conditions mus definede tb orden I . r to overcom effect e environmente eth th f so , assessmen resistancf to e must alway made s b compariso y eb n with standard entries. High level soif so l fertility may be reflected in a high degree of tolerance of the host plant which can mask differences in susceptibility. Here again, if trials are being considered, one has to be certain of a good correlation with nature.

The leve infestatiof lo usee b do nt will depen botn do h cro d insecpan t and mus studiee tb eacn di h worthwhil s casei t I . e investigatine gth relationships between the host plant and the insect population used for artificial infestation. Auto-regulatio populatiof no n level occun sca r

111 density-dependeno t e du t factors which gover dispersae nth d competitiolan n of the insects at the infestation sites. The level of infestation may be varied according to the aim. A severe insect attack will result in an alnonr o l e response. Lower level infestatiof so n would allo assesse wth - men moderatf o t e level resistancef o s e optimuTh . m infestation leves i l probabl allowine on e y th glarg a e spectru responsef o m expreso st s themselves, thus permitting better discrimination.

. 7 Selectio factorf no s contributin hoso gt t plant resistance

Varietal resistanc regulationee actth n so , distributio d fluctuationan n of pest population agro-ecosysteme th n i s . Certain plant genotypee b y sma preferre disfavourer do insecty db ovipositionr sfo , shelter and/or food. Besides this host genotype specificity, insects may prefer specific developmental stage crof so p plants, certain plant part d organsan s etc. The factors which govern insect behaviou nature th degred d ean ran damagf eo e may be of physical, physiological, morphological or biochemical nature. The mechanism and effect of resistance in insect/plant relationships is likely, therefore specifie b o ,t eaco ct h case.

The thickness, hairyness, shape and size of plant organs may have a role in reducing infestation. Physiological aspects such as content of cell sap, pH, osmotic pressure as well as size, density, function of stomata and vascular bundles may be important for sucking types of insects. chewinr Fo g insects, silica content percentageh ,as ,limitine b etcn .ca g factors. Identificatio biochemicaf no l factors responsibl resistancr efo e requires more sophisticated research, nevertheles vere b yy usefuma t si l to determine the nature or causes of resistance in order better to manipulate plant selection. Such factors contributing to resistance may be studied genetically theid ,an r stabilit differenn yi t environments shoule db tested before the usee biochemicaf o selectionn yar i d e us e Th l. factors limitee b y ma d insofa theis ra r conten harvesten i t d products should animalsr o harmfu e b n ma t .o no lt

The search for chemical and other causes of resistance can be exciting and success could have far-reaching implications. Eve involvemen, nso n ti this aspect should not take precedence over practical phases. The goal of resistanca e programme release shoulth e higf db eo h yielding, high quality cultivars with built-in plant protection.

112 If suitable resistance cannot be found in natural populations, mutations in factors contributing to resistance may be induced to obtain adequate genetic variability for selection. For long-term host plant resistance, it would be desirable to combine many resistance factors in a genotype with good agronomic characteristics.

8. Rating of insect resistance and management of resistant varieties

. a Screening technique ratind san g system resistancr sfo e shouls a e db simpl rapid ean possibles da . Although thi vary sma y wit peste hth , there can be standardization of techniques among workers on similar pests once reliable procedure e establishedsar oftes i t nI .expedien o t develop resistanc singla r pesy efo eke t without regar other dfo r pests. Nevertheless efforn ,a t shoul made db combino et e source resistancf so e against several insect pests and diseases even though special evaluation breedind an g technique requirede b y sma knowledgA . inheritance th f eo e of resistanc usualls ei y helpfu determininr lfo bese gth t breeding approach. Resistance is relative and thus the quantitative assessment of a given cultivar must be related to other adapted cultivars of the same species. Any level of resistance that can be reliably measured and transferred can be useful. Care should be taken that resistance of a cultivar is not being compared unfairly to insecticide treated entries where better plant performance may also be due to some extraneous factors.

b. Insect biotypes overcoming resistanc realitya e ear . Development of such biotype mory sma e readily occu aphidsn ri , small Dipterd aan leafhoppersj pests with short life cycles. Also numbee ,th specief ro s wher developmene eth biotypef o t bees sha n demonstrate rathes di r small. Therefore feae biotyp,f th r o e selection exaggeratedshoule b t dno . However, studies on the genetic variability of pest populations should be made where possible both to detect genes giving the ability to overcome resistanc develoo t d ean p additional strategie exploitinf so g resistant crop varieties.

