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mTEGRATEDMANAGEMENTOFCHARCOALROT m COMMON BEAN m KENYA

A set of four publications

Reprints Series, No. 19

No. 19a.

No. 19b.

No. 19c.

No. 19d.

CONTENTS

lntegrated Management of Charcoal Rot in Common Bean in Kenya

Reprints Series, No. 19

Charcoal rot in common bean with special reference to Kenya. W. Songa and RJ. Hillocks. International J. ofPest Management 42(4):213-219. 1996.

Legume hosts of Macrophomina phaseolina in Kenya and efTect oC crop species on soil inoculum levels. W. Songa and RJ. Hillocks. 1. Phytopathology 144:387-391. 1996.

Screening common bean for accessions for resistance to charcoal rot (Macrophomina phaseolina) in eastern Kenya. W. Songa, RJ. Hillocks. A.W. Mwang'ombe, R. Buruchara and W.K Ronno. Experimental Agriculture 33 (4):459-468. 1997.

Survival of Macrophomina phaseoljna in bean seed and crop residue. W. Songa and RJ. Hillocks. International 1. ofPest Management 44 (2): 109-114. 1998.

Nos. 19a and 19d are reproduced by kind permission ofTaylor and Francis. No. 19b is reproduced by kind permission ofBlackwell Wissenschaft. No. 19c comprises publishers' reprints.

\ ¡

INTERNATIQNAL JOURNAL OF PEST MANAGEMENT, 1996 42(4) 2~;)-219

Charcoal rol in common bean with special reference to Kenya

{Keywords: Macrophomína phaseolma, charca si rol. beans, Kenya!

W. SONGAj and R. J. HILLOCKS¡

tUníversity af Reading, Department of Agriculture, E.arley Gate. Reading RG6 2AT, UK ';Natural Resources Instítute, Chatham Maritime, Chalham, Kenl ME4 4TB, UK

Abstract Charcaal rol causad by MacrophOmina phaSeO!ma (Deutaromycetes: Coelomycetes} IS found throughout t"le troolCS and subtroplcs and has a wide host rMge Together with most 01 tila legume crops, Ihe col'nrnon bean (phaseofus vulgaris) is a goad nost for the fungus which causes a ranga 01 symptoms, dependlng on environmental conditJOns and age oí the p¡ant. In addltlcr :0 charcoa! rot, which is a s1em or stal" rot disease. the pathúgen alSÚ

causes damping-<tff and seedling. blight in oeans, Char:::oal fO! JI;

the mature plant is associated w¡th senescence which!s accelerated by water stress. The disease is mosl damag'ng in afeas of un"eh­able rainfall ano high tempera1ure. In Kenya. beans 8!'€ us~ally grown In míxed stands with maize, sorghulT, or mille: POpl,.;latlon pressure has led to the culttvation 01 beans on land pro'le to crought M. phaseolma is ene of the most importan: pathogens affectlng al! the main crops of the iarming systems In the semi-arld areas of eastern Kenya and resistance to charcoal rot lS a pnerity ¡f besns are to be mcreasmgly grown in these areas The paper reviews Ihe literature 00 charcoal rot of beans and on other crops where sHn¡lar work has not beso reported specH¡cally tor beans,

1. Inlroducllon

Charcoal rot 01 beans (PhaseoJus vuigaris) is caused by

Macrophomina phaseolina (Tassi) Gojd. (Deuteromycetes:

Coelomycetesj. The pathogen ís widely distributed in the

tropics and sub-trapics and has a host range which ¡neludes

more than 300 plant .pecíes (Cottíngham. 1981). The lungus

can cause seedling disease in legumes and other crop

species and is responsible tor stalk rots in cereal craps as

well as root and stem diseases in numerous crop specles.

These diseases are known variously as charcoal rot, black

rot and ashy stem, depending on the host. For the sake 01

consistency the disease will be referred to as ehareoal rot

in this review. The fungus causes economic losses in areas with a ho:

climate where crops are exposed to periods of moisture

slress (e.g., Dhíngra and Chagas, 1981). II is quoled as tne

single mast important pathogen of cowpeas, sorghum and

mung beon in the Bay regían 01 Somalía (Gray el al., 1990) and IS the maín disease affecling legumes in the sem¡~arid

areas of Nigería (liTA, 1984), Charcoal rot is important

on beans in the warmer areas of produetion in the USA (Hagedorn, 1991). L.lin Ameríca (Díaz-Franco, 1984). Indl.

(Salí.ch.ndra el al., 1979), the Carribean (Echavez·Bedeland

Beaver, 1987) and Atrlca (Emeehebe and McDonald, 1979: CIAT. 1981).

In Kenya, íncreasing population pressure has led te the

cultlvation of tood crops tn eastern parts of the country,

prevrously regarded as unsuitable for crop production

owing to their unreliable rainfalL The semi-arid areas of

Kenya, whlch include most ot Eastern Provmce (Figure 1).

contributa 35% of the country's total bean production (Gítu

and Ngalyukia, 1989), Wíth their continued cldtlvation in

increasingly drier environments, there is a need to produce

bean varíeties with improved drought tolerance and resis~

tance to Maerophomina (Muigai and Rano, 1990),

Having a worldwide distribution and wide host range,

there ig a large literature on M. phaseaJina. The Internahonal

Centre for Research lO the Semí-Arid Troplcs (ICRISAT) has

publlshed a bibliography of Iiteralure up to 1987 (Síngh el al .. 1990) and the bioiogy and pathogenicity of the fungus was

reviewed by Dhingra and Sinclaír {1978}, The purpose of this

paper was to revlE~w the literatura concerning M_ phaséoJina

on beans, in relation to conciusions drawn from work on other

crops and to emphasize its importance in the semi-arid

regions of eastern Kenya.

2, Symptoms

M. phaseoJina causes seedling disease ¡n bean as well

as the more cOflspicuous ashy stem or enareoal rot symptom in older plants. AI1hough they are manifestatlons of the same

syndrome, the nature of the aetiologlcal link between seed­ling disease ané chareoal rot IS not clear

The first visible symptam on the seadliog is a sma!! dar\(

brown ¡asioo en the cotyledon which spreads down cnto tha

hypocotyl (Figure 2) or, sometimes, the lesion may appear

first at the base 01 the nypocotyL Early infection results in

pre-emergenee damping-off Or seedling mortalíty, soon atter

emergence (Figure 3), In established seedlings, ¡esions

spread down the hypocotyl, girdle it and cause the plant to

collapse. If the lesion develops late or the plant has some

reslstanee, the hypocotyl ls not comp~etely glrdled and the

plant may recover from the rnfection. Plants which surVlve the first 2-3 weeks aftar sowing usuaJly survive until1lower~

ing when the first symptoms of the ehareoal rot phase of

disease appear at the base of the stern as grey, necrotic

areas, bearing numerous smal! black sclerotia, As senes­

cenee progresses, the infeclion spreads up the stem and

selerotia may eventually appear on the pods (Figure 4),

ieading to seed ¡nfecHon. Plants which develop charcoal rot symptoms relatively early in their growth exhibit signs 01

accelerated senescenee, such as foliar chlorosis and fewer seeds reach maturrty.

0967-087':/96$12-00 r 1996 Taylor & FranCI$l...tá

214 W. Songa and R. J. HllIocks

-------... .. __ .. _-.. _--Sudan

'" w a; ~ '" .. ~ ~ '" 1;; e o ~ '" " ~ '" o z

, \

Figure 1. Sketch map of Kenya showmg Slj(vey area wher8 ISO lates of

M. phaseofina were co!!ectec..

3. Morphology and cultural characterislics 01 the causal organlsrn

Macrophomina phaseofina (synonym: Macrophomina

phaseoli, AhlzoctOntB batatícofa, ScJerotium bataNco/a) can

be readily 'so(ated fmm mfected host tissues on standard

medIa. It has a ~lgh optima! !emperawre tor mycei¡aJ growth

0132-34 C. covenng a 9cm Petn dish or potato dextrose agar

(PDA! ¡n 480

Young hyphae are colourless, becornmg :¡ght brown wíth

age. Within a few days of growth on PDA. abundant sclerotja

are produced which range rrom 100 to 300 ¡1m In diameter.

These are smooth or ¡rregular i:1 shape, black In colour

and r:ch in O¡IS (Hol!íday and Punítha¡¡ngam. 1970. Dhmgra

ane SinclalL 1978). Sc'erotia constitute the pnncipa. propa­

gu¡es for dlssemination and are resístant to extremes 01

temperature and humldity. Within ',he mfected host sc!erotia

appear in large numbers when the tissues beg1n :0 senesce

i

Figure 2. Infecflon ongmatlng fmm the :;:otyledons and spreadlflg (O

(he hypocotyi

" / "

Figure;) Post emergcnca sée(Jfing dlsease In beans growlng ul soif moculated wlth ,'1;( phaeo/¡na

Siack, globose pycnidja are $ometlmes sean on the host

and can be induced jn culture (Watanabe, 1972). They are

100····20011m in diameter anct contain smgle-ce!led fusiform cOnldla (Dhingra and Sinc!alr. 1978),

4, Variallon in the causal organisrn

Macrophomina phaseoJina 15 a plJnvorous pathogen ana

isO lates from one plant spec¡es are aften found to ,nfect a ranga of other hosts (Ho¡¡¡day and PLJnithalingam. 1970). ;"ee

et al. (1986) for instanc8, found that Isolates trom bean. cotton

FlgrHfJ ..J. Charcaa! rOf :ít mature f.eid-grown beans Qften extends :;) l~fJ

pods resI.Jltmg Ir mfec!lOn ':>f the se€td

and groundnut were al! pathogenic on cotton, Similarly.

Diourte (198?) reported that isolates from sorghum, growild­

nut, bean and cotton all cross·moculated each of the other

hosts although there was a trend towards greater virulence

on the host from which each strain was initlally isolated.

However, there r$ some evtdence that certain Isolates exhibit

a degree of host specíflcity. Isolates causing ashy stem of

cQwpea in Botswana also ínfected beans. bul not sorghum

(Burke el al., 1986). Care must be exercised in ínterpreting

this result as 1t is easier to induce symptoms on legumes,

following artificial ¡noculatian, than on the cereal5 which are

so dependent on pred!sposítion. Further support tor the

occurrence of host specificity ís to be found in the work of

Chohan and Kaur (1977) who found that three tBolates of

M. phaseolina which were hlghly aggresslVe On cottúrL okra

and blackgram, did not cause symptoms on ma¡ze or groLllid­

nut Ahmed and Ahmed (1969) haye attempted to separata

ísolates 01 the pathogen from jute lOto physiologica¡ races

Pearson el al. (1987) were able to dlstmguish ¡salates of

the tungus ffOm maize from those iSolated from soybean

on the basis of the.r growth cnaractenstics on a medlum

supplemented with potassium chlorate. lsolates of the fungus from different regtons (Dinghra and

Sinclair, 1973a), hosts (Buadgi and Hegde, 1985}, the same

host, or, even different parts of the saffie oíant (Dnmgra

and Smclalr, 19730), exhibit wide vanation in cultura! anó

morphologtcal characters Such as growth rate, sclerotia!

proouctlon, sclerot!al size and ab¡ltly to produce pycmdia

(Watanabe, 1972, Ch,damberam and Matnur, 1975), However,

these differences hava not been IlOked to host specialization

or to aggressiveness.

5. Oisease incidence and yíeld 1055

Under warm. mOlst conditíons, fo!lowing a long dry

season and In the presence of higt1 inoculum levels of

M, phaseolina. seedling mortality 10 legume crops can be

high" For Instance, in 1983 in southern Nigeria the fungus was

responsible for 70Q/o cowpea seedlíng mortahty {liTA. 1984;.

However, seedling loss is not normally as h!gh and the

survíving plants, especJally among the long season va,..iet¡es,

have sorne capacity to compensate tor early stand loss. Loss

estimates tor Africa are not available but yield losses of

up to 65% have occurred in bean crops grown in the USA (Zaumeyer and Thamas, 1957),

Although the disease has been known in Kenya for many

years (J.M. Wa!ler, personal communica1ion) it has become

more prevalent in recent years wíth the cultivatlon of land in

progressively drier areas. M. phaseofina was observed on

sorghum, causing extensive lodging in the crop produced

on the short ralns (Oct.-Jan.) near Makuen1 in Machakos District (see fígure 1} (Waite et al., 1984). Mukunya el al.,

{1983) reported serious incidences of the dlsease at spedfic

locations in the semi-arid area 01 Kenya. SeedJ¡ng mortality ot

10-14'% has been observed in beans grown in experimental plots and farmers' fíelds in Machakos Otstrict (W. Songa.

unpublíshed). The disease has since been observed aU over

eastern Kenya on many crops inctuding beans (Stoetzer er al.,

1984). Tabla 1 shows a list ot lsolates collected ·in eastero

Kenya by Songa (1995) and the crop spec,es ¡rom which they

ommon bean 215

Table 1. Crop hast and !Oca/Ion In eastern Kenya [rom wmch l!jotates ef

M ptlaeo!ma were coj¡ec~ed dL.nng 1892 (Songa. 189ój

Onglt'l In Kenya

!solale Hos! crop LocAl:Jon DIstnct

33 P¡w~"tJ¡!f' ¡'¡¡(rafe K,mg.~ldl MiJ(.;hah.v:.

\\'54 /' '·,I!;;U~/I K;ltum;¡)l¡ MachaK(lS WS' .\;¡;rf!Jw/11 hu (,/1''' KalUm,tm Ma(.;hakll~

\\'5:-\ l' ndf.!or/I MWln!11 KlIUl

WS!O P.l'lIlgun, Kiboko Makllem \\'S 11 P I'I/Igarll K.ibokc- MaJ.,lle"m \\'512 ¿eu/!¡un Kamp;oy¡¡oMil\\t: Makuem W514 P. rUh!(ffl\ Kampt-ya-M¡¡Wé Makueni W516 Pdlllll'l'!um glfJtlCllnI ishiara Emou WS17 f\ )'uh:orJ' Masmg¿ Macollko!; WS1Q S n[{'u!l/" Ch¡al.anga Emb.¡ WS:ü LCiI f!!1Il , Manmant; Meru WS21 5;. nu o/m :-V1.tnmanl: Meru WS22 S hl{oím j\-l.H:manu Meru WS24 p ¡:(t1!/fIlJll Manmunl! Meru WS."!5 p gíWIU/1Il Slakago Embu WS~8 P ndgw 1\ Slllkago Err.r.u WS34 P n¡{gof/I Sl:ü.age' Emou \\/S35 P r¡dgauI Klh,'ezl '4akucl1l

were isolated, OiUerel1ces m seed weight 01 35~50% com~

mOOt)' occur between moculated aod non-inoculated plots in trlals conducted tú seresn baan germplasm for resJstance

to M. phaseolina at KlboKO Experimenta I Station in sastern

Kenya (W. Songa. unpubl'lshed). A recent report r€cords

charcoal rot as en important cause oi yteld 105S in beans

grown in the semi~arid areas of Kenya with losses oUen

exceedmg 300 kg ha-1 (Wortmann and Aller:. 1994).

