Plant-Parasitic Nematodes in South Australian Horticulture, With

WAITE INSTITUTE

AUSTRAIIAN PLAIIT-PANASITIC NEMATODES IN SOUIH

ON HORTICULIURE. WITTI PARTICUI'AR UVIPIIASIS

STIIBBY ROOT

by G.R. Stirling, B.Ag.Sc. (ttons') laetaiae

South Australian Department of Agriculturet

Loxton Research Centre

Loxton.

DePartnent of Plant Patholoryt

l^Iaite Agricultural Research Institute'

UniversitY of Adelaid'e '

A thesis subnitted. for the degree of M'Ag'Sc'

UniversitY of Àdelaid'e

Novenberr 1974 3.4"6 Host range 62

J.4.6.1 Weecl hoets 62 t.4.6o2 Native hosts 6t

1.4.6,, Addítional host range info:mation 6S

1.4"T Control 66 1.4.7,1 Control of p. lobatus on m¡.rsery

peach trees 66 ,.4.7.2 Control of p. Iobatus on nursery citrus trees General Discussfon 1.4.8 7o ,"5 Paæat¡ichodonrs minor 72 Population fluctuations 1.5.1 on peach trees 72 A diseàse s¡mdrorne 1.5.2 of onÍons 74

1.5.2.1 A field survey 74 palhogenicity 1.5.2.2 of p. mÍnor to onions B2 1.5.2.1 Relationship between numbers of

P. minor a,nd plant size B1

1.5.2.4 Nenaticide application B5

i.5.2.5 General Diecussion B9 1.5.2.6 A disease d.istribution pattern

following peach trees 9o

t.6 Trichodorus roxtoni (ttenatotta: Doryrainida) a new specÍes of stubby root nematode from south Austraria 9t

4. ACKNO}ft&DGEil'IENTS 95

5. APPENÐICES 96

6. BIBI.,IoGRAPIIT 107 TABLE OF CONTENTS Page

SUMMÂRY

1 a TNTRODUCTION 1

20 THE OCCURRENCE OF NEIVIATODES ON HORTICULTIIRAI AN}

VEGETABI,E CROPS IN SOUTH AUSTRAIIA 6

2.1 Peach 6

2.2 Vine 11

2.3 citnrg 1t

2"4 Nurseries 15

2.5 Tonato 18

2.6 onion 1g

2.7 General discussion 20

, STUBBY ROOT ÑflVIATODES AND SOUTH AUSTRÀLIAN HORT]CULTURE 2) 1.1 Literature review 2t 3.2 Collection, extraction and storage of samples j1

1.1 Root growth of peach trees J4 1.4 Paratrichod.orrrs l-obatus )t

5.4.1 Population fluctuations in peach nurseries 17

1.4.2 Vertical distribution in the soil 42

1.4.1 Relationship of tree size to p. l_obatus

numbers 45

1.4.4 Effect of temperature on population increase 46

1.4.5 Pathogenicity 5o

1.4.5.1 Field symptoms 50

1"4"5.2 Glasshouse experiments 51

,,4"5"1 Laboratory studies 57

1"4"5.4 Discussion 60 this thesÍs contains no rnaterÍaI which has been accepted for the anard. of a:\y other d.egree or d.iploma in any University and no material previously published or written by another person, except when due reference is nad.e in the text.

signed 'SUMMARY

surveys were u¡d-ertaken to deter¡nine the occurrence of plant-parasitic nematod'es in south Austrariats peach, vÍne and citrus orchards, tomato and onion crope, and hortlcultural nurseries. Root-knot nern¡tod.es (Uetoidogyne sp.) were widespread and. economically inport,ant in pea,ch orchard.s, vine_ ya^rd's a¡rd' tonato crops, and were a najor problem in nurseries. The stubby root nematodee paratrlchod.orus foÞtos- and p. nirìor frequently occurred_. P. minor was common on peach, vine, citrus, tonato and onion, and generally occurred' in nore tha^r¡ half the sa.urprea processed from a particular crop, nhile robatus P. lras present in zo-tq" of sampree from rnost crops. Nearly arl citrus orchards, and more tha¡r one-third of Riverland vineyard.s, were infested with cit:rrs nematode (Tylenchurus senipenetrans), but the nenatod,e clitl not occu.r in nurseries" The verti".ì ¿i"t"ibution of P. lobatus in peach orchard.s was simil-ar to that of root distrÍbution. Both nematode numbe¡s a¡rd root weights were highest at a depth of 1! crn. Grasshouse experinents showed that the optimum tenperature for populatÍon increase of p. r-obatus on peach was in the range 25-tooc' rn peach nurseries, P. robatus popurati-ons increased rapidry to a maxi'mum at the end' of the treesr first ercason of growilr, u.ruL then declined. 0n removal of the peach trees, populations were maÍntained on volrrnteer weed.s. A sipgtifica¡rt negative correlation (r = -0. 129) was obtained between the height of nursery peach trees and. numbers of p lobatus associated. wi th those trees.

Many weed.s were shorm to be hosts of p. lobatus, but the nenatod.e was alr¡o found. in soil near native plants in virgin scrubla¡rd. synptons probably caused' by P. l-obatus were observed in peach, apricot and citrus nu¡series, a.nd' the nenatod-e was shovm to be pathogenic to citrus a¡d apricot, a'nd to feed' on peaoh roots. The fumigant DBcp proved. ineffective in controlling P. Ìobatus on peach, but excel-Ient control- was obtained. on citms using the non-volatil-e nenaticide phenaniphos. There were indicat- ions that the p. control of lobatus on nurs ery citrus trees inproved root growth.

?' mi'nor was shor+n to be associated with a disease of onions which occu¡red mainly when onions llere groÌrn after removal of a horticul-tural cropo rn the field, seedlings were stunted and yellow, with dead leaf tips and' severely stunted' roots. order plants had. abnornally branched root systems' Higher nu'nbers of P. ninor occurred. around the roots of stunted plants tha¡r near healthier prants in the sa^ne fie1d., and. a pathogenicity test showed that the nematod.e severely stunted onion roots. Trichod.orus l_oxtoni t a new species of stubby root nematod.e fron peach a¡¡d citnrs orchard'e at loxton is described. The nematod.e has some characters typical of genus paratrichodorus the and others typical of the genus Trichodoms eensu stricto. WAITE II.,IST|TUTE 1 LIBRARY

1. INTRODUCTION There are fou¡ main centres of horticultural production in South

Australia (fig:ure 1b). A r,ritie range of crops are SEovrn in a¡rd. near Adelaitte, inoludlng apples, cherrfeer g?apevines, alnonds and a variety of vegetables. An extensive vine growing region exísts in the Barossa VaIìey, while horticulture in the South East has become increasingly inportant with recent developments in the viticultr¡ral and. vegetable industries. The major part of the state's horticultu¡e is centred. along its largest wateruay - the River Murray (figure 1c). About 22'OOO hectares are irrigated fron the river, with the najor crops being grapevinesr cítrrrsr peaches, apricotst pears, almond.s a,nd vegetables, particularly tonatoes, onions and pumpkins.

The River Munay flows thror:gh Ern area with rainfal-l and temperatures characteristic of inla¡rcl, serni-desert areas. Average annual rainfall varj-es from 21O nm in the north to 280 nm in the south. The average su¡nmer is long and wa*rrn to hot (nean claily narclnun tenperatures generall,y exceed 26oC for five nonths of the year, November to March ínclusive). Winters are relat- ívely mild ( the lowest nea¡¡ claily ninimum tenperature is about !oC, bei.ng recorded in July). RainfaÌI, soil tenperatute, air temperature and. sunshine data for Loxton ca¡r be seen in Figuree 2a arß' 2b. Alor:g the river, the most domina¡rt land forms are a series of round.ed.t east-west orientated, dÍscontinuous, aeolian clepoeited parallel sandhillst with flats and. depressions in between. The soils of the sandhills consj.st mainly of d.eep coarse red.d.ish sand.s, occasionally grading to loany sa¡ds. The flats consist of relatively shallow (10 crn - JO cn deep) red.dlsh sand.s, sa^¡dy clay loamb, Ioa.uy sa¡rds or sandy loams overlying line rubble or ca1- crete" Soil in the depressions tends to be more clayey. In atldition there are areas of river terraces used nainly for viticulturer with deep red.dish grey clay soils. (fotter et aI 1971, trrretherby 1971). 2.

Most of South Australia's i:rigated. horticulture is concentrated. along the River lfurray fron the Victorian bord.er to Morgan, i-n areas known coll-ec- tively as the Riverla¡rd.. Other irrigation occrl-rs further up the river in

Victoria and New South l¡'Iafes. The nearect ie an area around Milclura known as Sunraysia. It has sinila¡ soile a¡rd clinate to the Riverlandr but a smaller ra.nge of crops, being restricted largely to vines and cit:rrs. Althor:gh there is virtual-Iy no recorded infornation on plant-parasitic nematod.es in South Australia¡r horticulture, nenatodes are widely recognised as inportant pests. Their significance is particularly noticeable in the warm, irrigated sarrdy soils of the Riverland., where root-knot nematod.es

(Meloid.o¡n'ne spp.) axe a major problen on mar\y crops, Other plant-parasitic nematodes occur on horticultural crops in South Australia, but Iittle is knorrn of their clistribution and economic importartce. This thesis is presented. in two parts. The work reported. in the first part was aimed at ad,d.Íng to our linited. knowledge of the d.istribution of nematod.es in South Australian horticultural crops, In the second. part there is particular enphasis on the distribution, ecology and economic importa¡ce of stubby root nematod.es (Trichodqlus spp. and Paratrichodorus spp.) a group of nenatocles that have rarely been studied in relatj.on to Australian horticulture. Most of the work was done in the Riverfand area because of its inporta¡rce in rel-ation to the rest of the state's horticulture. Figure 1a. AustralÍa 1b. South Australia, showing its four nain centres of norticu-ltural prod.uction. 'lc. The River Murray, South Australia.

(irrigation areas are shaded) a Moigon Coæ

LoYedoy Lotdûì

Reæh

Wolker LÛÜì9 ¡ldY{rrì HI

fig 1o u Ädeloide

B 4 \ )

fig. 1b

f ig.'lc

a a Figrrre 2a. Mean nonthly na:rinr.rm air tenperature (oc) (116>.1971)

Mea¡r monthly nininr.m air temperature (oC) (116S-1971)

Mea¡r monthly rainfall (mn) (116+-71) at Loxton Research Centre. 30

Meon Þlox TemP.

6 I0 Meon Min TernP. :_ ul É. Ð *<

OE, u¡ o- - 0 ul l- 30 Ð

z'Tt Þr 3 3 0

J FMAMJ J AS OND 0 Flgure 2b. Mea¡r nonthly !.00 a.m. soil temperature (oC) (lnguet , 1972 - Jury, 1974). Mean monthly hor:rs of sunshine at Loxton Research Centre. (OC TEMPERATURE I. N' (¡ oN (tr o atr o ¡- -ll ¡/ = rc.B I = ¡o.gl¡ll oooJ N' ('I o o Þ 3 (n o z a 0 \. o o (sJtll:tllHsNns 6"

AND VEGET A31,8 CROPS 2. 0c OF NM{ATO DES ON HORTI

IN SOUTII

2.1 Peach IntheRiverla¡rdregionthereareapproxinately16o0traofpeachtrees' l40Ohaclingstonea¡¡d2oOhafreestone.A].lthetreesareonElbertapeach rootstockexceptsomepla.ntetleincelg63whicha¡eonV,Iightrootstocks. Theplant-pa::asiticnematodespeciesintheseorcha¡dsweresurveyed. duringlgTl-72,ædtheírdistributionrelatedtosoiltexture'

Methocls Sa,rnpl.eswerecollectedfroneighty-eightpropertiesinfivectistricts and. Renmark-Paringa). tt'e (waikerie¡ I¡rrup, ],oxton.Ivloorook, Berri.Barmera' nr¡mberofpropertiessa.npled.ineachdistrictwasinproportiontotheto. talareaofpeachesgTownandpropertieswereselectetlbythefocafdist. rictad.visergas}beingrepresentativeofthesoilsand.managementpracti- properties blocks sa.rnpled on the selected ces in that dÍstrict. The peach werelargertha¡ro.{hainareaa¡rd.containedtreesnotmorethantenyears old. block kg eac$ were collectetl frorn each Two soif sa'nples (about 1'5 witha!cndiarneterauger.Eachsanpleconsist,ed.ofsixcorestakerrata tlepthof15-25cnthroughouttheorchard.Northcotelsmethods(1971)were (or two on each bl-ock' A 500 g sub-sa'mple used to aasess the soil texture 25ossub.sa.rnplesforheaviersoils)wastakenfromeachsarnple.Thenema. (Seintrorst 1962)' and id-entified" todes were extracted by elutriation Roots(aboutloog)werecoflected'fromsixtreesoneachblock.They wereindexeclforroot.knotnematodeasfollowS:O,nogalls;1,1t,o24 cent; t'o pet cent; 1' 50 to 74 per per cent of the roots ga]Ìed'i 2' 25 49 4,TstoggpercentiJ,al.-therootsgalled..Nematodeswereextracted of technique (Southey,19?o). Females fron the roots by the Baermarur fu¡urel using perineal patterns' Mel-oidogrne spp. llere id'entified' 7.

Results

0c currenoe of nematodes Table 1 lists the nenatodes recorded. in the survey and their frequency of occu¡rence. Nenatodee were recorded as present if they were

for:¡

Citrus nernatode enchulus semi-penetrans) lantae were found. in several soil ssnples, but only occurred when peach trees were interplanted. with citrus. They were not liste¿I in the tab1e, as their host is probably citrus and not peach. Root-knot nematodes (Ueloid.ogyne spp. ) occurred frequently, but were not idertified. to specj-es leveI on all blocks. Those iden-

tifiett were all fou¡d to be Me loid.os¡ne iavanica. Effect of soil texture

The percentage of btocks in each category of soil texture - sandt

sandy Ioa.n a¡rd loa^ms and clays is shown in Table 2. The highest mean root- knot ind.ex was recorded. on the sand.y soil-s, and the index d'ecreased' as

soils became heavier (lalte 2). Of the orchards on sand a¡rd sandy-loam soils 1/ per cent contained trees with heavily galled roots (root-knot indexes of { or l). The nr¡mber of times a nematode occutred in a parLicular category of soil texture is expressed as a percentage of the total mrmber of blocks with that soil texture (laUte 2). trlon these figures the nematodes faII into two gIoups. Thoge in the first group tend. to occur more conmonly in the coarse-texturetl sa.ndy and sa^nd.y-1oa,n soils, whereas those in the

second group occur in all soil texture categories' I,

TÆl,E 1

AND TIIEIR NB{.ATODES RECORDED ON PEACH

0F 0c CURRENCE

FreouencY of Nenatocle Ocurrence *

68.2 ltYlenchorh¡mchue sPP' minor 50.0 46.6

46,6

16.4

10.7 Xiphinena â.merl-c anum 21.6 Cric onemoitles xenoplax 20,5 Paratrichod.onrs lobatus 14.8 Pratylenchus rnrlnue 1.1 HeIicotvlenchus sP.

number of blocks on * trbequency of occu¡rence is the whichthenenatodeoocr¡rredexpressedasaper- centage of the number of blocks surveyed' q

TA-BLE 2

RELATION SHIP BETWEEN SO]I TEXTURE AND

IRE YOF OCCURRENCE ON PEACH

SoiI texture category

Sand. LOâmS and

1.05 Mea¡r root-knot index 1.91 trbequencY of nematode occurrenc è (/") Meloi spp. 61.+ 16.8 11.o 8.7 Nematodes Pre- trichodorus mr_nor 71.9 42.1 4.4 donina¡rt in lobatus 21.9 11.6 21.1 21.7 coarse-textrred nerlra 4lnerica¡run 19.2 8.7 soils Criconemoicles xenoplax 28,t 21 ,1 ug vulnus 17 .4 21.1 4.4

26.1 6).2 71.9 Nematodes occur-(Paratylenchus spp' ( ring in alt (Tylenchorhynchus spp' 58.7 80.0 78.1 \ soil- textures. (Pratylenchus ninyus 28.1 47 .4 41.5

4.4 Hel- icotvlenchu.s o.o 0.0

in each Percentage of blocks 26.1 soil texture category ,2.1 21 .6 '10.

