CP 0117 Breeding for disease and resistance in

R.J. WILLIAMS and D.J. ANDREWS

Summary. The present status of the control of biological agents caus- ing yield losses in pearl millet is reviewed. The possibilities of control- ling diseases, pests, weeds and grain-eating birds by breeding cul- tivars with durable resistance are discussed. In future breeding research in this crop, areas needing to be emphasized include: evaluation of the nature and inheritance of disease resistance; development of strategies to increase the durability of resistance to diseases; investigations into the possibility of using complex multiple barriers to disease pathogens; additional survey work and the development and use of effective screening techniques for insect pests; evaluation of integrated control strategies against ; development and use of screening techniques to identify and develop cultivars resistant to witchweed; and investiga- tion of cultural practices and breeding techniques to control shibra in Sahelian Africa.

Pearl millet, Pennisetum americanum (L.) Leeke (syn. Pen- nisetum typhoides (Burm.) Stapf. and Hubb.), is the staple cereal of many millions of the world's poorest people in the semi-arid regions of tropical and subtropical developing countries in Asia and Africa. In India, about 14 million ha of pearl millet are cultivated annually, primarily in the northern and western states of Rajasthan, Maharashtra, Gujarat, Uttar Pradesh and Haryana (about 87 percent of the national total), with important production areas also in Andhra Pradesh, Karnataka and Tamil Nadu in the south (see Table 1 and Fig. 1). In Africa, the pearl millet crop is of most importance in the Sahel, with each of the seven countries in this region growing about one million ha or more of pearl millet annually and collectively growing about 14 million ha each year (see Table 2 and Fig. 2). Other important pearl millet-growing regions occur in eastern and southern Africa, though in these regions other millets, such as finger millet (Eleusine coracana Gaertn.), contribute significantly to the FAO production data generally listed under the heading of "millet" (FAO, 1981).

______The authors are with the Pearl Millet Improvement Programme, Interna- tional Crops Research Institute for the Semi-Arid Tropics (ICRISAT), 136 Patancheru PO, Andhra Pradesh 502 324, India. This articlVole . is31 base, No. d4, o1983n a paper presented at the FAO/IITA Expert Consultation on Durable Resis- tance Breeding, Ibadan, Nigeria, 23-29 October 1982. In African countries and in India, the national average grain yields of pearl millet are generally in the low range of 400-600 kg per ha (FAO, 1981), and in some African countries where pearl millet is a major crop the average yield is less than 400 kg per ha (see Table 2). On experiment stations, however, yields of 2-3 tonnes per ha are regularly reported (ICRISAT, 1976, 1977, 1978, 1981), and undoubtedly many farmers occasionally achieve yields in the 1-2 tonne-per-ha range with traditional varieties when conditions are highly favourable for the crop in a particular season. The basic objective of the Pearl Millet Improvement Programme being carried out at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) is to develop technology that will ultimately enable Figure 1, Reported area planted to pearl millet in southern farmers in the semi-arid tropics to achieve Asia in 1978 (one dot equals 20 000 ha) higher yields more consistently from their pearl millet crops. The first step in this process has to millet production all these factors need atten- be identification of the major constraints on tion and their interactions with sociological, increased production, followed by the develop- economic and political factors need to be recog- ment of effective and acceptable measures to nized and dealt with. This article confines itself reduce or eliminate those constraints. For pearl to discussing the control of the biotic yield millet in the semi-arid tropics, the abiotic reducers by breeding cultivars resistant to dis- environmental factors of moisture stress and eases and pests. low fertility are undoubtedly major contribu- tory-factors to low grain production, together with the biotic factors of diseases, insect pests, Pearl millet origins, distribution and breeding parasitic and non-parasitic weeds and the in- system herent low productive capacity of some tradi- tional cultivars. For the improvement of pearl This crop appears to have been domesticated along the southern margins of the Saharan TABLE 1. Area cropped with pearl millet in 17 states in India in 1973-74 highlands, between 3000 and 4000 BC, and today its main centre of diversity occurs in the Area Area Sahelian zone of Africa between Senegal and State State (1 000 ha) (1 000 ha central Sudan (Brunken, de Wet and Harlan, 1977). Migration and trade caused the crop to Rajasthan 5731 Punjab 147 spread to southern Europe, the Kingdom of 1 Maharashtra 2215 Delhi 22 Saudi Arabia, eastern and southern Africa and Gujarat 2149 Bihar 16 Uttar Pradesh 1063 Jammu and the Indian subcontinent probably by the begin­ Kashmir 15 ning of the Christian era (Rachie and Maj- Haryana 956 Orissa 4 Karnataka 610 Pondicherry1 1 mudar, 1980) and to the Americas probably in Andhra Pradesh 582 West Bengal 0,4 the middle of the nineteenth century (Ball, Tamil Nadu 401 Himachal Pradesh 0.01 Madhya Pradesh 218 1903). Subcentres of diversity exist in regions Total 14 130 where the crop has evolved over long periods in response to local selection pressures, e.g. the Source: lndian Agricultural Statistics, 1973-74 longer days experienced in northern India. 1 Union Territory

FAO Plant Prot. Bull. 137 Which persists in the cultivated crop (Brunken, de Wet and Harlan, 1977). The highly outcross- sing nature of the crop has important implica- tions for breeding for stable disease resistance and for increased vulnerability to floral diseases

in F1 hybrids. In the United States and India, cytogenic

male sterility has been used to produce F1 hy- brids (Rachie and Majmudar, 1980). In India, hybrids have been selected for increased grain production and are now being grown there on. more than one million ha per annum.

Biotic yield reducers

Diseases. More than 50 fungal, bacterial and viral pathogens of pearl millet have been reported (Ramakrishnan, 1971; Ferraris, Figure 2. Reported area planted to pearl millet in Africa in 1973). However, the pathogens that cause 1978 (one dot equals 20 000 ha) major damage to the crop are much fewer. The most important disease in Africa and Asia is downy mildew, caused by Sclerospora Since introductions to the Americas and graminicola (Sacc.) Schroet. In India, this dis- Australia are fairly recent they constitute a ease occurred in epidemic proportions in the somewhat relatively narrow genetic base. early 1970s and devastated the hybrid crop, Pearl millet is hermaphroditic, with pro- which was cultivated on more than one million nounced protogyny, which produces up to 70- ha (Safeeulla, 1977). It also destroys much 80 percent cross-pollination (Rachie and Maj- pearl millet every year in Africa (Delassus, mudar, 1980). In its centre of origin and diver- 1964; King and Webster, 1970; Jouan and sity (Sahelian Africa) it freely crosses with its Delassus, 1971; Girard, 1975; Williams, 1984). wild progenitors (Pennisetum violaceum and P. Ergot, caused by Claviceps fusiformis Love- fallax), producing the mimetic weed shibra, less, can incite severe disease on hybrid millet

TABLE 2. 1980 millet production data for countries in Africa with at least 0.1 million ha in millet1

Area of Average Area of Average Country millet cultivation yield Country millet cultivation yield (million ha) (kg/ha) (million ha) (kg/ha)

Nigeria 5.03 636 Zimbabwe 0.38 474 Niger 3.07 446 Ethiopia 0.27 724 Mali 21.40 536 Ghana 0.24 273 Sudan 1.30 346 United Rep. of Tanzania 0.22 727 Chad 21.15 522 Egypt 20.17 33734 Senegal 20.95 684 Togo 20.17 724 Upper Volta 0.90 444 Zambia 0.13 462 Uganda 0.55 818 Mauritania 20.10 190 Rep, of Cameroon 20.45 889 Africa total (17 079) (666)

1 Sourco:FAO(l9B1). FAO Production yearbook 34:106. 2These 'millet' data appear to include data, as there are no separate sorghum data for these countries in the relevant section of the FAO Production Yearbook, In Egypt. Mali, Togo and the Republic of Cameroon the sorghum values are likely to have been substantial proportions of the figures given for millet- -3This value almost certainly includes yields from Irrigated sorghum-

138 Vol. 31, N. 4, 1983 in India (Safeeulla, 1977; Arya and Kumar, Insect pests. About 300 insects have been 1982), particularly when rains occur during the reported to feed on pearl millet in different flowering period. It is generally less of a prob- parts of the world (Sharma, Davies and Arora, lem in open-pollinated traditional cultivars. In 1981), but the number that can cause serious eastern Africa, however, ergot is important in damage is probably no more than a dozen, and open-pollinated varieties and in West Africa it those causing serious damage on a consistent can be devastating on short-duration, photo- annual basis are much fewer (Verma, 1980). period-insensitive cultivars. Ergot is also Several polyphagous insects, such as locusts important because the alkaloid-containing and grasshoppers (Schistocerca gregaria, sclerotia of this pathogen contaminate grain, Locusta migratoria and Chrotogonus spp.), thus creating a health hazard for consumers. army-worms (Mythimna spp. and Spodoptera Smut, caused by Tolyposporium penicillariae exempta) and Heliothis armigera, sporadically Bref., can cause serious damage in northern cause severe damage in pearl millet, but these