6, Epidemíology and dísease development

Tn€ pathogen surviv€s in the soii m crop residuas jn

the form 01 sc!erotl8 and the ínítla! infection derives either

from so¡¡~borne inoculum or from tne plantlng of ínfected

sead íS!ngh and Singh, 1982), The pathogen is known to

be seed-borne In a number of hosts including soybean

(Gangopadhyay el al" 1970) and camman beans (Abawi and

Pastor-Corrales, 1990a) and can be carried within the seed

coat (Dhingra and Sinclair, 1978). The fungus was detectad

tn 30% 01 cowpea seed samples collected from markets

In northern Ntgeria (Emecnebe and McDonald, 1979).

Dry conditions favour surviyal oÍ sclerotia in the soí! but

mycehal growth and ¡nfection raQuire mols1 condttions and

are favoured by a temperature above 27"C (Hageoorn, 1991).

Provided there ís sufficient soil moisture tor fungal growth

and high mocuJum levels. seedling lOS ses jncrease with increaslng temperature up to 45 ·C. While 5eedling 1055 ;n

beans 15 dependent on hlgh inoculum potenUal, adequate soil

moisture and temperatures aboye 27 C. symptom expression

in the mature plant is not related directly to soil inoculum but

is depenaent on the physiological predisposition of the host

(Songa, 1995). Predisposition í5 tríggered by flowering afld

subscQuent oosel of sene:scence, provlded this occurs at

oigh temperatura (above 32·C). Moisture stress at flowenng

seems to be an important predisposing critenon, at least

ín sorghum (Edmunds, 1964). It is still uncertam whether this

is due directly to the physiological eftects of moisture stress,

W, Songa and R

or, beca use drought condltions lead to early senescence. In

beans. plant mortality increased from 9;% under ideal soil

moisture conditions to 64%' after 18 days of water defic¡t

(Magalhaes el al., 1982).

The exact nature ofthe aetiologica¡ link between seedling

JnfectlOn and symptom express!on in the mature plant is not

fully understood. The evidence from work with cowpea

(Bourne, 1992) is that infection of the root and crown region

may occur at any time during the life of the plant. The

pathogen appears to invade the base of the stem, then

remains dormant untll the plant becomes predisposed to

infecrion after toe onse:t of flowering. Demooy and Burkeld

{1990} reported that lesians on cowpea hypocotyl could

ramain cormant tor up to 1 month befare becoming activated

by drought or senescence,

There is littla reported work on the aetiolo-gy of

Macrophomina infection in beans, more has been published

on the subject with respeet to other crops but some of the

reports are contradictory. The apparent contradictions exist because of the faHur€ to distinguish between infecHon and

symptom expression or te d¡stingufsh between seedling

djsease and mature plant d¡sease~ Charcoal rot seventy in

eottan (GhaHar and Erwln. 1969, Thakar, 1984) and in sorghum

(Edmunds, 1964, Odvody and Dunkle. 1979) tS tnversely

correlated with soll mOlsture leve!s. However, Bruton et ar (1987) showed that ¡nfechon of cantaloup vines was favoured

by wet conditions which led later to hi.gh levels of disease.

The stage of development at which a plant is most Ilkely

tú exhibít symptoms 01 Macrophomina tnfectlon varies to

soma extent with hos! species. Legume crops tend to De

more susceptible at the seedling stage than are the cereal

crops. However, here again the distinction needs to be made

between the optímum time far ¡nfecHon and the main penad of

sympfOm development which are cften temporal1y separated,

Norton (1958) consldered that the pathogen can invade

sOíghum root5 at any stage, but no further development

oeeurs untB the plant becomes drought stressed, The alter­

natlve v!ew ís that drought stress lS a prereGut51te for root

penetratlon (Edmunds, 1964. Odvody and Dunkle, 1979). Some

have argued that root invasion only occurs at physlologleal

matunty, even if dry condittons preva!! at an earlier stage 01

erop development. However, Cloud and Rupe (-:994) found

that sorghum roots were invaded by the fungus well befare

flowerLng, during a períod ot crop moisture s1ress, Ycung

and Alcorn (1984) were also able to isolate Macrophomina trom 1~month-o¡d plants 01 Euphorbia lathyrys aUhough

symptoms did not become evident until 7 months later. In

soybean, plant maturity was found to be the only factor

affeetlng sclerotial production whicn was independent of

mOlsture stress and temperature. The main factor required

tor severe disease was senescence whlch was enhanced by

moísture stress. F!ower remova! has been shown to delay or

orevent the appearance al charcoal rot symptoms (Wyllie and

Calvert, 1969).

7. Association with other mícroorganisms

Macrophomina has a pcor cornpetitive saprophytlc abllity and is very responslve to changes ¡n soll lungistas!s.

Reductlon of bacterial populations has been correlated wlth

increased sclerotial germination. while increased microbial

activity can decrease sclerotial viability (Filho and Dhingra,

1980), Rhlzobium strains indigeneus te Pakistan were

reported to ínhlbit growth of M. phaseofina in culture (Zaki

and Ghaffar, 1987). Aspergillus flavus, a common soí¡~

inhabiting fungus. has besn reported to decrease ¡nfecHon

by M. pnaseolina in peanu! kernels (Jackson. 1965).

Nematodes may al50 have sorne potenhal to íncrease

susceptibility to Macrophomina, either through íncreased

root invasion or by enhancing the effects 01 water stress

AI-Hazmi (1985) has demonSlraled increased rool rol

of bean in the presence 01 root-knot nematoce íMeloidogyne

incognfta). Ths fsaion nematode Pratylenchus zeas and

M, phaseolina act synergisHcally ta reduce plant growth ¡n

sorghum (Bee-Rodriguez and Ayala. 1977). Norlon (1958)

reported similar results with P. hexincJSus. Root~knot nema­

todes cause serious yield losses of beans Jn sorne parts of

Kenya (Ngundo and Taylor, 1974) and leslon nematode 15

more or less ubiQuitou$ in the country's malze-based crop­

plng systems and the common bean is a gQod alternative host

for p, zeae (Jones and Hillocks, 1995). The rOle of the

nematode complex 10 eastern Kenya ;n predisposing beaos

to charcoal ro! (aquires further research~

8, Control

8, 1 . Cultural measures

Crop management systems that raduce Inoculum levels

and conserve soil moisture are effective in reduc:ng :he

incidenee of stalk roL Stalk rot incidef1ce in sorghum was

decreased from 39% to 11 % In minimai tillage compared with

conventional tillage (Doupnlk el al., 1975). Sow¡ng date can

also be manipulated in sorne areas to ensure that the crop

is less Ilkely to mature during periods of hlgh temperatura

and unreliable rainfalL Intercroppmg has been reported as

a method of reducmg charcoa! ~ot inc!dence. Disease

Iflcidence in eotton was decreased :)y ¡ntercToPPlng Wlt~

Phaséo!us aconitifolia due tú tne son cover provlded and

consequent lowering oí soll temperatura (Rajpurghlt. ~983).

In Kenya however, beans are usually grown as an ultercrop

{Njungunah et al .. 1981) with maize or sorghúm, both of which

are good hosts for the pathogen. Sorghum grown as a mixed

crop ras been reported to suffer !es$ damage trom charcoal

rot than sole erap sorghum (Khune et at, 1980). Crop rotation

may be useful in decreasmg dlsease mCldence If asusceptlble

erap is grawn after a Ie-ss suscept!ble crop (e.9" Frankie el aL.

1988), A contrasting view was expressed by Short el al.,

(1980) who found that viable sclerotta persist aver a 2-year

fallow penad and thei( numbers ínerease rapidly when a

susceotiDle host IS grown. They conclude that rotatlOn is

unlikely to be effective as a control measure.

82, Chemical treatment

There are few reports of fungícides being usad tú control

charcoal rot on beans. However, there has been sorne mter­

est Ir. their use tar this purpose on soybean. In order of

efflcacy, benomyL thiophanate methyL thiram, thiabendazo!e,

tnforine and captan deereased viability of sclerotia in soil and

Charco,al rol in cornmon bean 217

in soyoean stem pieces (!Iyas et al" 1976) Seedling infe::tlon

was controlled best by Denomyl and thiabendazole (lIyas el alq

1975). The use of fungicide applled to the seed rnav be

effective in decreastng losses to M. p(¡aseo{ma in crO:JS

which are partlcular!y vulnerable at the seedllng stage In

toe case ot ¡ute tor instance íChattopadhyay el al.. 198;\.

significant contro,1 al seedhng disease was obtamed wltb

carbendazim and pentachloronitrobenzene íPCNB). Aoawl

and Pastor-Corrales {1990b) state that seed trea:ment vvnh

benomyl or éarboxm is eftectlve in controllmg charcoai "ot

01 beans during the seediing stage. In India. carbendazlm

was no! effective as a seed !reatment to control root rol on

beans but PCNB and captan gave sorne control (Satischandra

et al., 1979). Soil fumigation with methy! bromide decreased

the number oi viable sclerotia and controlled infectlon 01

pino seediings (Watanabe el a'", 1970). However. In the case

of sorghum, where the e ¡seas e ís more prevalent atter

flowerlng, PCN8 djd not control the dlseasc in {he f¡eld

despite giving 87% inhlbitior. 01 fungel growth in vdro

(Anahosur et al .. 1983)

8.3. Biologicai control

The eftect 01 organic .sorl amendments or pOf;ula­

tíon levels 01 M. phaseolina, depends On the carbon to

n¡trogen ratio 01 the resldues, A decline in sol! popuiatlOn 01

the pathogen foilowed the applicat;o~ of resldues of vanous

crops or of glucose~sod¡um nitrate. However. pOQ'Jlatlúns

¡ater increased in sail treated with wheat or com straw Out not

in soil treated with glucose sodium nltrate ar wíth nitrogen­

enriched straw (Filho and Dhingra, 19S0}.

Treatment wfth Trichoderma harzianum oecreased dls~

ease incidenls by 37 % in beans grown in pots and decreased

charcoal rot of maize in the fleld by 28'% (Elad et ar., -:986),

Root rot 01 mung bean and other crops caused by

Macrophomina was controlled after seed was dlppec In a

suspenslon of Rhlzobium stralns (Zakl and Ghaffar, ~987)

Similar results were reported lor soybean by CnakrabGrty

and Purkayastna (1984) who concluded that the effect \Nas

due to the fungitoxie action 01 rhizobitoxlne.

Soil solarization was found to decrease the populatlon ot

viable sclerotia of M, pnaseoJina bLt many rernaíned viable

due to the high temperature tolerance 01 the tungus (M¡hail

and Aleorn, 1984).

8.4. Host-plant resistanee

Resistane€ to Macropnomina has been identi11ed in some

bean varieties such as ·Negr¡to· (Oruogra and Sínclair, 1978).

The beao improvement programme at CIAT (Centro Inter­nacional de Agricultura Tropical} has developed metnods

to screen for resistance to charcoal rot {Abawi and Pastor­

Corrales. 1986). Using these methods a number of lines witn

sorne resistance to the disease haya been fdenti1ied {Pastor­

Corralesand AbawL 1988).10 sorne cases resistance is linked

to drought toleranee {CIAT, 1983). Sean lines resistant to Macrophomina are avallable trom the CIAT germplasm

collection and are IIsted by" Abawi anó Pastor-Corrales

(1990b). The fines A70 and A474 are particularly susceptible

and are useó as susceptible standards In screening tests.

Avila et ai. (1982) founo sorne correlation between resistance

and seed coat colour and recammended the use 01 black­

seeded types on heavily infestec soils.

9. Screening for resislance in Kenya

Recognizíng the importance 01 Phaseolvs bean In small~

holder cropping systems in Kenya and the need far low cost

dlsease control measures. much emphasls has been placed

on breedrng tor disease resistanee within the Kenyan

National bean improvement programme, which IS coordi­

nated from Thlka Research Statlon, north~east 01 Nairobi.

Selection for resistance te ct',arcoal rot is conducted from

Katumani Drylanc Research Station, near Machakos in lhe

semi-and zone 01 eastern Kenya. EvaluatlOn of resistance is

based on greenhous€ and fie<c' screenlng in whlcn plants are

inoculated using colonizad rice gralns as the inoculum

source (Abawi and Pastor-Corrales, 1986)_ Moderate levels

of resistance have been iderlif¡ed jn lo:::al and introduced

genotypes. At Kiboko Expenmental Station where nigh tem­peratures and low ramfall creater exceHent conditions tm

tl1e develOpmeot 01 charcoal roL a large liumber 01 lmes are

being evaluated 10" resístanse in adja:::oot inoculated and

non-inocu!ated plots.