Cross resistanc severar efo l specie insectf so seldos si m found, even though these may be closely related taxonomically. The exception may be resistance that is attributed to physical properties of plants.

113 . Induce9 d mutation insecr sfo t resistance Induced mutations may "be used to supplement germplasm, where de- sired traits are absent or are only found in an unsuitable genetic 'back- ground.

Until now, ther "bees eha n hardl seriouy yan s attemp induco t e mutations for insect resistance . Therefore, the prospects for such an approach canno predictede tb analogn I . induceo yt d mutation diseasr sfo e resis- tance one can, however, expect that useful genetic variation of insect resistanc alsn ca inducee ob mutagey db n treatments.

The practical utilization of induced mutations requires a clear concept in terms of objectives, means of selection and subsequent breeding procedures. One has to be aware of the fact that useful mutants are rare even in mutagen treated populations. Therefore, populations in the order of 50.000 VL plants or their progenies have to be screened for recessively inherited mutant mucd san h larger populations mutatef ,i d dominant trait wantede s ar "Manua e Th . Mutatiof lo n Breeding" issued consultee b y ma detailr A dfo E treatmenf A so I y b t procedures, choice of mutagen, handling of mutagenised material, etc. Paragraph 6 of these conclusions ("How to screen for insect resistance") is applicable also for the selection of mutants, but particular emphasis will have to be laid upon uniform infestatio avoio nt d escape mutantf I . s with moderate level resistancf so e considereear usefuls da , they woul- se d e havb o et lected under moderate infestation levels. Where causes of resistance are known, selection may be practised profitably upon morphological, chemi- caphysicar o l l criteria contributin resistanco gt e (see paragrap. h7)

Mutation induction certainly could hel breao pt linkage kth e between resistanca egena gend e ean governin undesiren ga d character. Additionally, induced mutation usefue b too a n interspecifin s i lsca a c crosses.

Education/Trainin. 10 hosn gi t plant resistance

Ther greas i e t nee increaso dt researce eth h fiel e forcth f do n ei host-plant resistance. This need includes not only entomologists, plant breeders and geneticists, but also people trained in supportive fields suc biophysicss ha , biochemistry, etc provido .T e these scientific per- sonnel we must start to educate at the student's level. There is strong

114 student interest in host-plant resistance research. We only need to pro- vide greater student exposure to host-plant resistance through under- graduate and graduate teaching and through student involvement in current research programmes.

Advanced scientists would benefit from additional training. Persons actively working in host-plant resistance research should have oppor- tunitie additionar sfo l training through workshops. Scientist pret sno - sently involved in host-plant resistance should be offered education methodse inth , materials utilitd ,an thif yo s field through special short courses. Information disséminâ througn tio h "newsletter reprind "an t exchange would provide a form of continuing education.

Administrators and politicians, who are often required to make po- licy decisions based on limited information and exposure, are best edu- valud an resistan neef e er o cate th dfo n do t crop varieties through demonstration resultsf so labor-intensive Th . e natur host-planf eo t resistance research may need to be emphasized in such demonstrations.

Research on host plant resistance is best accomplished through team- wor persony kb severaf so l disciplines. Such teams develop best through personal contact, mutual interest and an atmosphere of continued learning, but administrators should be made aware of the need for close working relationships in this particular type of programme.

Insect resistant crops mus appreciatee tb farmere th y db . This requires effort extensiof so n personne practicad lan l demonstrationf so effective results.