Discussion

The nematode genera and. species present in Riverland peach orchard's

axe broadly sinilar to those associated- with peach elsewhere (Thomas 1957 t

I1end.rix et al 1965). Root-knot nematodes are probably the most inportant of the genera present, as they are known to cause problens on peach in they marÐr areas of the worlcl (Sfrarpe et al- 1969). In Riverland orchards'

were common on the coarse-textured. santly and sand'y-l-oa¡l soils'

Root-lesion nena todes (Pratvl,enchus sPP. ) are often associated- with decline diseases and reprant problens of peacn (mcnlroy 1972). rn a Georgia suïvey, P. vuLnus r*as always associated with a rapid d'eterioration of fee- (t969) der roots, a.nd reduced tree vigour (rl-iege\ 1969). Barker and clayton substarrtiated. the importance of P. vul-nus and sugges ted, that PratYl-enchus speciesotherthan@and}penetransareof1irrited.impor.hanceon

peach. ,l conmonly occur around d'ecl-i- IU Ring nenatodes ( Criconemoid es xenoplax) rll;i{ t ning peach trees in Catifornia (Hendrix et aL 1965). Lownsbery (1959, 1961) nematodes and a¡rd. Mato (1964) faile¿ to show an associatíon between ring peach tlecline d.isease, but later experiments (Lownsbery et aI 1971) showed and. in- that Criconcmo ides xenopfa:c can rerìDce the growth of peach trees l' crease their susceptibirity to both Pseudomonas syrin8ae a.¡ed waterlogging'

peach is ¡orown to be a host of dagger nematode (Xiptrinerna anericanum)

(Lownsbery 1964) but evidence of its pathogenicity to peach is lacking' The trichod.orus effects of the stubby nematodes Paratrichod'oms þþ!g9 "td Pata minor on peach are unknown. Tylenchorhynchus spp. r Paratyl-enchus spp. and Helicotvlenchus spp. have never been shown to damage peach roots, afid' are not likelY to be imPortant. No attenpt was made to rel-ate tree heal-th to the occur¡ence of parti-

cuLar nematode species because of the Iarge mrnber of environnental,cultural the occr:r1enc( and. managerial factors which ca¡r affect tree health' However, Ì 11.

are a potential of seveTe root symptons suggests that root-k¡rot nematodes problen,particularlyoncoarse.texturedsoils.Theknor¡nassociationof Ít nay p. vulnus with decline diseases and replant problens suggests that

become more importa¡rt as orchard's age, a¡rd are replanted'' inporta^nt The sur\re}, showed. that the nematodes consÍd.erect potentially soils' This on peach occLrrred. predoninantly in the sand'y a^nd' sandy-Ioa.m has often preference of some nenatodes for soils of a particular texture

been reported (wallace 1971).

2.2 Vines vineyard's Sur'eys by Sauer (116Z) and Meagher (t 969b) in Sunraysia frequency of occur- establishecl which nematodes occurred. there, arrd their the sunraysia region rence (taute 1). Because of bhe close proxinity of and climate' the to the Riverland. area, antl the sinilaxity of their soils range of nematode sa$e crops in each aTeà aTe likely to support a similal extensiv'ely survey species. consequentÌy, it was considered. ururecessary to the nematod'es recor:ded the Riverland.ts 11'OOO hectares of vines. Instead', purposes have been in soil sampres coll-ected by the aulhor for advisory recorded during a col_lated. (latre 1). Tahle I also lists the nematodes SurveyofdecliningvinesintheloxtonaIlea.,soilsanplesinthissurvey peach survey' were collected as descrihed. previously for the

Discussion Thedatacollected.appearstoconfirntheearliersug8estionthata vineyards' si.rnilar range of nematocles ocoul in sunraysia and Riverland vineyards was wel-r sum- The effect of nematodes occurring in sunraysia the fact that root- rrarized by Sauer (geZ). More recent work has confirmed nematode parasi'tes of vines ll knot a¡rd citrus nematocle are the most inportant frequently asso- in the Riverla¡rd and. Sunraysia. They are wid.espread, and have proved- so important ciated. with d.ecl-ining vines. Root-knot nernatod'es 12.

TA3T,E ' NEIvIATODES RECORDED. AND TI.IEIR FRESTTENCY

OF OCCURRENCE ON VINES IIT TIM SUNRAYSIA

RIVERLAI{D ^AREAS

Nenatod.e trbequency of occurrence (/o)

Criconenoides 1., I 1' 2t Eelicotvlenchus o.2 0.1

28.2 t9 7o 100

10.9 1g 15

t1.o 50 41 100

Rotvlenchulus 0.1

Scutellonema ,.1 B (Paratrichodorr¡s 0.7 15 B

45.9 28 15 19

65.j 5o 52 19

Xiphinena 2.1 1

No. sanples 1115 Unknown 5t 11

Dat a from: Sauer Meagher River- Lox.ton (1962) (gegn) land vine advisory d.ecline sa.urples sur\rey 1). that extensive research and extension prograJllmes have been undertaken in Snnraysia on resistant rootstocks (Sauer 1967 t 1972, 1974, Hawson 1970, Eeslop 1971). A sinilar progranme has al-so been started in the Riverl¿urd.. Trials by Sauer (1966) and Stírling (unpubl-ished. data) have shown significant yield responses following the control- of citrus nematod.e wibh nema- ticides. Root-lesion nematocles are the only other frequently occurring nematode parasites of 1íkely importance. Às they often oc()ur together with root-knot ancl citrus nematode, thejr effects on vines in the field are less l¡e1f rrnderstood.

..a2 ) Cit:rrs

Methocls

The plant parasitic nematode species in the Riverland-'s 5r500 ha of citrus orchards were sulveyed. cluring 1974. Sa,nples were collected' frorn fifty-one properties. The properties lter'e selected, ancL the soil samples collected and processed, as d.escribed. previously for peach.

Results Table { Iists the nema,tocles recorded. in the survelf and their frequency of occurrence. Al-so listed are the results of a sulvey carried out in Sunraysia citrus orchard.s by Meagher (1969a).

Discussion

The nenatotles which occurred. in Riverlanrl orchard.s were simil-ar to thooe occrrrring in Sr:araysia, except that both Paratríchodorus spp' a¡d

TYlenchorìi]¡nchus sp" occurred. more frequently in the Riverl-and"

cit,l'Ls nematod.e is undoubted.ly the most inportant nematode parasite of citrus in the Riverland.. It has been reported. from all najor citrus knovm as 6rowing regions of the wor]d., and causes a condition in trees slovt decl-ine. Affected trees exhibit red-uced vigour, chlorosis and falling 14"

TABI,E 4

NM/IATODES RECOFÐED AI\TD TI]EIR FTEOUENCY OT' OCCURRENCE

IN RIVERIAND A\ÏD A CITRIIS ORCHA.R.DS

of occurrence (/")

Riverland. Sunra¡¡sía (ð.ata -ex Mãæer (t969a).

-\ [vrenchulus seniDenetraJrs 98"0 97.5 Pa¡atrichodorus ninor 45.1 cq (recorcled, as Trichod.orus Iobatus 17.6 Paratrichod.orus sencru lato ) Trichodonre lortoni 2.O

TJrlenchorhlrnchus' sP. 21"5 Èatylenchus mirtyus 19.6 21.1

11.8 7.5 2.o 2.5 15.

of l-eaves, twig dieback and consequently, red-uced frrrit production (Cotrn

1972).

Meagher (l96ga) suggested that it was not possibJ-e to attach too much significartce to the nernatode genera other tha^tr Tyl-enchulus, which were found in Sr:nraysia orchaJds. The only adrLitional Senelra fo¿nd in Riverland to orchartls were rylenchorhynchus and Ivieloid.ogyne. There is no evid.ence suggestth"t@dalragesci-trusroots,whi1eroot.knotnema- todes only rarely attack citrus. M' incognita was reported infestin'g citnrs in Austratia by Colbra" (fllA). Van Guncly et aI çlWl) afso showed that the roots of some cit:rrs species were galIed. by M. iavanicar M. incog-

nita acrita and M.hapla.Inbothcases,reproductiond.id-notoccur.More recently, GiIl ( 1971) reported that a biotype of M. iavanica had been found in california which reproduced on three species of citnrs. Attempts llere potenti:r'Ily being mad.e to eradicate the infestation as it was considered inportant. The root-knot nerntod.e larvae found in the soil on one Rj'verland. citrus property, coul-d not be traced to infection of citr:us r:oots' was detec- A weed host was probably the source of the 1ow popula'tion which ted, as deadlY nightshad-e Plants Solanum nign:m) gtrowing in the orchard' werc galled.

2.4 Nu¡series

It is inportant to know which nematodes occur in fruit tree m[series planting as horticultr:ral crops can easily be infested with nematod'es by infested. nursery stock. A¡derson (1965) published- infornation on the occur rence of plant parasitic nematodes in New South l'/a1es nurseríes' In the was carried' absence of infornation from other parts of Australia, a survey out in South Australia.

Method.s Most of the nurseries in South Àustralia vere vi-sited between October 16.

1g71 and, April 1972. The soil type in each nursery was noted, a^nd. infornation on the previous histoïtf of the soil hlas collected.. A 5 cm dj-ameter auger was used. to remove five cores of soil (approxinately 1 kg) from the root zone of each clop. The five cores were combined and a 5OO g sub- sample removed. Each sâmF1e was elutriatea (Seinfrorst 1962) anð' the pÌant- parasitic nenatodes were id.entified and' counted'.

Resul ts ancl Discussion

The nenatode associatecl with the various crops are liste<ì- in Table l.

Stubby root nenatodes were very commonr pa.rtiøularly in citms and stone- fruit nurseries, where they often occurred in high number.s. The occurrence of root-knot nernatodes in alutost half the vine nurseries surveyed, rrust be regard.ed as seriousr as they are serious pests of vines in South Austral-ia. Regulatione designed to prevent the sal-e of nematode infested. rbottings have been in operation in Victoria for many yeals

(tteagher 1g69b) I md sinilar regulations could welL be consid-er:ed- in South Australia. Although Anderson (1165) shohred th¿i.t citrus nematode was connìon in the citrus nurserj-es of New South lrrales, it was not found in South Australia¡r nurseries. Uvery effort should be made to keep nursely stock free of this nematode, which is a recognizeð' pathogen of citrus and grapes' The genus pratylenchus contains species known to tlanage a wide range of crops. Its presence in vine¡ apple and. afmond nurseries ce:r:tainly poses a threat to new pla¡tings, and. warrants control mea'slr-res being consid'ered'' The other genera which occllï un<ìoubtedly contain pathogenic species, but as theyúere encountered infrequently, they coul-d not be consid-ered of najor econorric ÍnPortance.

Consi

More detall-ed records showing the relationship of nematode occurence to O> Q FbI-TJ'dE{HH Èd È"ð-=FúÞF:-4 o <È=oH()ÐEd E O Edtdz()F¡cl EJEU) (l c)d û F EI Paratrichodorus z r J f\J) Þ Þ O f\) <) l-obatus Ëd o Paratrichodorrrs 2 ¡=d J \Jl .-¡ \.¡¡ \Jl 2 E I I Þ minOf Ê Ë F{ E U) d Ed tr o FÚ Ê FJ H Jlll tttÞ Meloid.ogrne sp. trt E o cn f+J B o Þ Ø l=Ë a) Pratylenchus g) H B r: lrl\-}¡lllJ coffeae E H P o () o E E ID td z Èatylenchus H l-¡ Þ 3 l¡l5ll\r'¡J mr-nJrus Þ b (j) r+ o E o (þ Ð U + tll Jlrul Jlt\) Paratylenchus sP. o F (n p H Þ zH l=d JlNII J f\) Tylenchorhynchus sp" Ð Hc Ë Xiphinema sp" Ën lrlllllr hd tr

tJllllll Ee1 3P.

rèiú\oo\r-¡o JfJJ No. of sa.mples exanined

--¡ 18.

soil type and previous soil history are inclrrded. in Append.ix 1. Although nu-rsery areas planted in virgin soil were unconmonr they generally contained few plant-parasitic species. No stubby root nematodes were found in a¡y of the nursety areas on virgin soil. Ilost plant-parasi-tic nematod.es (but particularly root-knot and. stubby root nematodes) were more commonly fou¡d. in sand.y soiLs than in heavier soils"

(o)ôE Tonato

More tha¡r 200 ha of field. tonatoes are gror¡nl in the Riverland every year. They a,re either grolffl as bush tomatoes and processed for juice, or:

trellised. and. marketed fresh cturing winter. In 1971-7{ a snall suTvey was carried out to determine the nenatodes present in the Riverlandrs tonato growing ateas.

Method

Samples were collected fron eigh'teen properties. The properties were selected, and the soil samples coflected. and processed a,s d-escribed pre- viousJ-y for peaches.

ResuLts and Discussion

Table 6 tists the nematorl-es recorded in thc survey and their fre- quencf of occurrenceo Root-knot nematodes are the most inportant and cosmopolitan nematode

pest of vegetables, a^nd tonato is one of its preferred hosts. Consecluently' it was not surprising to find. th¿¡,t root-knot nematod.es occurred frr;quentì-y during the survel. ÀIthough Riverla.nd tonato growers invariabfy use nena,- ticides for root-knot nematode control , severe crop losses remain comrlol-''e A photograph of a tonato seedling with roo'bs severely stuntecl by p. ninor (Cottra^n 1964) is the only published, informatión on the effects [email protected].

P. mirrlms are u¡likely to da^rnage tonato. Krusberg (1959) sbowed that a 19. species of Tylenchorhynchus fed on the epid.ern 1 cells of tomato roots but oaused no obvious danage, while P. ninrus is a common but unimportant inhabitant of RÍverland soilso

TABI,E 6

NUVIATODES FECORDED AND THEIR FREOIIENCY OF OCCIIRRENCE

ON TOMATO IN TIIE RIVERLAND

Nenatode % t)ccurrence

MeLoidos-vne 9P. B1 Paratrichod.orus ninor '7)

Paratrichodorus lobatus I

Pratylenchus nÍnJnrs 2B

Tylenchorhynchus 11

2.6 Onion

OnÍons ¿re one of the most importa¡rt vegetable crops grown along the River Murray. A surrey of the nemato,les occurring in onion fielcÌs in this area is described nore fully in section J.5.2.1 Onty two plant-parasitÍc nenatodes were observed in soil sampLes collected from the nineteen field.s surveyed.. T. mj.nor occurred in eight

sampJ es a¡rd. Pratylenchus sp. in three. In addition, the roots of stunted- plants in one field. vere found to contain fenales of root-knot nema'tode

(plate 1 ).

Discussion Evid.ence is presentetl in section 1.5.2 which suggests that T.minor is an inportant parasite of onions in the sandy soils along the Ri'ver

lvirrray . Pratylenchus and Meloidogyne sp. are unlikelY to be of economic Plate 1a, b. Roots of onj_on plante, collected from the fleiarand infested with root_knot nematod.e (Melotdo¡¡¡¡ne sp. ). ) ì I

- i--i , r:,y\l\:i)i:,.\íl. r:! i. r¡ \. .'. l-'. ..,1..\.-\.1 ' '.¡\..,1r\.\i\i\, 21 . significa¡ce on onions in this ârêâo The roots of oniorrs growing in areas infested with Pratylenchus sp. showed no siÉl¡:s of the fesions typicaily pro¿uced by this nenatode. Root-knot nematod.es are not usu¿ìI1y ccrnsidered' inportarrt pathogens of onions. Thj-s was confirned during the surveyr as they were only obserrred once in an area environmentally srrited to root- knot nenatodes. In tirís case a high population had. probably been t'uilt up on a previous crop of tomatoes.

2.7 General Discussion There are two outstanding features of the infornation collected and described in previous sections. Firstly, the surveys highlighted the wide- epread ttÍstribution of root-knot nenatod.e in nurseries, horticultu¡al clrops a.nd vegetable crops. This was not unexpected, a,s root-knot nematodes are wel-1 recognÍzed as inportant pests throughout South Australia's fruitgrow- ing a"rea. Secondly, stubby root nematodes were found. to be widespread. P. minor was fourid on all crops studied, and. generally it occtttred in more thar half the sa.mples processed. fr:om a particular crop. P. l-o'batus was not as conmon, but occurred in 20 - 1U/" of sarnples from nosb crops. Most of the soils used for horticul bu-re in the Riverland area are very sandy¡ partÍcularJ-y the upper soil. layers. There are d.ifferences in the textures of soils supporting d.ifferent crops. Genera.lly citrus is grov¡n on the sandÍest ridges, and. vines in the heavier soils of the flat's an¿ depressions, while peaches antt apiicots occupy soils of intemediate texture. Vegetables grow in soils of any texture aI'bhough onions tend to be restricted. to the sandier soils. Mecha¡icer1 analysis has shown that

sand. particles comprise 90 - 95/" of a typical citrus soil, BO- 9Ø, of peach soils, and 75 - B5/" of vine soils. In each caser the sand component consists of about equal pa.rts of fine sand. (particle diameter 2}tt- 2OO n)

a¡rcl coarse san¿ (particle dia¡eter 2OO)l- 2 nrt) (Wethertyrpersonal communi- cation. , rr)

Stubby root nematodes ar:e re-l-atirrely large nenatodes¡ P. minor and. P. lobatus befng respectively 0.6 - O.7 mn and 0.8 - 1.0 nn in length. Wallace (1961) reported. that na:¡imum nenatode nobjlity occurred when the particle size was $ ttre length of the nenatode. The particle sizes which occur in the Riverlar¡drs sandy soils are such that these soil-s shoulcl be icteally suited to stubby root nenatodes. ThÍs nay explain their widespread. occurrence in Riverlancl soiIs"

The sa,le¿l content of the heavier soils in whj-ch some vines and. peaches are g?or.¡¡1, a.nd. on which some nursterles are established, is clnly 55-60/".

Reduced. particle size, a¡rd consequerrtÌy pore size is probably the rearron why stubby root nenatodes were rarely forrnd durÍng the surveys of nursenies and peaohes, on pla^nts growing in loarry or crayey soils.

llherr conpa¡able data was avaÍlable fo:r both Sunraysj.a and Riverla,nd regions, it appeared that stubby root nematoCes occur:red- more fre.luently in the Riverla¡rd. One possible explanatjon is that Surraysia soils generall,v tend to be heavier tha¡ those of the Riverland, J-argely becaus,a there are less aeolian deposited s;rnd clunes in tha,t arear (Wetherhy, pe::'sonal cr-rn¡munJ - cation). 25.