Acknowledgemenls

The Kenya Agricultural Research Institule (KARi). the UK

Overseas Development Admlnlstratíon (ODA) and Centro

lr¡ternaClonal de Agricultura Tropical (C1AT¡ are acknowlM

edged for permisslan to reter tú aspects al wOrk carned out

ur:der the KARIIODA Croo ProtectlOn PrOject and KARIICIAT Bean Col!aboratlve Research Project.

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J PhylOpatholog) 10M. 3~n-JYI (19l)(ij ( 199(i Black\\'ell \Vissellschafb-Vcrlag. Berlin ISSN 0931-17S5

[ lIire/"sily of Rcadillg. (k/wrlll/clIl uf AgriCIIIIII!'C. f·u!'lc.\ Gil/C. Rn/(ling RG~ ~.·1 T Uf...'

Legume Hosts of MaaopllOmina phaseolina in Kenya and Effect of Crop Species on Soil Inoculum Levels

W. SONCiA and R. J. HILLOCKS1

Authors' addresses: lunlyersi!) of Reading. Department 01 Agriculture. EarJey Gate. Reading and Natural Resources

Institutr. Chatham Mantime. Kent. LK

With one figure Received October 31.1995: accepted February l~. 1996

Abstraet Studies were conducted in eastcrn Kenya 10 determine lhe common legume crop and weed hosts of Afacrophol1lino phaseolino (Tassi) Goid .. the inciter of charcoal rol dlsease. The cfreet of maize. sorghurn. bean. and cO\\'pea 011 lhe soil inoculum leyel \\as also investigated after field inoculation. Al! the legume crop~ and \veeds tested \\'ere found 10 be infected by the pathogen after artificial inocu­lation. C0111mon bean. soybean. cowpea \\ ere the 1110S1

susceptible while pigconpea. green gramo and hyaCl11lh bean wcre moderately susceptible. Groundnut. chickpea. Cas.\ia spp. and C/'ow!al'ia spp. were least susceptible after artificial inoculation. Monocropp1l1g 01" sor,ghullL maize. cowpea and C01111110n bean for three consecutive crop scasons increa~ed ;\1. P/w.\('o/úw soil 1Il0culu111 in a::.cending order.

Zusarnmenfassung Leguminose\ürtspflanzen \'on Macrophomina p/¡a.~eolina in Kenia und der

Einftuf\ der angebauten Kulturpftanze auf das bodenbürtige lnokulumle\'el

In Ostkenia wurden Versuche durchgefühn. um dle am haufigsten vorkommenden Leguminosen-und Unkraut­wlrtspflanzen von A1acrophomillo p/Ulseo!il/O (Tassi) Gold, Erreger der charcoal rot Krankheit. zu ermitteln. Oer EinftuG von Mais. Hirse. Bohnen und Kuherbsen auf das Inokulumlevel wurde auch in einem Feldversueh naeh künstlicher Inokulation unlersucht. Alle untersuch­ten Leguminosen und Unkrautspezies wurden durch das Palhogen naeh künsllieher Inokulalion befallen. Die Ackerbohne, die Sojabohne und die Kuherbse waren am anfalligslen, die Taubenerbse, die Mungobohne und Faselbohne wiesen dagegen eine mittlere AnfaUigkelt auf. Die sehwaehste Anfalligkeit wurde naeh einer künst­Iiehen Inokulation bei den Erdnüssen. der Kiehererbse, Cassia spp. und Cro/alaria spp. beobachlet. Eine dreima­Iige Monokultur mit Hirse, Mais. Kuherbse und der Aekerbohne erhahte das M. phaseolina-Inokulum in ansteigender Rangfolge.

Introduction Alacropho111i1w phaSl'o!inll. the eharooal rot di::.ease pathogen. has a wide host range exceeding 300 planl species illcluding legume and cereal erap plants (Reichert and Hellinger. 1947: Ohingra and Sinclair. 1977). In leg­umes. infection is evident from the seedling lo mature plant stage \\'hile in cereals infection is usually observed after onset of anthesis. At the seedling stage infection usually occurs during moist conditions and at te111-peralures above 27 e (Hagedorn. 1991) while al lhe mature planl stage physiological predisposltion of the host precedes infection. Predisposition may be trig,gered hy droughl stress(Anonymous, 1985: Sehwartz. 1989). ftowering and subsequent onset of senescence. provided this occurs at high temperature (above 32 e). In beans. plant monality was found to increase from 9% under ideal soil moisture conditions to 64% after 18 days of waler deficil (Magalhaes el al.. 1982). Oisease evalualion in legumes can be easi!y done at both seedling and mature plant stages.

The plurivorous nature of ll1. phaseolina enables this pathogen to survive on many alternative hosts in the absenee of crop hOS1S. Although this natore of lhe patho­gen limits the effectiveness of sorne cultural management melhods sueh as crop rotalion, the manipulation of crop­ping systems to reduce the inoculum level in soils is stiJl promising (Singh el al., 1990: FrancI et al.. 1988). erop species vary in their reaction to M. phaseolina depending on their inherent resistance. The more susceptible crop speeies suceumb 10 lhe palhogen earlier and enable lhe pathogen lO mulliply on them and inerease lhe levels of inoculum in the soi!.

Phosl'o/us bean is one of the favoured legume crops grown in the maize-based cropping systems of eastern Kenya. It is. however. highly susceptible to M. p/lUseolinCl. The objectives of this study were to compare the reaction of common bean and other alterna ti ve legume crops to M. phaseolina. The effecl of monocropping lwo legul1)e and two cereal crops for three seasons on soil inocuium

l S (OP:rJ!'hl CI~"rHnc'~ (enler C()d~ S\ .. \\~menl 0931-1785 '96 4408-0387 S 11.50/0

388

levels of Macrophomilla phaseolina, and charcoal rot dls­ease incidence in a subsequent bean erop was ,,150 inves~ tigated,

\-latería!s and Melhnds Artificial inoculadon

Legume crup und irl!l!d hosls o/M. phaseolina "ine Iegume CTOpS ¡¡nd níne !eguminous weeds common in charcoal rot disease 'hol SpOIS' were used In ¡he sludy, The legume eraps were: common bean (P!wseo/us L'u(qans L¡. cowpea (Vigila unquiclI/tlla (L) Walp). grecn ¡¡ram IViql10 radiaw (LJ Wilcz, Soybean (G/ni"e lIIax (L)

Merr.), chickpea (Cicer ariefÍnum L), hyaeinlh bcan (Dolic[¡os lab lah L). garden pea (Pisam salifa", L Sens ampl,). pígeonpea ICajanas cajan (L) evlillsp.l "od grouod nUI (Arachis hvpogea L), The germination of the weed seeds was not uniform and only three species whleh had good germination were eventually used in inocu­latioo tests. Two of lhe se¡ected weeds were Crota/"rf" spp. and ooe was a Cassia spp. Of lhe two Crola/aria spp_ one \Vas early tlowering and the other late.

The ,!Ud, 01' legume erop and weed hosts 01' J/_ pilase­olinu \Vas (arded out in a greenhouse maintained at ! 8-30 C. Fise secds 01' each legume erap aod weed were planted per po! in four replications. Inoculation was done using rice grains colonized by M. plwseolilla (Abawi and Pastor-Corrales, 1986: Songa, 1995) iso!ate WS !7 from common bean. A single planl was removed from eaeh 01' ¡he pOI' al 15, 30, aud 60 d"y' after emergence for determination of the presenee 01' t he fungus in the rool, lower 'lcm alld upper stem. The procedure for isolation of the pathogeo was as follows: nine pieees were cut from eaeh ofthe plant parls ¡¡ud washed thoroughly in dislílled water, slerilized in 05% NaOCl for I min and then rinsed m distllled waler. The plan! tÍssue pieees were lhen dried on blottrng paper and plated on POA. Three tissue pieees from eaeh plam pan were plaled per Petri dish in lhree replicati011s_ Observations fOl growth of JL plwseolllla were made after mcuhation at 33 e for 6 days_

Fie\d experimfnt

Ellec! 01 crup species cn ,he lerel vf M. phaseolina ami diseas(! incidence in heuns

The study of lhe effeet of erop species on the level 01 . H. plras(.1o!ina inocu\um level in the :míl was conducted al Kiboko resean:h slation in custern Kenya, A mixture of bean, malle, cowpea ami sorghum crop debris infested with Al. phaseolillu. were I.:hopped and incorporated uni­fonnly in the soí! 01' the study lield at the beginning of the I;!xperiment. This ensured some initial inoculum level in the field whieh \Vas located in an area WhlCh had been left fallow for 2 years. Monoerops 01 malze. sorghum. cowpea and common bean were planted in plors 01' Uve by five m for three consecutive crop seasons follol,.ving the rccommcnded agronomic practices. After rhe tlrst plantmg, the plOIS were subsequently prepared by halld 10

avoid moving sOlI from one plot to another. Occasionally, irrigation was glven but only when wilting symptoms \Vcre apparent. At the end of each season. [he crop debris 01' each plal \Vere ehopped "nu hand ploughed mto the

SO:-':UA and HILLOCKS

plOL The control plots were left fallow. There were four replications in a randomized block designo

In the fourth scason ull lhe plOlS \Vere planled \Virh common heao IcY_ GLP 1004) lo enable uniform ev"lu­ation ol' discase incidence io lhe plOls_ The disease level in the plOlS was assessed at 14 days after emergence and a! harvest. Evaluations were carned out 10 monitor both the seedling and mature plant stages of the diseaso_ The parameters taken were: number of plants germinated. number of seedlings infecled, number al' infected planlS al harvesL total number of plan!s at harvest and vield per plol, .

ISO/Olfol1 al' M _ phaseolina jí'om fhe p/OIS (1{ four deplhs

The JI. phaseo/ina sclerotia leve! in lhe soíl \Vas deter­mined at the beginning ol' the experiment and everv 3 months thereafter for a lotal period of I g monlhs. The isolatian of M. phaseolina sclero!ía from the soi! was done by taking soil samples from depth, (0-5,5--10, 10-15 ¡¡nd IS-20cm) in each ploL At eaeh sampling date soíl was laken from ""eh plOI aud Jepth al foar differenr points ¡¡long lhe diagonals of the plo¡ nt random. The soil from similar depths in e"eh pi o! was tnen bulked 10

constitute " sample for the plor. Isoiauon 01' M. p/wse­olina from the so¡i was done as dcscribed by Papavizas and Klag (1975)_

Resul!s Artificial inoculation

Legume crop (/ml¡recd /lOst.\' o! A4. pllOseolinu The pathogen \Vas isolated from the raNs of cornmon bean. cowpea. pigeonpea, greeo gram, hyacinrh bean, soybe~n and the carly flowering erola/arla spp. 15 days after inoculation and ¡n chickpea. groundntlL CassÍa spp. and ¡he late Aowering Crola/aria spp. after 30 days (Table 1.1 t Plants from which 1\4. plJ(Jse()/ina \Vas lsolated from rhe stem after 60 days were tho5.e whose roots were al~ rcad:: colonized at 15 days after inoculatiolL In dlickpea. groundnuL Cf/ssia spp., <.lnÓ the late rlo\'vering Cl'OwtaJ'io spp_ tile pathogen did not sprcad bevond the roots. The pathogen was found in the upper stem !!1 .:ommon bean. 50ybean, hyacinlh bean and pigeonpeu_ External disea,e symptoms were observed only in common bean. cowpea. soybean and greengram (T able 1) .

Fietd e-"\Ihníment

Eralualion uf/ere! oIM, phaseolina in mO!locropped 1'101\" by iso/afion /ron1 lite ¿mil The :C"d of ,cleratia m the soil at the beginning oi' ¡he experíment was found to be on average 11.2 s(.·lerotw per g of soi!. Significant dífferences (P 0_05) were found betwee~ plOIS with diff.:rent crap treatment, in the level of sclerotia at each sampling (Fig. 1). There was 11 general tendency for the :'.clerotta le\"el to increa::.c JI1 the soil from harH;,sting lO the planting 01' the next crop. Cowpea ~md comman bean plots had signifieantly (P = 0_05) higher average number oi' sc\erotia per g of ::;oil than 50rghum and falJow control plots after three seasons of mono­cropping (Table 2). The ,clerolia levels in the maize ánd sorghurn plats were not signifieantly !p = O.05} different

Table 1 iSOlatlOll of M, phawolirw from roolf>.IO\\é'r stem:-, uppcr sten:~ um] syrnplorhS on stem of sorne legumc crops and \\eed" after .artifiCial moculallon w¡th l~olate WS 1 -: [ron: commo-n beun

Legllme

Common bean Cúwpe-a Plgeonpca Greco g-r"m Soybcal1 Hyacmth bean ChlCkpea Groundnul CO.l'.I';a;,p, Crowíarw spp \late ftl)\\ering! (rotalaria spp, {f!¡\rl;. ftowenng'

Plan¡ ran ~_._-_.