. RecommendationC s

1. Host plant resistance should be considered as one of the primary lines of defense in all pest management programmes. To meet this objective resistance to insects should become an integral part of plant breeding programmes. 2. If priorities are necessary, preference should be given to developing insect resistanc thosn ei e crop plants whicr ,fo h practical control

115 is lacking or where current methods of pest control present critical environmental hazards.

. 3 Host plant resistanc hi^ila s ei y promising strateg insecf yo t control, "but it requires sustained long range work and a team approach. Funding organizations will hav recognizo et neee adequatr eth fo d long-terd ean m funding.

4. International organizatioreshould support the collection, evaluation and maintenance of germ plasm valuable for improving insect resistance of crop plants.

5. International organizations such as FAO and IAEA should include plant "breeding for insect resistance, the development of corresponding ento- mological technique researcd san relaten hi d fields, amon researce gth h topics eligible for research contracts or other means of support.

6. International organizations such as FAO and IAEA should offer training opportunitie plann si t breedin insecr gfo t resistanc related ean d fields through fellowships, consultant services, training course seminarsd san .

7. FAO and IAEA should disseminate information on plant breeding for insect resistance and related technology to interested parties through appropriate means such as newsletters.

. Internationa8 l organization d IAEan A s O shoulsucFA s ha d stimulatd ean suppor optimae tth l exploitatio resistanf no t crop varietie pesn i s t management.

9. The Advisory Group in particular recommends that large scale regional "Researcprojectn o e on Developmend se han th suc s a h Integratef o t d Pest Managemen Basir fo t c Sahele Cropth y attention i s"pa tlio nt e potential of breeding for insect resistance.

Advisore Th y Grou pd IAE mak urgean o repore At O eth s FA thif o t s meeting available to the Sahelian countries and the researchers involved e projectinth welcomet .I opportunite sth y offere projecy db t stafo t f utilize the services of the project for experimentation under Sahelian conditions.

116 AÎTNEX

GUIDELINES AND RECOMMENDATIONS

Concerning

MUTATION BREEDING FOR RESISTANCE TO INSECTS

BY I/ 2/ P.L. Dieleman & O.M.B. de Ponti

CONSULTANTS TO IAEA 197, Decembe17 5d an 6 r1

I. INTRODUCTION At the invitation of the Joint FAO/EAEA Division of Atomic Energy in Food and Agriculture, a consultation was held at IAEA, Vienna during 1975, Decembe17 id witan 6 rh1 personnel froInsece mth Pesd tan t Control PlanSectioe th td Breedinnan Geneticd gan s Section objectivee Th . thif so s consultation were: (a) to discuss and establish guidelines for the two Sections in relation to a possible joint programme of Mutation Breedin Resistancr gfo Insectso et ; adviso t Agencnee(IDe e convenin)r eth th fo d n yo Advisorn ga y Group on this subject. During a preliminary discussion the objectives of both Sections as well as their mode of implementation were explained. The consultants were also given an expose of each Section»s concept of Mutation Breeding for Research to Insects.

Departmen Entomologf to y Agricultural University HAGENINGEN NETHERLANDE ,TH S

Institut Horticulturar efo l Plant Breeding WAGENINGEN NETHERLANDE ,TH S

117 II. GUIDELINES . 1 With regar topico dt s raised durin meetine gth Consultantse gth * comments arfollowss ea : 1.1 There are no differences in principle "between "breeding resistancr fo ) fungi(a o et , ", viruse d ("b- san in ) sects and mites. Existing differences are mainly caused "by the moMlity of animal parasites and are, therefore, often connected with technical aspects of the selection. complexite Th plan f yo 2 1. t resistanc insecto et illustrates si d "by the following quotations : "A valuable "beginning has made in the use of insect-resistance plants to control insect populations and damage. A little progress has also "been made in understanding the "basis of re- sistance which is proving to "be more complex than many have though "be"o t t .ti Painter (1958) "From even a limited review of existing literature the complexit planf yo t resistanc insecto et apparents si t I . doubtfus i l thay exampltan resistancf eo explainee "b n eca d "basi e singla th f o sn o e simple "biological characteristif co the plant". "Ther greaa s ei t neefundamentar fo d l information on all of the phases of insect "behaviour". Beck (1965) 1.3 The natural existing diversity of a crop can "be enlarged "by mutagenic treatments, "but the huge problems connected with mutatio underestimatede n "b "breedin t no y gma e attentioTh . f no the IAEA should be directed primarily to those host-parasite relations where: ) basi(a c knowledg relatioe th f eo presens ni t efficienn a ) (b t screening techniqu bees eha n developed