, STUB¡Y NOOT NEMATODES AND SOUTÊ AIISTRALIAN HORTICIILTIIRE

The genus T¡ichodorus nas first establishecl by Cobb 1911, anð. contained three speciee until ten new species were ad.dett by A1len (1957). Since then nany new species have been described, with Vlyss (t970) puU-

Iiehing a key to 11 specÍes, and Esser (lgll) a key to 15 species. Allen (1957) indicated that the species included in his review fell into two groups, as juttgecl on the presence or absence of a bursa in nales.

ÏJyss ( 1970) carne to a sinilar conclusion, and. arranged the Trichodorus species occurring in l,,/est Gerna"ny into two groups. The species in Group '1 were characterized as: body cuticle swelling strongly upon fixation; male with bursa; the fÍrst a¡rd second preanal papillae in the spícuIar regicnt the third 1.5 to 2 bod.y-witlths in front of the second; with one or no ventro-nedía¡¡ cervical papiIla. Female with weak and ind.istinct scl-erotization between vulva and. va6ina. The cuticle of species in Group II diti not swel-f so strongly on fixation, and, nales d.icl not have a bursa. The first preanal papilla was in the anterior half of the spicular region or slightly anterior to the proxinal end.s of the spicules, the second and. third papillae were at tines more than one body-wicith in front of the first a,nd. second. respectively and there were two or three ventro-med.ian'cervical papill-ae.

Females had stro4g a¡rd, tiistinct sclerotization between the vulva and vagina. Sitltliqi (1971) suggested that these groups needed better tlefinition, as the fema.Ie characters clid not appear as reliable as the nale characters of the bursa and, supplements. A study of 25 species showed that the females of

Group II could. be cha¡acterized. by the presence of a pair of lateral vul-

vaI bod.y pores within one body-wi

gen. n. for the species in Group 1 a,r¡tt further subdivided. this new genus into three distinct subgroups - the new subgenera Paratrichid-orus,

A-1antadorrrs a¡rcl Nanid.orus. The species of Group II were placed' in a re- definecl genus Trichodorus sensu stricto.

S¡rnptonoloÊjy

stubby root nenatodes were first recognised as plant parasites in

1951 when ChrÍstie a^nd Perry fo¿nd. a species inj¿ring the roots of beetst celery a¡d. sweet corn in Fforida. More than thirty d'ifferent stubby root nen¿tode species have now been d.escribed.. They are known to occur throughout the world, antl they cause economic damage to a wlde variety of crops' The feecling of stubby root nematodes devitalizes root tips and' stops g¡owth. In nany Ínstances affected tips ehow little or no discolorationt necrosis or other evidence of inj¡ry. The effects of the devitalized root tips on the d.evelopment of the root system as a whole varies widelyt depen-

d.j-ng on the kind of plant, the abundance of the nematod-es, and the age of

the plant when feeding occurs. In some i-nstances the only effect is a reduction in the size of the root system without any obvious abnormality' In other instances the root system is obviously a¡1d conspicuously abnormal, with a stubby root or rcoarse rootr type of abnormality (Ctrristie, 19'9)' P. christiei affects nany clifferent plants, including suSar car}e (lpt ana Koike, 1962), cranberry (Zuckermatrr' 1961), blueberry (Zuckerman' 1962) tonato (n:roae and Jenkins, 1957), grapefruit (Standifer and Perry'

1960), onion (Uoff a^nd Mai, 1962), cotton (Alhassan and Hollis, 1966), St. Augustine grass (Rhoades, 1g62)rpine (Ruehle, 1969)' Synptons such as a red.uced root system, stunting of ind.ividual roots and the absence of necrotic lesions, occuryed. on all plants stud.ied. Abnornal- proliferation of bra¡rch roots was repolted. for cra,nberry, tomato arrd onion, ancl swelling of root tips for cra¡berry and. onion. Ruehl-e (1969) also reported that the nicorrhizae normally well developed on pine rootsr were few or lacking 25.

when roots grew in soi] infested. with P. christiei. There is linited evi- d.ence to suggest that the symptoms causecl by other stubby root netnatodes nay differ fron those caused by P. cbriqliç!. T. viruliferrrs was observed on apple roots from a¡r undergror:nd root laboratory by Pitcher ( 1967). He was the first to describe necrosis of roots da.naged. by a species of

Trichodorus (sensu lato), although the effect was not produced. und.er sterile cond.itions. Browning a¡rd shrinkage of the epid.ermal cells occurred in newly attacked. roots, foIlowed. by cracking of the epiderûis. Injury usually occuned a¡ound. the entire root ci-rcr:mference. T. proximus was forrnd to cause large, d.eep, irregularly shaped. lesions on the roots of St. Augustine grass (Rhoades, 1965). Although nost of the lesions occurred at the root tips, some lesions occurred at scattered. in- terr¡afs along the entire length of nany rootÊ.

Feed.ing Most studies have shown that stubb¡rroot nematodes feed on aII areas of a root - the distal end. or root tip, the hairless region and the proxi- mal part lined with root hairs (nfroAe and Jenkins, 1957a; Zuckerman 1961, 1962; Rhoades, 196r; Pitcher, 1967). However, actively growing root tips

provid.e the nost suitable feed.ing sites (Zuckernan ,1961; Rhoades, 196'S i

Alhassan and Hollis, 1966; Russell and Perry, 1966; Pitcher, 1967; \r/yss, 1971; Hogger, 1971). The root tip area consists of the root capr the neri-

stenatic region, a¡rd. the region of elongation. Most authors d.id not d'if- ferentiate between these regions, but both Russel and Perry (1966) an¿

Zuckerrnan (gel) inaicated the preferred feed.ihg site within the root tip

was the meristenatic region, and region of elongation, innediately behind- therootcap.Thestud'ybyPitcher(lg6l)of@onappleroots,

showed clea.rty the close relationship of this nematode to the root tip. Direct observation, and particularly tine-ì-apse cJ-nematography dra.matically

emphasized. the nematodesr affinity for the elongating zone 1-l nn behind- ?6.

the root tip. Nenatod.es accumulated. in masses of one huldred or morer ancl until extension growth was halted there was a stead.y progression of the rnain ne¡natode nass along the root, cells which had passed through the elongating phase being aband.oned in favou¡ of thosé just entering it. Wyss (lgll) notett a similar nassing of T. sinilis around the root tips of tobacco and strawberry. Generally, nicroscopic observations on the feeding of stubby root nematodes have been mad.e with nenatodes feed.íng und.er sterile cond.itions on the roots of seed.Iings growing in thin J-ayers of aga* . Rhod.e a¡rd Jenkins (t957a) first observed P. christiei feecling directly on the roots of tonato and rye. They noticed that the stylet was thrugt in and out at ten thrusts per second, but was never extend.ed more than three or four microns past the lip region. There was a convulsive gulping action at the opening of the lumen of the oesophagus and an expansion and contraction of the basal bul-b. As feeding continued, the protoplast of the attacked cell shrank fron the cell waII. The entire process lasted- for about l-10 secondsr and then the nematode moved to another cell. OnIy living roots v¡ere parasitizedr and feeding was restricted. to the epidermis and outernost cells of the cortex. p. christiei fed on cranberry and blueberry roots in å sin¡ilar nalrlel" except that the d.uration of feeding on a cranberry root cell was from 'l to {.! minutes. (Zuckernan 1961r 1962). The feeding of T. similis on epider- mal cells and root hairs of Brassica IsIg l,las d'escribed in d'etail- by lrJyss (lgllU). ffre conplete feetling process lasted. only a few minutes, and consisted. of five phases. After a period of investigationr the nenatoders Iips pressed. fi:ml-y against a cell waII. The spear punctured the cell with a series of quick thmsts which slowed. to only 2 thrusts per second. after half a minute. During salivation, a drop of sal-iva formed inside the ceI] close to the injection point¡ and- cytoplasn accumul-ated anci was ingested.. The

Lunen of the oesophagus opened on protraction of the spearr and closed 27" iruned.iately on its retraction, allowing food. to pass to the intestine. After withd.raual of the spear a feeding tube, which formed in the stonatal lu-men, remained. finnJ-y fixed. arou¡d the puncture hoIe. Russetl and Perry ?gee) reported three general types of feeding fron P. christiei on wheat roots; external ly on roots, externally gn root hairs, and within root caps. Nematodes fed. in the region of elongation behind. the root cap for periocls ranging fron 10 second.s to 10 minutes. A. grazLng type of feed.ing lasting 10 - 60 second.s was observed. in the ol-der portions of the roots. FeetlÍng intervals on root hairs ranged fuom j second.s to 5 minutes. Stylet penetration of cells appeared to be accomplished by a direct piercing of the cell wall rather than the rasping action suggested. by Rhode a¡rcl Jenkins (t957a). Entry of nematodes into root tissue was observed. only at the root cap. specimens entered the root cap to a distance of more .Ad.ul-t than J0 )1, a.nd appeared to be feed.ing upon or in cl-ose proxinity to the apical neristen of the root"

The feeding of T. Droximug. as observed by Rhoades (ge>), was gener- aJ-ly sinilar to that of P. christiei . Rhoad.es suggested. that the stylet ]-n was used,nmecha¡rically breaking cell walls, since it was thrust repeatedly aluring the entire feetling proceEs. The large lesions which d.eveloped. following feeding occurred becauee nematodes often returned. repeatedly to the

same l-ocation to feed., a¡rd also other nematod.es seemed to be attracted to areas where feecling had occurred."

Stubby root nematod.es are non-moblle when feeding. The cephalic region is always naintained approxinately at right angles to the food. source (nnoae and Jenkins, 1957a; Zuckerman, 1961; Russell and Perry, 1966), tut

the bod.y nay assume a variety of positions"

HistopathologT Microecopic stud.y of tomato root tips affected by P. christiei sug-

gested a Ioss of neristematic activity by parasitized. roots. There was no ¿.o. definite root cap or region of elongatÍon, and the region of mitoeis was much smaller in size than nomal. Differentiation of cells had. progressed. to the extent that protoxylem elements with spiral thickenings had developed. almost to the apex of the root, whereas ciifferentiation in no:ma1 roots was initiated nuch further back from the root apex (nhode a¡rd. Jenkins, 1957a). fhe progressionþf tissue maturation into the root tips was also described by Standifer a¡d Perry (1960).

Ruseell ancl Perry (gee), having observed P. christiei feeding within the root cap, suggested. that this type of feed.ing could bring about a cessation of apical neristematic activity through injection of oesophagal secretions by the parasite d.irectly into the meristem. This would el-imi- nate the neceosity of translocation of these secretions from the epidernal cells of the root apex to incite the characteristic eymptoms of cessation of root elongatiòn a¡rd tack of visible necrosis. In ad.dition it provided one explanation for the occurrence of severe stubby roo'b synptoms in the presence of low populations of P. christiei as d.escribed by Christie and. perry (t95t ). An altJrnative explanatlon was offered by Pitcher (1967), who noted

that the phenomenon of aggregation of stubby root nematodes around the tips of growing roots had been found. in seven species of Trichodorus (sensu @). He suggested. that it night prove a conmon feature of feeding by stubby root nematodesr including P. christiei. Therefore, stubby root s¡rnptons could resuÌt fron the tra¡rslocation of chemical inhibitors from the

elongating zone to the meristem; such materials night be prod,uced directly by the nematodes, or be elaborated. by the host in response to nematode- protluced.sti¡¡uIus.Pitcher|sobservationswith@andapple

roots showed that rhizoplane populations ca.n be surprisingly Ìarge in relation to'rbacþror.rndfr soil populations, and he suggested that the distribution of P. christiei night be sirnilar. This would explain how low soil 29.

populations of P. christiei cou1d. incite severe stubby root s¡tmptoms.

Host range

Stubby root nematodes are polyphagous nematodesr feed-ing on the roots

of nany different plants. P. christiei is one species '*hose host range has been investigatett extensively. Rhode ancl Jenkins (t957a) found that only { of !6 pla,nt species tested were non-hosbs, althor.lgh species varied in their ability to support nenatode populations. Coursen, Rhode and Jenkins (lgfg) extended the host list with 66 nore plant species and varieties.

Transmission of plant viruses Species of the d.orylaimoid genera Xiphinena, Longidorus and Tricho-

dorus (sensu lato) are the only known nematod.e vectors of ptant viruses. Nenatode-tra¡rsnitted viruses have been d.ivided. into two groups on the bas-

is of shape . Those with polyhedral particles were n¿ùmed nepoviruses (Cadman,

1961) and are tra¡rsnitted by Xiphinema and Longidorus species.The second.

,l il,i g'roup rod.-shaped tubular particles. They were iI contain viruses with or Ì named netuviruses (Harrison, 1964) and- rena^ned tobraviruses by Harrison et al, 1971. The two viruses in this group, tobacco rattle virus and pea early browning virus, are transmitted. by Trichodorus species. Efeven

Trichod.<¡rus (sensu laLo) speuies ale noh/ ltrrown to be vectors of these

I viruses and these are l-isted by TayIor.C. (lgll) Harrison (197J). "rld Control perry (i951) found. that P. christiei was not difficult to kiJ-I by soil fumigation but it re-establ-ished itself more quickly than any of the other nematodes that occuned. in his experiments. The rapid return of high

stubby root nematod.e populations following soil fumigation has often been t I reported since (Rhoades, 1966; 1965t 1969; Ivlorton, 1968). Rapid. populat- Íon increases are possible because the life cycÌe of stubby root nematodes

is short. For slample¡ the life cycl e of P. christiei is c ornpleted in only

16-17 days at 1OoC, and 21-22 d.ays at 22oç. (niroae and Jenkins, 1957b), r to

Christie and. Perry (unpublished d.ata) also attributett rapid' population ,i increases to the d.estruction of natural enemies, including predacious nenatodes, by the fumigants. pre- The return of stubby root nematod.es to higher leve]s following '1tl- plant soil fr¡migation is particularly noticeable with the fumiga^nts (em) dichJ-oropropene antt 1r2-dichloropropane (m) ana ethylene dibronid'e

(perry, 1951; Rhoades, 1966; 1968; 1969; Morton, 1968). However, initial control was ugually sufficient to protect plants during the early growÍng

period. when vulnerability to nematode d-alrage was greatest (Perry t 1951;

Rhoades, 1961). Christie (1959) suggested that funigants such as 1t2- clibrono-J-chloropropane (mC1:), which tend. to linger in the soil longer sensu tha¡r DD and. EDB, night retard the rapid' buildup of Trichotlorus lato). This suggestion was confirrned by Rhoades (lg6g), More recently, a rang;e of even lon- orga.nophosphate and carbamate pesticides whicffiersist ln the soil root ger tha¡ DBCP, have been found to be effective in controlling stubby

nenratod.es (Broctie, 1968; Rhoades , 19('9; ÙIorton, 1968)'

Stubbv root nenatodes in Àustralia Five species of stubby ro6t nematod'es have been recorded in iustralja' p. minor ,ras first described. by corbran (ll>6) fron Queensland, a^rrd is associated wittr a wide ra;nge of plarr.ts in Queensland a¡rd New South llales (Colbran, 1964; Arderson, 1965). Colbran (1964) published photographs of some debate damage caused bY P. minor to tonato seedlings. There has been in the past on the possible synonyny of !$!g!þ! *ith þ!gg' The general d.imensions of the females are very similar, the excretoly pore is

in the same position, and the shape of the vulva and vagina in lateral view is similar. Neither species appea¡s to have la'teral or caudal pores'

Both. species have a ventral l-obe at the base of the oesophagUs overlappiug the intestine. Males are ra^re in P. christiei and unknown in P. minor. A]-Ien(1951),',dHooper?gez,ß7))[email protected] 11.

p. (flZo), Esser (lgll) SiddiqÍ (1913) a sJrnonym of minor. However¡ lrtyss "rrd recognized then as distinct species, on the basis of a snall difference in onchiostyle length.

p. Iobatus was d.escribed" by Colbran (ge>). It was found arountl the roots of citrus and. ginger in Queensland, aurd in a peach orchard in New

South hral-es. P. lobatus has been associated. with poor growth and stubby root synptons of citrus seedlings in New South ¡Iates (Ucleodr 1!68) and tobacco in Victoria (Mea6her, unpublished clata). The only other stubby root

rrematodes recorded j-n Australia are P. porosus (colbran, 1964i Anderson, (Anderson, and renifer (siaaiqi, 197t). 19(,ù,- -t. P. teres 1965) ?.

Sa^mPIes 1.2 Collection.- Extraction and. Storage of

1.2.1 Collection Nenatode populations are d.ifficult to estinate becauge of their pat- chy d.istribution in the field. Estinates are j.mprovett by increasirrg the

number a¡rd. size of samples examined.. During this study, relatively la:rge

samples l/ere processed as the soils exanined r^¡ere generally sandy. The largest soil sa.npl-es from which nernatodes could. be readily extracted weighed about g. Linitations 1n the tlne and ür¿¿tlpower available prevented 'OU the processing of numerous individ.ual samples. Instead, soíI was collected

from several sa^mpling points, bulked, and a representa,tive sub-sa.npl-e

processed.. Because stubby root nematodes tend. to aggregate near rootst

nurnbers in the soil surrou.nding roots often do not reflect the numbers present at the root surface. For this reason, soil sanples were always collected fron the root zone of host plants"

1.2.2 E:ctraction Unl-ess otherwise inclicated., nematodeci were extr.'acted by eJ'utriation

using the method. of Seinhorst ( 1962). Sarnples were washed irrto a¡r Ehrlen- meyel flask through a 2 mm dia,neter dornestic sieve. The Ehrlenmeyel flask zc

was removed from the elutriator after ten minutes and the to-bal elutration process took only'1! ninutes. The elutriate was sieved throu.gh two JOO nesh (approxinately 50¡ ) sieves and. the residues war¡hed. into a snall 5Ol¿ sieve inlaid with a double layer ofrrKleerLex'r. This was alfowed to stand overnight. Samples were d.iluted. or concentrated so that 2 mI alir¡uots con-

tained at least 1OO nernatodes, which rùeïe counted in a dish simil-ar to that

described by Doncaster ( 1962).

