Seeddransrnitted p sts ana diseases of legumes. f fi rice-based cropping systems B. K. VARMA and C. J. LANGERAK

The paper gives an overview of the Kedborne pests and diseases of soybean. cowpea. g m n gram. chickpea. pigconpen. and peanut. which can all be used i n rotation with rice. Insect pests. nematodes. and diseases of common occumnce. potentially important ones that can occilsionully become serious. and those that cause great economic losses are listed. The distribution of pests and diseases i s also given. along with the rote of seed transmission of important virus diseases and data on crop losses. Safeguards arc discussed to . check . 'the spread orpests and diseases that can be introduced through exchange of legume seedq. thus countering any benefit likely to be derived from a legume - rice rotation.

Legumes form a very important component of a rice-baud cropping pattern in the potentially most productive farming system in the tropics. The important grain legume crops used in rotation with rice are soybean (Glvcine max [L.] Merr.). cowpea ( Vigna unipuiculara [L.] Walp.), green gram ( Virqnu racliara (L.] Wilczek), chickpea (Cicer arielinum L.). pigeonpea (Cujanus cajun [I,.] Millsp.), and peanut ( A rachis hypogaea L.). Dovetailing these crops with rice has great potential. as evident from the cropping systems research results at the International Rice Research Institute (IRRI) ( I RRI 1983).

The spread of some of the economically important crop pests and diseases is linked with the movement of seeds, which act as their carriers within a country and across national frontiers. &cause 90% of all food crops grown in the world are propagated through seed (Neergaard 1979). it is essential for us to know which pests and diseases are likely to be transmitted through the seed, and their world distribution, so that appropriate plant quarantine measures can be taken.

The seeds of legume crops are important carriers of insect pests, fungi, bacteria, and viruses. Together or singly, some of the pests and pathogens constitute aserious threat to the cultivation of legume crops and therefore will affect the use of legumes in a rimbased cropping system. Exotic pests and diseases present a greater hazard than local pests and pathogens to crop breeding and plant introduction programs.

lnlernational Crops Research Institute for the Semi-Arid Tropla (ICRISAT). ICRISAT Palancheru P 0.502 324, Andhra Pradcsh, India; Government Seed Testing Statlon. Binnenhavcn I, Postbus 9104, 6700 HE Wageningen. Netherlands.

SFED-rRASSUIl'rF0 PFSTS hND IZISE4SES OF I E(i1:WFS 191 In RICE SCEL) HFAI-TH

This p a p r deals with the major seedborne pests and diseases of legume crops that can be used in rotation with rice. their distribution. economic imponance. and control.

01. thc insect pests that attack legumes. beetles beiong~ng to the family Bruchidae arc important. Bruchids are essentially storage pests, but inlestation by some .peein starts in the field when acrop is nearing maturity. The :idults do not damage the seed. T l r y lay eggs singly on the seed surIace. The epps are \ ibihlc to the naked eye. and tht larvae bore inside the cotyledons on hatching. ' r l~r Iarviic are internal feeders: theil damage to the cotyledons and sometimes to the cmhrvo cclnstitutcs a wiou! germination pl.oblem in addition to creating rtoraije lor:cs. Tllr import;;nt \pecie! recorded as dillnagin& and breeding on dry seed are in Ta'hlc I.

In pulses. ('ulk~sobruc~hus t?tut~~iIurus and <'. t~itittrtr.\r.r arc [he most cc)tnmor and Jcbtruai\.e pests ol' dried seed in :lsia. The t \ ~ o \p;.cic. att;r~i. morc than I d

.:conomicall!. importilnt Legunle \eeds &c,rld\c~Jc. ('. ;:/rrr.\t5c~ii ~j 4 rel;\ti\c!y 12s:

known 5prcies as Inr us economic damage ib ~unccrncd. hut Southyate 11978 cc,nsider\ it adotninant species in tropical South ;\nlrric;.. in India. C: uttuli\ prefer to attach green gram. although it occurs in associut:~,n \vith C'. rhirlc*trsi,. C rltot1.siutlir.r is an important storage pest of cowpra in A1ric;r. and its spread heyonc that continent would be serious. Pigconpea is attacked b! the largest number a hruchids. C. t l~~'ohro~nue and C', tlolic.ltosi are conlined to the Indian subcontinen1

Table I. Important insect pests recorded on some legume seeds arid theu distribution.