India and West Africa. As with ergot, F1 hy- insects are probably best held in check by using brids appear to be more susceptible to smut than insecticides. open-pollinated varieties. There are reports of serious damage to pearl Of the leaf diseases, rust, caused by Puccinia millet in northern India by white grubs (Holo- penniseti Zimm., is potentially important in trichia (Lachnosterna) consanguinea Blanch), southern India and eastern Africa. Severe out- particularly in the states of Rajasthan and breaks of blast, caused by Pyricularia setariae, Gujarat (Gahukar and Jotwani, 1980; Rachie have occasionally been reported in northern and Majmudar, 1980) and the authors have India. seen patches of pearl millet in farmers' fields Less important, although potentially damag- and entire fields on experiment; stations killed ing, diseases include seedling blights (Helmin- before flowering time by white grubs in Rajas- thosporium spp. and Fusarium spp.) and cer- than. The shootfly (Atherigona approximata tain leaf spots, such as zonate leaf spot Mall.) kills the central whorl leaf, particularly (Gloeocercospora sp. and Dactuliophora elon- in later sown crops, but generally the plants gata Leakey), curvularia leaf spot {Curvularia grow so rapidly that the larvae are not able to penniseti) and cercospora leaf spot (Cercospora kill the growing point. However, when condi- fusimaculans Atk.) (Rachie and Majmudar, tions preclude rapid growth, dead hearts or 1980). damaged inflorescences may occur and yield losses in the range of 20 to 60 percent have been Most of the research published on disease reported (Natarajan et al., 1973; Gahukar and resistance in pearl millet has been performed in Jotwani, 1980). Other insect pests reported to India, where the diseases considered important cause occasional damage to pearl millet in India enough to warrant control through resistance are the midge Genomyia penniseti Felt. and var- breeding are downy mildew, ergot and smut ious sucking insects, such as perpusilla (Williams, Singh and Thakur, 1982). Downy Walk., Rhopalosiphum maidis Fitch, mildew has received most attention in the past Empoasca spp., Aphanus sardidus and Myl- ten years, with ergot and smut now following locerus spp. However, at the present time the close behind. These three diseases cause signifi- only serious pest that seems to warrant major cant yield losses. While ergot and smut attack control efforts in India is the white grub. The mainly hybrids, they also attack varieties if other insects mentioned are potentially serious rains are frequent during flowering. The dam- pests and new varieties should be checked for age caused by the leaf diseases is not usually high levels of attack by particular insects under severe and depends on the stage of crop natural field conditions. development. There is a need for studies on the relationships between incidence and severity of In Africa, the stem borers Acigona the leaf diseases at various stages of crop ignefusalis and Sesamia calamistis are reported development and yield reduction. as pests on pearl millet in the Sahelian and

FAO Plant Prot Bull. 139 Sudanese zones, with the former pest being the ence of shibra, which mimics the pearl millet more important (Harris, 1962). The millet plant in appearance but is virtually non-produc- earhead caterpillar (Rhaguva albipunctella) tive in terms of harvestable grain. Because it is was very destructive in the Sahelian regions of a mimetic weed, it escapes removal during the West Africa in the early 1970s, with estimated normal weeding processes, persists in the crop, losses of up to 50 percent being reported (Ver- competes for environmental resources and con- cambre, 1978; Ndoye, 1979). The midge G. tributes pollen to the varietal gene pool. At penniseti has also been reported to cause severe maturity, shibra heads shatter and disperse grain yield reduction of mid-season Souna mil- their seeds to reinfest the fields. The authors lets, which flower in late September in Senegal have seen up to 20 percent of shibra in farmers' (Coutin and Harris, 1968). In the ICRISAT fields in West Africa and believe it to be a gen- Millet Entomology Programme for West eral and serious problem throughout the re- Africa, based at the ICRISAT Sahelian Centre gion. in the Niger, research priority is being given to Control of the shibra problem needs a combi- A. ignefusalis and R. albipunctella (Nwanze, nation of cultural and plant-breeding activities. 19S2). A multi-faceted integrated control pro- Shibra plants should be rogued prior to anther gramme is envisaged, with -plant resistance shedding, and shibra gene contamination needs being a major component. to be eliminated from local cultivars through breeding. Parasitic weeds. Of the several witchweeds (Striga spp.) known to occur in Africa and Asia, Birds. Flocks of grain-eating birds consume S. hermonthica is the most serious parasitic vast amounts of pearl millet grain annually in weed on pearl millet in Africa and causes severe India and Africa. In India, sparrows (Passer losses in the Sahelian region. S. asiatica appears domesticus L. and Gymnorrhis xanthocallis), to be the most common in India and southern parakeets (Psittacula sp.) and crows (Corvus Africa (Rachie and Majmudar, 1980), though sp.) are probably the most important bird pests there are few reports of this weed as a serious (Rachie and Majmudar, 1980). In Africa, problem in pearl millet. In sorghum, however, where birds are believed to be the most serious the cultivation in India of new hybrids highly pest of millet (Rachie and Majmudar, 1980), susceptible to S. asiatica has resulted in an the principal pest is the weaverbird (quelea, alarming increase of this parasite and a change Quelea quelea L. in the Sahel, Q. quelea to other crops on land traditionally used for aethiopica Sundeval in mountainous areas of growing sorghum (House and Vasudeva Rao, eastern Africa, Q. quelea centralis Van Some- 1982). ren in East Africa and Q. quelea lathami Smith Large areas of pearl millet in the Sahel have in southern Africa). been devastated by S. hermonthica. In the It is debatable whether any degree of bird authors' opinion, it is essential to find the control can be achieved with genetic characters sources of resistance to this weed pest in order of the host plant (heavily awned millet may be to improve cultivation of pearl millet in the subject to less attack, but there are conflicting Sahel. reports on the effectiveness of this character); to date it would appear that the most effective Non-parasitic weeds. Weeds should obvi- method of discouraging birds is to scare them ously be controlled in all crops (especially dur- off by traditional methods. In West Africa, an ing the early stages of crop development) if the international effort against bird pests — the yield potential is to be achieved. There is, how- Organisation commune de lutte antiacridienne ever, a special and important weed problem et de lutte antiaviaire (OCLALAV) — has been operating for some time and uses various affecting pearl millet in Sahelian Africa that is methods of bird destruction, including fire and much more difficult for farmers to control than explosives to destroy nesting colonies and the conventional weed problem. This is the pres-

140 Vol. 31, N° 4, 1983 spraying of poisons such as parathion and phos- Sahelian Africa these are grain-eating birds, drin(Pradat, 1962; Bruggers and Jaeger, 1982). downy mildew, witchweed and probably Such communal action needs to be continued in Acigona stem borer and Rhaguva earworm; in West Africa and strengthened in eastern and India they are downy mildew, ergot, smut and southern Africa, where the depredations of probably white grubs in the northwestern states migratory birds cause enormous grain losses of Rajasthan and Gujarat. Host plant resistance annually (Bruggers and Jaeger, 1982). will have to be the major defence against downy mildew, witchweed, ergot, smut, stem borer The need for and use of surveys. More pre- and Rhaguva earworm, although the integra- cise information is needed on the incidence, tion of appropriate cultural and chemical con- severity and losses caused annually by patho- trol measures needs to be investigated in order gens and pests of pearl millet, particularly in to make the control more effective and more Africa. A great deal of this information can be durable. collected in the Sahel during the first phase of the FAO Integrated Pest Control Project, and similar activities are needed in eastern and Resistance screening techniques southern Africa. In India, there appears to be more monitoring of problems in pearl millet, The rate of progress that can be made in the though there is a need to establish a more pre- improvement of a crop for any genetic charac- cise national pest and disease monitoring sys- ter will depend primarily on the effectiveness of tem for this crop. the screening technique. In projects on identifi- A few notes of caution are pertinent on the cation of disease and pest resistance, consider- use of information from surveys. First, in order able attention needs to be given at the outset to to translate incidence and severity data into ensure that the screening techniques are reli- meaningful yield loss data, the relationships able and relevant. Reliability requires that between these parameters need to be deter- adequate levels of inoculum be provided mined through experimentation. Moreover, uniformly throughout the populations of plants while surveys will indicate the present problems being screened and that environmental (with traditional cultivars and cultural prac- parameters be maintained within a range con- tices) they do not necessarily indicate what new ducive to infection/infestation and disease/ major problem might emerge as a result of the damage development. Relevancy requires that introduction of new varieties and cultural prac- the host be challenged by the pathogens or tices (e.g. ergot was regarded as a minor prob- pests in as natural a way as possible, and this lem on pearl millet in India prior to the large- will in turn require a sound knowledge of the

scale use of F1 hybrids). Thus, the most impor- biology, epidemiology and bionomics of the tant potential pest and disease problems also pathogens and pests and the diseases and dam- need to be identified from survey work and new age that they cause. The requirements of relia- genotypes should be exposed to these prior to bility will generally preclude a completely large-scale introduction. Even then, not all natural means of host challenge, but highly potential problems will be identified and vigi- artificial methods of inoculation/infestation and lance will be needed during the introduction plant maintenance should generally be avoided phase of new genotypes and cultural practices, if reactions are to be obtained that have rele- particularly if exotic parent material has been vance to the crop growing in the field. used. A second important aspect of screening is the Despite a lack of knowledge about the method used to assess plant varietal reactions. occurrence of and losses caused by pathogens Standard rating scales are essential to provide and pests in pearl millet, there are problems so objectivity on the part of workers and from sea- severe that their control is known to be of pri- son to season. It should be clearly recognized, mary importance for increasing production. In however, that as pearl millet is a highly outcross-

FAO Plant Prot. Bull. 141 ing crop, with considerable variability occur­ important for evaluating relationships beween ring within cultivars, valuable sources of resis­ disease and yield (Williams and Singh, 1981) tance can be identified within populations that and for studies on the possible occurrence of are generally susceptible. Thus, as long as a partial resistance. reliable screening technique has been em­ ployed, ratings of varietal reaction should be Ergot. Suspensions of conidia from fresh made on individual plants within test lines in honeydew produced on pearl millet are the order to evaluate the potential for selection most effective inocula for inducing ergot in this within lines. crop. The optimum flowering stage for inocula­ tion is when the greatest flush of fresh stigmas Downy mildew. The traditional method of occurs on the inflorescence. However, if the screening for resistance to downy mildew in stigmas receive pollen before or at the same pearl millet was to plant the test material in a time as inoculum, the pollen predominates and "sick plot", i.e. a field plot into which zoospore- little ergot will develop (Thakur and Williams, containing crop debris had been incorporated 1980). Thus, in screening for ergot resistance, it (Chahal et al., 1975; Deshmukh, More and is not possible to rely on a completely natural Utikar, 1978). The use of a sick plot, however, system of plant challenge by inoculum pro­ has several drawbacks (Williams,. 1983) and a duced on interplanted inoculum donor plants, more efficient and reliable resistance screening because it is essential to ensure that inoculum technique was developed in the mid-1970s in precedes pollen in reaching the stigmas. This is which test lines were challenged by zoospores best achieved by a system of bagging tillers at from sporangia produced on highly susceptible crucial stages. The elimination of pollen inter­ "infeetor rows" planted throughout the screen- ference should be combined with uniform ing area (Williams, Singh and Pawar, 1981; inoculation, using viable inoculum to avoid Williams, 1984). high frequencies of escapes (Thakur, Williams and Rao,1982). Two basic parameters have been used to define susceptibility (or, conversely, resis­ A rapid and reliable method of assessing the tance) to downy mildew in pearl millet. The proportion of infected florets on an inflores­ most frequently used is the percent incidence of cence, which utilizes a set of standard drawings plants that show systemic symptoms, irrespec­ of pearl millet inflorescences with various pro­ tive of the severity of symptoms on individual portions of infected florets from one to 90 per­ plants. Arbitrary figures have then been estab­ cent, has been devised (Thakur and Williams, lished below which the variety is regarded as 1980). resistant. The data for the incidence score can be collected easily and rapidly in the. field and Smut. Although there is still a great deal to be this method is probably the most practical one learned about the epidemiology of pearl millet when large numbers of breeding lines are being smut, which is incited by Tolyposporium screened. In order to obtain an accurate inci­ penicillariae, it has long been known that floret dence score at the end of the season it is neces­ infection is effected directly by airborne sary to score the crop more than once. sporidia produced by germinating sporeballs The second scoring system that has been used and not as a result of systemic colonization of combines disease incidence and severity into a the plant (Bhat, 1946). Various workers have disease index (Williams and Singh, 19S1). This tried direct inoculation of inflorescences, gen­ rating is done only once, after flowering, and erally by injection at the boot-leaf stage of thus needs to be combined with an earlier inci­ development with aqueous suspensions of dence score, as described above. The latter sporeballs and/or sporidia, with conflicting method is more laborious than the incidence results (Patel and Desai, 1959; Husain and method, but it does provide a more accurate Thakur, 1963; Pathak and Sharma, 1976a; measure of the amount of disease. This is Bhowmik, and Sundaram, 1971). All these