) therlaca (c naturaf s ko ei l source resistancef so .

1.4 It is hardly possible to predict the probabilities of succes mutatiof so n breedin resistancr gfo insecto et s becaus knowledgr ou o et e experienco thern s ei e with this field of research. 1.5 People working on resistance to insects should be informed PAO/IAEy b A abou existence tth collectionf eo materiaf so l treated with mutagens. 1.6 The choice of projects to be contracted by the IAEA must be discussed with specialist cron si p insectslosseo t e sdu , as well as specialists in Integrated pest Control. 2. With regard to the components of a planned Breeding Programme for Resistance to Insects (and Mites) Consultante th ; s emphasiz specificite eth eacf yo h host/ parasite relation; therefore great care is needed with generalizations. Never- theless ,generaa l give e b fram n n eca unde conditioe rth n tha wilt ti adaptee lb d to each specific case followine Th . g necessaril t ordeno s ri chronologicaya l one.

118 pese Th t (and 1 disease2. ) problem specifia f so c crop muse tb studied. Question askee "b do st include existin:e th wha e tar g control methods? Is the crop affected "by one or more insects? Are there minor pests tha increasy tma e after "breeding resistance agains majoe tth r pests because wide spectrum insecticides (andperhaps even fungicides longeo n e )rar used gooA . d know- ledge of the insect in its habitat is necessary, i.e., its life cycle| alternative hosts, natural enemies, environmental factors. 2.2 Development of reliable and efficient screening techniques. Mass screening is probably a prerequisite for efficient breeding work, especially if after a mutagenic treatment resistant mutants have to be detected in very large populat- ions of plants. In developing glasshouse and laboratory tests, much care shoul give e dsufficienb a o nt t correlation with field tests teste Th . s mus vere tb y discriminativn ei orde scoro rt e relatively small differences. 3 2. Searc sourcer hfo resistancef so : these should include recent and old varieties from all over the world, collections originating from the "Centres of Diversity", cultivated or wild related species, existin newld gan y created mutant material. Because of the enormous amount of material to be tested, an advisable procedure would be repeated testing in steps of decreasing varietal (or other) numbers and increasing sampling intensit accuracyd yan . onlf I y moderat 4 2. e resistanc founds ei , attempts mus made tb e to increase the resistance level by intercrossing, aimed at transgression for this character. For this purpose, tests wit higha h discriminative characte necessarye rar * resistancf I foundt no s 5 e,i searca 2. h shoul initiatee db r fo d factors whic combinef hi d "coul synergisy db m create desired resistance. 2.6 In order to predict the percentage of resistant in- dividuals in segregating offsprings, the genetics of the resistance mus investigatede tb therf I .e ear different sources of resistance, the identity of genes should be investigated. studyiny B mechanisme g th 7 2. resistancf so might ei e tb possibl deteco et t other selection criteria thae tar easie assesso rt shoult I . notee db d that generaln ,i , resistance to insects is quite complex and one must be careful with focussing on only one mechanism. resistance Th e8 mus2. incorporatee tb hign di h yielding varieties that posses numbesa othef ro r agronomical qualities. If linkages with undesired characters or crossing barriers appear, a mutagenic treatment may contribut solvo et e this problem. resistance th f I e alon 9 2. e doe providt sno e complete pest control, i.e., the resistance is partial, supplementing integrated control measures should be examined. Satis- factor partlya controf o ye resistanus le baseth n do t