._--~ .. -----RON:. Lower Slem l'pJlC¡ ,¡,,¡¡¡ S:" mplom~ on .. h,'m

~~~_ .. --"-~-._,,-~,,-_ .. -

Da)-:. <lfter emergel1ce 15 30 61) i5 ]0 60 15 30 60 15 JO 61)

,~--.. _-~_ .. _~- .. --- .. _- ---.. _-,~--

• • • • • • O • • • • • • • • • • • iJ iJ ~ • • • • • • O • • O O • O ~

• • • O e • [! :] :-; O • • • • • • • O • • • • • • • • • • • O o • O -" • • o e ,~ O e o - O o • • [1 [1 r o ~ - !...3 W ---' o • • '-' :J • e o '-' O o • • O ;:¡ CJ O w · , CJ -,

~,

• • • o • • o =:¡ O ", --- -~----_ .. _---------~---------- -----._-

• M. pIWJt'ol¡¡¡u lsolated: [J ,\1 phast:'ulwu nO{ isolateJ

50

Bean

Maiztl

Fal!ow

50

,/

J I

40 I :g A ;\ , 0

í j\ I 1;

/ ti \/ E \ E /\ \ I ~ 30 ~

~ /' I Q. , • / \ / .~

~ / \ I u

I \ I <1) ,/ , + \

I 20 ,. '-I / \ ,

, / \ I , í / '-

11/ \ \ I '-

V \ \\1, 10 _i ~ .'

O

Flg, 1 $cleroria leve! in plOts Apri¡ July Oct, Jan. April July OeL

mú-nocropped witn bean, mU1ZC. p ... Plan, Harvest Plan! """"'" Plan, Harvest Plan, and fallo\\' control al Kibokc In

1993194 Maize w Plant Harv.,. Plant Harvest Plant llarv,,' Plant

390

Tabié 2 ScJerot¡a1 leve! m netd 5:oil after monúcroppíng cowpea. common bean. rtWJze itnd \orghum for tbree seasons

Crop

Common bean Cowpeu Ma!Zl: Sorghum Fallow íconLroJi

LSD

Mean sclemua level pe~ gram soil

Me¡.tn SD 31.Y±14"9 293&± 14.4

1"L1"h:!:; 16.6 24.9~± ¡ L2 15J1'± Jl.2

3,09

·~eum w¡th toe same [CHef nol slgmncantly (p = í).Ú)) dltfcrent.

but \Vere significantly higher than in the control plots. There was no sigmficant (p (W5) difference in lhe num­ber of scferotia isolated from different deplhs in lhe monocropped plors of the same erop spl3cies.

El"atufltioH oOerel (~f'rvL phaseolina in p/ots lising commolI bean Tile number ol' germinaled bean plant, in the different previously monocropped plots was nOl signíftcantly diíferent I P 0.05), The plots previously monocropped \\ jth commoll bean had significuntly (P = IlJ15) higher bean seedling infection than those monocropped wilh malle. sorghum and fallow (Table 3). There was no sig­mlicant difference (p ~ 0,05) in the number of infected bean seedlings in plots previously monocropped with r.:ommon bean ami eowpea but there was a significant difference between these plots and (he lallow control plOlS, The number of infected plams at harvest did not significanllv (p ~ (W5) dilfer by monoeropping, The nwnber vf plants al harve,t was signíficantly IP = 0,05) lower in p!ots prcviously monocropped with eommon beall ;:han \vith cowpeu. maize, sorghum and fallow. However. ¡here was no signilícant dilference (p = 0.05) in ¡he number 01' plants at harve,t In plots monocropped Wiih malze. sorghum ami co\vpea. A significant IP = 0,05) negative correlation (l'. = ~O.9) \Vas [ound be:\\een lhe number of infected bean seedlings and lhe number 01' plant, at harve,!. Yield was signibcantly dilíerent IP = O,OSi between common bean and rallow

T¿h:1! :,

and vvas pasitíveiy corelated (r. = 0,9) wíth the number 01' plants at harve't and negatively correlflled (1', = ,0.9) with number of mfected seedlings,

Discussion ,''Vlacrop/lDl'nina phaseolina ... vas isolated from the root5 oC cowpea. common bean. hyacinth bean. pigeonpea. green gram. and one weed 01' erala/aria ,pp, 15 days afler inoculatian. For chickpea and groundnut this was lhe furthest the pathogen was able lo penetrate the hosl In common bean. soybean. cowpea and hyacinth beun. ¡he pathogen was found in the lower stem ¡ 5 days after inoculation, These results impí, ¡hal chickpea dnd groundnut were able lo restriel runher entr)' "fthe patho­gen beyond ¡he root5, The pathogen \Vas found in ¡he stem in hyacinth bean. pigeonpea aud the early ftowering Crofalaria spp. but no symptoms were obseryed, whereas, cIear s.ymptoms \\'ere manifested in soybean, common bean. and cowpea. If disease symptom expressjon is taken as a measure 01' lhe pathogen 's sUécessful colonizaríon 01' lhe hos!. then soybean. common bC<lli and cowpea were very susceptible. These crops would increase the ¡nocu~ lum oC the pathogen in the soíi and \Vould be unsüitable for use in erop rotaríon for control orthe pathogen.

Symptoms were not ápparent on green gram unül 60 days after ÍnoculatÍon. Thls implied a good le\el 01' res¡st~ unce in this erop. The absence of s: mptoms in chickpe"t und pigeonpea suggests more reSI:,tance to the pathogen in these crops and \Vould thcrefore. be 5uitable for erop rotation in inrested fields, These crops are drought tol­erant and \\'ould ti!: \Ve!l in farming sy~tems of areas where charcoal rot dbease 15 prevalenL Pigeonpea \\as reponed by Singh ~t aL 11990) to be susceptible to M. I'lwwoli"u in India. The results in thlS study do :1ot agree \\'Hh this obser\'ation but reíterate the minor importance of ¡,;harcoal rot in plgeon~a in semi-arid ;;:::astcrn Kt!nya where most vf the crop is cultivatcd ¡Songa et aL 19~1 " Sorghum grown ín the sume area is often severcly infccted ¡Waite et aL. 19X-l.¡ but no díseu)c úccurn:ncc ofimpúrt­unce has been observed or report~d on pígeonpca.

Tile observation that the pathogen could exist in hosts without any symptoms agrees with Edmund:; í 1964.) ,\ho suggested that latent infectíon probably occurs in tlle crown of most sorghum plants. Ir would be worthv..!lHe

Etr~cl of ,,'rop ..,pe(:I':~ _m dwrCO;,l1 rol ¡Jis,;:w;.e 100..:idem::e "m <,;ommon 'Jean .. rter OhltWCrOpplng rOl" ¡hree :,casnns

C"1nmon ne:1l1

Cm-pea Maw,; S\)rghum Fallow LSD

:'\lllmh~r 01' gcrmmawo hea:1 lnh:c!d bC;.¡1l

,>ce¡Jling.:>. plOl -.edhng:. plOl

~L2·'

:l~.ll n

, 1 ~,

~5.5-"

-+6.0' 15.11

\h,~llb \\ ¡¡n ..,J.tnC ien~r no! s¡gnificamt;. dOferent ¡ P = {} 051

'.c. ~;r mfec{cd b\!dll plal1b plot

.tl haíV¡;-.f

166.5·

17'¡8' ltí5JY 160 il:~¡-'

13g.U~

23A8

\;umba ofb".l!) pLWb pi;)! ,lt

11,11 \ ..:~¡

;:01)'

:''':'(10'' 3-ú~.J ,h

35fd,h

"'71\ w :;·+.55

Yidd of commúp

bcm plot I kg.)

1--'"7'

1.9K'" 2,~: ' ... :.25 .... 2.53'" il71

-,,---

HO!>ll' nf _ti"" I

to carry out more studies on eomman weed species to determine those "eed, that maj be susceptible and con­lributing to ¡nnease leveh; or íno<.:ulum in the soil.

Monocropping \\'lth commOn bean.c()\vpea, maize and sorghum inCTea~ed charcoal rot diseasc incidence com­pared with fallo\\ plot,. The increase "as more ir. the plots monocropp~d with common bean and cowpea. The number of infected seedlings. lhe llumber of mfecled planlS al harveSI and number of plan!s al harvesl appear lO be good paramelers for indicating lhe level ofinoculnm in the 5011. The significant negalive correialion between Ihe number ofmfecled seedlings and Ihe number of plants at harvest suggcSls that most infected seedlíngs do not survivc tú maturi(~, Comnwn bean and cowpe~-J. mature earJier than malze or sorghum. This probably permits early formation of sclerOli" on tileso erap residues. Wyllié and Calven (l96q 1 showed flowéring aod pod formalian !O be the eondil1oning factor> for sclerotla formation. This may explain ¡he obsened tendenc)' of sclerolíal pro­pagules to increast;: in the ':ioil after harvestíng, especialIy the susceptíbie Iegumes.

It \Vas interesting to observe that the plo!s Illon­ocropped witÍl legumes resulted in signlficanll)' (P = 0.05) more disease incidenee lhan those lJ1onocropped with cereals. This was unexpected since majze and sorghum have more dry maner and provide more organic substrate for the pathogen·s lJ1ultiplication. 11 could be tha! due to thelr late muturil\· M. plla.leaNlla is not able to colonize the malze and sorghum erop debri, effectively due 10 the ver)" dry condilions usualI) experienced at the end of the seasol1. 1n addiüon the hlgher organic maneI' content from the crop debri, in these pIOIS may encourage olher competitive micro-organisms like bacteria and acti­nomycetes which reduce colonÍzalion b~ Al. plwscolinll when soil mOlsture conditions improve fGhafTar el aL 1969: Dhingra el al.. 1976). Inoculum level5 were in­crea sed by common bean. cowpea. maize and sorghum in lhat order. Francl el al. (1988) also reponed thal soybean-sorghum rotalions were slightly better than soybean-com rotations in jowering;\4. phaseolil1G in the soil. These results suggest that crop rotation among hosts of M. plzaseolina ma\' s¡ill be a good charcoal rol man­agemenl option. Work on longer elfeCIS of crop species and popu~aüon dynamics of the associated micro-organ­isms in the sollls required.

.Nl

Literature AhaWL G. s .. M A p¡\Stor~(\)rri.lk~ 1!%6). Scrccnmg and \Irulcncc

ofi:-otate,- of ;\1. plw,l<'olilw 1,) hean~.l:\bslr.) Phytopathol '16.1064. ·"nollynl\)lJ~ (19~:;)' Annual TechnH':'11 Report DOri1ml~\\n RepubiJ:

Uni\Cr~ll: orPuen,,' RIco CO\~'rca CRSP PWICC

Dhíllgr¡· .. O. D .. J H- Smcl,nr ¡ l~n7J. :-\n amwlatcd b¡bllogrilph: or M;u:rophomma rna,>l'olm ... 191J~19"5 l:niverSld.¡de Federa! de V¡.;o,,;:. VH:osa. MG. BraziL ;,md ümH'rsH~ of Illmm:, Urb:m. IL USA

Dhm!!ra. O D .. F. D. Tenne, J, R Smda¡? (1976): Melho¿ for the detennmauon o;' compdratn;; s¡iprohyiÍc coloniz.allon of \oij fungL Tran) Br l:1}CO!. ~oc. 66 (';;1, +!7~56.

Edmunds. L K_ (1964): C'ombl11ed relauon o[ plam n'lüturit~. temo perature tlnd soil moislLtre w charem\! stalJ..·rot devdonrr.ent in !!ram sorghum Phytopatholog~ 54. 514.5¡-. . w

Frand. L L T. D Wyllie. \-1 Rosenb;'ock (ln8). Influenc:: ofcrop rol.I\lon" on ["lOpUhlIlon densit~ úf Afuuol'hommfl piuH('(¡!m¡;i In ,>oil Jnfested wlth Hd{'{(j(!era!¡,~\tm(>.), Phmt Dl5:. 12. 760-764

Gharrar. A. G A. Zen!l1lycL D, e Erwm (ii/69¡' Effect ot omaníc amendmeni", OH 5e\enly or I\ía<rophomma roOl rOl ol'co!ton. P¡:n w~ patholog;; 59, C67·-1169. .

Hagedorn.D,J. \ 19(1). Ashl I't"}' h{,(II1/ In, R Ha!f(ed.J. Compendlum 01" Bean DI,.ea~es. pp. t 7-1.>. AmérKi.lll Ph;topathológical SOClel:-, Minne"ota. USA.

Magalhae) A.A. de. M. M Chúudhur~. -\ A Millar. r.,.'1.:vI Albu­querque de tl9821. EITec: of ~01i waler deti¡:¡: O~ Macrophomma phaseolma mfcctlon of bean ~grop. BrJ.$ 17,407---411

Pap<lvlza:.. G c.. r-,' G. Klag ¡ !975L hola¡¡on <lnd quamltame deter. mmatlOn oC U'lI.TopllOmw,; ¡ílwwo!/IIa fmm :.oil. PhYlopathol. 65, 182··)87

RClcherL L E. Hellinger (I'}.r¡ On lh\: {iCt:urrence. morpllolog}. <lnd pant"lilsm (lf SdeJ'm¡t¡m hmallco}u. Pa¡e~:!ne J. BOl R-ehm 0t SI:L ! 6, I07~147.

Schwd.rtz. H. F iI9l::9J: I'vliscellaneOll\ fungal p • .lthogens In: Sch\\artz. H. F. G.E. Gdhez teds). Sean productlon probJems:. Dhc~l~e. '>Ol: and chmatlc cons-tralnts 01' Piw.\w¡/¡!\ ¡{liqu!'i,. CIA T. Ca:!. ColombIa, 23g pp,

Slngh. S K .. Y L ;"'ene. :\1 \ Redd:- ¡ 199(lj: lnlluence of c,óppmg system;-, on Mocmphomlfla phÚ\NJ/ilJéI popululion:. lB <¡ell. Plan¡ Di". 74, 81:;~¡"J4,

Songa, W 0995r Vonation arÓ sunwdl of Macropj¡(1f1mw phalt'oímll m relatlOn lO <>ereenmg commo:n beml (Pha~eo¡u;, \ ul!!an~) for resl51~ unce PhD. the,,¡5. U!HveTSlt;. cf Reading. o.

Songa. V. A .. P. Omungd. M \'. Redd~ (1991): Survey of Pigconpea W:lt and olher diseases m Machakos. ilTld Knul DIstricts of Kenva. ¡nt. Pigeonpea ]\.ew~lett 14.25-26. .

Waite. B H .. A. Shakoor. I R Kermah J W K<I::'.au fl91i4;, Evaluallon of reSlstance of ;,orgnum \anetie;-, to charcoa] roL Easl Af;. Agnc. ForeSL J 44~ 359--:-63.

Wylhc. T, D., 0_ H Calven {19M;' Effect of flower remova! and pod s:él on formation of sclerOUá ánd tnfectton of Gh cinc max bv Maaophomma phaseolma. Phyiopatho:ogy 59,1243-1245. M

INTERNATIONAL JOUANAL OF PEST MANAGEMENT, 1998, 44(2) 109-114

Survival of Macrophomina phaseo/ina in bean seed and crop residue

{KeywOrds.' MaCfophcmma phaseolfna, charcoal rot. Oeans. seed Infection, crop res!due)

W. SONGAt§ and R. J. HILLOCKS¡

tUnlverslty of Readmg, Department of Agrículture, Eariey Gate, Reading, Berks RG6 2AT. UK

tNatural Aesources lnstitute. Universi1y of Greenwich, Chatham Maritime, Kant ME4 4T8, UK