142 Vol. 31, N0 4, 1983 authors indicated the important role high The rating of reactions of cereals to leaf dis- humidity plays in causing infection. eases is fraught with pitfalls and difficulties. In more recent studies, Thakur, Subba Rao The main questions are: at what growth and Williams (1982) evaluated several aspects stage(s) should the assessments be made; on of smut-inoculation methods and concluded which leaves; in what way; how does one cope that the most effective and reliable method was with variability in time of flowering among the injection of a fresh sporidial suspension (ca. 1 x test lines; and, can epidemiologically important 106 sporidia/ml) into the boot just prior to parameters be measured? These questions can inflorescence emergence, immediate bagging only be answered effectively if there is sound of the inoculated tillers and provision of high knowledge available as to the biology and humidity for the period from inoculation to epidemiology of the disease and of its effects on symptom appearance. The rating of the reac- plant development and yield. Many foliage tions of plants inoculated with T. penicillariae pathogens can quickly colonize senescing leaf includes combinations of incidence and sever- tissue, and thus ratings made too late in the ity. As for ergot, standard drawings have been maturity of a line will overestimate its suscepti- developed to assist in the estimation of the bility. Conversely, ratings made too early in the proportion of diseased florets on individual maturity of a line will underestimate its suscep- inflorescences (Thakur and Williams, unpub- tibility to certain diseases. Accordingly, lines lished data). The mean and range of severity with variable flowering and maturity dates within test lines provide valuable selection should be scored at a fixed physiological criteria. development event and not chronologically.

Foliage diseases. Foliage diseases have been Multiple disease resistance. Since effective, studied much less than the three diseases refer- reliable screening techniques have been red to above. Those that have received most developed for the three major diseases (downy attention are rust and blast, with occasional mildew, ergot and smut) it has become possible reports of work on resistance to other patho- to screen for sources of multiple disease resis- gens such as Helminthosporium rostratum tance. This is done by subjecting the same Dreschler (Singh, Choudhary and Bhatnagar, plants to several pathogens and selecting indi- 1980) and Cercospora penniseti (Burton and viduals that carry resistance to all the diseases. Wells, 19S1). In screening for blast and rust Screening for combined resistance to downy resistance, most workers have relied on natural mildew, ergot and smut in multiple inoculation infection in the field (Pathak et al., 1976; Duhan trials was begun at ICRISAT in 1982 (Williams and Thakur, 1980; Williams, Singh and et al., unpublished data). The selected test Thakur, 1982), but Yadav, Agnihotri and lines, elite progenies from the ergot and smut Prasada (1980) inoculated seedlings with a screening projects, were grown in the downy "highly pathogenic strain" of the blast fungus in mildew nursery (Williams, Singh and Pawar, a greenhouse test. 1981) and, at the boot-leaf stage, tillers of selected downy mildew-resistant plants were Rust and blast are diseases in which "infector inoculated with sporidial suspensions of rows" have been effectively used to provide Tolyposporium penicillariae, other tillers were uniform inoculum for resistance screening in bagged to be inoculated later with fresh hon- other cereal crops, and there is no reason to ey dew suspensions of Claviceps fusiformis and believe that such screening would be less effec- still others were bagged with no inoculation car- tive in pearl millet. The critical factors that ried out. Downy mildew-resistant plants were need to be determined in order to use the infec- screened in this way for ergot and smut resis- tor-row screening technique effectively are the tance; they were selfed so that selfed seed could environmental conditions conducive to sporu- be harvested from individual plants with multi- lation and infection and the required time and ple resistance. spatial distribution of infector and test rows.

FAO plant Prat. Bull. 143 Insect pests. The authors are unaware of any susceptibility, particularly in genetically vari­ studies in which pearl millet has been effec­ able populations, and a great deal of research is tively screened for resistance to any insect pest. needed to develop effective and relevant There have been, however, reports of cultivars screening techniques for resistance to witch- that appeared to be less damaged during severe weed. Plant pathologists should be involved in natural infestations of germ-plasm and breed­ such work because of the similarities in working ing lines (ICAR, 1969, 1971, 1972, 1974; Jot- with soilborne plant pathogens. At the present wani, Sukhani and Matai, 1971; Leuck et al., time there is a pitifully small research effort into 1968; Kalode and Pant, 1966; Sandhu, Luthra the pearl millet witchweed problem in Sahelian and Singh, 1976). Reliable screening Africa, and this must be vastly increased if techniques have been developed in and progress is to be made in reducing the effects of sorghum for identification of resistance to stem this major yield constraint. borers and shootfly (Jotwani and Davies, 1980) and these should be readily applicable to pearl millet. The task will probably be much more Sources of resistance difficult for Rhaguva resistance because, while little is known of the life history or biology of Diseases. Sources of disease resistance in the pest, its unpredictable appearance and dis­ pearl millet were reviewed by Williams (1983). appearance at different sites in different years Details are summarized below. are well known. Downy mildew. Two major efforts have been Parasitic weeds. Little work has been done on made to screen the world pearl millet germ- resistance to witchweed in pearl millet, though plasm collection for resistance to downy mil­ progress has been made in identification of dew (Murty, Upadhyay and Manchanda, 1967; resistance to S. hermonthica and S. asiatica in Williams, Singh and Thakur, 1982), under con­ sorghum (Ramaiah, 19S1; Vasudeva Rao, ditions of natural disease development and also Chidley and House, 1982). The basic strategy latterly using uniform inoculation techniques has been to develop Striga-sick plots by incor- (Williams, Singh and Pawar, 1981). In both porating large quantities of seed of the appro- studies the highest proportion of resistant priate Striga spp. There is, however, a major accessions were identified in those from Africa. problem in ensuring uniformity of challenge, In the later study the central region of West because it is difficult to distribute witchweed Africa, particularly northern Nigeria, southern seed uniformly throughout large screening Niger, the Upper Volta and Mali, provided the areas, and soil heterogeneity provides different richest sources of resistance. However, only a environmental conditions in different parts of relatively smalt proportion of the more than the screening area during the critical period for 14 000-entry world germ-plasm collection has infestation. The only way to overcome this been effectively screened for downy mildew problem is by sufficient replication, in space resistance, mainly because of the success and time, and the use of frequent systematic obtained in developing sources of resistance susceptible checks. At the ICRISAT Centre, from initially susceptible lines or populations sorghum has been successfully screened for through recurrent selection and, to a lesser resistance to S. asiatica using three processes: extent, mutation breeding. There is a need, (i) preliminary screening with one check for nevertheless, for a greater effort in classifying eight test plots; (ii) advanced screening with a the downy mildew susceptibility/resistance of check alongside each test plot; (iii) multiloca- the remaining accessions in the world germ- tional screening at known "hot spots" (Vas­ plasm collection. udeva Rao, Chidley and House, 1982). Irradiation of seed of susceptible lines is A second major problem in screening for reported to have yielded new sources of resis- resistance to witchweed is just how to measure tance (Murty, 1973; Pokhrtyal and Jain, 1974;

144 Vol. 31, N° 4, 1983 Murty, 1974; Jain and Pokhriyal, 1975). A ing materials since 1978. The authors quoted potentially valuable new male-sterile line above have recently described the ICRISAT derived from a selection programme at programme's successful efforts in developing ICRISAT among progeny of irradiated suscep- ergot resistance. In the germ-plasm of the more tible lines (Kumar et al., unpublished data) has than 4 000 entries screened no high level of been used to make several experimental hy- ergot resistance was detected, although selec- brids, some of which have entered the Indian tion among the progeny of crosses between national evaluation programme. It will be sev- lines that were consistently relatively less sus- eral years, however, before the true value of ceptible yielded many lines that developed only this resistance source becomes apparent. low levels of ergot (<1 percent florets infected)