Crop Insect spec~es D~stribut~on

. . - . gcen gram, soybean C mucularus

('o\vpca, pigeonpea. peen gram Gllosoi~ruchrts plfa~~'f)lf. !.la. \ t r~ca, Europr. I:SSk Phikp*)ines. West Indrcs

Co wpea

Pigeonpea

C. analb R K I L ; ~ . ,Asia. Africa, Europ ,\usrralia. Indonca~. Japa t-lung Song, SldavsL. Philippmeb

C rhodesicrnus \Vest .\irica, Sipern. Uganda, Kenya, Tiuuani South Africa

r.,, ,. Bntchidius atrolineartrs . .\let.

Speclrlaris en.tlrrants Kcnya C. theobromae India. 3ri Lank? C dolicltosi Indh. Burma Acanthoscelides :r.ceA-i Cuibhcan I s W s , Ccnu

and South America Specul&s sulcaricollis Kenya S erytlrmeus Nigeria. Kenya

Peanut Gryedon serratus ~sh. Africa. Middle Ea Isracl. Slexico, South America. West Indies, Taiwan. Thsiinnd

but the extent of their damage is not well known. However. infestation with .4 ~u,,rho.~celi(Ie.r :ereki has been recorded to mmh JOPr in storage f Sout hgate !Q79) in the Caribbean Islands. tvhile Spt~c~~t1ari.v .sull~uric~ollis and S. c*r~.//rrue~rs arc . ~ , e r k n ~ ~ n species. but their iisslxiation with piponpea seeds cannot be ~ynored.

C'ur~.rclot~ .~erruricv is it major pest of stored peanut. causing cor~\iderahlc damage to undecnrticated and deconicnted nuts. Unlike other hruchids. \vhich infest ,tored legumes. the full-grown grub leaves the seed or pod aitcr cutting on exit hole ;trlcl pupates outside in ii paper! cocoon. Other insects msociuted with peanut Lcrnels are Triholitun t u.vrancic~)r. O r r ~ ~ u ~ ~ ~ ~ h i i t c s suritrm~rett.\i,s. 0. ttrer(-uior, l:plrtasriu r~u~rrullu. and C'c)rc:t.ru ~~cplrulo~ti~~u. They arc cosmopolitan ~ n d are p here fore not conridered bcrious quarantine hazards. They may. howcver. carry

seedbornc lirngi (Mqumder ct al 1973) that coilld he dangerom.

. . S~tdborne nematodcs ;ire \,cry rare in legume seeds. Jl~erc are only ruo spccrc5 of' nc:~tatodes -- the lesion nernattdc I Pru~~~1~1r~~lrtr.s brut-/i,r.i/rrr.vl iind thc rcst;~ ncmatode r i~~i r r l (~ t ic . /~or~/~*~ cirutlrit1i.j) - recordkd on peanut pods or sceds from ,\ustralia. \Inca. Egypt. USA, and C'igcria. and one species -the so.h;in cyst r l~rna tod~

I l ic~rrn)ti~~r~r ,yi~.c~itlt*.~; - on soy bean seeds fionl Egypt. USA. and l a p w . The lesion nematode is a major pest 01' peanucin the USA. I t is thund in thc

roots. pegs. and shells of mature pods hut has never been reported in the seeds. Hundreds of nematodcs may he prcscnt in each dark-chlored necrotic lesion on the bhclls. Their imponance is heightened by their association with Sl~lt~roriun~ rolfiii. the fungus responsible for peg rot (Minton 1984).

The testa nematode is a facultative endoparasite that is present in numbers up tn 25.000 uithin the tissue of the shell or seed testa. Its presence predisposes the seed to ~nvabion by soil fungi (Table 21.'