Abstract. The $unval of Macrophomina phaseofma In bean see{) and crop rBsidue was investigaled. Studies on seed ¡nfection and sUNlval of fue pathogen were conducted In the laboratory. Steril¡Zabon of saed or storage for 6 months decreased the number of infectad seeds by up to 50",4,. Seeds from plants with no disease symptoms were 2.5°j" Infectad while seeds from severely lniected piants had UP to 13.5% mfectlon. Survivat of too pathogen In crop rasIDua was investigated 10 fie!d so!! in eastern Kenya. Up to 3tY?ó ot sclerotla were found 10 be vIable atter 21 mon1hs in ñeJd $oil. SoU molswr€ and temperatura did not influence survlval up 10 a depth of 20 cm.

1. Inlroduction

The mes1 serious disease of common bean (Phaseolus

vulgans L) in semi-arid easlem Kenya is charcosl ro! (Songa

and Hillocks. 1996a,b) caused by Macrophomina phaseolína

(Tassi) Goid. Yield loss lo charcoal rot has besn estlmateo to be

up lo 300 kglha (Wortmann and Allen, 1994). The incidence of

charcoal rot disease has increased in recent years because of

increasing cultivation 01 marginal land due to population

pressure (Songa and Hillocks, 1995b). Ssedlíng mortality of

10-14% ís common in experimental plots and farrners' fields

(Songa and Rano. 1995). M. phaseolina is a soll·lnhabillng

fuogus that grows poorly in soil and survives as sclerotia which

provida Ihe inrtial inoculum (Smith, 1969; Walanabe et al., 1970). This pathogan 1$ also seedbome (Andrus, 1938: Gangopadhyay

el aJ., 1970; Abawi and Paslor·Corrales. 1990). Sinee the level of

sead Inlection depends on severity 01 plant Infeelion, selecllon of

seed from symptomless plants ís expeclad to reduce the initlal

imaclían. Infected seeds are distortad. blemíshed and carry

sclerotia and pycnidia of the pathogen. Five percent reduction in

seed weígh1 and as much as 600/(, reduction in emergence fmm

diseased ssed has been reported in susceptible varietles

(Gangopadhyay el al .• 1970). Andrus (1938) found natural seed

transmisslon of M. phaseolina In Hendersoo Lima bean sead to

be approximately 85% in unsteritized seed and 57% in surlace~

sterilized seed, indícating that the fungus is found not only on the

surtaee but also beneath lhe ssed coal. Gangopedhyay el al. (1970) showed that 13-24% of soybean seed lrom infecled

plants harbour the fungus. Artificial Infecnon of bean seed has

besn demonstrated and a hlgher percentage of seedling

mortallty obtained Irom sueh pre-Infecled ssed than healthy

seed plantad lO heavlly infested soil (Andrus, 1938). The

importance of cotyledons In primary Infeelions by M. phaseolina

was emphasized by Kendrick (1933) and Tompkins and Gardner

(1935). Wlth Ihe pa!hogan establlshad In lhe cotyledon. it is nO!

important whether the infec!íon of the seed comes afier i1 IS

planted or before harves!. smce It 1$ likely !hal !he intecllon of

seed in the pod may oeeur Ihrough contaet with Infested soll.

Severe infechon early in the season results in more seed infection due to high inoculum levels on Ihe planl and soi!.

Conditions favouring ear1y ¡ntectton, such as warm temperaturas or low soil moisture, will encourage systemic seed infection,

whereas moiS! condítlons towards the and of the growing season

would be expected to encourage pod infectlon. This natural seed infection may account ter ssrious outbreaks of the dfsease

occasionally observad in farmers' fields, The majonty of small­

scale farmers who produce common bean use their own seed

from the previous crop tor cuUivation in the next season (Rono

and Shakoor. 1990). The use 01 clean dlsease-free seed would

reduce the ¡n¡tital inoculum and lower the severity ot me dlsease.

It would. therefor., be worthwhile to determine Ihe exlen! of

infaCllon of seed frorn plan!s wíth varying dlsease seventy. the

effeet of storage on the vlability of sclerotla and other sources of

inOculum carry oveL

Sc!e(otia are relaased in the soU by decaying stems and

roms ot infestad plants. They are resIstan! to extremes 01 temperature and humidlty (Dhlngra and Slnelair, 1975). Soil

temperature and morsture are ¡mportan~ factors determining

the saprophytlc actlvity of M. phaseolina in soi! (Dhingra and

Chagas, 1981). High temperature enhances 1he saprophytic

actívíty 01 M. phaseofina through raducad eompetítion from

other soil micro"'Organisms and growth in natural soils ·es reduced wrth inereasing moistura (Nortan, 1953). The

reduction in activity st íncreased moisture Jevels has been

aMbuled to incmasad bacterial aclivity whlci1 causes lysl. of

mycelium and Inhibition of sclerotia gerrnlnation

(Bhattacharya and Samaddar, 1976). High soi! moísture also

reduces the survivar of M. phaseoJmB sclerotia In soU

(Dhingra and Sínelair, 1975). Cook el al. (1973) reportad

that M. phaseolina survived as sclerotia in com and

sorghum stalk residue for 18 and 16 months. respeclively

in Nebraska, In soybeanRinfested root and stem segments

the population of sclerotia was found to be as high or higher

after 2 years In Mlssouli (Short et al., 1980). Survival 01 M.

phaseoJina sclerotja associated wfth bean residue has not

been determined,

§Present address: Kenya AgriculturaJ Researeh !nstitute {KAR1}, National Dryland Farming Research Centre, Katumant, PO Box, 340, Machakos, Kenya.

0967-0874l98 $12.00 n 1998 Taylor.& Francís ltd

110 W. Songa and A

In arder. theretore, to develop effectíve control measures tor charcoal rot di5ease basad on cultural control practicas, it is

essential to delerrmne the role 01 seed and erop debris in the survival of (he pathogen. In fulfilment of 1his requirement, this

study haO the lollowlng oblecllves:

1, To determine the extent 01 common bean seed

inlec!Ion in relalion to seventy 01 plant inlection,

2. To determine the extent 01 intemal inlactlon and

surlaea ¡nlestation 01 saed.

3. To determine the ellect of storage on viabilíty 01 sclerotia.

4 To Cletermone the survival 01 M phaseolína sclerotia in

bean residue al vanous depths.

2. Materials and methods

2. 1. Seed as saucee 01 inocu/um

Common bean genotype GlP 1004 was planted in a

ehareoa! rot 'hot spaf at Kiboko ;n eastem Kenya. The trial was malntalned following recommended production practices

including :ertiiizer application, ¡nsed control and weeding, A1

r.arvest the plants were harvested In ¡hree categolies depend~

ing on the :evej of infectioo. The categol1es were:

(1) plants with no ashy stem symptoms. (2) plants wíth ashy stem symptoms but pods w,thout

symtoms, and

(3) plant. with ashy stem symptoms and pods bearing M phaseolina scleratia.

Seeds lrom each category o! planls were tested for lhe presence ot the pathogen wíthout surface sterílization and after

surlace stetilizaúon as ctescribed below. T o test the effect ot

stOf"dge on the pathogen. enough seed was reserved and keot in

Kilner jars at room temperatura and the expeliment was

repeated 6 months later.

2.2. Non-surface slen/ized seed

Fifty unstenlized seeds rrom each category were placad on

múlst filter paper placad on plastlc trays previously cleaned and

wipad with alcohol and enverad. Them were tour replícations in

a campietely randomized design. The trays were incubated al

33 e with a 12 h dL. 12 h D lighl reg,me. The trays were maintained moist by adding distllUed waler when they became

dr)'. Obs€lVation lar the presence of M. phaseolina was done

using a binocular microscope from 3 to 7 days after jncubation at

33 C. The number of seeds that produced colonies of M.

phaseolina on the seed coat, characterízed by numerous black

sClerotia, were notad, Seeds wlth other fungal growth W9m

lransferred 10 PDA for identificatioft The expeliment was

repea1ed once.

2.3. Surface s/enlized .eed

The procedure trere was as descnbed above tar unsleri!ized

seed and the only difference was that the seed was surface

sten!lzed by Irnmefslng 111 1% NaOel (10°.-;, dilutíon of commer~

c,ally available solution diluted with distilled water) lor 5 - B min

and thoroughly rinsad in distilled water (Mihail and Alcom,

1982). Ona percenl NaOCI kills M. phaseolina ",ycelia lhat may

be on lhe seeds and reduces sign<!icanlly lhe viability 01 .elerolia (Papavizas and Klag. 1975).

2.4. Survival ín bean crop debns in fleld soíl at different depths

An experiment to determine the longevity 01 M. phaseolina In

bean debris was conducted at Kiboko research station in

eastern Kenya where charcoal rot dlseasa iS prevalent. The

soll 15 a wel! drained sandy clay loam overlaying a sandy elay

(tabla 1). About SOO 9 01 bean debris (root and stem segments measunng 6~8 cm), heavdy intested with sclerotia of M.

phaseofina were placed in nylon net bags and bulied in the soil al lour depths (0-5. 5-10. 10-15. 15-20 cm). There were

eighl samples butied lor each deplh in three replícations. A

tabelled wire peg was insertad at each point where a sample

was burlad ta facilitate retrievaL The experimental design was a

randomized complete block. The lield plo! was kept lallow and

W8S mamtalned to keep the labanad wire pegs Visible. Sojl

moistU(9 ánd temperature measurements were taken as

descrlbed below. The experiment commenced in ADnl 1993

and ended in December 1994, covenng a :olal penod 01 21 monH,;s.

2.5. Determínation of sc/erotial viabílity

The sclerotia vlabillty at the begll"lnrng of the experiment was determined by plating 100 sclerotra from infectad erop

debrís on selectiva medium PDA·DOPCNP (basal medium

comaming p-(dimethy!amino) benzenediazo sodjum sulpho~

nate [DASS, Dexonj, oxga!L and pentachloronitrobenzene

[PCNBí al SO. 2.000 and 100 mgíl respectvely) (Papavlzas and Kiag, 1975). The debris retrieved from the soil was air

dned and ground using a caffee grindec The debris was

transferred to 177 !Im and 44 ,Hrn Sleves ;f'¡ tandem and wet

sH?ved using dis;iI!ed water. The ccntents of the 44 ¡1m slsve

were transferred to a beaker contaíning 0.5°·;:. NaOe! for 5-8 mln and the contents oi the 177 um sieve were discarded.

The contents of the beaker were transferred back to the

44 um Sleve and rinsed thorough!y with distllled water, The coments of the $ieve con1aining sclerotla were carefully

tansferred 10 a mter funnel fittad w,!h f'lter ::lape! uSlng a

wash bottle Wlth distilled water. The scle:olla on the filter papG( were picked out using a stenlized pm under a

binocular microscope and plated 071 the selectiva medium,

Observa110ns for M. phaseo¡ina COIOnles were made afier 6

days' incubation at 32 e, Percentage gem:lnatlon was taken

Tabie 1. Percentage 01 sand. silt. and clay part/efes in different 18yers ef (he SQ¡i prohle at Kiboko. Kenya (Kenyá 50/1 5urvey. unpub/ished data)

Depth (cm) Sand S,II Clay ....... __ . .... ~_ .. _ ..

0-19 74 5 21 19-35 70 5 25 35-72 54 5 41 72-'10 54 7 39

Expl Agrie. «(997), volume 33, pp, 459-468

Printed in Greal Britain

Copyright © 1997 Cambridge Un,,~rsily Press

SCREENING COMMON BEAN ACCESSIONS FOR RESISTANCE TO CHARCOAL ROT (MACROPHOMINA

PHASEOLINA) IN EASTERN KENYA

By W, SONGAt, R, J, HILLOCKSt, A w, MWANGO'MBE§, R, BURUCHARA, and W, K. RONNOII

t Department I!f Agrículture, The Uní1!ersity I!f Readíng, Earley Gale, Reading RG6 6A Y, UK, tNatural Resources Institu/e, University of Greenwich, Chatham

Marítimo, Kent ME4 4YB, U K, §University of Nairobi, Dopar/mml of Crop Seicoce, PO Box 30197, Nairobi, Kenya, 'Centro Internacional de Agricultura

TroPica! (eIA T), EastAfrican Bean Research Network, PO Box6247, Kampala, Ugnada, and I I Ke'!1" Agricultura! Rcsearch Institute (KARI) , National Dryland

Farming Research Centre, Ka/umani, PO Box 340, Afachakos, Kenya

(Accepted 20 ¡Hay 1997)

SI,;MMARY