1.2.1 Storage It was often necessary to store soi,l samples for some time before laboratory plocessing. Sa.urples ca¡ usually be stored at low tenperatures in a refrigerator without excessive deterioraticn (Taylor, A, 1971). HoráIevert

when extraction method.s were usetl which relied on neflratod.e nobilityr P. Ioþatus could. not be recovereil fron soif maintained. in a refrigeral'ot al a

temperature near OoC. Meagher (per:sonal cornmunication) had also noted that p. lobatus was susceptible to storage at lou tenperaturers. The followir,g

experirnent was set up to determine the effer:t of storage temperature on the survivaf of P. lobatus in soil.

Mater:ia1s and Method.tl P. tobatus infested. sandy soil was passed. through a I nesh sieve, nixed thoroughly, subd.ivid,ed into seventy-five {O0 g sub-sa,nples, and p}aced in plastic bags. The soil fron fifteen bags was elutriated. immediately and twenty bags were placed in each of three refrigeratols, and subjected to storage temperatures of either {, I or 12oC. Twor sevenr fourteen a¡rd twenty-eig'ht days Iater, five ba6s rrlere removed from each refrígerator a¡rrÌ tLre

nenatodes extracted. by elutriation.

Results

The m:mber of P. Iobatus recovered after vari.ous times of storage at three stora6e ternperatures, is shown in figure ]. Figure l. The effect of tenperature and tine of stora8e on the population of p. Iobatus. Points narked. with ar¡ asteriek (x) are sig_ nificantUr clifferent fron the initial popu- Iation (p = .05). 560 t * E o 520

o /.80

lrLO 8b o ¡ /.00 \ f 2'c 360 lmfl r-l

U.' É. ul 200 co 4Cta f- z 160 LSD 5% t t 120

0 2 7 1L 2E

TIME(DAYSI 14"

A g¡adual decline ln P. lobatue nu-mbers occurred when soil was stored oc. P.lobatus at 4 When etored. at 12oc, there ltas a significant increase in populations initially, probably due to the hatch ing of eggs present in the food soil. Nenatod.e m:mbers then decreased, probably because the nenatodes' reserves were fu1ly utilized' for respiration' A temperature of 8oC aPPeared- the nost staisfaotorY for storage of P. lobat;us because populations in sto- and at reci sa.urples renained. relatively stable over a period of one month, no stage differed. significantly fron the initiaf levef. t.t Root Growth of Peach Trees this As per-rch was frequently a host of stubby root nematocìes during study, it was inportant that its patterrr of root growth was understood' for peach Cockcroft and Olsen çlllZ) described the patter¡ of root growth trees growing in sand.y loa^m soil overlying clay, in the Goufbourn valley of victoria. They reported. a poalc in the production of new roots durÍng spring (Octoter and. November), with a smaller autrunn peak (lpr11)' ¡ew roots were produced during the rest of the year' There is l-ittle evidence for a.n inherent periorlicity in root procluc- tion. It is nore likely that the perioclicity observed is a result of varia- tions in soil ternperature, soil- moisture, oxygen or food supply (Kramer stres- and Kozlowski, 1960). The trees stud.ied. by Cockroft a¡d Ofsen were confined' sed. for water because of low soil. water stcrage and- the shallow, nature of their root systems. Other environme¡tal ccnd'Ltions under which they were grolrn also differed from those in the RÍverlarrd. As their resufts peach nay not l-rave applied under Rivqrland conditions, a study of root

growth was und.ertaken in that aîea. 15.

Materials and, Methods Thirty coles of soil were col-lected at random a'b a deptlr of 1J-2J ctn, from wit,hin the dripline of mature trees on the Loxton Research Centre.

The core.:s were collectetl, wi'bh ¿u ! cn diarneber auger, and gloups of f'jve cores were bulked into one sample. Yourrg trees frorn the Loxton Research

Centre nursel.y wele sample

r¡/as bulked- In the -l aboratoly, a 1 kg sutr-sample removed fron each sub-sample, sieved throrrgh a J mesh (l .SZ nm .iperbure) L;ieve, and the peach

roots removed.. The number of white, unsuberiz,ed- roots in each sautple was

corrnted.

Results and Discussion The d.ata collected is recorded in figure 4. Both mature and nursery

trees had. similar patterns of root growth. l¿lhite roc;ts llere present during

winter, spring a¡rd. autumn, absent in l-ate suÍ)merr and present in fow rmm- bers throughout the rest of the surnmer'. Drring the period Jalruary-April for mature trees, and December-l{arch for nuls;ery trees, significantly fewer white roots occurred. compared with the rest of the year. It is d.ifficult to id-entify the environment¿¿l- factors wltich alter during s1¡ûrpr to cause a reduction jn root growth. SoiI tempelatures do not rise sufficiently in aurnmer to irùribit root growth (figure 2b), Lark of root production is not due to courpetition between roots and devefoping fruit for: carbohydrates and, nutrients, as a similar pattern c¡f root growtlr

was observed. in mature and nursery brees. l{oisture stless is the most likely cause of the l-ack of summer root growth. sandy soil-s have a low water holcling capacity, they drain readily :r.nd. they also Lose moj-sture easiJ-y by Figure {. The seasonaÌ patterzr of white root production of

mature a¡rd. nu¡sery peach trees, at Loxton. Points on each line which are me.rkerì with the sa¡re letter are not eignificantty different (p = .o5). 2W c l{rsery Trees c

J 160 o c .n c ol,! c o o C'ì c tl o 120 o c tn o o F o o o É. trJ W*"*u t- 80 o ô = cd = olL o z. LA d b b d d

0 IJASONDJFI¡lAHf 17. evaporation. During the Riverl-and.'s hot d.ry summers, when evaporation rates are high (lZ4O mm from atrl 'rArr class pan dr.lring the mon t;hs November-April inclusive) ttrere are alnost certainly period.s when soils are 1ow in avail-- able moisture. This is particulal,Iy true in the upper soil layers, where most feed.er roots are concentrated.

The Riverland has a l-ow natural winter rainfal-I, and. its sojls are warm and- sand.y-condjtions which are not cond.ucive to root rotting orgarri-sms.

As new roots are u¡likeIy to be produced when trees are dormarì.1,, the presence of white roots during winter is probably due to l-¿eck of deteriorat- ion of roots alread.y present.

).4 Paratrichod.orrrs lobatus 1.4.1 Population fluctuations in peach nurseries fn nost, conner'cial nulseries in South Austrafia, peach seedl-ings are grorrrn from seed plantett d.uring winter into soil funigated wíth DD (dictrloro- propene -dichloropropane). They are budded to the required scion variety d.uring the following autr:mn, grol^r through the next season arrd a,re sold d.ur:- ing the second, winter. The area then renains idle rrntil- replanted as a nrr- sery a varying number of years fater.

Although P. lobatus is wid.espread. in peach nurseries (Section 2.4), sgnples col-l-ected from several nurseries have showrr that the nematod.e is not detectable on peach seedlings during their first few mon'bhs of growth. The nenatode usually renrains rrndetected rrntil late i-n the first season

(March-April) r*hen populations increase rapidly. The following series of soil sa^mplings was carried out to stutly P. fobatur; popnlations or-r peach trees, both in the nursery ancl following their remc)valo

1.4 .1 "1 PopulatÍons on peach trees A snall area of Elberta peach trees on Wight rootstocks, growing in a comrnercial nr:rsery at Loveday, were sel-ected in May 197 1, As the nursery 18.

was knor¡In to be infested with P. l-obatus, the nematod.esrpopulations fluctuations were studietl over a-bwelve month periori. The trees had growl from seed pJ-anted into soÍI fumigated with Dn d.uring the winter of 1970. They were bud.ded in February 1971, and were to be sofd during the winter of

1972,

Ten soil sa.mples, each corrsisting of four cores of soil taken with a ! cn auger at a ctepth of 15-20 cm,'were coll-ected at ínterwals of about one month. Nematodes were extracted fron a 500 g subsanple, and counted,.

Results P. lobatus numbers were highest at bhe first sa.urpting time (Jule), decreased. gradually during the following twelve months, and were loltest before the removal of the trees the followirtg winter (figure 5).

1.4.1 . 2 Populations foÌlowj.nE removal of peach trees A¡ area of peach trees ad.jacent to those sampled in the prevÌ-ous section were renoved in June 1971. Volunteer weeds then beca¡e established-t and the area remained. u:rdisturbecl except for a cultivaiion for i{eed colr- trol d.uring the spring of 1971. The area r¡¡as sampled periodicall.y' for six months and then aga,in 2$ years l¡-ter. Sa.mples were co-ì.lected as described in the previous section.

rn Ja¡uary 1974, approximately 1 .5 kB of soil was coll-ected. from areas where weed.s were absent, and from,near the rc¡ots of ten different weed specÍes. Nematod.es were extracted fr:om two 500 g sub-samples and colrn- ted.

Resul-ts

P. lobatus was present at all- sa.mpling times, and was still present in the area 2þ yeaxs after the removal. of peach trees (talte l). lle rrena- tode was recovered. from soil near the roots of four weed species (tatre a) but not from soil where weed.s were absent. 19.

TABIE 7

popuT,ATroNS oF p. roBATUs (mnmuns pER

5OO S SOTT,) AT VARIOUS TIMES FOI,LOWING REMOVAL

OF PEACH TREES IN JUNE 1971

Date >/t /tt t/a/tt 11/9/71 tl/t/lz t6/t /t q

f 1 Population $i!tj 147 : t5 7e! 4a zo9 - 69 eJa

TA-BLE B

pRESENcE (+) on ArsENcE (-) o¡'p. LOBATUS

IN T1/'/0 500 e SOfL SAMPLIIS COLl¡jCT¡lD tr'ROlv]

NEAR 'IIIE R00TS 0F A RANGE 0F |,/EEDS

Cynodon d.actyl-on + (za T. lobatus 5oo s)

Portulaca oleracea +

Sonchus oleraceus +

Eragrostis cilianensis +

Echium plantagineum Tribulus terr:estris Digitaria sa.nguinalis

Chenopodium album

Cucr¡mis rqyriocarpus

Cenchus tribuloid.es

Discussion

The absence of P. lobatus in s,amples oollected. from peach trees during their first feu nonths of growth is not surprising, as DD fumiga,- tion for root-knot nematode control is stanclard practice in peach nurseties. Initial infestations of P, tobatus are probably eithe¡r Lranspor'l;e¡rl jrt from other parts of the nursery, or nultj-ply frc.n 1ow populations wlL:ich survive the fumigation treatnent. Figure l. Populatione of p. Iobatus on peach trees ciuring their final_ year in the nursery. NUMBER 0F P.LOBATUS/5009

o äÈgE É Ë q

ur o

- tr,

3 41.

A rapid increase in popuì-atlons during bhe l-ate autunn - ea^rly wirrter ls possible because peach roots a¡e actively growing and P. Ìobatus is similar to other stubby root nematode specles in havlng a short life cycle (Sectton 5,4.5.J). nne expeoted. l.ncrease in nematode populations during spri.ng dfd not ocotr.F, although thle [,e norl¡al1y a periori of actJva root growth (ffgure 4). Envlronmentaf condttlons at the tlme suited nematode multfpllcation, as sanples oollected from an adjacent aroa treated with

DBCP (Sectlon 5.4.7,1) showod that the resldrral populatl.on lncre;.rsoci clrrr- ing thls period.. Thls sr:ggests that the high population of P. lobatus may have da,maged the naw root growth in sprtr¡g, resultirìg in a decl-ine jn the nu-mber of actively growing roots avaiÌabte for feeding. A decline in P. lobatus populatione could be expected to foLlow such a red.uction in food supply,

The lack of root growth during srunner and ear.ì-y autumn may prevent a resur$ence in nematode populations and probably explains the 1ow populations observed d.uring the rest of the season" FoJ-lowing the removal of peach trees, P. l-obatus was abl-e to survive without irrigation, despite the low natural rainfall of the area. In situa.- tions where nursery areas are re-used every few years, it is unlikely that nernatode populations would decl-ine significantly when land. was left idle. There are enough weed. hosts for popula tions of P. lobatus to be maintained when cond.itions are suitable for weed growth. Even in situations where widespread sanpling ind-icated the presence of a low nematod.e population, pockets of high population occu-rred.. For exámpte, in January 1)l!, the population of P. l-obatus was measured. as only 6 nematod-es per )00 g soil, but around ccuch grass roots, densities as large as 128 nematod.es per lOO I r{ere measr:red.. 42.

1.4.2 Verticaf distribution The vertical d.istribution of P. Iobatus on peach was studied because accurate population estimates cannot be ma.de unlesis sarnpl-ing is ba,sed on a kaowledge of the vertj.c¿r.f d-istribution of the nematode.in the soil. Irour trees in a Loxton orchard were selected and. soif benea.th these trees was d,ivicled into four sectors, north, south, east and wee¡t. Sanrples wele taken at the d.ri.pline fron each sec:tor in March, JuIy and. September, moving cl-ock- wise within each gector each time to prevent res;autpling the sane spot. A 10 cn diameter auger was used, anrl 5OO g soil was col-lected. from d,epths of 7.5 crr lJ cm, JO cm and 45 cm (1 2 cm). Âltogether, 6{ sanples r¡Iere collected, these being four depth samples from each of four sj-tes per tree, f:rom four trees. The soil was e¡ieved through a ?- mm dotnesl;ic sieve, and the roots less than 1 mm in dia,meter were cofl-ected, dried and weighed. Nematorì.es wele then extracted from thè soil and the number of P. lobatus and the number of other' nematodes \¡rere counted.

esults At all sampJing timest both P. l-oba,tus numbers and root weights foJ- lowed a simiLar pa.ttern, with peaks at 1l cms. Ihmbers of other nematodes followed. a d.ifferent pattern, being a maximum at 7.! crns' and. declining'with depth (figure 6). løen counts lrere expressed- as a percerit,age of the total number of P. lobatus or others extra,cted from the cclmplete rlepth santple (figure 7) the peak j.n P. lobatus numbers aL 15 cms was, even more sign-ifi- cant.

Discussion Most plant-parasjtic neruatodes tend to conoentrate at a, pa.rticular depth in the soil. In decid.uous forest soils, for examp}e, the upper hori- zon which has a layer of d.ecaying J-itter and. trigh organic matter content, contained high numbers of nematod.es. These fed. on bacteria and other Figure 6. The d.epth d.istributíon of numbers of p. robatus nunbers of other nematodes and weight of roots. 3000

March sarnpte .-. Juty sampte o-o Sept. sampte r-' 2000

LSO5yo

1000 I rI '2t, Ø É. UJ (I) 20ä =lz UJ ßñ o õ o - .12 2 IC¡^ zl,¡J ô 0s.¿

.04 100

0 7.5 1 30 DEPTH (cms) o Figure J. The depth clistribution of P. Iobatus (or others) as a percentage of the total F. lobatus (o"

others) in each d.epth sa^npIe. 60 March samPte .-. Juty samPte o-o 50 Sept. samPte '-

30 LSD5o¡o

20 l¡l li l 10 Ø 0 o 50 ö¡! a c l.O

0 7'5 30 /.5 DEPTH (cmsl 45. organic pïod.lrcts of decomposition. In deeper regions, the amount of hr,mus d.ecreased, and. the spear-bearing genera, which fed on roots became more predominant (Bassus, 1962). nu this situation is commonly repeated., resul-ts showing maximun P. lobatus populations at 15 cms, and. a disüribution pattern with d.epth following that of root distribution, are typical of the pattern expected with a plant-parasitic nematod.e. Similarly' the depth of other nematod.es was typical of that usually observed.

1.4.1 Relationship between tree size and P. lobatus mrmbers Seventy-four Elberta peach trees on Wight rootstocks r¡Iere selected during January, 1972. Sixty were selected at random, and then seven trees Iarger than average, and seven trees snal-ler than average, r¡Iere ohosen. The trees were gror¡ring in a nurserly at Loveclay, and were known to be infested. with P. fobatus. Data on tree size and- nunbers of P. lobatus in the soil surrounding the trees was collected with the aim of d,etermining whether a rel-ationship existed between these two variabl-es. The height of each tree, and its diameter I cms above the bud union, was measured.. Two cores of soil were col-fected. from each selected tree with a ! cm diameter auger. The cores were collected from near the buttr but on opposite sides of the tree, at a d.epth of 15-20 cns. After combining the two cores a 5OO g sub-sanple was removed and. the nematodes extracted and. counted..

Results

The data col-lected is illustrated in figure 8. Correlation analysis using the sixty trees selected at rand.om showed that the height and. d,ia- meter of trees were highly correlated- ( r æ 0.948). Also there vras a significa¡rt (p = O.O2J) negative correfation (" = - O,291) between tree height

and. P. lobatus numbers. l¡Ihen the seventy-four trees rlere used in the analysis, the correl-ation coefficient (r) was -0.129. 46.