Levels of resistance to downy mildew in ini- by the F6 generation. tially susceptible populations have been Similar attempts to develop ergot-resistant increased through a process of recurrent selec- selections have been made at other locations in tion within populations while maintaining or India in the last few years (S.S. Chahal, per- improving other desirable and adaptive fea- sonal communication; Harinarayana, 19S2) tures of the population (ICRISAT, 1981; Wil- utilizing the improved screening technique. liams, Singh and Thakur, 1982; Williams, However, the high ergot susceptibilities of the 19S3). One of the products of the ICRISAT hybrids and varieties in the 1981 yield trials of Pearl Millet Improvement Programme's recur- the All India Coordinated Pearl Millet rent selection project has been released for cul- Improvement Programme (ICAR, 1982; Wil- tivation by the national programme in India, liams , 1983) indicate that the resistance has not after it had been shown to combine high yield yet been incorporated into high-yielding hy- stability and downy mildew resistance during brids or varieties. several years of multilocational trials in the sub- continent. Smut. Prior to the late 1970s there were few Since 1976, the levels of downy mildew resis- reports of sources of resistance to smut in pearl tance in entries submitted to the hybrid and va- millet. Murty, Upadhyay and Manchanda riety preliminary yield trials of the All India (1967) published a list of reactions to smut of Coordinated Millet Improvement Programme 1 508 entries in the world collection, with indi- have steadily increased, so that by 1981 almost cations that several accessions from Africa and all entries had no more than a ten percent inci- India were possibly resistant. Pathak and dence of downy mildew in screening trials at Sharma (1976a) reported 11 of 322 lines of ICRISAT (Williams, 1983). diverse origin to be relatively less susceptible to smut and Yadav (1974) reported six lines to be Ergot. In the 1960s and early 1970s attempts smut resistant. More recently, screening for were made in India to locate sources of resis- sources of resistance to smut has become a tance to ergot, with little success (Kumararaj major activity in the ICRISAT Pearl Millet and Bhide, 1962; Shanmugasundaram et al., Improvement Programme, with several 1968; ICAR, 1971; Pathak and Sharma, hundred lines being screened each year and 1976b), primarily due to the lack of an efficient, about 30 lines being evaluated annually in mul- reliable screening technique. In the mid-1970s tilocational testing (ICRISAT, 1981). These the phenomenon of pollen interference in ergot reported sources of resistance, however, have infection was detected (Thakur and Williams, not yet been successfully utilized in the 1980), which had major implications for screen- development of improved varieties and hy- ing pearl millet for ergot resistance. The brids, as witnessed by the high smut susceptibi- improved screening technique (Thakur, Wil- lity of the entries in the various 1981 yield trials liams and Rao, 1982), described above, was of the All India Coordinated Millet Improve- developed on the basis of this information and ment Programme in screening trials at has been used to screen germ-plasm and breed- ICRISAT (ICAR, 1982; Williams, 1983).

FAO plant Prot Bull. 145 Rust. In the evaluation of 1 508 germ-plasm these two diseases has also been developed in accessions by Murty, Upadhyay and Man- these lines (Williams, Singh and Thakur, 1982). chanda (1967), three lines were free from rust The ergot, smut and downy mildew reactions of and 81 entries appeared to have low susceptibil- the five lines with the highest levels of ergot ity (with a score of 2 as registered on a 1 to 5 resistance in 1981 are presented in Table 3. scale). Other resistant lines have been reported in the literature (Ramakrishnan and Sun- Insect pests and witchweed. Effective screen- daram, 1956; Suresh, 1969). Screening and ing techniques have not yet been developed for selection of world germ-plasm for rust resis- identifying resistance to insect pests and witch- tance commenced at ICRISAT in 1975 and, weed in pearl millet. However, apparently less although no artificial screening technique had susceptibility has been reported to stem borer been used, late planting at the ICRISAT (Sandhu, Luthra and Singh, 1976), shootfly Centre farm and at Bhavani Sagar in southern (ICAR, 1974) and S. hermonthica (Roger and India allowed a reliable challenge of the test Ramaiah, 19S1). These apparent sources of materials (Singh and Williams, 1978). More resistance will need to be re-evaluated when than 20 lines have been consistently resistant to reliable screening techniques have been rust in these trials (less than ten percent of the developed. surface of the upper four leaves supporting rust pustules at the soft dough stage of seed matu- rity) (Singh and Williams, 1978). Tests For stable disease resistance

Blast. Screening for sources of resistance to Multilocational testing. If reliable disease- blast in pearl millet has been carried out at a few resistance screening techniques are used cor- locations in northern India, on a relatively rectly on a rich, well-chosen germ-plasm collec- small scale, generally relying on natural infec- tion, then it is probable that resistance to most tion with no inoculation. Sources of resistance diseases will be identified at the "home" loca- reported in recent studies by Pathak et al. tion. However, the question remains as to (1976), Duhan and Thakur (1980) and Yadav, whether this resistance will be effective when Agnihotri and Prasada (19S0) have been listed the varieties are grown in another region or by Williams (1983). another year, with possibly different pathogenic races and different levels of agro- Helminthosporium leaf spot. Singh, Choudhary climatic parameters, (i.e. is the resistance stable and Bhatnagar (1980) screened 118 pearl millet lines for resistance to Helminthosporium ro- stratum by inoculating seedlings with conidial suspensions of the pathogen. Eleven lines remained symptom free. TABLE 3. Sources of multiple disease resistance in pearl millet in India1

Curvularia leaf spot. In the trials of Patil (1972) Mean ergot2 Smut3 Downy mildew4 none of 108 test lines were free from disease Line severity severity Incidence [%) (%) (%) caused by Curvularia penniseti var. poonensis.

One line was highly resistant at the seedling ICMPE 134-6-9 2 0 7 stage and 13 lines showed adult plant resis- ICMPE 134-6-11 2 0 0 ICMPE 134-6-41 2 0 3 tance. ICMPE 134-6-34 2 0 4 ICMPE 134-6-25 2 0 4 Susceptibility check 41 54 45 Multiple disease resistance. The lines being developed for ergot resistance at ICRISAT 1Source: Williams, Singh and Thakur, 1982. - 2Bassd on the 1981 IPMEN have been routinely screened for downy mil- results of 10 locations in India.-3Based on 20 inoculated heads during the 1981 rainy season at the ICRISAT Centre. - 4Based on the ICRISAT Centre 1981 dew and smut reactions, so that resistance to rainy season downy mildew nursery.

146 Vol. 31. N° 4. 1983 or unstable?). The most satisfactory way of by ICRISAT. The evidence indicates that some answering this question is to subject the vari- West African lines multiplied for several gener- eties to multilocational testing so that the resis- ations at the ICRISAT Centre in India have lost tance is evaluated against many populations of the original high level of resistance experienced a particular pathogen under a wide range of in West Africa. environmental conditions. Test locations in the Wide differences in the downy mildew sever- centres of origin and diversity of a crop are par- ity values among locations have been observed ticularly valuable. If these are the centres for several entries, not only between India and where the host and pathogen have co-evolved Africa, but also among locations in West over a long period, that is where the greatest Africa. This indicated the probability of varia- range of pathogenicity can be expected. tion in pathogenicity among populations of Sclerospora graminicola. In 1978, therefore, an International Pearl Millet Downy Mildew Dif- The International Pearl Millet Disease Re- ferential Trial (IPMDMDT) was initiated to sistance Testing Programme (IPMDRTP) examine the validity of the apparent differen- tial reactions of entries in previous years and to In 1976 the International Pearl Millet Disease identify potential differential hosts for further Resistance Testing Programme was initiated as study of the pathogenic variability of this patho- a joint activity between scientists in national gen . The trial confirmed earlier results and pro- programmes and ICRISAT, to evaluate the sta- vided clear indications that considerable bility of reported sources of disease resistance pathogenic variability exists within the pearl and to begin to examine the virulence of diverse millet-infecting pathotype of S. graminicola. populations of the pathogens of pearl millet. The potential differential host cultivars iden- International nurseries have been distributed tified are now being used for intensive inves- to cooperating scientists in several African and tigations into pathogenic variability in S. Asian countries annually for the purpose of graminicola at the University of Reading, UK, identifying sources of stable resistance to where initial studies have confirmed major dif- downy mildew, ergot, smut and rust. ferences in pathogenicity among isolates (Ball, 1983). Downy mildew. Multilocational testing for downy mildew resistance in pearl millet has Ergot. The resistant lines identified from been conducted cooperatively with national crosses among relatively less susceptible lines programme staff in India and in several West (Thakur, Williams and Rao, 1982) were tested African countries in two stages. In the first at several locations in India and Nigeria in the stage, a 150-entry Pre-International Pearl Mil- 1981 International Pearl Millet Ergot Nursery let Downy Mildew Nursery (Pre-IPMDMN) (IPMEN). The most resistant entries at Indian was tested at a few key downy mildew "hot- locations in this trial were five lines from the spot" locations in India and West Africa. The cross J-2238 x J-2210-2. In Nigeria, however, best entries from the Pre-IPMDMN in one year these lines had much higher levels of ergot, and were moved forward into the full IPMDMN the the best entry found there came from a cross following year for testing at many more loca­ between two Nigerian lines. Other lines that tions. Some entries from West Africa have per- had little or no ergot at the ICRISAT Centre formed well across seasons and locations developed more ergot at certain Indian loca- throughout the IPMDMN programme, al- tions, the reasons for which require investiga- though there have been occasional occur- tion. Progenies from other crosses are being rences of more than ten percent downy mildew, developed in the ICRISAT ergot resistance generally in West Africa. The detailed results development project, which should provide are available in the reports of the Pre- additional diversified ergot resistance sources IPMDMN and IPMDMN, published annually in the near future.

FAO Plant Prot. Bull. 147 Smut. The International Pearl Millet Smut in variety populations. New varieties, if Nursery (IPMSN) was initiated in 197S and developed without serious levels of inbreeding, testing has been performed annually. Some will contain all the genes present in the original entries have shown consistent resistance to population but in different frequencies, smut in India and in some locations in West depending on the selection pressures applied. Africa (Williams, Singh and Thakur, 1982). This has two effects: (i) varieties are unlikely to show total resistance to a given population of a Rust. The lines identified as resistant in the pathogen (but the level of resistance expressed ICRISAT screening programme (Singh and may be totally effective in providing economic Williams, 197S) have been tested annually at control); and (ii) the residual variation for resis- several locations in India through a cooperative tance can permit the variety population to be testing network in the International Pearl Mil- reselected for resistance to a new pathogen or let Rust Nursery (IPMRN), which was first other disease. initiated in 1977. Eight entries have given resis- Single-cross hybrids are an artificial state for tant reactions at several locations in tests con- a cross-breeding species such as pearl millet, ducted over a period of two to three years (Wil- and the history of grain hybrids in India since liams, 1983). More work is needed on resis- 1965 bears testimony to their vulnerability to tance to this disease, with an evaluation of the disease and relatively short life expectancy. variation in parameters that will contribute to The positive aspect of this history, however, is slow development of esodemics. that, although in use for only five years, hybrid HB3 contributed food worth thousands of mil- lions of rupees, and so has its replacement Utilization of disease resistance BJ104. This raises a question, of fundamental consideration to all breeders working with Two main breeding approaches are possible in genetic resistance to pests and diseases, of how pearl millet: (i) recurrent selection in breeding much resistance is required for economic pro- populations (often termed composites), which tection. Incorporating resistance to pests and are operated with a minimum amount of diseases is only one necessary aspect in the breeding of new varieties or hybrids with inbreeding (S1 progeny testing has been found to be the most effective method, though also improved yield and quality. There is a view that the most resource consuming); and (ii) the con- incorporating excessive levels of disease resis- ventional pedigree system where variability tance, which are out of proportion to the generated in variety crosses (or by mutation) is expected life of the hybrid in respect to its other separated into discrete lines by inbreeding. attributes, amounts to over-kill and a waste of These two methods have different conse- valuable research resources. The Indian hybrid quences for the nature of the genetic resistance HB3 is cited as evidence supporting this point. most likely to be retained after selection. Two However, had it not been for the downy mildew types of end product are used commercially: susceptibility of HB3 it would probably still be varieties (including traditional landrace va- grown today, as the yield levels of the currently rieties) and single-cross hybrids. These also have used hybrids are in no way superior. Thus, the consequences as to the type of genetic control converse view can also be supported, that if of resistance that can be most easily utilized. HB3 had possessed stable and durable downy mildew resistance, the massive use of resources A variety may be defined as an inter-mating to find replacements would not have been population in equilibrium, which is the natural needed. Breeders have found that using one genetic state for pearl millet, and for a given resistant parent in hybrid combination is often pathogen it can contain a number of resistance sufficient to confer resistance in single-cross genes, both major and minor, and being dupli- hybrids. It remains to be determined whether cate or additive in effect. Dominant or partially this is a wise practice or whether the presence of dominant resistances are easiest to manipulate