Cornmon bean (Plulseolus vulgans L.; germplasm was scrcened for resistance to charcoal rot (Macrapllómino. pluJ.seoHna) under field conditlons at Kiboko and Katumani, eastern Kenya. Of the 313 bean accessions evaluated, 50 lines ,"¡ere resistant and six were tolerant to M. pluutfJ[ina, the charcaol rot incidence was less than 25% and between 25% and 50% for the resistant and tolerant linn respectively _ YleIds ranged from 135 to I05l kg ha - J comparffi with 55 kg Cor the susceptible control A4{)4. Time to maturity djd not seem lO influence or affect the susceptibility or resistance to Al" pnaseolina ofthe val'ious bean accessions,

lNTRODUCTION

Charcoal rot of common bean (Phaseolus vulgaris) is caused by Macrophomina phaseolina (Tassi) Goid. The pathogen is widely distributed in the tropies and has a wide bost range (Cottingham, 1981), The fungus can cause disease in seedlings and mature legume plants and it is responsible for stalk and root rols in cereal crops, In hot areas prone to moisture stress the fungus causes economic losses (Dhingra and Chagas, 198/), Increasing population pressure has led to the cultivatíon of food erops in the castern parts of Kenya previously regarded as unsuitable for erop production due to the unreliable rainfall (Gitu and Ngalyukia, 1989; Songa and Ronno, 1995; Songa and Hilloeks, 1996). These arcas experience severe chal'coal rot incidence and sustainable management of M, phaseolintt is vital ífbean production is to inerease in the regíon,

An integrated approach to the management of diseases and other pests is

tPreSf'nt addres¡;: Kenya Agrkuhural Res:earch Institute, Nacional Dryland Fanning Research Centre, Katumani, PO:&x 340, Machakos:, Kenya.

460 W. SONGA et al.

preferred because it relies on several methods for control. Host plant resistanee, where available, usually assumes a central position in the integrated disease management approaeh. This is because it is easily adopted, requires few inputs and is therefore economically advantageous. Common bean is reported 10 have resistance 10 ivl. phasealina (Pastor-Coralles and Abawi, 1988; Echavez-Bedel and Beaver, 1986; 1987). Pastor-Corrales and Abawi (1988) developed an interna­tional charcoal rot bean nursery of 40 accessions based on greenhouse and field data. However, resistan ce to disease may vary depending on the environment and the cultivar (Beebe and Pastor-Corrales, 1991). For this re aso n it is important for each country to screen germplasm and develop resistant varieties which are adapted to the environmental and climatic conditions that prevail within a given country. Screening for resistance to M. phasealina was done at charcaal rot 'hot spots' at Kiboko and Katumani in eastern Kenya (Songa et al., 1992; Songa and Hillocks, 1996). In addition, early maturing (drought escaping) genotypes were compared with late maturing genotypes for resistance to M. phasealina under field conditions. The objectives of the work in this paper were therefore:

l. To screen common bean germplasm for resistance to M. phasealina. 2. To develop a common bean charcoal rot nursery for use in bean improvement

programmes in the semi-arid areas of eastern Kenya and other areas of eastern Africa.

3. To test the hypothesis that a drought escape mechanism may confer resistance to M. phasealina.

MATERIALS AND METHODS

Screening camman bean germplasmfaT Tesistance Screening common bean germplasm for resistance to M. phasealina was

conducted at KARI centres, Kiboko (960 m asl) and Katumani (1575 m asl) in eastern Kenya. The inoculum used for field inoculation consisted of a mixture of isolates of M. phasealina from eastern Kenya. It was prepared as follows: whole grain rice seeds in beakers covered with aluminium foil were sterilized by autoclaving with water in a one-lO-one ratio (1 g rice seeds to 1 mI water) at 121°C for 15 minutes and then caoled. A 0.8-cm disc, cut from a seven-day-old culture of M. phasealina on patato dextrose agar (PDA) was transferred into each beaker containing rice seeds and incubated at 30-32 oC for 15 days. The fungus colonized the rice seeds within 14 days. The colonized rice seeds were used for inoeulation al planting by placing three rice seeds per bean seed before covering with soil. This rate ofinoeulation was found suitable in preliminary experiments in this study (Songa, 1995).

A IOtal of 313 cammon bean accessions eonsisting of local, improved and introduced germplasm were evaluated for their reaction to M. phasealina. They were evaluated in batches over three seasons. Eighty, 101 and 162 accessions were evaluated during lhe long rains, March-July 1993, the short rains, October 1993

Common bean resistance lo charcoal rol 461

toJanuary 1994, and lhe long rains, ~arch-July 1994, respectively. Orthe 313 accessiom evaluated ínitially, 30 accessions were evaluated a second time. The susceptible líne A 464 from CIAT was used as a control in each 01' the evaluatíon trials. Each accession was planted in two rows, each 2 m in length per replication. Each row was planted with 30 seeds. One of the twa rows for each accession was inoculated and the other was left as a control. Inoculation was with AJ. phaseolina­colonized rice seeds as described eadier. The experimental design waS a rando­mized complete block with three replicatíans. The parameters measured were plan¡ stand count al 14 days aner emergence, number of infected seedlings, number ofinfected plant' at harvest, total number of plants al harvest, grain yíeld (kg ha -)) and percentage charcoal rot incidence. The accessions that performed at least three times better than lhe susceptible control, A 464, with respect lo the number of infected plants at harveSl, yield and good agronomic characteristics, were selected la constitutr lhe charcoal rol nursery. Lines with good adaptabilíty but marginal performance in the aboye mentioned parameters were re-evaluated.

Drought escape and resistance la M. phaseolina Reactions of early- and late-maturing accessions lo !v!. pha.reolína were com­

pared 10 determine if time to maturity influenced resistanee to the pathogen. Field experiments were eonducted at lhe KARI centres, Kiboko and Katumani. Ten early- and ten late-rnaturing aecessions were used in the sludy and the early- and late-maturing lines reached 50% flowering between 25--37 and 38-45 days after emergence respectively. Each aceession was planted in two rows (30 seeds per row) of which one was inoculated using rice seed colonized by the pathogen and the other left as !he control. The early and late maturing accessions were planted alternately in a randomized complete block design in three replicatíons. The susceptible line A 464, which is early maturing, was included as a control. The parameters measured were number of emerged plants, disease incidence at 14 days after emergence, number oC days to 50% flowering, disease incidence and number of plants at harvest. Due to the difference in malurity lhe parameters taken at harvest had a time difference of ten days.

RESUl.TS

Screening commQTI bean germplasmfor resistance to M. phaseolina The 313 accessions evaluated varied in their rcactions tú M. phaseolina at both

!he Kiboko and the Katumani screening sites. The disease incidence was usually higher at Kihoko than at Katumaní (Table 1). Significant differences in emergence count, number of infected plants at harvest, stand eount al harvest and seed yield were abserved between accessians (Table I and :1;. Charcoal rot incidence ('lo) and seed yield (kg ha -!) were lhe most indicative of the overall response af common bean accessioIlS lo !v!. phaseolina (Table 2) Sorne accessions, for example V 8025 and BAT 1651, appeared susceptible at lhe end of the season, but the seed yield was still satisfactory. No significant differenee in charcoal rot

462 W. SONGA el al.

Table 1. J'{umóel if errurgtd plants atUi number rif plants inJected ufith Macrophúrnina phascolina at harVfst j01

tu:ml)'./our rltwsions o/ common btan ftáwmng helwn:!! Mirf) ami thirty:fiw days afia waluahd al Katumani mui Kívo!w during t/u: tong rairu in 1994t

Katumani Kiboko

Number of Number Number of .:\'umber emerged infectcd at emerged infected at

Accesruon Introduction Origin plants harvest plants harvest

GLP819 20~2~3~35 Kenya ]7.8 1.8 20.3 11.3 GLP 1032 Extender USA 13.8 l.0 20.5 9.5 GLP29 Porillo·I·H Unknown 18.5 l.B 19"6 8.6 GLP41 Diacol Nima x Verdon Uganda 14.8 1.I IB.l 8.5 GLP 987 Panarninto Corriente Unknown !6.0 0.3 2!.3 8.! GLP990 Turrialba 1 USA !5.8 0.0 20.1 8.1 GLP65 Dark Red Kidney USDA 20.1 2.! 23.6 8.0 GLPl102 Vcracru1. i·A-6 Colombia 17.5 1.0 nI 8.0 GLP425 75·N2B-2829-5-lBK Puerto Rico 19.5 0.8 20.1 8.0 K9¡38B Kenya 16.! 0.8 19.1) 7.8 GLP938 FFOOO!2-3-IMF5 Colombia 17.6 0.8 18.5 7.6 GLP !044 Lazy Housewife Seychellcs !7.6 l.B 22.5 7,6 GLP 988 San Pedro Pinda Unknown 18.5 2.3 21.1 7.5 K23¡45A Unknown Kenya 15.6 0.1 20.1 i.5 GLP973 :Vfountaincr White Unknown !9,8 0.0 23.1 7.3 GLP 351 Red Haricot KenYll !). ! I.! 24.5 ).3 K,3/26B Unknown Kenya 17.6 0.0 20.3 7.3 43338 Unknúwn Kenya 19.6 2.8 21.6 ).3 GLP 1004 Mwezi Moja Kenya 16.5 2.0 21.0 7.3 GLP294 Rose Coco Kenya 12.! 0.6 20.5 7.1 GLP 1121 PI 203937 Colombia 19.5 1.5 19.8 7.0 A464 G4004 x Al7 CIAT 18.4 5.0 21.2 11.5

Mean 16.99 0.87 18.7 .1.l4 s,e, 0.16 0.05 0.16 O.JI

tThírty seeds were &O\.\'n per row and the numbers given as emerged and infected are average;; of the replications of the inoculated rows.

inódence withín accessíons was observed between inoculated and uninoculated plols. The susceptible control, A 464, was also useful as an indicator of !he uniformity ofinoculum in the field. Based on ¡he field data collected, a nursery of 54 accessions (Table 2) is now lo be lested against infeclÍon by M. phaseolína in difrerent bean growing areas of eastern Kenya.

Droughl escape in relatíon lo resistance Early maturing accessions had sígníficantly more seedling ínfeclion and more

ínfected plams al harvesl Ihan the late maturing accessions. The numher of seedlings ¡ha¡ emerged and the number of plants al harvest were no! sígnificantly difrerem for ¡he two maturily groups (Table 3.). The early maturing accessions were observed lo have more ínfectíoll and wíltíng than the late maturing accessíons al both Ihe seedling and post-flowering slages at Kiboko (Table 3.). However, at Kalumani Ihe late-maturing accessions GLP 65, GLP 927, 43309,

Common hean restslance lo charcoal rol 463

Table2, Chan;oai ((JI incidmee (%) aM sud weigkt (kg ha -1; ojreslslanl and lOleran! hean acamiJl;!S t!tJ4luaudjor !kiT mutúm to Macrophomina phaseolina al Kibof.o, Kef!~

Incidence of Accessiún Introduction Origin char<:oal rot Seed weight

Sourus IJf kMwn TesiJtance BAT 1289 Latín America erAT 28,1 Tolerant 248,0 BAT 1385 Latin Amen,ca crAT 15,6 Resistant 285,0 HAT 1669 Latio America CrAT 42.3 Tolerant 335,2 BAT 1400 Latin America crAT 19,0 Resistant 252,2 BAT 1293 Latin America CrAT 14,7 Resistant 211,; SAl' l651 Latin America CrAT 26,4 Tolerant 535,2 BAT 1297 Laün America CrAT 17,2 Resistant 135,2 HAT 125 Latin America CTAT 31,6 Tolerant 350,7 V 8025 Latin America CrAT 46,6 Tolerant 300,5 V 8017 Latin Arnerica CTAT 21,6 Resistant 519,5 V 8010 La tio America CrAT 9,2 Resis[ant 376,7 EMP,86 Latín America CIAT 13,6 Resistant 332.5 G 5059 Latin America CIAT 13.2 Resistant 1050,2 A55 Latin America CIAT 145 ResistaIlt 434,2 CG 82·69 Latín America CIAT 22.0 Resistant 413,7 CG 82·79 Latin America CIAT 19.2 Resistanl 385,2

Newt'l' identified fiGUreeS of re.rutancc