Discussion The purpose of correl'ation analysis is to measure the intensity of the association observed between aJry pair of variables, and. to test whether it is gteater tha¡r could. be expected by chance al-one. In this caser an association between tree height a¡rtl P. lobatus nu-mbers was established. Although the establishnent of such an association leads to reasoning about causal- relat- ionships between the variables, significant correlat-ion ca.¡:not be equated with causation. The coefficient of determinatj-on ("2) rr"" 0"086 or O.1OB, which means that abouf 9-11y'" of the variation in tree height is aesociated with variation in P. Iobatug numbers. There are many other factors in a nursery situation which could be associated with the renaining variation in tree height- factors such as soil moisture, genetic variability of seedlings, other pathogens and soil nutrients. A1so, the error with which P. lobatus populations rdere measured. was probably quite large. It is very difficult to obtain a¡t accurate estinate of nenatod.e populations arorrnd growing trees, because only a linited ¡morurt of eoil and. roots can be removed, and the distribution of nenatodes in the soil is uneven. In addition, errors occttr d.uring sub-sampling, a¡rd in the extraction and counting procedures. InitialJ-yr a variabfe which accounts for only 9-11/" of the variation in tree height may seem in- significant. However, such a variable assumes greater significance when seen in relation to the many other factors which also contribute to this variation in the field.

1.4"4 Effect of temperature on population increase

Methocls

Peach seedlings (var.Elberta) were grown in 15 cm eanthenware pots filled. with stea.n-steril-ized. sand.y soi1. '¡úhen the seedlings were three monLhs old, four d.ifferent tenperature treatments v¡ere inposed. Temperatures Figure B" Correlation d.iagra.n. Height of peach trees (cn)

v. Numbers of P. Iobatus per lO0 g soiI. TREE HEIGHT (cms)

c, ooooc)oN¡\GN@öÑ

N I a a a

a a a a a ta. a

g a

a ñu th g r a lp lr c, I a Etc lø IË a

IË

a- g

g 48.

of 15oC and. JOoC weïe obtained in h[isconsin soil tempera.ture ta,nks, and.

2OoC and. 25oC were prod.uced. in controlled. environment cabinets. Apart frorn initial problens in ad-justnent during the first week, temperatures were controll-ed wibhin I loC of the required temperature, except in the lOoC water bath, where varíations of 1 2oC occurred.. Ten seedlings were trans- ferred. to each temperature and a fourteen hour day was imposed. Each pot was inoculated. with approxinately 150 P. lobatus and 800 other nern¡todes by pouring a suspension of the nematodes into holes in the soiÌ around the roots. Six and twefve weeks Later, five pots in each treatment r^rere sampled.. Nematod.es were extracted, fron five hr.mdred grarns of soil, and the dry weight of both tops and roots of the seedlings was measurecl.

ResuLts

Harvests were combined. for statistical analysis, as this d.oubl-ed the number of reptricates per treatment. Nunìbers of P. lobatus at 2 5oc "rr¿ ,ooc were significantly d.ifferent from numbers at 15o0 and 2OoC (figure !.) The number of other nematodes increased. almost linearly with temperature. There was no significant d.ifference between the final top and root weights at the different temperatures (taule 9.).

Discussion Ideally, plants should have been grov¿n urrd.er si-mifar conclitions except for temperature, but the equipment for this was unavailable. The data indicated that P. Iobatus had. a relati vely high optimum tenperature for population increase, but the temperature range used. was not high enough to deternine the optirrum temperature precisely. trbrther tests showed that peach seed.Ìings did. not grow well at )5of: and ttrat only ì-ow popula.tions of

P lobatus were supported. at that temperature. Therefore, it seems likely that the optimm temperature for population increase of P. lob¡-ltus is in

the range zSoc - 1OoC, which is not surprising as the species appears to Figure !. The effect of temperatu¡e on population

increase of P. lobatus and. others. 3000

2s00

2000 ISDS.¿

I I UI -¡ ! É, r500 $ Il¡J 3 1000 2 ¿00

300

200 ,-*l

r00

0 t5 20 zs 30 TEMPERATURE (OC) 50.

be ind.igenous to Australia, where high soil temperatures are conmoll.

TABI,E 9

THE ETTECT OF TEWIPERATÜRE ON TIilI '!/JEIGIIT OF TOPS

AND ROOTS OF PEACH SEEDTINGS

Temperatur" (oc) I. S. D.

15 20 25 JO j./" * Top weight (e) 2.96 1.11 1.72 1.57 o"B2

Root weight (e)* 1.29 1 .41 1 .16 1.17 o.4B

* Means of ten seed.Iings.

Pathogenicity fiJ ,.4.5 ¡'ir i 1.4.5 .1 Fielct slrnptoms

Assessment of the damage caused. by stubby-root nematod,es in the fietd

is ha.npered. because few obvious symptoms are produced. Trhe feeding of stub-

by root nematod.es d.evitaLizes root tips and. stops growth. In many instances ,¡ ',1 tlevitalized. tips show little or no discol-oration, necrosis or other evi- d.ence of injury. The effect on the root system as a whole varies widely, but in some instances the only effect is a reduction in the size of the root systen without arry obvious abnormality (Cfrristie,1959).

Synptours probably caused. by P. lobatus have been observed on ci-tnrs

peach and apricot in the field. Most observations v/ere mad.e in nurseries, where P. Iobatus is often present afone and in high numbers. In orchard.s,

s¡rnptons nay be conplicated. by the presence of other nematod.es, such as

root-knot, root-lesion and, citrus nematode r 51.

Citrus

Synptoms probably caused- by P. Iobatus have been observed in South

Australian citrus nurseries at Rennark and- Loveday. Trees oupporting l.

lobatus popurations of 1000-1!00 per 500 g soil hacl severel-y stunted. feed.er roots. In some cases, feed-er roots were no longer than one certi-

metrer with nost being only a few millimetres in length. Root tips were

generally swollen. Soil particles remained clinging to affected. roots when they were removed from the soil, so that roots tended- to be brown rather

than the normal yellow col-our (llates 2a, b.). Above groLrnd, trees gen- eral1y lacked the bright green col-our typical of healthy trees. Tirey often showed the effects of water stress during the day, with the leaves curling so that the paler und.erside of the l-eaf tend-ed to face upwards.

Peach and. aprico.t

'À l[f Trees growing in soiÌ containing lOOO-1750 P loba.tus per lOO g soil ì,.1 i had. fewer feed.er roots than would nornally be expected. Feed.er roots were

generally shorter, considerably thlckened, and. often had swollen t1ps

(ttates 1a, b. ). tops were often stunted, but poor grov/th of peach and apricot trees is cormon in South Austral-ian nurserj-es, and soil-borne path-

ogens other than P. lobatus are probably invofved j-n some of these situations.

J.4.5.2 Glasshouse experiments Citrus

Methods

Twenty 15 cm pots were fitled. with steam sterifized soif (a 9:9tZ T mixture of red. sand, washed. riyer sand and. peat). In early January, thirty

pineapple sweet orarrge seeds were planted in each pot, and the pots were

pÌaced in a glasshouse" Five hundred. P. lobatus were added to half the pots

fifteen d.ays J-ater. Plate 2a, b. reft: citrrrs roote corlected from a nuÌserrr infested with p. l_obatus.

Ríght:. Cltnrs roots collected from a nursery not infested with p. lobatus a \ ì \ \ I \ I I I \ \

\-1 b ') ì/ì P1ate 1a, b. Left: Apricot roots from a nursery not infested with P. lobatus. Right: Apricot roots from a nursery infested. with P. lobatus. q

B 54.

Six months later, the citms seedlings lìrere removed- frorn the pots, a.ntl lightly shaken to remove soil- frorn the roots. The soil remaining on the roots was washed. into a large beaker and the nematodes extracted. by d.ecan- ting a,ntt sieving. The plants in each plot were cut into topsr tap roots and. feeder roots a¡d. the dry weights of each recorded-. Nernatodes were extracted- from a 500 g subsa^urple of soil taken from each pot.

Results

The root systems of plarrts inoculated with P. Iobatus ÏIere sparse and much red.uced. compared with uninoculated plants. Feeder roots were frequently short (usually onLy 2-5 nm l-ong instead. of lO-iO mm) and. sometimes had. swollen tips (ftates 4a, b. ). ttrere \â/as no d.iff erence between inocul-ated and control plants in the dry weights of tap roots and tops, but the dry weight of feeder roots was significantly red.uced in inocul-ated plants (ratre to). P. l-obatus v/as recovered from the soil- in all pots which had been inoculated. Populations had increased. 1O-2, tines from the initial population.

Numbers of P. lobatus in the rhizosphere v/ere very high with a population of more than IOOO nematodes /lO e soil being recorded. P. fobatus \^ras upto 75 times more concentrated in the rhizosphere than in the surrou¡ding soil.

TABLE 10

DRY IJEIGHTS OF TOPS I,'EEDER ROOTS AND TAP

ROOTS (CruUS) OF CITRUS SEEDTTNGS INOCU-

LATED AND NOT INOCULATED \À/ITH P. LOBATUS

Tops Tap roo ts Feeder roo'bs Inoculated 17.48 ! z.f 4.2, ! o,7o 4.62 ! o.a4

I Not inoculated. 16.14 ! t.fi 1.78 ! o.4o 6.45 : o .95 *le( Significance n. s. n. s. Significant ( t-test ) (rls = 4.i9) Plate !a, b. Left: Citnrs seedlings not inoculated. with p. lobatus. Right: Citrus seed.iings inoculated with P. lobatus.

4c Close-up of root synptorns of citms not ínoculatett and. inoculated. with p. lobatus. Scale in centi-metres. lr'

tl..à. :rl-- i;.t -_ r - 2ì----ì:-;:= _ A R 7v *--- !'z- \ o'.'. -:!.-.--.' \ :l_\

b ùx 56

Te¡r bottoml ess polythene tubes 2! cm long x 4 cn d,ianeter were filled with sterilized. sandy soil. Two week old apricot seedlings were stratified for size, d.ivided. into two sirnilar groups of five plarrts and planted. individ.ually in the tubes. Five tubes were embed-ded in each of two 10 litre plastic buckets fil-l-ed. with sand, and- placecl in a hlisconsin tanlc maintained at a tenperature of Z5oC. The tubes in one bucket were each inoculated. with

500 p. fobatus by pouring a suspension of the nematodes around the base of the apricot seedlings.

The plants were removed twelve weeks later, the roots studied closeJ-y an¿ the d.ry weights of tops, tap roots and feed"er roobs were measured-. Nen- atodes were extracted fron the soil in each tube using the two-fl-ask technique (Seinhorst, 1955). In an ad.d.itional experiment, twenty cm polythene pots were fiffed- with sandy soil infested with a popula,tion of approximately IJOO P. I obatus per lOO g. soil. Twenty sinilar pots were filled with steam sterifized sandy soil-. Two apricot s¡eeds were pJ-ir.nterì:Ln eacì'r pot, arr

Results Tn the first exper:iment, P. Iob¿rtus was re-isolaterl l'rom afl inocu- 'betweerr l-ated tubes. There v{as no sigrrificant d.ifference inocul-ated and .bhe control- plants in the dry weight of tops and 1;ap roots. Howe:ver:, weight of feeder roots produced by inoculated plants was significantly less t'han that prod.uced. by control pla,rts (t'able 1'1 , Plates !a, b.). EN )lo

fn the second. experintent, 9t/" of the seeds solln in ster-Lle soil had, emerged a¡d plants l¡ere six-eight cm Ìrigh after three week$. OnIy 15i/" of

{;he seeds sown in P. Iobatus infested soil had emerged and. the plants were snall-, with severely stunted root systems and swollen roots (ltates 6arb.).

TABI,E 11

DRY WETGTTTS OF TOPS. ¡']EEDER ROO'IS AND TAP

ROOT'S ( GRA]V]S) OF APRICOT StrE)I,INGS INOCU-

L¡.TED AND NOT INOCUIATEI) }/ITFI P. LOBATUS

Tops Tap roots Feed.er roots

Inoculated. 1.29 ! s.45 o.26 ! o.1t 0.12 10.04

! Not inocul-ated. 1 .27 : 9."7 0.24 I 9"¡g o. t9 1 o.1o

)e Signif icance n.s rl.. s. Significant

(t-test) . t4 ='?'95)

1.4.5.1 Laboratoly studies Observations on the feed.ing of P. lob¿Ltus on pea.ch and apricot rc¡ots were mad.e using the following nethods. 'Ihe testa was removed. frorr peach and apricot seed.s, which we,re surface s'ber.itized. in 1O'/" sod.ium hypocÌ,lo- rite for 15 minutes and. then washed in steril-e d-istilled water. After ger- mj.nation on noist sterile filter papelr in a, petri dish, a seed was trans- ferred to the surface of a petri d.ish containing 1y'" urat'er agar' w11;h 10Cl ppm streptonycin ad.d"ed.. Some seecls produced healthy roots which grew th.r:ough the a,gar arrd specimens of P. lobatus vere add.eri to these, and. observed under the microscope.

peach ancl apricot seedl-ings r,rere also grown ulder steríIe cond.itions in test tubes. Thirty gra¡ns of sand (particle siz,e 15}lt- 25)lt) was add-ed.

to 20 cm test tubes, which were then pluggecl with cottorr wool and sterilizcld. After add.ing three cc of sterile water, the sand was shaken to increase pore spaces a¡rd to alfow for ae!¡,tion, and pre-gerninatecl , surface-sberil-ized ?late 5a. Roots of apricot seedlinge not inoculated with P. lobatus.

5b. Rootg of apricot seedlings inoculated. with P. lobatus. \' ./ ..''5/, a- .' ¡' ,l fi Plate 6a" Apricot seed.lings inoculatea (feft) a¡rd not inooulated (rtght) with P. lobatus prior to gerninatÍon.

6b. Aprico* seecllings inoculated (right) a¡rd not

inoculatea (feft) witrr P lobatus príor to gerninatÍon.

6c, An apricot seed.ling lnoculated wÍth P. lobatus prior to gemination. (\t \ t\ (rsci.t Òaaa¡l

¡¡aaaa ac¡ror a¡öaao at.', . ¡ ù!.-ta : at¡aaa t aa.aaa t ( (( - -J

t ?. oo aa ÈYìI.o?' - ù ¡ra

a a ata a o a! a o e 1 a a a o a d 3a' 60.

peach or apricot seed.s were p1a.nted.. Grou.ps of about 20 hand--picked- P. Iobatus were added., and. the tubes incubated at' Z5oC in a grow.bh room for up to three weeks. Nematodes Ïrere extracted. frosì the sand by decanting and sieving through JOO mesh sieves.

Results

problems occurred. d.ue to contamínation of the seeds with fungir probably because the surface steril-izatiorr technique did not kill fungi which had grown through the endosperm of the seed. Ilespite thisr some seetl-s were steril-e, an¿ P. l-obatus was observed und.er a microscope, feeding on peach roots (1>tate J). Feed.ing did not occur immediately, as the nema,todes seerned to::equire about a day to become orientated arrd accl.inatized. The nematodeis fed over the whole root surface, but tendr¡d. to be more concentrated near the root tip, They remaj-ned motionless while feed.ing and even when search- ing for another: ceII, only the head and not the booy was observed to mov'e"

Each nematod.e fed on a cel-I fot 40-45 seconds. DurÍng this period- the stylet was observed to move j-n and out very lapidly for the first 10-15 seconds. The thrrrst;s then became slo'¡er untif finally there uere ]-ess than two thrusts per second. Eggs were deposited by feeding adult females, a.nd some of these d"eveloped lalr'ae which hatched. Growing seedlings in test tubes proved. a sinple walr ef rrultiplying

P. lobatus. Us ing either peach or apricot as hosts, ini'[ial inocu].um of approximately 20 individuals increased to 1OO-1BO in about 1! days.

1'4.5.{ Discussion [']rese stuciies have shown that the behaviour of P. lobatus is sirnil-ar to that desoribed for other stu.bby root nematode species on other crops.

A reduction in root growth in pathogenir:ity tests with potted plants ha.s been obtained with P. christiei on several perermial crops (Zuckernan11961,

1962, Ruehle, 1969)" P. lobatus caused seve e symptoms on apricot Plate /. Paratrichodorus 1obatus feeding on the epid.ernal ceIle of a peach root. a î¡l

I+

tl I rl r *å ß tt à, .)8.. "3.: t !¡. í '4 )i ^/L 1-..ffi, , * "{.. .lõ; Át

when added before seed, germination, and less sievere symptorns when add.ed after roots hacl formed.. Sinilar resul-ts were obtained, when P. christic-i was added. to blueberry cuttings before ¿¡,nd after rooting had started

(Zuckernan, 1962). ltre phenomenon of aggregatiorr around- the tips of growing roots has been observed in seven stLrbby root nomatode species (litcher, 1966) , The high P. l-obatus populi:.1;ions extracted. from the rhizosphere on citrus, and the observation tha'l; nematodes tend. to concentrate near the root tip when feerling, reinforces Pitcherrs suggest:ion that aggregation near roots is a common feature of feedj-ng by members of the gemrs

Trichodorus sensu lato. AIso, the feeding process of P. Iobatus on peach wae not u¡like that described by other author:s for P. christiei,'l'.p-rcrxi- mus and. T. sirnilis (nnoae & Jenkins, 1957a; Zuckerma¡, 1961; RusseII and.

Perry, 1966; Rhoades, 1966 and Wyss, 1971b).