Seeds of soyhean carry cysts of the sovhctan cyst nematode, either Ioosc or n):ked w ~ t h \oil. The losses caused by H. ~11.r~inc~s have not . e t been quanttt'icd '7111

mi:! he signilicant (, Epps 1969).

I t I \ consicieled safer to uhe seeds than vegetative plant propitgules to transier plant n~atrrial ( Asia and Pacific Plant Protecrion Commission 1980. Phatak 198 I ). \escnhrlcss. there are many seedborne diseases. pilnicularly viruses. in legumes. xlme i>f tvllich are classified as dangerous to the crops. The mqior seedborne diseases i t ! icqume crops are given in Tables 2-5.

soy bean hoyhean seeds are associated with many fungal pathogens (Table 4), which krerioratr seeds and impair their viability. Heavy infections of ,tern cankcr I)rclporrlrr ~ ~ h u s t ~ o l o r u n ~ var. burururts) have resulted it1 considerable yield losses in

[ ' ~ n a d a ( Wallcn and Seaman 1962). Dunleavy ( 1956) reported a 654 licld incidence

112 RICE SEED HEALTH SEED-TRANSMITTED PESTS AND DISEASES OF LEGUMES 1-

Tabb 2. Smd-maanitted coilborne t u r n Aiuv d come imporM Irgtislsr

FvrPrlum app. Root rot F. oolani Collu rot F. cquuetf Wilt F: semitecmm Wilt F. oxyrpomm f. ap. Wilt

tmcheiphtlum

F. oxyrporum f. sp. Wilt ckefi

E oxyaponrm Wilt f. so. udum

Gm Vu, Vr, Ca Vu, Vr Vu, Vr, Cc Gm

Worldwide Worldwide Worldwide Worldwide USA, Europe. India

USA. Brazil, Afrta, Malaysia. Thrilmd, Australia. India Ah, Africa. Mexico, Middk East, USA, South America Asia. Africa, Mauritius. Trinidad

(=k udum) Macrophomina Ashy stem blight. charcoal rot, Cm, Vu, Vr, Ah Worldwide

phas&lina redling rot Pythium aphani Seed decay, seedling Vu Nigeria, Tanmir,

dcrmatum mortality, stem rot Brazil Rhizoctonia Dry root rot C1 Asia, Australia.

bataticola Ethiopia. Middle East, USA, Turkey

Cc India, J d c a R solani Damping off, foot a d bur l Gm, Vr, Ah Worldwide

atem rot Web blight Vu, Cm Worldwide

Sclcrotium rolfsii Stem rot Cm. Vu. Ah Worldwide Myrothcctum Collar rot Vr India

mridum Sclemrinirr Stem rot Gm. Ca Worldwide

sclcmriorum

' ~ r n = Glycine -, Vu = V&na uryrlculata. Vr = V&na mdIatq Ca a Cicer arierlnum, Cc = Cdanus cdan, Ah = Arachis hypogaea

of pod and stem blight (D. phaseolorum var. sojue) in Iowa, USA. In Brazil, the latter pathogen has also rendered sensitive cultivars unsuitable for cultivation (Bolkan et a1 1976). Among the foliar diseases, frog eye leafspot (Cercosporasijjino) and brown spot (Seproria glycines) have caused I5 and 179% crop losse~, respectively, in the USA; and web blight (Rhizoclonia solani) produced 80% crop infection in China (Allen 1983. Williams and Nyvall 1980).

Bacterial blight caused by Pseudomonar syri&ae pv. glycinea inhibited germination of soybean seed by 68% in the USA (Sinclsir 1975); similar results wen obtained in India (Nicholson et a1 1973). In the USA, this disease caused great monetary loss in Iowa (Kennedy and Alcorn 1980), but thecrop loss due to bacterial pustule caused by Xanrhomonat cumpesrris was 1% (Lavioktte a a1 1970). According to Watson (1970). P. syringae pv. glycinea was introduced into New Zealand through infected seed.

Of the viruses, soybean mosaic virus (SMV) is the most serious and widespread. It has reduced yield by 9-2046 in Bulgaria(Bov and Boyadzhiev 1977) and by 20% in

IW RICE SEED HEALTH SEED-TRANSMMED PESTS AND OISEASES OF LEGUMES IW

Table 4. !id-uuumittd fungal a d bacterial di#rsr of soyban with 8 waridwide db bution.