148 Vol. 31, N0 4, 1983 resistance in both parents will provide more Also, variety development work has greater durable resistance. There is a debatable view relevance to African needs. held by many breeders that commercial single- During the formation of the ICRISAT base cross hybrids in pearl millet will need to be composites in 1973-74, care was taken to replaced every five years or so, for as progress is include parents of Nigerian origin, which con- made in breeding this is likely to happen for ferred good resistance to downy mildew reasons of yield and quality as well as for because of their origin. Other composites were changes in disease susceptibility. derived from breeders' populations from the Niger, the Upper Volta, Senegal and Uganda. Downy mildew. Identifying, distributing and Of these, populations from Senegal and utilizing stable downy mildew resistance has Uganda initially contained insufficient resis- been a major goal of the ICRISAT Pearl Millet tance to downy mildew in India, but this was Improvement Programme from its inception in rapidly increased through reselection in the 1973. While sources of resistance have been ICRISAT downy mildew nursery (Williams. identified that were effective in both India and 1983). In order to select for increased downy West Africa, it has become apparent that, dur- mildew resistance in composites, the material is ing the utilization of such sources in India, resis- exposed twice during each selection cycle. Dur- tance to downy mildew in West Africa has been ing the progeny testing phase one replication is progressively reduced. A good example is pro- grown in the downy mildew nursery and the vided by the World Composite (WC) from best plants selfed in all progenies. Seed from Nigeria where it exhibited good resistance to these plants (not remnant seed) is used to rep- downy mildew (and other diseases); after selec- resent the selected progenies in the recombina- tion in the ICRISAT downy mildew nursery for tion generation, which is also grown in the several generations, this composite and va- downy mildew nursery. Only disease-free rieties made from it continued to show excellent plants are used in recombination. This process resistance to downy mildew in India, but they permits selection for downy mildew resistance showed deteriorating levels of resistance when between and within progenies during the test- tested in Nigeria. The overall conclusion has ing phase and again during the recombination been that selection for downy mildew resis- stage within the selected progenies, which, tance for West Africa has to be conducted because they were previously selfed, continue there. Crosses beween lines from India and to segregate for resistance/susceptibility. Africa are sent as F s or F s for selection in the 1 2 The purpose of deriving partial and complete region of Africa where they are to be utilized. inbreds from variety crosses is to: (i) identify Though most material from Africa is resistant annually sets of useful lines from the F3 to F5 to downy mildew in India, it is unadapted in generations for distribution to cooperators as a other ways (excessive lateness and unbalanced routine supply of new variability; (ii) use them tillering) and thus needs reselection in India. as parents to make synthetics; (iii) test them for Both breeding approaches in pearl millet, as use as hybrid parents. Each of these objectives described previously, have been used in the requires that the lines be screened for downy ICRISAT programme to breed for yield and mildew resistance, once or twice for objectives downy mildew resistance. This programme has (i) and (ii) but repeatedly for objective (iii). It is put slightly more effort into breeding varieties in this last case, where lines show that they are rather than hybrid parents for two reasons: potential male-sterile maintainers, that the first, the greater part of the national effort in downy mildew nursery is most intensively used millet improvement in India was already during breeding, since all the generations of directed toward hybrid development; second, selection and backcrossing, up to the fifth or stable resistance to downy mildew was easier to sixth backcross, are grown exclusively in the obtain in improved varieties, which also have downy mildew nursery. During the develop- higher levels of resistance to ergot and smut. ment of several new male-sterile lines and

FAO Plant Prot. Bull. 149 TABLE 4. Summary of ergot reactions of test crosses that resistance is recessive and/or possibly that using ergot-resistant (ER) F5 lines on three male-sterile male-sterile cytoplasm is connected with sus- (ms) lines during the 1980 rainy season1 ceptibility. Crosses between different lines with

Mean ergot severity (%)2,3 high levels of ergot resistance produced F1 gen- ms No of F1 lines hybrids mg lines ER F5 lines F1 hybrids erations that were not all as resistant as the parents, indicating that resistance is controlled 111A 189 76 <1-20 63-8S by at least several genes with additive effects. 5054A 216 80 <1-20 84-9S Similarly, synthetics made from intercrossing 5141A 237 83 <1-20 65-92 several sources of resistance showed moderate

1 2 resistance, and the inclusion of any susceptible Source: R.P. Thakur et al., unpublished data. - Mean of 10-30 inoculated 3 heads, - Ergot severity range of 30 ER F5 lines used in test crosses. parent lines suppressed resistance (see Table 5). The implication is that to obtain ergot-resis- tant hybrids, resistance, preferably from the evaluation of existing male-sterile lines and same source, will be needed in both parents of their isogenic maintainers, evidence was the hybrid. A project to achieve this has been gathered to show that the Al cytoplasm (as car- initiated at ICRISAT, using two common male- ried by Tift 23A, the female parent of HB3) sterile lines and several desirable pollen does not contribute to downy mildew suscepti- parents. The ergot-resistant synthetics can bility (Kumar et al., unpublished data). probably be improved rapidly, both for yield and resistance, through the use of an ergot- Ergot. Ergot is prevalent in both India and resistant inbred tester. Africa, though the pollen-interference Crosses made to compare the effects of phenomenon is usually sufficient to provide cytoplasm on ergot susceptibility provide some protection in varieties. However, heavy ergot indication that male-sterile cytoplasm may be attacks can be induced in varieties by unusually associated with susceptibility, but this observa- humid weather conditions, abnormal sowing tion needs further testing. (and hence flowering) dates or the presence of some earlier-flowering susceptible genotype Smut. The fact that lines with high levels of (such as a hybrid). Hybrids produced using resistance have been obtained from a range of cytoplasmic male sterility are generally highly backgrounds, including breeding material, by susceptible to ergot, and it is in these that resis- selfing and selecting under disease pressure is tance is urgently needed. Conditions for ergot attack seem to be more favourable in many African countries, and it may not be possible to use hybrids there for this reason until effective levels of resistance to ergot are bred into hybrid TABLE 5. Ergot reactions of three synthetics made from ergot-resistant F5 lines and one from a parents. mixture of ergot-resistant and susceptible lines1 The work required to generate ergot-resis- tant lines and the results of crosses between Ergot severity (%)3 Synthetic(x)2 these lines and susceptible seed parents provide Mean Range evidence on the inheritance of ergot resistance and how it should be utilized. The fact that high ICMS 8031 (5) 12 5-30 levels of resistance could not be found in any ICMS 8032(6) 15 5-40 ICMS 8034 (5) 14 5-35 germ-plasm source and could only be obtained ICMS 8102 (5)4 50 1-100 from crosses between lines with moderate resis- WC-C75 (variety check) 24 10-50 tance indicates involvement of several genes. BJ-104 (hybrid check) 54 25-80 Crosses between ergot-resistant lines and sus- ceptible male-sterile lines have given totally 1Source: R.P.Thakur and S.B. Chavan, unpublished data. -'Number of lines used in constituting the synthetics. -3Mean of 10-20 open inoculated susceptible hybrids (see Table 4), indicating heads. - 4Synthetic made from two ergot-resistant and three susceptible lines.

150 Vol. 31, N0 4, 1983 promising for the prospects of utilization. In TABLE 7. Male sterility and smut severity (%) in 30

test crosses on MS-81A using F4 sister lines as pol- susceptible x resistant test crosses a range of 1 linators susceptibilities occurred, indicating that resis- tance may be partially dominant (for highly 2 F ratio Test cross status Mean Range resistant hybrids, however, it is likely that both (transformed data) parents will need good levels of resistance), and crosses between resistant lines are highly resis- Fertile (n = 14) 33.6 16-62 3 tant. 4.34 Sterile (n = 16) 47.6 10-S8 The recovery of smut resistance in progenies

of crosses between agronomically elite, but sus- 1Source: K. Anand and R.P. Thakur. unpublished data. -2Based on 10 inocu- 3 ceptible, lines and smut-resistant parents has lated, bagged heads. - Indicates statistical significance at p < 0.05. proved relatively easy compared with ergot,

and by the F5 generation more than 50 percent of the lines retained after selecting under inocu- lation in the F2 to F4 generations recorded smut families, 244 S2 lines were extracted and more severities of less than 10 percent (see Table 6). than 50 percent of these had less than 1 percent In the process of crossing smut resistance into smut when tested at Hissar in 1981. The 54 best

a B line, 30 F4 progenies derived from the ini- have been recombined to form the C1 bulk, tial cross between the B line and the smut resis- which represents the basis of a further cycle of tance source were test crossed on to an A line. selection for yield and for resistance to downy Of the test crosses, 14 were male-fertile and 16 mildew and smut. were male-sterile. The members of the male- sterile group were statistically more susceptible Multiple disease resistance. Large-scale screen­ than the male-fertile group (see Table 7), indi- ing for resistance to downy mildew, ergot and cating that pollination reduces smut severity. smut can be operated on the same plants by Since good smut resistance had been iden- using the several screening techniques that tified from a variety of backgrounds, a smut- have been developed. Only those lines showing resistant composite (SRC) was formed in 1978 acceptable levels of downy mildew resistance, using 37 low-susceptible parents. When 562 which can be assessed by the time of flowering, half-sib progeny were tested in 1980, nearly 80 are inoculated with the ergot and smut patho­ percent were found to have smut severities of gens. Sources of downy mildew plus ergot resis­ less than 10 percent. From the best 117 half-sib tance and downy mildew plus smut resistance have already been found, and several closely related lines have been identified with resis­ tance to all three diseases (see Table 3). A dis­ ease-resistant composite will be formed when TABLE 6. Smut reactions of 95 F5 progeny derived from a cross between smut-susceptible and smut- parents with sufficient genetic diversity and 1 resistant parents each carrying multiple resistance have been identified. Smut severity (%) No. of Frequency class* progeny Shibras. Shibra gene contamination can be 0-10 50 53 eliminated by a process of inbreeding for one 11-20 13 14 generation, evaluating S1 progeny, and recom- 21-30 14 15 31-40 6 6 bining only the best 25 to 50 of these, which 41-50 7 7 show no shibras, using remnant seed. This pro­ 51-60 3 3 61-70 1 1 cess has a double benefit as it permits positive 71-80 1 1 selection to be made for other traits, particu­ larly yield and downy mildew resistance. The