1.4.6 Host::alge

1.4.6.1 Weed hosts P. l-obatus infested. sojl was collecterl in mid Februarry from ¡rn infested. nursery, æd mixed. with coarse sand in the ratío Jz1. Iive 5OO g srrb- sanples r¿ere elutriated to determine thc population of P. lobatus .in the soil-. 1400 g of this soil was ad.ded. to each of {8, 1J cm, pots. Two pla,nts each of 21 weeds which cormonly grow in the River-l-anrl wcre sel ected and planted. ind.ivid.ually in those pots. Two pots were feft unplantea (faflow).

The pots were placed in a sh¿rd.ehouse and watered regularly. Nj-ne weeks

Iater a 500 g soil sample was remo\.erl from each pot, and. the numbers of

P. l-obatus in the sa,urple was d.etermined

Results

The initial population of P.l-obatus was !14 I Al per 5OC g soij-.

At the end. of the experinent, '11 5 an,1 176 P. lobatus per lOO g rvere recovered from the two pots in which no plr-rnts had grourn. 61.

As two pots were used- for each plant species, the highest, final population density obtained in these two pots wa.s considered a better measu-re of a plant I s potential as a host tha,n the average of the final popu.lir.tion densities in each pot. Table 12 shows the highest population density of

P. lobatus obtai-red. in each pair rlf pots, and. also a categorizatlon of that population as foLlows:

1. Final population at l-e¿rst th-r'ee times inj tial. population 2. Final population greater than init;irrl pop'Lrlation

1. tr'inal population greater th¿¿n that obtained in falfow pots, but less than initia,l populatj.on 4. Final population less than tha,t in fa,ll-ow pots.

Discussion

In,terpretatj-on of da-ba obtained from host range experiments is diffi- cul-t because infornetion on the actual nematode population inj.tially capa- bÌe of reproducing is usuellly lacking. lùot all nematodes cclurnted- nray be able to find a root ancl f eed, while nem¿ltorLe eggs present in the soil are not corrnted unless special techniclues are userl. Iïowever, it is probable that plants categorLzed. 1 or 2 are good hosts of P. fobatus. Those categorized. J are probably able to mair-bairr P. lobat.us populations, while those in category ! are probably poor hosts or non-hosts. Altirough these categories were only chosen a::bitrarily, they rr.re supported by data coLlected i-n the field and. reported. in previous section (1.4"1.2). The four: weeds recorded. as havi-ng P. fobatus populations nea.r their roots irr the fiel-ri.

(tatrte B) alJ- proved good hosts in the host r:a.rrge test" 64

TABLE 12

FINAI POPULATION DENSITY OF P. LOBATUS

ON VA.R.IOU S \,IEED I1OSTS

population densitY Con¡non na.me Scientific na,Ine tr'inal- (category) (nenatode numbers )

2816 Kikuyu g?rass Pennisetum cl-andestinum 1 2587 Portulaca weed. Portulaca oleracea 1 EraEro stis cilianensis 2 121O

2 1 170 Pacltly melon Cucumis nvriocarPus 1O92 Couch g?ass Cynodon dactYlon ¿ Bathurst burr Xanthiu¡r s¡inogu-ÍI Z 624

¿ 6oB Sow thistle Sonchus oleraceus

5BB Tonato weed., Suena üolegr¿¡q @4La,1e- t 525 Potato weed. He liotropi un europaeum 1 Petty spurge Euphorbia peplus 1 510 Rolly polyr Buckbush Salsola kali 1 468 411 Onion weed. Aspho delus fistul-osus 1 aEa z ¿) CaItroP Tribulus terrestris ) I 240 llild nustard Sysi¡nbrium oriental-e 1 2 Amaranthus viridus ) 182

1BO Salvation Jane Echium pla4!øgineurr t 120 lJire weed PoIvEonr:-m aviculare 4 Fat hen Chenopod.ium album 4 16 -a Variable groundsel Senecio fautus 4 )o ¿oa/ Three cornered. jack Emex australis 4 15 Innocent weed Cenchrus tribuloid.es 4 11 Crab grass DiEitaria sa¡rzuinalis 4 0 Fafse caper Euphorbia terracina 4 65.

,.4.6"2 Native hosts A¡ area of virgin scrubland. about I kn from the bo¿nd'ary of the

Loveday irrigation area was sampled. to obtain infornation on the presence of p. lobatus in virgin soil. Soil samples were colfected which corrsisted of four cores removed with a ! cn dianeter auger fron the root zone of the followíng plant sPecies.

Needle-bush acacia Acacia rigens Porcupine grass Triodia irritans Good.inia sp. Cassia nenophYlla Eutaxia nicrophYlla

[yoporum p]atycarPr¡m Unbrella bush Àcacia ligulata Halganea cYanea ,,t Rough halganea il ,; Hop bush Dodo naea attenuata rf Diarretla revoluta

Onion weed Asphod.elus f is tulosus Eucalvptus pileata

Native poplar Codonocar¡üs cotinifol-ius I

El-utriation of a 5oo g sub-sampte of soil- frorn each species showed' that P. lobatus llas present in low numbers (]ess than 20 per IOO g) near A. rigens and C. nemophyl-Ia. It was not observed in the samples fron other plants.

1.4.6.1 Atld -i- bional hos t ra,nse infornation During the course of this study, some additional infornation on the been nultiplied- on host range of F. Iobatus was obtained'. P. Iobatus has sweet corn (Zea mavs) and. mallee (Eucalyptus calycogona) in pots. The supporting high P. lobatus populations were I root systems of sweet coln 66

red.uced., and nanJr fine fibrous roots were stunted.

1.4.7 Control

1.4.7.1 Control of P. Iobatus on nuraery peach trees

Because high populations of P. Iobatus often occurred in, peach nurseries, a trial was establ-ished to determine whether the nematode could. be controlled. successfully, and íf so, whether improved. tree growth resul- ted.

A row of one year old llight peach seedlings which had. been bud-d-ed to Elberta cturing the previous sprirg, ì¡rere used. for the trial . Plots each 1.5 m along the row and 1.5 m across, and- contai-ning sixteen trees, were narked out, but three trees at each end of the plot served as barriers.

This red.uced. the actual length of the plot to 1.0 m, containing only ten trees.

As Rhoades (tl68) found that DBCP was the best of the fumigants in ¡.t :,? retarding the rapid build up of stubby root nematodes foll-owing fumi-gation' (n) Fumazone (17e. 6/" w/v 1-2 d,ibrorno-J-chloropropane) was tested at a rate of 40 Ifna. The chenical- was applied. to eight plots by hand injection on a )O cm g'rid, the injection holes were filled and water was applied to seal- the soil. The soil was sampled for nematodes by collecting four cores of soil from each plot with a 5 cn dj-a.neter auger. Cores were coll-ected at a depth of 15-20 cm and at a d.istance of 15-tO cm from the row. Samples were collected. before the fumigant was applied., and. then J, B and 16 weeks Later.

The cores of soil coll-ected from each plot were bulked, a 5OO g sub-sample

was removed, and- nematod.es were extracted and. counted.. The height of the

ten plants in each plot was measured. 16 weeks after application of the

DBCP. I t 67"

Results The results of this trial are shown in Tabte 1J. Before DBCP uas app-

,.,i. lied. the plots to be treated and those remalning, contained similar P. lobatus populatione. P. Iobatus nunbers were significantly reduced in population DBCp treated. plots three weeks later. As a substantial nematode renained., plots were treatecl in the sa.ne way five weeks after the initial treatment. The eff ect of retreatment showed in sa"nples taken cluring the eighthweek,when@popuIations}IeIevery1owinthesep1ots.By the sixteenth week, populations in the treated. ptots had again increasedt although they reinained significantly lower than populations in untreated plots. There }¡as no significant d.ifference in tree height between treated

a¡rd u¡treated plots after 16 weeks.

TÀBLE 1' * P. I,,OBATUS POPULATIONS IN PLOTS TREATED V/ITH nl TIMES. 1¡ DBCP AND LETT AT OUS I TREE GHT+SIXTEEN IúIEEKS ATTER TREATTVIENT

Before 1st Af ter 'l st After 2ncl Àfter 2nd- Tree Treatmen t Treatment Treatnent Treatrnent HeiEht z.+(cn)

Date August 2J Sept. 1 l Oct. 1B Dec. 15 16 Week 0 1 B 2nð. treatrnent Sept. 27

Treated. 47' 119 1B 276 tB.7

47 Ilntreated. 4BB 505 761 582 "O ìe* fI.s. Signif ica.nce fl. s. ** ** (p*.oo2o) (p=.0016) rP=.0011)

I with 'n Mea¡rs of eight Plots + Means of eight Plots, ten p1a^nts/P1ot. 68.

Di-scussion

The results of this experiment showed that high populations of P. lobatus rapid.ly returned. following furnigation with DBCP. In the literature review it was shown that this also occurs with other species of stubby root nematodes, although aJ-I this work invol-ved the pre-plant, treatnent of a¡u:ua1 crops. Adequate control in perennial crops is likely to be nore d.ifficult, as anJr nematode which escapes the funiga¡rt ca¡r imnediately con- tinue feeding, as hoet roots are always present. Oostenbrink (1!16) suggested that the d.istinct improvement of plant growth in soil treated. with a specific nematicid.e, indicates that nenatod.es are the chief cause of a d-isease. The use of nenaticides for this purpose is linited. in situations where population levels can only be low- ered for a few vreeks. It is unlikely that a growth response in the host could be expected when nematodes are controlled. for only a relativel-y short period. in the life span of the cropo

1.4.7.2 Control of P. l,obatus on nursery citrus trees

An area of trees in a Loveday citrus nursery showed. signs of water stress ar¡d. Iack of growth on hot surnrner d.ays although from experience, the nurserJrman considered that soil noisture was ad.equate. High numbers of P. lobatus l¡ere present in the soil, and the roots showed symptoms typical of stubby root nematode d.a^mage. 0n January 8th 1)ll sixt,een J m x 1 m p1o-bs, each containing approxi- nat,ely 21 trees were marked out in the affected. area. Phenamiphos (ethyI (nethytthio) isopropyl phosphora^midate) granules were applied to the soil- surface of eight plots at a rate of 40 kgfna, a^nd, eight plots were left r¡¡¡treated. The ne¡naticid.e r^ras washed into the soil with a 60 mn irrigation applied in¡nediately after application. SoiI sa.nples were colfected fron the plots on March Jthr May 21rd anð. August 14th. A 5 cm dianeter auger v,as 69.

used. to collect four cores of soil from each plot, at a d.epth of 1! cm. A

To 5OO S sub-sa.nple was processed., and. the m:mber of P. lobatus corrnted. ind.icate whether treÞs were in a state of active growthr trees vrere assessed individ.ually on lv1ay 25th anct scored for the presence or abserlce of newly forrred. leaves. On removal of the trees fron the nursery on September 9th, their root systems vÍere inspected-.

Results Eight, twenty a¡rd thirty-one weeks after application of the nematicid.e' sanpJ-es collected from treated. plots contained significantly Iower m¡mbers of P. lobatus than sa.urples fron untreated plots. (fat:-e t4). During the twentieth week similar nr.¡mbers of trees in both treated and, u:rtreated. plots were actively growing. 79.1y'" of the 16{ trees aseessed in treated plotst and. BO.@o of the. 170 trees in untreatetl plots, had. recently produced new leaves. By stud.ying the root systens of trees on removal it was possible to differentiate treated. and untreated plots. Trees from untreated plobs showed root s¡rmptons typical of those caused by stubby root nenatode in the field' a¡rd. described in section 1.4.5.1. Atthough trees in treated plots al-so exhibite¿ synptons, they contained a rnuch la,rger proportion of clealrheal- thy roots. Despite the ready d.etection of this d.ifference in root growtht the nurserJ¡nan d.id not consider it economically inportant as he soLð' 77.4/" of the trees from treated plots, and. 79.4y', from u-ntreated plots. 7o

TABrE 14

P. LOBATUS POPULATIONS IN SA]VIPIES FROM PLOTS OF CITRUS

TREATED ]/,IITH PI]ENAMIPHOS. AND IEFT UNTREATED, EIGHT'

TI^IEMY AND THTRTY-ONE TEEKS AflIER TREATMENT

NO. P. TOBATUS/5OO g SOII

7 h/74 2J /5/74 14/B/74

f a Treated. 24: zo Y!za t8:40

-J- f Untreated fir! fi6 161 : 71 2OJ : 111

Significance (t. test) *rtlË *9êl+ rtJ(+ (p ( .001)

Discussion This experirnent demonstratea tnJefficacy of phena.niphos in controlling P. Iobatus on citrus , and confirmed. the results of Brodie (t96e)' Rhoades (1169) a¡rd Morton (f16S) with other stubby root nematodg6pecies on other crops. The inproved root growth resulting fron tfreLse of phenaniphos night have been refleeted. in a¡r increased number of rnarketable trees if P. lobatus had been controlled. for a longer perj-od. AIso it is tlifficult to determine whether better establishment in the fie1d, and earlier production would have occurred because treated. trees had improved root systems.

1.4.8 General Discussion Althor:gh initial infornation on plant-nenatode relationships is often obtained from pot experiments, it is usually unwise to extrapolate these results to a field. situation, where growing conditions are very different" For example, P. lobatus reduced the quantity of feed.er roo'bs 71.

on apïicots and. citrus grown in pots. This reduction in root growth was not reflected in reduced top growth. llowever, the top growth of pl-ants growing in id.ea1 cond.itions in pots a¡rd, rarely stressed. for moisture, is less like1y to be affected. by a reduction in the number of feeder roo bs than are plants which periodically suffer the stresses of a field. environment. In the field., where moisture supply, soil fertiJ-lty and temperature are often unfavourable for plant growth, lower numbers of nenatod.es may be suffícient to cause injury. The effects of nematodes on mature plants caru:ot be d.eterrnined know- ing only their effect on yorng plants. The severe d.a.mage caused. by P. loba- 1¡g to germinating apricot seeds and to yourlg citrus seedlings showed that it is a potentially importa¡rt pathogen in nursery seed beds. However' the economic losses caused. by the nematode in older pla^nts are not as easily recognized, as such severe synptoms usually d-o not occllro

The extra water required for trees which wilt prenaturely because their roots have been strrnted., may increase costs of production in the nursery. Eowever, as the root systems of stubby root nematod.e affected. trees are generally consid.ered.-good enough for the trees to be narketerlrnursery- men regard. the nematod.e as having a negligible econonic effect. The fruit- g?ower who buys the trees probably bears mos b of the cost of stubby root nematod.e in nurseries, as nematode affected trees may have slower initial growth rates tha^n non-affected trees. The nematode may assume greater economic significance to nnrser1men in future, when container SrolJn trees with well developed. root systems and lacking symptoms caused. by stubby root nema-

tod.e, are marketed.. Nematode affectecl trees are then likely to be consi-

dered inferior, a¡rci will probably sell at a lower price.

As p. Iobatus is widespread throughout South À¿straliar s irrigation areag, the spread of the nernatode on nursery stock is not as important as

it would, be if it rarely occurred. However, it carurot be consid.ered good. 72. agricultuïal- practice to spread a potential pathogen in this way" Determining the effect of a nematode on mature trees is a complex

task, and. even now we lack basic information on the economic effects of such lnportant nematodes such as root knot rlem¿ltode ancl r:it,rnrl nematode. Although p. Iobatus populations j.n orchard sojls are generall-y lcwr the

nematode tend.s to accuurulate near root tipsr and populations at feed'ing sites nay be consid.erably greater than soil populations woul-d suggest.

These aggregations of nematod.es probahly feed co¡tirrually on new feed'er roots, strrnting nany of them. Although sur:h losses may seem Lnsignificantt the continual debilitation.d root systems which occurs over a long periori of time in perennial cropsr nay produce greal;er losses than those camsed by more spectacular but spasmodic d-iseases.

1.5 Para trichodorus minor

1.5.1 Populat ion fluctuations on Peach trees In r\ugust 1971, a treo was selected. in a peach orchard at L6x'bon

South which b.að. a populatiorr of P. minor around- its roots. Periodically ovet a period of nearly three yeals, soil samples were coLlected from wji'h- in the drip line of this tree. Ten sarrples ller'e colfected at each sampling tine, with each sa.mple consisting of for¡r col.es takerr with a ! cn diameter g auger at a d.epth of 1 5-25 cms. The nematodes were extracted from a 5OO

sub-sa.mp1e anrL counted " An estinate of the arnount of weed. growth around. the tree was obtained by renoving all above ground naterial from five randomly selected quadr:ats 0.1 square metres in area. The naterial was <¡r¿en-d-ried and weighed'.