119 variet achievee b y yma d through additional biological control, cultural measures limiter pesticides,f o o e dus , preferably selective ones to preserve natural enemies. 3. When considering the Coordination of a Project on Host Plant Resistance, attention shoul followinge givee db th o nt : 1 3. host plant resistance shoul consideree db tooa n s li da integrated contro pesr lo t management systems. vien I 3.1f wo detectioe »th 2 introductio3. d nan hosf no t plant resistance shoul joina e db t actio researcf no h teams: e.g., agronomists, plant breeders, entomologists. Any Agency contracts should be awareded preferably to research teams. 3.3 Cooperation (consultation) from the very first with expert research teams working on basic and applied research of the insect-host relationship concerned is important. 4 3. Screenin fielf go d crops shoul carriee db preferablt dou y under natural growing condition arean si s wher pese eth t is predictable and severe during screening time. - The equipment during this first step of the project can be relatively simple; mostly a field lab and outside insectary are needed to carry out some rearing experiments and collect biological data. - When artificial infestation is necessary, procedures will be more costly due to the need of mass rearing, cages, etc.

3.5 Mostly the solutation of an insect problem by host plant resistanc reaches ei d stepwise: starting wit detectioe hth n genetif o c factor resistancf so finishind ean g wite hth release of (partly) resistant varieties. It should be noted that: firse th t ) ste(a p take year5 s3- lesr so s (including the development of screening methods); estimatee th ) (b d yearly cost 130,00e sar 0 project; (c) it is only worthwhile to start a project when continuity of funding until the problem is solved can be guaranteed. Planning for a ten year project seems to be reasonable. III. RECOMMENDATIONS 1. The Consultants recommend that the Agency convenes an Advisory Group on Mutation Breeding for Resistance to Insects, to discuss all problems connected with this very complex fiel researchf do stimulato t d ,an e breedin insectf go - resistant crop plants, including the appropriate use of .

120 Advisorc ho d a ye GrouTh p. 2 should include experts from various region: son ) cro(a p losses; ("b) integrated control; ) entomology(c ; ) plan(d t "breeding. 3. The Agenda of the Advisory Group should include some introductory papers followed Toy specific recommendations guideline e "baseth n o d s preparee th y d"b Consultants. One of the questions the Agency should ask the Advisory Group is «hat in their opinion constitutes a realistic "budget for implementing Mutation Breedin Croa f pgo Plant Resistan Insectso t Advisore Th . y Group should draw up a list of contacts to "be established "between IAEA Plant Breeders - and Pest Management Organizations.

121 LIS PARTICIPANTF TO S

Has sein KHALIFA Cotton Breeding Section Shambat Agricultural Research Corporation Ministry of Agriculture Food and Natural Resources Democratic Republic of Sudan Thoma LEIG. sF H Universit Californif yo a Davis, California 93 253 U.S.A. Henry J.B. LOHE Plant Breeding Institute Cambridge U.K. Alezander MICKB Joint FAO/IAEA Division Scientific Secretary P.O. Box 590 1010 Vienna Austria Isaac MOORE Joint FAO/IAEA Division Scientific Secretary 0 59 P.Ox .Bo 1010 Vienna Austria Prem NATH FAO Expert c/o National Horticultural Research Institute P.M.B. 5432 Ibadan Nigeria Mbaye NDOÏE ISRA CNRA Bambey Senegal Orlando M.B. de PONTI Institute for Horticultural Plant Breeding Wageningen The Netherlands N.G.P. RAO Indian Council of Agricultural Research IARI Regional Station All India Coordinated Sorghum Project Hyderabad 500030 India Rafik SKAP FAO Regional Plant Protection Officer F.O.B. 154 Dakar Senegal Ken STARKS Departmen Entomologf to y USDA-ARS Oklahoma State University Stillwater U.S.A.

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