Seed Pathogen Diseam transmiuion Reference

(%I

Diopnrrhe phaseolorum var. baratatrs

D. phaseolorurn var. soioc (con. st. Photnopsrs)

Pcronospora matrslrrrrrca Aeudomonas syrinqae pv .

glycinea Xanrhomotros curtrpestrrs

pv. glj,cines

Purple blotch. purple spcdr. PUQ~C .Wed ~Uln Seedling blight. 1581 Vcrma and Upadh) anthracnose (1973) Stem canker. pod and stem blight Pod and stem blight 20 Wilcox a d Abney

(1971) Downy mildew Bacterial blight 3-64 Nicholson and Sinc

(1971) Bacterial pustule

the USA (Ross 1977). and germination by 12-36% in India(Sutheri 1981). Thevi., predisposes seed to infection by Phomopsis sojae (Hepperly et a1 1979). Tobam ring spot virus (TRSV) impairs seed viability and may also reduce yield by W (Crittenden ct al 1966). the crop loss depending on the percentage of incidence i seed (Allen 1983). TRSV also infects green gram (Allen 1983, Shivanathan 1979 Cowpea mild mottle virus (CMMV), although a minor disease in cowpea has be found serious in soybean in Thailand (Brunt and Phillips 1978) and the Ivory Coa (Thouvenel et a1 1982). and it appears to be of considerable importance in tropic soybean.

Cowpea Ascochyta leaf spot t Ast.ot.hyra yhaseolorum) is potentially the most destructi disease of cowpea in Africa, causing severe losses in cooler regions (Williams 197r In Nigeria. a 7 5 4 crop loss du? to R. sol&; and P)rhium aphanirertnaruum se infection, a 35-5Wc yield loss due to anthracnose (Collerorrichum lindemuthianun and seedling mortality due to wilt ( Fuurium oxysporum f. sp. tracheiphilur were reported (Allen 1983. Singh and Allen 1980). Wilt was responsible for 7! mortality in India ( Singh and Sinha 1955). Emechebe and McDonald (1979) a Emechebe ( 198 1 ) also reported serious cowpea diseases in Nigeria caused by capsici, C.. rrunr~urrmr, and .Macrophomina phareuIiny.

In India. bacterial blight of cowpea caused by .Yanthomonas vignicola u responsible for considerable seedling mortality, and 62% disease incidena v ohserved with an initial seed inoculum of only 1% (Shehawat and Patel 1977).

There are more than 16 seedborne viruses of cowpea, some of which have hi transmission rates and cause more than 50% yield loss in the fkld. Cowpea aph borne mosaic virus (CAMV) was nsponsibk for complete loss of the crop in Nigc in 1973 (Raheja and Leleji 1974). Other serious. internationally important vi diseases in tropical .America. East Africa and West Africa mported by Alkn (19

Tabla 5. bprtant rssd-hnmhd f o b fwgd and bactarhl dlarsl d mum lqu-

Pathoeen Dimasus Distribution

Soybean Cercuspom soiina Frog eye leaf spot Asu. Guatema4 Venuueln.

Brazil. USA. Canada, Cameroul~.

Ascochyta phaseolorum Col/erotrichutn capsici a d

C ttuncatum C lindemurhbnum ,Yonthornonas campesrris pv.

viqnicola

C capsici, C. tritncatum . Etsinoe pl~aseoli Pseirdomonos syringae pv. phasmlicola znthomonas campesrris pv. ?Iiaseoli (fuscans)

E ~ o p c , USSR. ~us t ra l i . Brown spot Widespread

Co wpra Led spot Brown blotch

Anthracnose Bacterial blight, bacterial canker

. . ' . Green gram . Anthracnose Scab Halo blight

Fuscous blight

Chickpro Blight

?rr.vtts cinerea Grey mold

PLpconpea 10m0 sp. Stem canker lotnopsis sp. Seedlim rot ?tryodiplodio rheobromm Scidling rot ~llerotrichunr cajani Anthracnose