GLP914 FF'OOO262·M(2)F4 Colombia 6,0 Resistant 729,5 GLP80a T endergreen USA l4.0 Resistant 825,) GLP 274 Rose Coco Kenya 3.4 Resistant 405.2 GLP 409 P566·A Colombia 8.3 Resistant 411.2 GLP927 FFOOO241F4 C'.olombía 15.8 Resistant 417,7 GLP 184 22/11113/5 Kenya 3.4 Resistant 709,0 GLP211 P·]]-D-L Kenya 20,2 Resistant 402.5 GLF805 K78(ex Kawanda} Kenya 30.0 Tolerant 403,0 GLP 967 SR/72¡LKY58 Kenya 13.3 Resistant 454,2 GLP 1092 California SmaJl White Colomhia 7,2 Resistant 733,2 GLP924 FFOOO2IHiMF4 Colombía 0,0 Resistant 995.5 GLP642 Field 18·1'47 Hal«", Colombia 10,9 Resistant 624.5 GLP270 Bura Yellow Renya 11.7 Resistant 664.5 GLP240 Canadian Wonder Kenya 0,0 Resistant 600.5 GLP584 Royal Red USA 5,4 Resistant 259.2 GLP 1206 Red Me. UISó Netherlands 10.9 Resistant 302.0 GLP 1106 Ganajuatn LO-A-5 Colombia 1.9 Resistant 775.2 GLP li02 Veracru't*1~AM6 CoJomb¡a 18.7 Resistant 616,5

.Newly Uienlijied J(jurces (jf rtsiJumee EIO Kenya 3.4 Resistant 637,-0 K13¡26B Kenya 0,0 Resistant 659,2 K9f38B Kenya 6.5 Resistant 752.2 13335 Kenya Hi.6 Resistant 578,0 43308 Kenya 5.8 Resistant 862.2 N 17 Kenya 7.5 Resistant 618.7 N47 Kenya 13.5 Resistallt 1051.2 N43 Kenya 3.3 Resistant 164.5 N26 Canadian Wonder Kenya 8,9 Resista,nt 774,7 N 38 Kenya 1.6 Resistant 999,0 N 36 Kenya 13.0 Resistant 946,2

464

Table 2 (cominued). Charwal fO! incidente (%) arld lecd l.L'eight (kg ka~/) rif rtStstanl and tokrant bean lVxes .. úms evolualedfof lhm Teac!ion to Macrophom¡na phaseotina ai Kihoko, Kmya

Inddence or Acces"ion Introductiún Origin charcoal rot Seed Weig!H

'S 45 Kenya 6,0 Relltstant 743.7 :.; 18 Kenya 8.6 Resistant 618.7 );6 Kenya 6,0 Resistan! 896.7 :-; I1 Kenya 13.3 Resistant 781.5 ~IWEZI ~lOJA Katumani Local Kenya 25,5 Reslstant 554.0 :';YAYO Rose Coco Uganda 73 Resistant 953.5 KATX-16 KatB9 x ~L\loja Kenya 11.7 Resistant 442,7 KATUMBUKA Pinto Kenya 9.4 Resistam 1001.5 Ka,B2 l\hkueni Kenya 18.2 Resistant 378,0

Knowl! slI.saplible cQntrols A 464 C1AT 35,7 Susceptible 55.0 A70 CIAT 39.2 Toleram 275.0

43316, 43335 and GLP 1130 were found to be relatively more susceptible íTable 4_;. The average numbers of days to 50% flowering in the early- and late­maluring accessions were 33.3 and 4.0.1 respectively at Kiboko and the average ternperatures at the time of flowering \Vcrc 25.5 oC and 23.5 oC for the early- and late-maturing accessions respectively (Fig. 1). No significant difference was observed between inoculated and uninoculated rows for any of lhe parameters measured.

D1SC¡;SSION

Several bean accessions were found to be resistant to Al, pilaseatina and the field evaluation procedure was effective in separatíng bean accessions into two general groups according to their reacdons, oamely, promising material for further evaluation and highly susceptible accessiollS. The absence of significant differ­ences between the inoculated and uninoculated plots indicated adequate levels of inoculurn in the plots which had been used to grow beans for several seasons. This was confirmed by the susceptible control, A 464. The reactions of susceptible cultivars wcre evident soon afler germination, Emerged seedlings of these accessions showed ¡he typical dark sunken lesions on the cotyledons caused by M. phaseotilla infection. The lesions often expanded and killed the seedlings wilhin 14 days. High levels of seedling infection usual!y resulted in lower stand counts al harvest (Table 3). These observations agreed with Gangopadhyay el al. (1970) who reported severe damping-off of soyabean seedlin¡,'S with plant losses up to 77 %. M ost of the accessions with good resistanee had low levels of seedling infection and smal! numbers of plants infected at harvest. However, sorne accessions, such as EAT 165 J, V 8025 and BA T 1669, had about 50% or more of lhe emerged plants infecled al harvest but stiU had satisfactory seed yield

Common bean resistance lo charcoal rol 465

Table 3. Re4ct!afiS vI ear()'~ ana late-maturmg nfan ;1((I'j'súms lo itifulion hy ~fa(;rophomina phascolina al Kzboka, eOJtrm KI!!lya

Numberof ;\"umbel' or Days to :Xumbcr of ..'iumber of seedlings seedlings 50:;"0 plants 3t plants infcr.ted

Acct':ssion MaturÍty group emerged ¡nfectcd ftowering harvest at harvest

GLP 101J4 carly 21.8 6.5 35.8 17.0 6.8 GLP916 early 24.5 3.8 36.5 18.8 4.1 GLP967 earJy 20.6 6.6 35.6 14.0 1.8 A 464 eady 24.8 4.3 35.3 17.6 7.0 GLPI121 carly 22.1 5.3 36.8 17.5 2.6 GLP236 early 18.6 7.6 36.1 16.1 2.0 43309 carly ZZ.Ü 2.5 36.8 17.5 2.6 GLP 381 carl}' 2·1.0 5.8 35.3 14.3 4.6 GLP 1092 early 21.0 9.6 36.1 16.0 2.3 GLP911 early 20.8 3.8 36.5 13.0 5.1 GLP IIS6 late 21.6 7.6 39.3 20.3 2.1 K23j45A latf' 22.0 4.1 40.5 15.3 3.3 GLP41 late 20.3 6.6 40.6 14.3 1.8 GLP 988 late 2l.l 6.6 37.6 20.1 2.3 GLP 768 late 20.6 50 39.6 14.8 2.0 GLP 1130 late 20.1 6.0 40.1 15.8 2.8 43335 late 21.5 3.5 39.8 17.3 3.1 GLP927 late 21.0 2.3 38.6 18.3 4.0 GLP65 late 225 6.8 42,8 19.6 3.1 l'i13 late 20.1 3.5 38.5 18.1 LB 43316 late 23,6 3,0 43.0 16.1 4.6

Mean 2168 4.4~ 38.45 16,7 9.7 s.e. 0.33 0.27 0.26 0.39 0.27

(Table 2). In these acce5sions the fungus was evident only on ¡he plant 5tems in advanced senescence and the lines were still selected for possible high toleranee to the pathogen, Late infections were more obvions after flowering during periods of high temperature and rnoisture stress especíally at Kiboko, This observation supported the severe infectíons of charcoal rot reponed ar high temperatures during períods of moislUre stress (CIAT, 1983; Dhíngra and Sinclaír, 1977). Infected plants were chlorotíc and less vígorous in growth. It was encouragíng to find thar sorne of the ímproved accessions for semí-arid arcas, such as GLP 1206, GLP 1092, GLP 914, E 10, :;¡ 36, N 1 I and :;¡ 43, performed well. Thís was partícularly so [or accessíons from the Uníversity ofNairobi bean programme that had also been found resistant to several foliar diseases (A, \V. Mwang'ombe, Universíty ofNairobi, personal communication).

With a few exceptions lhe early-rnaturing lines were significantly more infected at both lhe seedling stage and at harvest (Table 3). Early-maturing GLP 967 and lale-maturing GLP 41 appeared lo be susceptible at the seedlíng stage but were re,islam at lhe mature plam stage. Both had 6.0-6,6 seedlíngs infected but only 1.8 plants ínfected at harvest. This observation suggested di/ferent resistance mechanisms at Ihe two plant stages. Sorne late-maturing

466

25

6 e.... 24 I!! j "'23 E

{E

W. SONGA el al,

50"k flowering (early)

o 10 20 30 40 50 60 70 80 Days !rom emergenee

Fíg. 1. Temperature at time of ftoweríng of the early- and Iate-maturing ;\o::essiom; at Kíboko during the shortraimin 1994,

Iines, 43316 and K23¡45A had a high incidence of seedling infectíon and also large numbers of infected plants at harvest. Sinee drought-to1erant accessíons may be late maturing, these observations did not lend much support to lhe view ofPastor-Corrales and Abawi (1988) who found that drought-tolerant cultivars were also highly resístant to lvf. pkasealina.

The reactions of the early- and late-maturíng accessions tú 1'11, phaseatina at Katumani were generally similar to those observed al Kíboko bul much less bevere (Tahle 4), Sorne aecessions fOf example GLP 65,43316, GLP 1130,43335, and 43309 had almos! egual numbers of infected plants at harvest at both sites. These accessíons were al! oflate maturíty and were the most susceptihle at Katumani, lt appeared therefore, that early maturing accessions escaped ¡nfectíon al Kalumani due to less favourable cOllditions Jor the pathogen early in the scason,

A! Katumani Iloweríng occurred between one and e¡gh! days later than at Kiboko dependíng 011 the accession. Delayed Ilowering al Katumani was particularly obviaus for Ihe accessíolls GLP 768, GLP 1130, K23¡45A, N 13 and

Common bea" resistance lO charcoa! rol 467

Table 4. Rrac¡if)ns of UJr(y~ and late·malun'ng hean flCufisl:ons to Ma<Túphomina phaseolina al Kibako and Katumani

Kiboko Katumani

Days to Number of Numberof Days to Number of Numherof Maturity 50(1/0 plants at infected plants 50\% plants at infected pJanrs

Accession group ftQWerlng harvest at harvest fiowering harvest at harvest

GLP 1004 carly 37.8 17.0 6.8 36.0 19.7 0.2

GLP65 late 42.8 19.6 3.1 44.0 22.6 2.1 GLP976 ear]y 36.6 18.8 4.1 36.0 22.6 0.1 GLP 1186 late 39.3 20.3 2.1 41.2 18.8 1.8 GLP927 latet 38.6 18.3 4.0 37.U 19.5 2.2 43316 late 43.0 16.1 4.6 44.2 24.0 4.1 GLP236 cady 36.1 16.1 2.0 35.7 14.5 0.0 GL!' 768 late 39.6 14.8 2.1 43.2 19.5 0.2 GLP3BI early 35.3 14.3 4.6 36.7 21.5 0.0 GLP 1130 late 40.1 15.8 2.8 430 18.1 2.' GLP911 cady 36.5 13.0 5.1 37.2 17.s l.l 43335 late 39.8 17,3 3.1 43.6 25.0 3.1 GLP967 cady 35.6 14.0 l.B 36.5 18,0 0.1 K23¡45A late 40,5 15.8 2,B 43.2 17.0 0.1 GLP 1092 early 37.1 16.0 2.3 36.5 18.0 0.1 GLP41 late W.6 14.3 1.8 41.2 18.8 0.0 Gl.P 1121 cad)' 36.1 17.) 2.6 44.8 17.2 2.6 :-< 13 late 37.6 20.1 2.3 39.0 14.6 0.1 GLP 9!l8 late 37.6 20.1 2.3 39.0 14.6 0.1 A 464 early 35.3 17.6 7.0 3.5.2 14.6 1.8 43309 early+ 36.8 17.5 2.6 44.8 17.2 2.6

Mean 3B.4 16.7 9.7 39.66 19.27 l.26 u:. 0.26 0.39 0.27 0.32 0.41 0.15

tGLP927 is late at Kiboko but early at Katumani, t43309 is ear1y at Kiboko but late at Katumani.

43309 which look 43.2, 43.0, 43.2, 43.0 and 44.8, and 39.6, 40.1,40.5, 38.5 and 36.8 from emergence to flowering at Katumani and Kiboko respectively (Table 4). These observations were expected sinee Katumani is higher in altitude (1575 m asl) and the mean temperature is lower lhan al Kiboko (960 m asl). The lower temperalures al Katumani may have been responsible for lhe lower incidence and seventy of lhe disease al this site. Sderotia ¡ormation has been linked mainly with flowering (Wyllie and Calven, 1969). The early-flowering accessions would probably be earlier in displaying susceptibilily and at a time when the tempera­ture was still relatively high and more conducÍve to the pathogen. The general trend for temperature was to decrease gradually [rom the beginning to the end of the scasan before increasing again al the beginning of the next scason as índícated in Fig. 1.

Acknowledgcments. Acknowledgement is made to lhe Kenya Agricultural Research Institule (KARI), Centro Internacional de Agricultura Tropical (CIAT) and lhe KARI¡ODA Crop Protection Project for their material and financíal assislance.

468 w. RONCA el al.

REFERENCES

Beebé j S. E. & Pastor-Corrales, M., {1991;. Breeding for disease res.istance. In Common Beam: RescalCh}or Crop lmpravement. 56l--617 (Eds A. van Schoonhaven and O. Voysest). Wallíngford, UK: CAB lNTER:-IA TlONAL ann GIAT.

CJAT (Centro Internacional de Agricultura Tropical) (1983). Btl1n Pmgrarnme Annual Report. Cal¡, Colombia: eIA T.

Cottíngham, G (19B1). N umbers ami di.stributÍon of sderotta of AflJCroplwmina p.h.as(olina Ín soils ofSouth Carolina. Planl DÚfilsr Rt:p(JTJer 65:355-356.

Dhingra, 0, Do & Chagas, D. (1981). Effect ursoil tempera.ture, moisture and nitrogen on competitive saprophytic ability úf .U(J.(:TilfillOmína phaJe1Jlina. TransatiÜms if Ilu BrÜiJ!t AfyeofolJical Socíety 77: 15-20.

Dhingra, O. D, & Sindair,J. B. : 1977). An Annotatcd Bibliograpn) qfMacropnomina phaseolina, 190~1975. ViCOS3, Brazi1; Universidade Federa! de Vicosa, ancl Urbana j OSA: University oflllinois.

Echavez-Bedel, R, & Bea\'cr,j. S. {1986). Rcsistance ancl susceptibilily ofbeans, Pkaseolus vulgaris L, to ashy stem blight, Al. phauolina (Tassi) Goid. Journal 01 the Agricultural University I)I Puerto Rico 70:4ü3-405.

Echavez~Bedel, R. & Beavcr, J. S. (19B7). Dry bean genotypes and M. pJumolinu in inoculated and non­inoculated field plots, ]ourna/ qftke Agricultural Univers#y rif Puerlo Rico 71 :335~390,

Gangopadnyay, S'I \Vylhe, T. D. & Lueders, V. D, (1970). Charcoal rot disease ofsoybean transmiHed hy seeds. Plan! Disease Reporter 54: ]088-1091.

Gitu, W. & Ngalyukia, C. A. K. (l989}. Agriculturt and Lúm[óCk Dala Compnulium. Nairohi: Ministry of Planning and National Development, Long Range Planning UniL