1 2 Source: R.P.Thakur and K.N.Rai unpublished data. - Mean of 10 inoculated, number of S1 progeny to be tested should be at bagged heads.

FAO Plant Prot. Bull. 151 least 500, preferably in two replications, but Resistance conferred by the additive action of plots need not have more than about 50 plants several genes, which retard the several proces- each. These S1 progeny are best obtained by ses of infection, colonization and the capacity selecting at least 800 superior heads from sev- to sporulate, provides a much weaker and less eral well-grown fields of the variety to be specific selection pressure. Thus, when used improved. These are grown in the off-season in against a highly variable pathogen population, very small plots (five to ten plants per plot) and single immunity genes are unlikely to be dura- two or three typical plants are selfed in each ble. Rather, they will be liable to sudden plot. At harvest, the single best plant from each "breakdown". Conversely, resistance confer- plot is selected, and some plots may be rejected red by the additive action of several genes that entirely. After evaluation of the S1 progeny, the control several aspects of pathogen develop- recombination of the 25-50 selected S1 plants ment and dispersal will not be subject to sudden using remnant seed must be done in the off-sea- "breakdown", and thus is more likely to be dur- son to avoid the process of recontamination able but may erode gradually over a long from other farms and from wild species. period.

Pathogen variability. Mutations to overcome specific resistance genes occur at random at a Prospects for achieving durable disease certain low frequency in pathogen populations. resistance As the production of infective propagules increases, the probability of a propagule that Stable resistance can be identified through the possesses the required virulence gene encoun- process of multilocational testing. Unfortu- tering a resistant plant on which it will be nately, there is no necessary correlation be- selected also increases. Where combinations of tween stable resistance and durable resistance. several resistance genes confront the pathogen, The only certain way to identify durable resis- its capacity for genetic recombination will be an tance is to grow a cultivar commercially on a important determinant of the speed of response large scale over a long period. There are, how- to the selection pressure of the host resistance. ever, certain features of the host pathogen and pathosystem that enable some degree of predic- Survival and dispersal of novel pathogen tion of the possible durability of resistance. genotypes. The epidemiology of a disease has When a strong specific selection pressure is important implications for the survival and dis- exerted on a genetically variable population, persal of novel pathogen genotypes and thus for the population moves in the direction of the the potential durability of resistance. Where selection pressure. The introduction of a dis- there is a distinct non-crop off-season, and the ease-resistant cultivar can exert a strong selec- propagules that initiate crop infection each year tion pressure on a pathogen population. Thus, come from a wild host reservoir, or where the when considering the likely durability of a new initial inoculum blows in from a distant location resistant cultivar, knowledge is needed as to the with an earlier crop season and different vari- strength and specificity of the selection pres- eties, there will be a low survival potential for sure, the variability of the pathogen and the pathotypes that are selected on the crop. survival and dispersal capabilities of novel Where the inoculum for one year's crop is pro- pathogen genotypes. vided by resting bodies or dormant mycelium in debris from the previous year's crop, then the Selection pressure. A resistance mechanism probability for survival of novel pathogen conferred by the action of a single gene, which genotypes is higher. The novel genotypes of a pathogen that produces vast numbers of air- precludes the development of a pathogen dur- borne propagules will be much more rapidly ing or immediately following initial penetra- dispersed than those of a pathogen that is soil- tion, provides the strongest and most specific borne and soil-transmitted. selection pressure on a pathogen population.

152 Vol. SI, N0 4, 1983 It is apparent that, in order to predict and the yield advantage of the hybrids with the develop strategies to extend the durability of greater stress resistance shown by more resistance of a particular host to a particular dis- heterogeneous composite cultivars. A thor- ease, a thorough knowledge is required of the ough knowledge of the genetics of resistance nature and genetics of the resistance, the varia- will be needed for this strategy to be utilized bility potential of the pathogen and the efficiently. epidemiology of the disease in the particular epidemiological unit in which the resistant cul- Downy mildew. Although it appears that "par- tivar is to be commercially used. tial resistance" to downy mildew is the norm in The biology of the four major pathogens of pearl millet (because it is unusual to find test pearl millet, S. graminicola, C. fusiformis, T. lines completely free from the disease), this penicillariae and P. penniseti, indicates their does not necessarily mean that resistance is probable ability to be able to respond rapidly to polygenic in individual plants as may be the specific strong selection pressures (Nene and case with a rust of a self-pollinated cereal. Singh, 1976; Singh and Williams, 19S0; Wil- Because of the outcrossing nature of the crop liams, 1983, 1984; Michelmore, Pawar and Wil- and the systemic nature of the pathogen, indi- liams, 1982). Thus, the nature and genetics of vidual plants are generally scored on a qualita- cultivar resistance are likely to be important tive basis (they are either diseased or they are determinants of resistance durability. not), whereas the score for the whole line is given as a quantitative score. Thus, 10 percent incidence does not mean that all plants were Nature and genetics of resistance diseased with an average disease score of 10 percent; it means instead that out of 100 plants Although penniseta are hermaphroditic, they 90 were free from disease and only 10 were dis- show pronounced protogyny, which leads to a eased. The 90 disease-free plants may all pos- normally high level of cross-pollination (Rachie sess the same single immunity gene, or there and Majmudar, 1980). Thus, in landrace cul- may be several combinations of different tivars, in which there is random cross-pollina- immunity genes, and/or they may possess sev- tion, considerable genetic variability can occur eral additive genes that slow down the patho- among the plants that constitute a cultivar. This gen so much that disease does not develop. If variability probably enables the crop to reduce the durability of resistance is to be assessed, it the effects of specific stress factors, including must be known which of these situations is act- plant pathogens (e.g. when considering a cul- ing for any resistant cultivar. The authors are tivar with five major-effect resistance genes, not aware of any critical histopathological these five genes can occur in 31 different combi- studies on the nature of resistance of downy nations after several generations of random mildew in any pearl millet cultivar. There are, mating, with the effect that the cultivar behaves however, several reports of studies on the as a naturally occurring multiline). inheritance of resistance (Appadurai, Param- baramani and Natarajan, 1975; Gill et al., 1975, F hybrids, which are produced primarily 1 1978; Pethani, Kapoor and Chandra, 1980) through the crossing of two inbred lines, have with somewhat conflicting and unclear results. reduced heterogeneity, which makes the hy- This probably reflects the difficulties that exist brids more vulnerable to disease epidemics than in attempting to study inheritance of resistance composite cultivars. The use of pollen from a in host cultivars of an outcrossing crop, when heterogeneous population to create an F hy- 1 such cultivars are generally neither completely brid would probably be less likely to create a resistant nor completely susceptible when disease-vulnerable hybrid than the use of an inoculation techniques that are less than 100 inbred line as the male parent. percent effective are used with pathogen popu- A recently suggested strategy (ICAR, 1982) lations undefined for pathogenicity. If inheri- is to use hybrid blends or mixtures to combine

FAO Plant Prot. Bull. 153 tance studies are to provide meaningful results, have been identified, further work is needed on ways must be found to ensure that the plants the nature and genetics of resistance to this dis- used in the crosses are definitely resistant or ease, but the parent plants used must be truly susceptible (susceptible diseased plants could resistant and susceptible, and effective stan- be cured by treatment with metalaxyl fun- dardized inoculation techniques must be used. gicides), inoculation procedures must be stan- The occurrence of quantitative differences in dardized and the isolates of the pathogen susceptibility on an individual plant basis and should be defined and maintained in the asex- evidence of the manner in which resistance ual state. levels can be raised within test lines suggest that There is no doubt that if durable resistance is smut resistance is polygenically controlled. Re- to be developed, particularly through the search is needed to test this hypothesis. strategy of hybrid blends, genes for resistance will need to be identified and manipulated. The Rust. Observations of the rust reactions of a recent recognition of a type of susceptibility large number of pearl millet germ-plasm lines that prevents the development of esodemics in southern India (R.J. Williams, unpublished (Williams, Pawar and Singh, 1982) highlights data) indicated that several resistance mech- the need to consider the type of susceptibility anisms probably occur. Large differences exhibited by test materials when an exodemic in pustule intensity and pustule size and appear- system of screening is employed. ance were seen and necrotic flecking, charac- teristic of hypersensitive reactions, was also Ergot. Until very recently there were no reli- observed. A great deal of careful research is able sources of resistance to ergot in pearl mil- needed both to substantiate these hypotheses let, and thus there are no reports of specific and to utilize the most appropriate characters in studies on the nature and inheritance of ergot a disease resistance breeding programme. resistance in this crop. However, quantitative reactions in this disease are obtained on an indi- vidual plant basis, so that one percent disease could indicate that all plants were diseased and Priorities for future research that the average severity per plant was one per- cent. Thus, with ergot, it is unlikely that Pearl millet has a rich and diverse germ-plasm immunity genes are involved. In addition, which the authors firmly believe contains all the Thakur, Williams and Rao (1982) concluded resistance genes needed to breed pest- and dis- that resistance to ergot is recessive and poly- ease-resistant cultivars in this crop. Germ- genically controlled, on the basis of results plasm has to be collected and evaluated in an obtained while developing resistant lines. intelligently directed manner, utilizing acces- Such resistance could be highly effective and sions from regions where high selection pres- would be expected to be durable in F1 hybrids, sures for the necessary characters are likely to provided the resistance genes are manipulated have occurred. The breeding system of pearl into both the male and female parents. millet and its relatively short duration indicate that rapid advances can be made in breeding. Smut. In the only paper found on the inheri- For diseases, the major work needed is in tance of smut resistance in pearl millet, Yadav evaluation of the nature and inheritance of the (1974) concluded that resistance was controlled identified resistances, and this knowledge must by either single- or double-gene action. This be used in the development of strategies to equivocal conclusion is probably the result of increase resistance durability. The possibility of non-uniformity in reaction of the parental presenting complex multiple barriers to patho- material similar to that referred to in the section gens (e.g. the combination of polygenic resis- on inheritance of resistance to downy mildew. tance and systemic seed-applied fungicides for Now that new stable sources of smut resistance downy mildew control) requires investigation.