Centtal and South Africa, .\sir Nigeriu

Africa, India, Brazil USA. Pucrto Hico, Brazil. India. Africa

India Amer~cr. Zirnhnhwe. Braxil USA, Europe

,. North Africa. West Asia. . Austrnlh. Canada, Mcnico. I luro~c, Middle East, Turkc), 'USSR Ar&rntula. Colombia. Canada. USA, Sps111. Asia, Australia

Puerto Kicu. T rinidad Pucrtc) R ico Puerto Rico Pucfto Kico. ffawuu, Indid. Brilai

~trtlromonas cajani Bacterial leaf blight I I I ~ I : ~ . " : l r~~~na . Sudan

Peorrur eudomonas sohnaceomm Bacterial wilt Inr!rmesia. . I t r i a . Japan. 1'5,t

e cowpea severe mosaic virus (CSMV). cpwpea yellow mosalc LIrus (CY MV j. and lwpea mottle virus (CMV), which have caused yield lowe.; t ~ p to %mi. Y S ( ; i . i~nd 1%. respectively. In India, the field incidence of cowpea handing mosaic viruh 'BM V) and cowpea chlorotic spot (CCS) varied from 13 t o OZN;. which rcdu~rd e yield up to 41.8% (Sharma and Varma 1975). while 111 L~gcriir. CCS L . ~ I U \ C ~ a 1% loss (Singh and Allen 1980). More than one virus may txcur in cowpea. A ixture of cucumber mosaic virus and blackeye cowpea mosaic virus lead5 to nergism ( Pio-Ribeiro et a1 1978) and to consequent stunting and sewre crop lass.

r w n gnm rdborne pathogens encountend on g m n gram (Table 2. 5 ) arc responsible for eemergence and postemergence disc- leslllinp to loss ~t . t ar~ l . 'The hactcrinl

1% RICE SEED HEALTH SEEDTRANSMIlTED PESTS AND DISEASES OF LEGUMES m

halo blight diseasc caused by Pseudomonasphaseolicola spreads very rapidly and i widely distributed on beans (PhaFeolus vulgaris) in temperate regions of the world A mungbean strain of P. phaseolico&introduccd with seed in Ohio, USA, caused ; 60% yield reduction (Schmitthenner et al 1971). &cause halo blight disease ca~ initiate epidemics at a very low level (0.01%) of seed contamination in French bea (Taylor and Dudley 1977) and is transmissible through green gram seed, it can b characterized as a very dangerous pathogen of gnat quarantine significana Another important disease of green gram is bean common mosaic virus (BCMY which reduced yields by 31-75% in Iran (Kaiser and Mossahebi 1974).

Chickpea Ascochyta blight (Ascochyra rahiei) and wilt I Fusurium o.crysporum f. sp. cicerl) ar,, two major seedborne diseases of chickpea. A. rahiei has been responsible for severe epidemics in Pakistan, Bulgaria, USSR. and Greece (Nene 1982). the extent of crop loss varying between 20 and 10092,; it cauhed a w e r e epidemic in the chickpeacrop in Canada in 1973. where the pathogen wa4 ~ntroduced through imported seed (Morrall and McKenzi 1974). Chickpea wilt causcd a 10% crop loss in Uttar Pradesh. lndia (Mathur et a1 1960). while Ha~kare and Nene (1980) found a 24-9496 yield loss depending on the crop growth ctagc during attack.

Pigeonpea Pigeonpea wilt (Ftrsarium udum) is the most destructive seedborne disease of pigeonpea in lndia and East Africa. Continuous cropping in the same field may lead to 50% or more plant mortality due to wilt (Sen Gupta ,1974). Rhi:orronia bararicolr in lndia and Phbma s$., ~hhnto~.;.iA sp.. @rr~-odiplodio theohromae. and Fusarium semirectum in Puerto Rico and the Caribbean Islands are seriou pathogens of pigeonpea that affect germination in the field. Pigeonpea anthracnose (Collerotric~hum cajani) is a common disease in Pueno Rko, and as early as 1921 Tucker reported a 36% loss in yield from 87'; infected pods.