Results

Populations of P. minor and d.ry weights of the weed.s have been plot- only nn ted in Figure 10. The winter of 1 9]2 was abnornarry drYr with 91 rain beirtg recorded between Àpril and Septenber. Consecluently, weed grorvth such as 1971 and' 1975, was less trran wourd be expected in more noïnraI years, Figure 10. ?opulat5.ons of P. ninor on a peach tree a¡rd. the dry weight of the weed.s growing beneath that tree,

during the period. Septenber, 1971 to April, 1974. Points marked, with the sa¡re l_etter aïe not significantly differen't (p = .05). o o

300

ob 200

ìlemotode rxrrÈçs 70 oì o o I b 7) o I tf) ¡ a b 60 I b € Él I ol tr zl ¡ G, ¡ - I bc -.1 I o-l=l I o.Tl I b b bc /.0 ¡ bc l¡- 100 ¡ o ¡ t € Ê. ¡ m t¡, I Weeds 30 m (o I (f I (n =l c 20 (6- z. c g o ? c 10 a c c I c 0 0 SOND JFMAMJJASOND JFMAMJJASOND JFMAMJ 1971 tgt2 1973 197t, 74.

months' when 1lJ anð' 194 n¡n rain fell durÌng these o1 1971 a¡rd the win- Nematode populations showed peaks in the spring ter-springperiod'sof1971,buth'erevelylowd'u¡ingtheSunmersoll9T2 of the sa'npling period are d'iffi- a¡rd 1 971. Populations d.uring the rest culttoquaittify,becauseofthelargeva,riationinnematodenr:mberswhich time' occu¡red. between sa.nples at any one sam¡rling

Disoussion Duringthesrrrveyofpeaohorcha¡ds'@occtrr:red.morefrequent- cultivation' This ly in orchards rmd.er sod. culture than in those r¡nd'er nay be more importa¡lt hosts suggeeted that weed.s grouing in peach orcharås [email protected]]-f.OtherworkhasshoUnth"t341ry=jsdíffi- culttonultiplyonpeachinpots,althoug}rith¡¡,sbeenobserveclfeedirlg the fluctuation in nernatode on peach roots g¡owing Ln af¡at' Consequently' populationsobge]îved'clurÍ.ngthisstrrd.yareprobablydeterminedbyboth peachandweed'rootgrowth.SÆpopulationstendedtobelowd.rrring thesu.ÚIner,whentherewasljttlerootgrowt,handtheorchardrema,ined in nematod'e numberst weed free due to cr¡ltivation. Despite the varia'ti.on to increase during there was evidence that P' minor populations tended both weed growth and peach the late autrrnn-winter-earl.y spring period, when rootgrowthweregreatest.Àcloserelationshipbetueer.nena,todenu.mbers a¡ldweedgrowthcouldhartllybeexpectedasm¿tteria]-fromrranyplarrtspecies being good hosts of P. minor and lras measu-red, with sone of these probably

others Poor hosts"

,.5.2 A d.iseas e syndrome of onions 1.5.2.1 A fielcl Eun¡eY Becauseonionprieeshavebeenhjgharrtttheareaoflanttavai].at']e forvegetablegrowingnearAclelaid-ehasdecreased,theareaofoniorls grownalonStheRiverMurrayhasincreasedtosevera]}.Lund'redhecta¡es d'uringthelastfewyeare.Althoughonionsglowninthemarketgarden 75. areas near Adelaide are frequently attacked. hy the stem and bulb eelwo::n (Ditylenchus ciinsaci), onions along the Rj-ver Murray generally do not experience nematode problens. However, d.uring the spring of 1975 sever.a:. grolrers reported onion crops that showed d.isease synptons which did not correspontl with arr¡r previously observed d.isease of onions. '

Stubby root nematod.es llere suspected of causing the diseaser as pr:e- liminarl¡ investigations sb.owed that they ï/ere associated with d.iseased plants. The absence of infornation on the rlistribution of the disease, and the factors asgocj-atett with the disease in the fielrl, Ied to the conmence- nent of a survey in Octoberr 1971. '

Methods

The nineteen fields surveyed were selected in a manner similar to that described prevÍously .for the peach su-rvey. The general trealth of the onions in each fielct was assessed., a^nd the farne? was asked. to supply its croþping history a¡rd infornation on ar\y environmental, cultural or nanagenent faotor Iikely to have influenced. the crop, Root,s and assocjated. soil from foul ind.ividual p1a¡ts ì¡fêIê,, cãtlêfu1ly renoved. with a spade, a 2OO g sub-r;ample of soil was e1u{,riated using the two-flask nethod (Soinhor:str 195>) and thtr nematod.es were identifietl and counted..

Results Both healthy a¡fl r:¡Ïrealt$ crops were observed during the surveye Often the reason for poor gïotrth was readily id.entified. However, a number of cases occurred where there ìdas no obvious reason wl,y plants rrter€) stunted. In these cases, the synptoms tended to var-y' with the a6e of the plants. During the f-trst few weeks of growth, seedlings lrere stunted and" tended- to be yellow an¿ to die at the leaf tips. Roots often grer.r only 1-2 cms (Plates 8r9). Qlcler plants exhibited. sinilar above ground synptomsr but roots were

short, irregular a¡¡d, abnormally bra.nchetl (Pla,tes 10, 11 arrd. 12). Plate 8a, b. Onion seedlings in the field. showing poor

establishnent, a.nd stu¡ted. seedlings. Seed- lings Ïíere approxinately three nonths old.

Bc. Healthier seed.lings fron the sa^me fj_e1d.. c 2: ) ? ,r ,'' -¿' > \,: l.-'\. . t ,' j i' c ,/ t?:-- , Tul ì\ . 'sl ,-' ,' ì'ú t ',ii-.

L I !D -t- / \- ( .l ll)" l'T,¡ I , + Þ t

i1 '{¡. ì É¡- Ë 'l,f F a','

f; Plate 9a, b. Str:¡ted a¡rti healthy plants fron field

shouri in plate B. if . .,. :- \ t- tr ! I Plate 1Oa, b. Stunted antl healthy plants from an onion field. t t,

I e

Plate 11a, b. Root systems of healtÌ¡y a¡rd stunted. pla.nts respectively, collected in the fj.eld. Roots of stunted pla.nts are short, irregu-

lar a¡rcl abnorsrally branched.. (scaIe in cns). -o

1,. Plate 12a. Roots of stu-ntea (feft) healthy (right) "¡rd orrior plants collected in the fieId. i{ ',J 12b. Roots of stu¡ted. onion pla¡¡ts. ---o¡-,

a ¡

:àÉ------81.

0n1y two plarrt-parasj.tic nenatodes were observed in the soil samples co1lected.. P. minor occurred- in eight sanpì-ès and þ[)@s sp. in three. In addition, the roots of stunted. pla^nts in one fielct were found to contairr

fenales of root-knot nematode.

P. minor occurred. when onions r¡rere planted after the removal of vegetables, Iucerne antl horticultural crops srrch as vines, peaches or citrus.

It was generaÌly not present when onions ì^rere growri in st-ril wh.ich had, not

previously been Írrigated. but harl been used. on.Ly for grazíng or growing cereal crops. fn situations where P. minor occurred , plants were always stunted, while in its atrsence, plants uere generally ÌLealthy. Detailed

results of the su.rvey are presented. in Append.ix 2.

Discussion

The inport a¡rce of Pratylenchus sp. and Meloidomrne sp. to onions has been discussed. earl-ier (Section 2.6).

There are several reports in the l-iterature of stubby root nem¿¡.todes

da.uraging orrions. Hoff an

onions - a general stunting of the plant was coupled wj-th a dieback of bhe terninal portions of the Leaves and. a general yel.lowj.ng progressing down- warci from the leaf tips. The root system was small-; not only were the roots unusually short, but they were also abnornal-ly branched and, in most cases,

slightly swollen just above the root tip . P. christiei was found. to be present in the soil sunr¡und.ing affected plants, and its pathogenici.ty to

onions was demonetraled.

Jensen and Koniceck 1)62, and Jensen 1961, d.escribed a sinilar clisease of onions, with which anothe¡.'stubby root nema,tode sper:j-es, P. allius, lras associated.. Affected. plants exhibited. syrnptoms of stu¡ting and. top yeIlow-

ing which rlere more conspicuous in da"np cool r,¿eathe:: before onions began

rapid growth, and uere less noticeable as the season progressìed, Rool,s 82.

consisted of a few short remnants which had l-ost their normal- white colour,

turned yellowish and becqme narked. with d.ark brown tips and numerous loca- lized lesions. P. ¡ninor has never been known to demage onions. Howeverr its close association to plants showing synptons typical of stubby root nematod.es'

suggests that it may be invofved in the d.isease. This possibility is exanined more closely later in this section. OnIy twice during the survey d.id P. minor occurl in an area where fu- cerne, or a horticultural or vegetable cl?opr had not grown previously

(Append.ix 2). One of these infestatioì" (Stengert) was adjacent to a horticultural planting a¡rd received water fron its sprinkler system. The grower recaLled that a large quantity of couch grass (Cynod.on dactylon) had grorvri there the previous season. As this plant proved to be a host of P. minoi in a pot test, this nay have accounted for its occurrence in this situation. .I Ilowever, the occurrence of P. minor on land previously used. for grazingt ìil l,i but carrying its thircl successive crop, suggests that in future it may be-

come more wid.espread with increasing mrmber of years of irrigated onion monoculture.

1.5.2.2 PathogenicÍty of P. minor to onion A technique sinilar to that developed by Radeweld e! aI (1)6)) was

used. to test the pathogenicity of P. minor to onion. Sixteen 2JO nL

Ehrlenmeyer flasks were fil-Ied. with moist, stearn-steril-ized. sandy soil. A 1.5 cn dia.neter glass tube was placed in the flask and two-thirds filled. with soil. A¡ onion seed. (variety blhite Spanish) was added. to the tube,

a¡rd covered. with more sterilized soil. I I Nematodes were obtained. by elutriating soil from an onion field. 45O

; P. ninor were added to each of eight tubes, and the eíght remaining tubes served. as uninoculated, control-s. The flasks containing the tubes were maintained. at a temperature of 2O-28o for seventeen days, when the tubes were 81.

removedr the plants washed and the roots observed. Nematodes r¡rere extracted from the soil- in the tubes (approx. 15 g) by decanting and sieving.

Results

Roots of seed.lings inoculated. with P. mÍnor were 1O.Bl 4.6 nm l-ong,

while the roots of uninocul-ated. seedJ-ings were !8 .4 ! 17.2 nri long. photo-

graphs of some of these seed.lings are shown in Plate 11. ALT uninoculated. plants had. one 1ong, heatthy root, whereas the prinary root of inoculated

plants was stunted., and. frequently a second root was present. P. minor was reisolated. fron the soil in all inocul-ated. tubes in numbers ranging from 40 to 180 per tube. This is the first report of the pathogenicity of p. minor to onions.

).5.2.J Relationship between nunbers of P. minor and. plan' size

During October 1971 an onion grower at Sunlands complained that his

young onion seed.lings r^Iere growing poorly. The area had been sown to onions

in late August, following the removal of peach trees which had. grown there for many years. By late October, a large proportion of the onions in the area of approximately one hectare, r¡/ere yellow and stunted, d.espite efforts by the grol{er to improve their health using fungicides and nutrients. Roots were

stunted, and in mar\y cases were only '1 -2 cms long. A range of plants were carefully removed from the area, leaving the roots and. so1l intact. Because nany plants were smalÌ and grow-ing close

together, ch:mps of several pla.nts were removed in some cases. Nemato,Ces were extracted. fron the soit by the two fl-ask technique (seinhorst, 19|])) a¡rd. counted.

Following a request from another onion gro\¡Jer, a property at Llrup was visited d.uring November, 1971. The crop consisted of lar:ge, healthy plants interspersed. with patches of stunted onions with yellowing tips" Plate 1Ja. Onion seedlinge inoculated (rÍght) and not inoculatea (feft) with P. minor.

1tb. Onion seecllings inoculated with p. minor. q H tuc L 85.

Eight plants with synptons typical of the disease were selectedr along with eight apparently healthy plants. The pla^nts were removed carefullyr leaving roots and. soil intact. In the laboratory, 200 g samples of soil were elut- riatett using the two flask technique and. the nematodes in the samples were counted.

Results The soil fron both properties r,{as in-fested. with P. minor and in each case it was the only pla.nt-parasitic nematode present. A photograph of the onion pla,nts collected from the Sun1a¡rds property, together with the con- centration of P. ¡ninor aror¡¡d their res pective root systens (recorded as the number of P. ninor per 10 g soil) is shown in P1ate 14. The number of P. mínor in the soil surround. in8 thE4coots of both heal-thy and. stunted plants fron the Lyrup property can be seen in Table 15. In both casest [email protected] than on the roots of healthier plants.

îABrE 15

NI]MBERS OF P. MINOR IN TI{E SOII SURROUN¡ING

Ti]E ROOTS OF I]EALTIIY AND STUNTED ONION PLANTS

ON A PROPERTY AT IYRUP

Mean No. P. minor /ZOO s soil Healthy û6!fi8 Stu¡ted ß4 ! z5t

t "5.2.4 Neuraticid.e Application In late October, a trial was establishecl on the property at Sunlands to determine whether the application of a nematicide would improve the growth of onion seed.Iings already affected by P. ninor. As organophosphates a.re more effective than fumigants in controlling stubby root nematodes Plate 14. Nr:mber of p. minor per 10 g soil associated with

onion plants coll_ected from a property at Sr:¡Iands.

87.

(literature review)r a¡rd. DBCP is phytotoxic to onionsrthe nematicide chosen was phena.miphos. Thirty plots 4 n x 2 m were narked out in areas where plante were str:nted, and. phena.niphos, at a rate equivalenl' to 22.J L/rra, rrtas splayed on the surface of the soil in fifteen of the plots, using a knaqsack sprayer.

Thirty-three mm raÍn fell cluring the drening of the d.ay of applicationr and this should have adequately washed the chenical into the root zone.

On the day the nenaticide lras applied., and. then three and six weeks Iater, the plante in each plot were given a health rating according to the followÍng schene: 1, small stunted plants; 2, moderately stunted plants¡ 1, slightly stwrted pla.ntsi 4,, heal-thy plants. Unfortunatelyr the invasion of the trial area by weed.s, and the death of the grohlerr prevented further observations, a¡d. final record.s of yields and nematode numbers, from being taken"

Results The results (figure 11) indicated. that in those plots where phenaniphos had been applied, plant health appeared to have improved.. Six weeks after application, an improvement in health rating had been observed in al-I fifteen treated plots, whereas there was littl-e improvement in the fifteen r¡ntreated plots: An irnprovement of two rating points occurred in seven of the phena^niphos treated. plots, but in none of the untreated plots.

Discussion It is doubtful whether the improvenent in plant health resulting fron phena^uriphos application, would have resutted. in an economic return being obtained. for the treated onions. Pre-plant treatments with nenaticides are more likely to give ad.equate controf of the disease, as young seedlings would then be protected from root da.nage d.uring their first criticaf weeks of growth. As phena.miphos is largely biologically specific for nematodest Figure 11. Change in p1a.nt health rating of plots

treated a¡rd. not treated. with phena^miphos. TREATED TREATED 10 10 I I

6 6

t, t,

2 2 o 0 cD 0 +l c 0+1+2 0 +'l E o I UNTREATED UNTREATED o.h 10 10 .LOos 2S ;yo?tJJ I I CF O.= 6 6 ô-o T3 L t, 2=u 2 2

0 0+t+l 0 0 +'l +l

FIRST SAMPLE SECOND SAMPLE

Chonge in heolth roting (0t1 or *2 ). 89. this experiment d.oes reinforce the euggestion that a ncmatode ie largcly responsible for causing this disease in the field..

1.5.2.5 General Discussion I¡fhen attempting to establisn that a disease is caused by a parti-cul-ar nematode, it is often inpossible to adhere strictly to the laws of pathogenicity as d.etailed in Kochrs postulates. For exampì-e, it is difficult to obtain pu-re, sterile populations of nematod.es, and to maintain the growth nedium of a plant in a sterile condition for l-ong enough to show s¡mptoms.

However, enough evid.ence has been accumul-ated. d.r:ring this stud.y to suggest that P.minor is pathogenic to onions. Duringthesurveyofonionpropertie"'@wasfoundon}yin field.s where stunted. plants occulred. When ind.ivid.ual plants were studied in selected fieltls, higher numbers of P. minor were associated with d.iseased plants tha¡t were associated. with healthy plants. The disease was produced in onion seed.lings inoculated with P. minor and. the nematod.e was re-isolated from soil surround.ing strrnted roots. Improved plant growth resul-ted. fron the application of phena.niphos, a pesticid.e which is l-argely biologically specific for nematod.es. Oostenbrink (1956) suggested that distinct inprovement of plant growth in soil treated with a specific nematicide indicated that nematod.es were the chief cause of a d.isease. In addition, symptoms observed in the fielcÌ were similar to those caused by other stubby root nematode species known to be pathogenic to onions. In a field situation, poor growth of plants is rarely the result of one factor. Frequently rnore than one pathogen is involved, a¡rd environmental- factors are also very inportant. Consequently, it Ís unlikely that P. minor is the sole cause of the d.isease syndrome. There l¡ras some evidence to suggest that environ-mentaf factors in particular played, a Ìarge part in the expression of the disease. lVhen properties Ï¡ere first inspected during the survey, gÌowers were asked. why they thought particular patches were stunted-. 90.

They generally attributed. the stunting to causes such as moisture stress, poor nutrition, wind d"a¡rage, weed conpetition a¡rd. frrngus diseases. Although in narry cases there was little evidence to reinforce the growerrs opinions, factors such as these are undoubtedly invol-ved. in the d.isease synd.rome. A tletailect stucty of the disease would be necessary to determine, the relative [email protected].. The increasing areas of onions and tonatoes be.ing planted in the Riverland. probably nark the beginning of a large vegetabl-e ind.ustry in the

area. The cost of ta¡rd. near the cities is becomi-ng too expensive for agri- culturer aJtd the Riverla¡:cl has an id.eal climate, suitable soils and adequate water for vegetable growing. Because ad.d.itional- water is not avail-able to

irrigate new areas, ar\y expansion in vegetable plantings will be at the

expense of present plantings. Stubby root nematodes are inportant pathogens of a¡rnual crope àI""rrt""" (Cfrristie 1959, Brodie 1968). \4lith the widespread d.istribution of stubby root nenatodes in the Riverland, it would be sur- prislng ff fu¡ther probleme rìre not found on othe¡ vegertable or()ps tn bhe future.