154 Vol. 31, N0 4, 1983 For insect pests, additional survey work must virulent than those in India and the insect pests, be undertaken and major research conducted weed and bird problems in Africa are different on the development and use of effective, mean- from those found in India. This all points to the ingful resistance screening techniques. There fact that much more research is needed on pearl will be a need for a clear understanding of the millet diseases and pests in Africa. The estab- bionomics of the important insect pests and the lishment of the ICRISAT Sahelian Centre near evaluation of integrated control strategies using Niamey is a step in the right direction, but rapid combinations of host-plant resistance, cultural significant progress is unlikely to occur unless control methods and possibly pesticide sprays, the diseases and pests of this crop are studied by dusts and granules. well-qualified staff within national programmes. For witchweed, the most important re- Training and motivation of local scientists search area concerns the development of a reli- to work on the diseases and pests of pearl millet able resistance screening technique and its use are obviously high priority needs. A network of to identify and develop witch weed-resistant cooperating centres should be set up to identify cultivars. and utilize host-plant resistance in the African A solution to the shibra problem in Sahelian continent. They should be staffed by well- Africa should be pursued by a combination of trained plant pathologists, entomologists and cultural practices and plant breeding. plant breeders, who will need to be provided In Africa it is important that pearl millet with the necessary resources to screen for and improvement programmes utilize the locally utilize sources of disease and pest resistance resistant cultivars as the basis for crop improve- effectively. ment, since exotic, so-called elite, improved In India, although a considerable effort is millets developed in India or the United States directed toward research on pearl millet dis- are generally highly susceptible in Africa to the eases, the resources provided are often less local strains of pathogens and pests, particu- than adequate. The research centres selected to larly in parts of West Africa. Flowering time, as carry out reliable resistance screening must be determined by planting date, genotype matu- provided with staff that is not frequently rity class and/or degree of photoperiod sensitiv- changed, irrigation equipment that will not be ity, is a critical factor in the severity of inflores- dependent on erratic rainfall, and a plentiful cence pests and diseases. supply of materials, such as selfing-bags mark- ing pens, seed storage boxes, fuel for water Regional research needs. It is apparent from pumps and vehicles, and so on. the references cited in this article that most of The stage is set for rapid advances in the abil- the published research on pearl millet diseases ity to control pearl millet diseases and pests and pests has been carried out in India. The through the use of host-plant resistance. The crop, however, is grown on a larger area in pace at which progress will be made depends on Africa than in India and the germ-plasm in the human and material resources that national West Africa appears to be a richer source of dis- programmes devote to the research areas ease resistance than germ-plasm collected in highlighted in this review and the degree of India. There are indications that the popula- cooperative activities among national pro- tions of the pathogens in West Africa are more grammes.

References

APPADURAI, R., PARAMBARAMANI, C. & NATARAJAN, ARYA. H.C. & KUMAR. A. Ergot epidemics of pearl mil- 1975 U.S. Note on the inheritance of susceptibility of pearl 1982 let in Rajasthan. In Recent advances in the biology of millet to downy mildew. Indian J. Agric. Sci., 45: microorganisms. Vol. 11, p. 439-451. Eds K.S. Biulig- 179-180. rami and K.M. Vyas. India, Dehra Dun.

FAO Plant Prot. Bull. 155 BALL, C.R. Pearl millet. USDA Farmers' Bull., 168. GlRARD, J.C. Downy mildew of pearl millet in Senegal. 1903 1975 In Proc. Consultants' Group Meetings on Downy Mil- dew and Ergot of Pearl Millet, 1-3 Oct., 1975. BALL, S. Pathogenic variability of downy mildew (Scle- Hyderabad, India, ICRISAT. 1983 rospora graminicola) of pearl millet. I. Host cultivar reactions to infection by different pathogen isolates. HARINARAYANA, G. AICMIP developments since 1977. Annuls of applied biology, 102: 257-264. 1982 All India Coordinated Millet Improvement Pro- gramme, Indian Council of Agricultural Research BHAT, R.S. Studies in the Ustilaginales. I. The mode of and Cooperating Agencies, College of Agriculture, 1946 infection of the bajra plant (Pennisetum typhoides Pune. (Mimeo) Stapf.) by the smut Tolyposporium penicillariae. Bref J. Indian Bot. Soc, 25: 163-186. HARRIS, K.M. Lepidopterous stem borers of cereals in 1962 Nigeria. Bull. Ent. Res., 53:139-171. BHOWMIK, T.P. & SUNDARAM, N.V. Control of pearl 1971 millet smut with systemic fungicides. Plant Dis. Rep., HOUSE, L.R. & VASUDEVA RAO, M.J. Striga -problems 55: 87-SS. 1982 and prospects. Working paper presented at the BRUGGERS, R.L. & JAEGER, M.M. Bird pests and crop ICRISAT-ICAR Working Group Meeting on Striga Control, 30 Sept.-l Oct. 1982, ICRISAT Centre, 1982 protection strategies for cereals of the semi-arid Afri- Patancheru, A.P. India, ICRISAT. can tropics. In Proc. Int. Symp. on Sorghum, Sor- ghum in the Eighties, 2-7 Nov. 1981. Vol. 1, p. 303- HUSAIN, A. & THAKUR, R.N. A new technique of inocu- 312. Patancheru, A.P., India, ICRISAT. 1963 latins pearl millet with Tolyposporium penicillariae. Sci. Cult., 29: 607-608. BRUNKEN, J., DE WET, J.M.J. & HARLAN, J.R. The ICAR. Progress report of the All India Coordinated Mil- 1977 morphology and domestication of pearl millet. Econ. 1969 let Improvement Programme 1968-69. Indian Council Bot., 31: 163-174. of Agricultural Research and Cooperating Agencies. BURTON, G.W. & WELLS, H.D. Use of near-isogenic 19S1 host populations to estimate the effect of three ICAR. Progress report of the All India Coordinated Mil- 1971 let Improvement Programme 1970-71. Indian Council foliage diseases on pearl millet forage yield. of Agricultural Research and Cooperating Agencies. Phytopathology, 71: 331-333. ICAR. Progress report of the All India Coordinated Mil- CHAHAL, S.S., GILL, K.S. & PHUL, P.S. Note on the 1978 reaction of pearl millet inbreds against the downy 1972 let Improvement Programme 1971-72. Indian Council mildew pathogen. Indian J. Agric. Sci., 48:190-191. of Agricultural Research and Cooperating Agencies. ICAR. Progress report of the All India Coordinated Mil- CHAHAL, S.S., GILL, K.S., PHUL, P.S. & AUJLA, S.S. 1975 Screening of the pearl millet germplasm for the 1974 let Improvement Programme 1973-74. Indian Council green-ear disease, caused by Sclerospora graminicola of Agricultural Research and Cooperating Agencies. (Sacc.) Schroet. Crop Improvement, 2: 65-70. ICAR. Progress report of the All India Coordinated Mil- COUTIN, R. & HARRIS, K.M. , distribution, 1982 let Improvement Programme 1981-82. Indian Council 1968 biology and economic importance of the millet grain of Agricultural Research and Cooperating Agencies. midge, Geromyia penniseti (Felt), gen. n., comb. n. (Dipt., Cecidomyiidae). Bull. Ent. Res.. 59:259-273. ICRISAT. ICRISAT Annual Report 1975-76. Hyderabad, 1976 India. DELASSUS, M.. Les principals maladies du mil et du sor- ICRISAT. ICRISAT Annual Report 1976-77. Hyderabad, 1964 gho observees en Haute-Volta en 1963. Agron. 1977 India. Trap., 19:489-498. ICRISAT. ICRISAT Annual Report 1977-78. Hyderabad, DESHMUKH, H., MORE, B.B. & UTIKAR, P.G. Screen- 1978 India. 197S ing germplasm of pearl millet against downy mildew, Sclerospora graminicola (Sacc.) Schroet. Indian J. ICRISAT. ICRISAT Annual Report 1979-80. Patancheru, Agric. Res., 12: 85-88. 1981 A.P., India. DUHAN, J.C. & THAKUR, D.P. Reaction of pearl millet JAIN, H.K. & POKHRIYAL, S.C. Improved pearl millet 1980 germplasm to Pyricularia penniseti. Haryana Agric. 1975 hybrids. Mutat. Breed. Newsl., 6: 11-12. Univ. J. Res., 10:81-82. JOTWANI, M.G. & DAVIES, J.C. Insect resistance stud- FAO. FAO production yearbook. Rome, FAO. 1980 ies of sorghum at international institutes and national 1981 programmes with reference to India. In Biology and breeding for resistance in and pathogens in FERRARIS, R. Pearl millet (Pennisetum typhoides). agricultural plants. p. 224-236. Proc. Int. Short 1973 Review Series No. 1/1973, Commonwealth Bureau Course in Host Plant Resistance, Texas A. & M. of Pastures and Field Crops, Hurley, Maidenhead, Univ., College Station. Texas, 22 July-4 August Berks., UK. 1979.