Peanut Peanut seeds are affected by several importint diseases. Ashworth et al (19611 reported extensive damage by seedborne Scleroriunt rolfsii and R. solani; thc former was responsible 'for lo%, diseased pods in the infected plants. and the lattel reduced seedling emergence by 30% and yield by 259; in the USA.

Of the virus diseases, peanut mottle virus (PMV) is the most widely distribute( . and serious seedborne peanut virus in the wor!d. In some areas, 7 5 - % % ~ of the croI can be infected (Paguio and Kuhn 1973). causing a yield loss as high as 30% (Kuh! and Demski 1975). In Georgia. USA. a 54% economic loss was estimated from 269 infected plants in I yr (Kuhn and Demski 1984)--calculated at USS11 million ir 1973 (Smith 1980). PMV can also be transmitted to soybean (Demski 1975) througl an infected peanut crop. Peanut clump virus (PCV) has been observed to redua yield by WO in India(Nolt and Reddy 1984), and marginal chlorosis(MCV) by 509 in New Guinea (Van Velscn 1961). Peanut stunt virus (PSV) has a very low sm transmission rate (0.2%). but 7080% crop losses might occur in the USA (Culp am

Troutman 1967). and the disease could be q serious threat to peanut production. A newly reported peanut stripe virus (PStV) may cat& yield losses up to 23% in the early stages of infection (Dernski et-a1 1984a, Dcmski and Lovell 1985). The virus was isolated from peanut germplasm lines introduced into the USA from China (Demski et al 1984b). The crop losses caused by various peanut viruses cannot be correlated with A e infection rate in seed: PSV. with a very low rate of seed transmission. o n cause heavy crop losses, but PStV, with high seed incidence. may cause relatively less damage.

Insect pests of legumes do not pose a large hazard if seed is fumigated. The danger could come from the spread o i economically important species. such as Cu1losohruc~hu.s rhollesianus from Africa and Cirrjrdon serrurus from the Indian subcontinent. to new areas. However. detection of latent infcstation of bruchids inside the seeds by X-ray, iei.kniques. and fumigation with methyl bromide at 32 g/m3 for 4 h under vacuum can control the pests effectively (Varma 1985). Fumigation may not be effective f& the control of peanut and soybean nematode5 without endangering seed viability. Instead. importation of peanut os kernels rather than pods. and selection of healthy, mature, clcan seed from nematode-free areas would assist efforts to prevent the spread of these pests.

Seedborne diseases are more refractory than pe'sts. Soybean viruses CMMV and TRSV. and bacterial pustule are restricted in distribution. and their dissemina- tion could be checked through-. strict regulatory measures. As an additional safeguard. a growing-on test of imported seed in an insect-proof scmnhouse could be followed whenever necessary.

The role of seed treatment in the control of soybean diseases is not very conclusive. Nevertheless. the use df a thiram + benomyl mixture or chloranil can control some of the fungal diseases and improve germination to a great extent Agarwal 198 1. Neergaard 1979).

The seedborne diseascs of cowpea. particularly anthracnose and the viruses. provide a major production constraint. The widespread occurrence of CAMV is rellected in its seed transmissibility. and there is every possibility of CSMV, CMV, CBMV, and CYMV finding their way to other countries through seed exchange unless plant quarantine meapures, e.g., pte-export inspection of cropls, and growing- on tests in the importing country, are rigorously enforced. Unfortunately, chemical seed treatment of cowpea has not been found very effective against major diseases. and therefore the use of resistant lines may be necessary.

In contrast to soybean and eowpea, green gram seed carries fewer pathogens of a serious nature. Halo blight is confined to the temperate regions, and BCMV has very limited distribution in the'tropics. Since most world g m n gram production is in the lndian subcontinent, it would be prudent to check the ifltroduction and s p ~ d of these two diseases in Asia. However. halo blight can k controlled by treating the seed with streptomycin or kasugamycin (Taylor and Dudley 1977), which should be required.

I

SEED-TRANSMITIED PESTS AND DISEASES W LEGUMES 1II

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