,.5.2.6 A disease d.Ís tribution oattern followins peach trees Generalty, when P. minor vtas s,ssoclated wlth str¡nterl onlon plantot the stunted pla.nts were patchily tlistributed throughout the field'. Ilowever,

lnlti¿r1 observatlons made on the property a'b liunlande Ettrowed that t,he uhun- ted p1a^nts appeared to occur in a d.efinite pattern in that field. The foÌ- lowing observations were aimed at d.efining that pattern, and explaining its occuBence.

The onions on the property were planted. in bands one metre wider with a gap of O.l metres between bands. Each band consisLed of eight individual

rows of onlons (ntgure 12.). F'lve randomly selectad transects wÕre t¡ra,

across the field, and. 2 m x 1 n plots were deflned at the points where the transects met the onion band.s (figure 1Z). mre plants in those plots were 12 tayout of onion plants in the fiel-d'" TndeiieË Ö:Î Ï'igure " j''r pl-ant heal-tlr , and'ùhe position of' 'lhoeie ¡tlatil;': relatíon to the previ ous planting of peacir t:r'ees ' Meon plont Position of Tronsect.2. Tronsect.l heolth roting pro\riorls of row pcoch rows

7t7z 1.8 <- 1.0 1.0 1.6 ?t 2.6 1.3 1.3 1-5 3-0 .- 2.9 1.7

1.c 2-3 2-3 1-5 1.1 - 2.7 ac- r--t 3.1 Ql Çt 1.6

7z7z 1-2

I Rows of onions

Plot 2m ¡1m 91. independ.ently rated. by two people, according to the rating scheme used in Section 1.5.2.4. The average rating obtained. for the five plots in any one ba¡rd was used. as an index of the health of the plants in that band.

Results a¡rd Discussion

The indices of pla.nt health for each band. are recorded in Figure 12.

They showed that there was consj.derable variation in plant health between band.s, a.nd. that there was a recurring pattern of 2-i bands of stunted pla.nts followed by one or two bands of healthier plants. The only factor which appeared likely to be linked. to this pattern was the location of the peach trees which had. previously been planted in that field.. I'Ihen their position was plotted', it was for¡¡d. that the healthiest plants grew where peach rowe had been located, while the stunted plants grew in what had previously been inter-row spaces. Coneequently, the pattern observed. was probably a legacy fron the peach orchard.. It is possible that following the removal of the peach trees, there were differences in P. minor populations which accou¡ted d.irectly for the differences in the degree of stunting in the following onion crop. Alternatively, a less favourable soil environ- nent (perhaps in terms of soil fertility or soil structure) which decreased. the plantrs ability to withstand attack from P. minorr may have been left in the inter-row spaces.

1.6 Trichod.oms loxtoni (Nenatocta: Dorylainid.a) a net{ species

of stubby root nematode from South Australia Introduction After Wyss (1970) found that the Trichodorus spp. occurring in l{est

Gernany could. be arranged. into two groups, Sid.d.lqi (lgll) assigned all speciee in the genus to those groups. He proposed the new genus Paratri- cho<1orus for one group arrd placed. the other species in the redefined genus Trichodorus sensu stricto QC

The species described herein has characteristics of both Paratricho- d.oms and Trichodorus sensu stricto. The stud.y was based on specimens fixed. in hot F.A. {:t (Sei-nfrorstrl)66) and, processed to glycerin using the rrethod of Seinhorst ( 1959).

Dimensions

Mares (r = 7) (.1 = 0.64 mn (0.59 - o.67)i a = 25 (19 - 12);

b = 5.8 (5.4 - 6.4); onchiostyle = 40 , (la - 44); spicures i2 ¡¿ (zl - 16).

Fenales (n = 8) T, = 0.69 (0.61 - 0.78)i a = 26 (e - b)i b = 6.0 (f.1 - 6.9); v = 55 ( 52 - 58); onchiosty),e = J) p (17 - +z).

Description

Male: Bod.y elongate - cyIind.rical, tapering gradually at either end." Posterior part of body ventralJy arcuate when relaxed. Cuticle snooth, swollen when heat relaxed a¡rd after fixing with F.A. Posterio¡' subventral oesophageal glands overlapping anterior end of intestirie.

Dorsal oesophageal gla^nd. nucleus near begiruring of oesophageal enlarge- ment. One ventromedia¡r papilla just posterior to the onchiostyle base, and the excretory pore one body wid.th posteri-or to this. Three ventromedia¡r supplementary papiJ-Iae present at the tail end.; the first within the spicule length, the second just a¡rterior to the end. of the spÍcu1es, and. the third. one bod.y width a¡rterior to the second.. Paired. post-anal ventro sub- nedian papillae present. Caudal porec alrnost terninaÌ. Spicules slightly curved. and irregularly taperi.ng, with transverse striations. The onchio- sty1e, a^mphids a¡rd. testis are typical for the genus. ,17 .

Fenale: General appearance as for nafe. Ventro-mediarr portion of oesophage base overlapping anterior end of intestjne. Excretory pore near the mid poi: of the oesophagus. Vulva a snall inconspicuous longitudinal slit. Two later, aI pores, not exactly opposite, situated slfghtly posterior to the vulva.

TVpe habitat: Soil aror¡¡rd. the roots of citrus , Section No. 538, Loxton frr gation Area, Loxton, South Australia. Specimens have also been found. near peach roots in the sa¡ne area.

Diagnosis

As the nematode described above h¿¿s characteristics of both -Paratri- chod<¡rls a¡rd TrÍchodorus sensu stricto, either the characters used to differentiate then need revision, or the genera shoul-d be recombined into one genus. Characters which suggeet that the nematod.e belongs to Paratri.cho- donrg includ.e the abno::na1 swelling of the cuticle when hea,t relaned. or fixecl in acid fixatíves, the posterior subventral glands overlapping the intestine, the inconspicuous vagina less tha¡r hal-f bod.y wid.th long, the position of the dorsal-oesophageal gland nucleus near the beginning of the oesophageal enl-argenent a¡rd. the presence of only one ventroned.ian cervical papilla. Howevet, the following characters are typical of Trichod.oms sensu stricto - the posterior part of the nale ventrally arcuate when relanred, lateral body pores within one body width of vulva, bursa absent, three almost equally spaced. prea.nal ventromedian supplementary papillae present, two of which a¡e not grouped. in the spicule region or clearly separated fron the third., a¡¡d a¡cuate irregularly tapering spicules. Siddiqi (1973) suggested. that the bursa and supplements of the ma.le were rel.iable characters, ancl that females could. be cha¡acterized by the presenoe of a pair of lateral body pores near the vrlva, a.nd. so this species has tentativeJ-y been assigned. to the genus Trichod.orus sensu stricto. Figure 1J. ÍIrichodoms loxtoni fi. sp"

A. Fen¿Ie B. Head end of fenale

C.. Head end. of nale D. Ventral view of rnrlva E. Vulval region F" Cross sectÍon of n¿le tail

G. TaIe end. of male A B

l l¡¡ - ã^t , gcoere.

E 0 0

E I I ll. t

il, I il, I t; il; i 95.

4. ACI0I0\,/IEDGEùIENTS r wish to tha¡¡k all the frrritgrowers a,¡:d. ilLrserymen who arl-owed me to collect samples from thej-r properties, and particularly Mr. B. staker for his help a¡rd interest in the work d.one at his nurseï.y. Thanks are also due to Dr' R'c' corbra¡r fo¡ confirmation of ny identification of p. Ìobatus a^nd P., nirro"; to Dr. J.M. Fj.eher and professo¡ H.R. wallace for thejr supervi- sion; to Miss S. Cha.nbers, Irlrs. P. lr/oods and. lir. T.,. Hancock for the statis- ticar analyses; Miss P. ÏJest, Miss lvl. Dowley a¡rd lfrs. B. Auricht for typing this thesis; and ¡tr. M. spurling, Mr. R. ,¡iebber and Dr. R. van versen for allowing me to conplete the thesis while r was enployed by the south Aust- ralian Departnent of Agriculture. The 1aboratory and fie1d. assistance of Mr. c. l,/ilnshurst gratefutry is aclmowredged. FÍnalry, r a,n grateful for the hel-p a¡rd encoura8enent given by ny wife Marcerle d.uring the course of this project. 96.

5. APPENDICES

Appentlix 1 The following tables set orrt the d.ata collected during the eurvey of nu¡series (Section 2.4).

The following abbreviations are rrsed..

1. Nursery and Sa;nple No.

Each nursery rrra.s given a code letter (A to S). If sa^npIes Ìrere collected. fron d.ifferent areas within each nurseryt these sa,mples were designaleð- 112, 1.... etc"

2. Region The region in which each nursery occurred. was abbreviated as follows: R Riverland.

B Barossa 'S Southern Districts a¡rtt HÍtIs.

1. Soil Type frJ rf I Three soil texture categories sere used:

S - sand.s

L san¿Iy loams a¡rd l-oa,ns C - san¿ly clays antl light cIays.

4. Soil- History Soil in each nu¡sery area was categorized. according to itrs previous history. V Virgin soil N P¡eviously used for nulsery 0 Previously used for other horticul-turaI crops.

Ne¡natodes T 5"

+ Present in low numbers

++ Present in higher numberg (greater than

1OO per 500 e soil) I J Nursery a,nct Sanple No.. Ð=rdÞËÏ Þ{ '=d È4 Þ IF a)tÉ'da)tdtdtdtdÐÐ Region

È:{ È:{ ÈJ u) a u) u) cn @ a) Soil Ty¡re zzzzzzo< soil Eistory

++ Pa¡atrichod.orrrs lobatus

+ +++ + + trlchodonrs nrnor

+ + + + +

+ ?ratylenchus çoffeae

+ Èatylenchus ¡rlrnJrus

+ + Paratylenchus sB.

++ @sp.

+ Xipùrinena sp.

.\¡\f) a ¡\) a td c{ Þ Þ Èd H H U tJ trl 6) 6) c) Q () (l JN)JlUJf\)JN)Jå\r{ fUJ Nursery a^ntl Sa,mple No. (2 P. <+ FJ F V)

F Ed Ð fú F !d Ð :d Ð fd :ú ã Ð Ð :d fd Region u u) a) a an a u) o) tn a a) cn a) a ta (t Soil ffire zzzzzzzzz< Soil Eistory

++ + Paratrichoclo:nrs minor

++ ++++ ++ + + + ++++ Faratrichod.orus lobatus

+++ hatylenchus nrriJrus

+ Tylenchorhynchus sp.

\o @ v p P E :É c{ Ê{ c{ Þ{ Þ Þ U t'd trl Mrrsery $¡np1e Noo N)J\).|¡\)JN)J ".n¿ ls IrÍ

a u) v) F td td td td Ð Ð td tú Fd Region

(2 C) C) b{ rn Cn U) Cn (n a) (n u) a) Soil 1}pe

Soil Histor¡r

++ + + ++ + + ++ Paratrichodonrs minor

+ + + + + + + Paratrichoilonrs lcbatus

+ + Paratylenchus sP.

\o \o C È lÞ ßES fu: x Þ ß f hÉ Nursery Sanp1e No. b "tt¿ I t-J li aa)ubdtdtdtdFËÐFd Region

c)(?v)a(na)v)ú)a)a) Soil T¡re

Soil History

++ + + ++ + + + Paratrichod.orus minor

++ + ++ + + Pa¡atrichod.orus f obatus

oJ a \tr a E(n IdFÐ c-{XÞEl Nursery and Sa,nple No. v.¡ f\) r Þ ts oE Þ Ê, U)U)U)U)|tntdTd|¡Ð Region

(> ()Huh{(nu)a)u) Soil Type z< Soil Eistory

+++ + ParatrLohodorus minor +

+ + + + Paratrichodorus lobatus

+ + + + + + Þatylenchus ûÌrnrus

+ { + + Tbrlenchorhlmchus sp.

@-ã >7-^)- <-rFUI + + + F¡atylenchus coffeae + + -t c---l

+ + Paratylenchus sF. o J o o\ o hÉ c{ Þ{ .ÐFdZo Nu:rsery and Sanple No.

tH. ql Ð td Èd aa)u)ct o Region o F ts a) a) a2 c)<)F{F B Soil Ty¡re o o É Zo zzz< Soil EistorT @

o E E ÞÞÞb. P ts H F. EE E E Ho.êt o E É ooooHHts.FJ

+ + Xiphinena sp.

+ hatylenchus coffeae

+ Helicotyle¡¡.chus sP. +

+ + Paratrichod.orus mr-nor

+ + + Paratrichod.orus lobatus

+ +

+ lYlenchorhynchus Sp.

+ + Paratylenchus sP. o N) APPEI{DTX 2

DATA COLLECTED DIIRING A FIELD SIIR\¡:EY OF ONIONS

GROIII{ ALONG TEE RIYER MURRAY IN SOTTE ATSTRAIIA

ocToBER - DECm,IBER 197'

GROI|IER.S NÁIYIE PREVIOUS CROPPTNG OBSERVATIONS ON TEE NÐ,IATODES PRESENT Ar\D AND DISTRICT HISIORY OF SOII I{EAITH OF ONIONS A-PPROXIMATE POPIIIATION Grazing BASTALEC -7t Healthy plants, although slightly (rite River) 1971 - 72 Onions yellow near sprinklers clue to 1972 - 7J Onions leaching of nitrogen from the 1971 - 74 0nioas soil.

MARTTNKO -68 GrazLng (eite River) 1968 - T1 Irrigated. Areas of stunted plalts. Pratylenchus sP. tegetables Roots with snall swellings and, Meloidogrne females 1971 - 72 Tonatoes proliferatÍon of roots neax present in svollen 1972 - 71 Onions swellings, particularly at root roots. 19i1 - 74 Onions tips.

G. DICERsO - 71 Grazing (eite River) Generally healthy. Sone stu¡ted 1971 - 72 0nicns areas d.ue to weed. competition. 1972 - 71 Onions 1971 - 74 Onions

O a G. DICERBO - 71 Gtazíng (rite River) 1971 - T2 Onions Eealthy pla.nts 1972 - 71 Onions 1973 - 74

FO CIIRTIS - 71 Grazing (ri.te River) 1971 - 72 0nions Healthy plants Pratylenchus sP" 1972 - 71 Onions 1971 - 74 Onions

F. CURTIS 1961 - 71 Lucen:e (rite River) 1971 - 72 Onions Healthy plants Pratylenchus sp. 1972 - 7J Onions 1971 - 74 Onions

S. MARKS - 72 Grazing (n:rnong \ lJand]-ng) 1972 - T1 Onions Hea1th.y plants 1971 - 74 Onions

B" SI{-IM -72 Grazing (Bow nil1) cereals 1972 - 7t Onions Eealthy plants 197i - 74 Onions

J '+$-o GRAZZIA}TO -72 Gra,zing,, (Bow ttil1) cereals 1972 - 71 Onions Sone leaf tip cta,nage d.ue to 1971 - T4 Onions wind.. Roots healthy

GRAZZIANO -71 Grazíng, (Bow ni1l) cereals Sone leaf tip cla.ma6e due to wincl. 1971 - 74 Onions Roots healthy

G. MARKS -7t Grazing, pla.nts P, ninor (eurnong cereals Genera1ly healtlty " Landing) 1971 - 72 Onions Soqe stunted plants with thick- (1-2 per 10 g soil ) 1972 - 7t Onions ened roots a¡rd nunerous lateral 1971 - 74 0nions bra¡rches.

B. POPE -71 Grazíng (Swa^n Reach) 1971 - 74 Onions Eealthy plants

B. POPE - 71 Peaches Severely stunted. young (srr^rr Reach) P. mi¡or 1971 - 74 Onions plants. Stu¡t,ed- roots. TìãPeï 10 g soil)

B. POPE - 7t Citrus (swan Reach) Patches of severely stunted P. minor 197J - 74 Onions yourg pJ.ants. (9-lg per 10 g soil )

J G J. EA}Ire - Tt Lucerne (werri.ngton) Patches of severely str:nted young p. mÍ¡.or 1971 - 74 Onions plants. (2-1 pér10 s soil)

A. STENGERT - 69 Grazing (Waticer Flat) 1968 - 69 Onions Eealthy crop except for a patch 1969 - 7o Gtazi:ng of severely str:ntetl pla.nts. P. minor 1970 - 71 Onions Soil taken from arou¡d etunted 1971 - 71 Grazing pla.nts. (¡e - 111 per 10 g 1971 - 74 Onions soil)

M. PII'IVIAN 1964 - 71 onions a¡rtl ( qraaf co) Potatoes Str¡¡ted plants with ye11ov leaf D 1971 - 72 Tomatoes tips. Roots stunted., thickened +. m]-nor 1972 - 7t Tom, toes a¡rd abnornally branched. 1971 - 74 Onions (Zg - J1 per 10 g soil

J EI]DSON - 75 Peaches ( SunJ-ands) Severely stunted. young plants. P. minor 1971 - 74 Cnions. \6-2tO per 10 g soil )

G. DICEnSO Vines Patches stu-nteci plants /- _ - - . \ -70 of with (rðrrup Herghts) 19To - 71 Onions dying leaf tips. Roots branched., P. minor 1971 - 72 Onions with swollen tips. SoiI tended (-lz-qg per 10 g soi].) 1972 - 71 NiI to cling to roots. 1971 - 74 0nions

oJ o\ a 107 "

6" BrBrrocRAPIry

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