GAHUKAR, R.T. & JOTWANI, M.G. Present status of JOTWANI, M.G., SUKHANI, T.R. & MATAI, S.H. Screen- 1980 field pests of sorghum and millets in India. Trop. Pest 1971 ing of bajra lines for resistance against white grub. In Mgmt, 26: 138-151. Investigations on insect-pests of sorghum and millets, 1965-1970, p. 155-157. Ed. S. Pradhan. New Delhi, GILL, K.S., PHUL, P.S., CHAHAL, S.S. & SINGH, N.B. India. IARI. Div. Ent. 1978 Inheritance of resistance to downy mildew disease in pearl millet. Cereal Res. Commun., 6: 71-74. JOUAN, B. & DELASSUS, M. Principals maladies des 1971 mils et sorghos observers au Niger. Agron. Trop., 26: GILL, K.S., PHUL, P.S., SINGH, N.B. & CHAHAL, S.S. 830-860. 1975 Inheritance of resistance to downy mildew in pearl millet—a preliminary report. Crop Improvement, 2: KALODE, M.B. & PANT, N.C. Studies on the susceptibil- 128-129. 1966 ity of different varieties of sorghum, maize and bajra

156 Vol. 31, N° 4, 1983 to Chito zonellus (Swinhoe) under field and cage con- PRADAT, A. Lutte contre les ravageurs: le probleme ditions. Indian J. Ent., 23: 488-494. 1962 quelea, Quelea quelea. Agron. Trop., 18: 137-142. KING, S.B. & WEBSTER, O.J. Downy mildew of sor- RACHIE, K.O. & MAJMUDAR, J.V. Pearl millet. Univer- 1970 ghum in Nigeria. Indian Phytopath, 23: 342-349. 1980 sity Park and London, the Pennsylvania State Univ. KUMARARAJ, S. & BHIDE, V.P. Varietal resistance in Press. 1962 bajri (Pennisetum typhoides (Burm.) Stapf. & RAMAIAH, K.V. Striga studies at ICRISAT, Upper Vol- Hubb.) to ergot (Claviceps microcephala (Wallr.) 1981 ta. Paper presented at the Second ICRISAT/IDRC Tul). Curr. Sci., 31: 76. International Striga Workshop, Ouagadougou, Upper Volta, 5-8 October 1981. LEUCK, D.B., TALIAFERRO, C.M., BURTON, R.L., BUR- 1968 TON, G.W. & BOWMAN, M.C. Fall armyworm resis- RAMAKRISHNAN, T.S. Diseases of millets. New Delhi, tance in pearl millet. J. Econ. Ent., 61: 693-695. 1971 Indian Council of Agriculture Research.

MICHELMORE, R.W., PAWAR, M.N. & WILLIAMS, R.J. RAMAKRISHNAN, T.S. & SUNDARAM, N.V. Further stud- 1982 Heterothallism in Sclerospora graminicola. 1956 ies on Puccinia penniseti. Proc. Indian Acad. Sci. Phytopathology, 72: 1368-1372. Bull., 43: 190-196. MURTY, B.R. Mutation breeding for resistance to ROGER, Z.G. & RAMAIAH, K.V. Recherche sur le Striga 1973 downy mildew in Pennisetum. Mutat. Breed. Newsl., 1981 du mil a l'lCRISAT, Haute-Volta. Paper presented at 2:2. the Second ICRISAT/IDRC International Striga Workshop, Ouagadougou, Upper Volta, 5-8 MURTY, B.R. Mutation breeding for resistance to October 1981. 1974 downy mildew and ergot in Pennisetum and to Ascochyta in chickpea. In Induced imitations for dis- SAFEEULLA, K.M. Genetic vulnerability: the basis of ease resistance in crop plants. Vienna, International 1977 recent epidemics in India. Ann. N.Y. Acad. Sci., 287: Atomic Energy Agency, 46: 89-100. 72-85. SANDHU, G.S., LUTHRA, R.C. & SINGH, J. Prelimi- MURTY, B.R., UPADHYAY, M.K. & MANCHANDA, P.L. 1976 nary studies on the resistance of pearl millet to Chilo 1967 Classification and cataloguing of a world collection of partellus (Swinhoe) (Pyralidae: Lepidoptera). Sci. genetic stocks of Pennisetum. Indian J. Genet. Plant Cult., 42: 222-223. Breed., 27:313-394. SHANMUGASUNDARAM, A., RAJASEKARAN, R., SELVA- NATARAJAN, U.S., GURUSWAMY RAJA, V.D., SEVA- 1968 RAJ, S. & RAMAMURTHY, T.G. Evaluation of sugary 1973 RAJ, S. & ANAVARADHAM, L. Extent of damage disease and green ear in cumbu varieties. Madras caused by shootfly (Atherigona approximata) on Agric J., 55: 37-38. bajra hybrids. Madras Agric. J., 60: 584-585. SHARMA, H.C.. DAVIES. J.C. & ARORA, J. Bibliog- NDOYE, M. New millet-spike pests in Senegal and the 1981 raphy of insect and non-insect pests of millets 1979 Sahelian Zone. FAO Plant Prot. Bull., 27: 7-S. 1914-1980. ICRISAT Sorghum and Millets Informa- ion Centre, Patancheru, A.P., India, ICRISAT. NENE. Y.L. & SINGH, S.D. Downy mildew and ergot of 1976 pearl millet. PANS, 22: 366-385. SINGH, G., CHOUDHARY. G.G. & BHATNAGAR, G.C. 1980 Resistance of Pennisetum cultivars against Helmin- NWANZE. K.F. Annual Report 1981, Entomology. ICRI- 19S2 SAT Sahelian Centre, Niamey, the Niger. 20 p. thosporium rostratum. Indian J. Mycol. Plant Path., (Mimeo) 10: 70. SINGH, S.D. & WILLIAMS, R.J. Review of pearl millet PATEL. M.H. & DESAI, M.V. Use of polythene bags to 1978 rust resistance screening. Hyderabad, ICRISAT. 1959 secure high infection by Tolyposporium penkillariae (Mimeo) Bref. in Pennisetum typhoides Stapf. & Hubbard. Curr. Sci., 28: 248-249. SINGH, S.D. & WILLIAMS, R.J. The role of sporangia in 19S0 the epidemiology of pearl millet downy mildew. PATHAK, V.N. & SHARMA, R.K. Method of inoculation Phytopathology. 70: 1187-1190. 1976a of Pennisetum typhoides with Tolyposporium penicil- lariae and evaluation of germplasm for smut resis- SURESH, S. A preliminary study on the reactions of tance. Indian J. Mycol. Plant Path., 6:102. 1969 pearl millet Pennisetum typhoides Stapf. & Hubb. inbreds and open-pollinated lines to "green ear" and PATHAK, V.N. & SHARMA, R.K. Reaction of bajra "rust" diseases. Madras Agric. J., 56: 88-90. 1976b inbreds and hybrids to ergot at Jobner. Indian J. Mycol. Plant Path., 5:199. THAKUR, R.P. & WILLIAMS, R.J. Pollination effects on 1980 pearl millet ergot. Phytopath., 70: 80-84. PATHAK. V.N., SHARMA, R.K., DASHORA. S.L. & THAKUR, R.P., SUBBA RAO, K.V. & WILLIAMS. R.J. 1976 SINGH, S.P. Reaction of bajra inbreds to Pyricularia 19S2 Development of an effective field screening technique leaf spot at Jobner. Indian Phytopath., 29: 211-212. for smut resistance in pearl millet. Patancheru, PATIL. P.L. Relative resistance of bajra varieties and ICRISAT. (Mimeo) 1972 hybrids against Curvularia. Maharashtra Vidyan THAKUR, R.P., WILLIAMS, R.J. & RAO, V.P. Develop- Mandir Patrika,7: 18-22. 1982 ment of resistance to ergot in pearl millet. PETHANI, K.V., KAPOOR, R.L. & CHANDRA, S. Gene Phytopathology. 72: 406-408. 1980 action and phenotypic stability for incidence of downy mildew disease in pearl millet. Indian J. VASUDEVA RAO, M.J., CHIDLEY, V.L. &. HOUSE. L.R. Agric. Res., 14:217-223. 1982 Genetic control of Striga asiatica in sorghum. Work- ing paper presented at the ICRISAT-ICAR Working POKHRIYAL, S.C. & JAIN, H.K. Breeding for disease Group Meeting on Striga Control, 30 Sept. - 1 Oct. 1974 resistance in pearl millet. Mutat. Breed. Newsl., 3: 1982, ICRISAT Centre. Patancheru, A.P., India, S-9. ICRISAT.

FAO Plant Prot. Bull. 157 VERCAMBRE, B. Raghuva spp. et Masalia sp., chenilles Working Group on Graminaceous Downy Mildews, 197S des chandelles du mil en zone sahelienne. Agron. 4(1): 3. Trop., 33: 62-79. WILLIAMS, R.J., SINGH, S.D. & PAWAR, M.N. An VERMA. S.K. Field pests of pearl millet. Trop. Pest 1981 improved field screening technique for downy mil- 1980 Mgmt, 26: 13-20. dew resistance in pearl millet. Plant Dis., 65: 239- 241. WILLIAMS, R.J. Disease resistance in pearl millet. In 19S3 Reviews of tropical plain pathology. Vol. I, Cereals. WILLIAMS, R.J., SINGH, S.D. & THAKUR, R.P. Sources Ed. S.P. Raychaudri. (In press) 1982- of disease resistance in pearl millet. Paper presented at the All India Coordinated Millet Improvement WILLIAMS, R.J. Downy mildew of tropical cereals. In Programme, Tamil Nadu Agricultural University, 1984 Advances in plant pathology. Eds D.S. Ingram and Coimbatore, 26-28 April 1982. P.H. Williams. Academic Press. (In press) YADAV, R.K.S., AGNIHOTRI, J.P. & PRASADA, R. Re- WILLIAMS, R.J. & SINGH, S.D. Control of pearl millet 19S0 sistance of bajra to Pyricularia leaf spot. Indian J. 1981 downy mildew by seed treatment with metalaxyl. Mycol Plant Path., 10: 197-198. Ann. Appl. Biol., 97: 263-268. YADAV, R.P. Inheritance for smut resistance in pearl WILLIAMS, R.J., PAWAR, M.N. & SINGH, S.D. The 1974 millet. Agra Univ. J. Res., 23: 37-39. 1982 enigma of BJ-104 - an explanation. Newsl. Int.,

158 Vol. 31, N° 4, 1983