PastofwCorraJes, M, A. & Abawi, G. S. (1933). ReactioIlS of selected bean accesslons to infection by Alacrophamina pkdJ(olina, Planl DU!!OJI! Reporta 72:39-4l,

Songa, W. (1995). Varlation and survival of Macroplwmú'uI pJuUtóltM in relatlon to screening common bean for resÍ5tance. PhD thcsis, Univt"rsity ofRead.ing, UK.

Songa. \,\', and HiUocks. R,j- (1996). Charc.oal rot in oornmon bean with special reference to Kenya. lnternatiofUd ]fJun¡al tif Pert Mau.agement 42:2)3~219.

Songa, W. & Ronno, W. K, (1995). Proouction constraínts of beans in semi~aricl eastern Kenya with spedai rcferenct:' to chaH~oal rol. In Brttdingfo"l Distase ResiJtance with Empltasis en Dtlrahili~y. Precetdings vi a RegIOnal Worksiwp for Et15ttrrl and Souimrn Africa, .Njoro. Kfmyfi; Octobef 2-fi, 1994,251--254 (Ed. D. L. Daniat). Wageuingen: Agricultural University, Plant Breeding Department.

Songa, W, A, Omanga, P. & Ronno, "VV. K, (1992). Sut'en¡ng for sources ofresistance to major discasesof bcans, pigecupeas, cowpcas, and chickpea ín semi~arid arcas 01" Kenya, [Unpl.lblished} paper pre.sented at che Third Kenya Agricultural Research Institute Confercncc held in Nairobi, 7··9 Octobcr, 1992.

Wyllic, T. D. & Calvert, O. H. (1969), Effect ofHower removal and pod set on formarion ofsderotia and infection of Gb'cirlt' max by !v!()(r¡¡phominfi phaseolillfi. Phytopatho!ogJ 5-9: 1243···1245.

Survival 01 M, phaseotina in bean semi and crop ~sjdue 111

as an index oí viabílity. During subsequent samplings. a mmimum 01 30 sclerotia from each sample refrieved every 3

months were pletOO on Ihe selecliva medium and observed tor germination,

2.6. Measurement of soil moisture

A single aluminium access tube with an internal diameter of

50 mm was installed In the middle of each plot repllcate to a depth of 40 cm al Ihe lime lile infected crop debris was buried.

Using a soil moisture neutron probe (Didcot Instruments, Abingdon, UK) readings were taken al 0-5, 5-10. 10-15

and 15-20 cm twlce a monlh during the fírsl and lasl week 01 each month tm the duration of the experiment. The following

ealibration equation was obtained from fjeld measurements at

10 cm depth:

o 3.34 ., 55.8i (R2 ~ 0.491

where O is the percentage volumetric mositure content and {:i is

the neutron proba eount expressed as a fracUon of the eount in

waler (Sell. 1976). SIX and eight soll samples were used lo determine bulk density anrl gravimetric soil water contenl

respect\ve\y. The volumetric water content was then calculated

from average bulk density and gravimetric water content.

2.7. Measuremen/ 01 soil temperature

Soil temperatura was measured at the tour depths at which

the infested crop debris were bunad in the plots. The

measurements were taken daily at 3~h ¡n'ervals trom 06.00 h lo 18.00 h using portable soil thermometers (EL504-024) rn

rugged brass cases wtth stems graduated al 5. 10. 15, 20. 30 cm to enable measurement at various depths. The tempera­

ture was not laken in aaeh replicate bu! randomly wrthin the plOI

2.8. Dalá ana/ysis

ANOVA was used to compare the seed Infection and jnfestatlon 01 surface sterilized and unsterilized see<:!. The Least

Significanl Dmerence (LSDj test was usad to separate group means where ANOVA indiealed significanl differance (P=O.05).

ANOVA was also usad to compare sclerotial survwal at different

depths in the soll.

3. Results and dlscussion

Seeds Ihat produced colonias oí M. phaseolína were soon

eoverOO willl blaek sclerolia and were easily rdentiliOO. ANOVA showed signiffcant dlffarence F:38.21; dt:2.36: P:0.05) in seed ínfection and infestation batween surtace steriljzed and

unsteri/ized seed o, the thrae categories of seed. LSD test for mean. <¡Qm¡la(¡SQ(\ showOO no signifIcan! difference (P= 0.05)

between surtace sterilized and unsterílized seed ot category

one, in the number of seeds that produced M phaseo/ina at harvest and 6 monttls later (table 2). However, there was a significan! difference (P=0.05) between slenlized and unster· ¡¡izad seed of category two and three fn the number of seeds infected wi!h M. pIlaseolina at ha"'as!. Category three had a signifieantly higher number of seeds infectad comparad wnh categories one and two for unsterilizs,. seed (table 2), Afier 6

monlhs 01 storage there was no signlflcant diffarence (P = O .05) be1ween category two and three in the number of seeds infected

wlth the pathogen and for the unsterifized seed, this was signfficantly (P= 0.05) lower than at harvest. 80th categories two

and Ihree seed hád signihcanlly higher inlected seed Ihan

calegory one. 6 monlhs after ha ",es!. Olher lungi found lo be assoclated with the infected and Infestad bean seeds were

Aspergi/lus niger van Tiegh.. Aspergil/us ffavipes (Bainier &

Sartory) Thom & Church., and Penicillium variable Sopp.

The rasu~s indicate Iha! by selecting clean heallhy lool<lng

plants lor seed, the innial inoculum due to seed infection can be

Tabie 2. Common oean seed infecflOn and infestatlon a1 harvcst and

after 6 montlu> storage

At llalVest SIX montf1s aher harves¡ Treatmenl Treatrnent

Category 01 Surface -·Surtace seed" sterlilzed UnS1erillzed sterilized Unsferihzed

Oo. 5.00 8.5 2.0 4.8 Two 8.0 19.3 7.5 11.3-Three 10.5 27.5 6.3 13,0

LSO(O m;, 4.55

aCategory one: plants witn no aShy stem symnloms and no symptoms Oíl

pOds; cale:gory two: plants with ashy stem symotoms OOt POdS wjthouI

sy'TIptorns: category three: plants with asny Sfem symptoms and pods

beaLng M pnaseofma sc!ero1!a

bMean nvmber of seeds mat produced M. pMstJóJma out ot 200 testea.

·00

\ 90 \

\

60

70

g 60

" \ • •

V t 50

• ~ ~

~ 40

30

20

10

Apnl Ju!1€' Sept Dec Marm June SepL De<;;. ,_ FI{}UNl 1. Survival o; M. phaseolifla sderOOa over time.

,,. W. Songa and f!

'educad by more !han hall, They also suggest ihal alter 6

months 01 storaga the", was less infestalion by M. phaseolina

fhan al harvest These observatioos imply a diminished rolé 01 mycelia and poor viability 01 sclerotla after 6 monihs 01 storage

al room temperatura. Unslertlized seed had almosl twica or

more infected seed than Ihe stenlized seed for all the categones

01 seed (table 2). Category thrae seeds, from plants with most

severa infection, had 13,0(% ¡nfected seed when unsterilized,

6.3°/<j when sterHized after 6 months 01 storage. Our results

generally agree with earlier reports on M. phaseollna infection in common besn and other legumes (Andrus. 1938; Abawi and

Pastor·Corrales. 1986. 1990). However. previous authors did

not consider the etfect of s'orage on the viability 01 the pathogen. Abawi and Pastor·Corrales (1986) observed fhat

seeds obtained from symptomless pods on infected plants

showed up to 28% infection and surlace disinfestation with 0.6/)/0 NaOCI reducad imecllon lo less than 5%. Gangopadhyay el al.

(1970) found 13-24% of soybean seed harvested from infected

plants harooured the fungus. The number af Infected seed 6

mon1hs after harvest was signifícantly less than at haNest

Surtace stenlized ssed also produced M. phaseolina

colonias, indicating that the fungus was established beneam !he seed Goa! In abou! hall 01 Ihe Infected saed. In general fhase

results $uggest that sunaca sterílization or storing common bean seed far 6 monl:hs before planting WélS effective in reduclng M.

phaseolina infestation by approximately 50%. Antagonism wilh

other micro-organisms may be another reason for the observad

inactlvatlon of inoculum in .taraga. Asperglllus spp. were among

40 ••••••••••••••••••• , ••••••••••••••.......•..........•••••.....................•••••

i ~~~ ........ ~ ............... -- ............ ~ ........ ~ ...... --~ E ~

-+-O·5cm

zo r----------------------........ ---~ ___ S·1Oom ApnI·Jun Juiy-Sapt Oct-Dec Jan-Mar Aprn-June JuIy-Sept Oct-Dec ~10·1Scm

1993194 ~ í 5-20'Crr.

~air~Qmp

Figure 2. SOII remperalure a( {OUf depth$ and ambtent temperature.

2<1 ............................. -- -- ." -- --.--.-- -- ... --.. • -- •••• -- -- •••••

15 .• -- .... ----

10

s~ ______ ~ ____ ~ ______ ~ ______________ ~ ______ __

Apni • Jun July • $ept Oct· Dac Jan, Mar Apnl • June July 5 .. 1 Oct- Gee 1_ Figure 3. SOll motStUte ar tour deplhS in the Sll..ldy tiel(L

-+-o.5cm ---'S-lOcm

~1O·15cm __ 15-20cm

Survival 01 M. phaseolina in bean seed and crop res/due 113

Table 3. Survivai 01 M, phaseohna scJerotlB in crop debns at tour demhs

jr, soN

Percentage germinatlon

Months after burial

SOi! depth (cm) 3 6 9 ~2 15 18 21 ..... _-

0-5 48.3 48.1 59.5 55.5 35.1 20.0 36.6 5-10 66.6 29.6 39.3 42.2 22.2 22.2 30.0

10-15 67.0 59.2 35.7 46.6 1 í.1 44.4 23.3 15-20 63.3 25.9 25.0 48.9 13.9 21.1 333

LSD(o.o5) 25.58,

other fungi isolated from the bean seed and have oeen reported

to reduce M. phaseoiina rnfection 111 pe-anut kernels (Jackson, 1965). This phenomenon needs further investigation and

suggests the potenrial use 01 biocontrol agents in seed

treatments.

At the beglnning of 1he experiment 96<Vo (n= 1 DO) sc\erotia

taken from infected crop debns and plated on the selectlve

medlum PDA·DOPCNB germina1ed. Survíval of sclerotia there~

after declined wlth time) as shQwn In figure 1, The depth at wh!ch

the sclerotia were bUrled dld not slgnificantly (P;;;;; 0.05) influence

survival (jable 3). Soíl tamperature decreased with Ciépth. as

shown in figure 1. The htghest average temperature was 38.5 e between o and 5 cm during the penod January - Marcn 1994

and the lowest was 29.0 C between 15 and 20 cm dunng the

period October- December 1993. SoU moísture increased with

depth, as shown in figure 2, The nighes1 soil moisture (20.3Q/o

VWC at 15-20 cm depth) was observed during the penod

October-December 1994 and soj! moisture was lowest {5.9"/c

VWC at 0-5 cm deplh) during July-Seplember 1994.

Th€ results in thís study mdlcate that up to 30C:·'Ó of M, phaseoJina sc!erotia ín bean crop debris were stlll viable aíter 21

months in the soi!. Théy suggest that crop rotations w!th non·

hosts or lallow periodo 01 less than 2 years are unlikely to be

effective in reducmg charcoa! rot drsease in ínfested fíelds, Our

studyalso indlcates tt1a~ sclerotial survival was not influenced by

soU moisture, sol! temperature or depm of bunal in 1he present

study.

The average soi! temperatura during the day was lowest at

29°C al Ihe 15-20 cm deplh and h.goes! at 3S·C a! 0-5 cm

deplh (figura 3). These .emperaturas are wíthin the optimal range

lor good growlh 01 M. phaseolina ISmith, 1969; Dhingra and

Sinclair, 1975) and this could explain jn part the absence of

significan1 difference in the survival Of sclerotia with depth.

Soil moisture was 6% and 20%, VWC a1 the 0-5 and

15-20cm depths respectively. Satischandra el al, 11979) observed that saprophytic activity was hlghes1 1m M.

phaseolina at 2oo/Q MHC and was reduced tour times at

80% MHC. The diflerence in moislure con!ent at Ihe deoths

lnvestigated was probably not large enough to inf!uence

SClerolia survívaL This pathogen does not survive tor long under anaerobic conditions (Satischandra et al., 1979) and

too moislUre effects would be more obvious in pooriy dralned

soils. Tne soil lex!ure 01 the s!udy fteld (table 1) ¡ndlcales Ihal ¡t is welr drained and anaerobrc conditions would not easily

oceur even after very héavy erratlc rajns that are typical of

this region. Too Insignificance (P"",O.05) of depth on survlva!

(table 3) suggests Iha! deep ploughing ",tended lo bury crop

debris would n01 control charcoa! rot dlsease Removal and

burning mfestad crop debris wouid be a more useful cultural

contrOl practice.

Acknowledgements

The roseareh reported in thís paper is pan 01 a 3-year sludy

lunded by the KARIIODA Crop ProtecbOn Projec!. We thank

ProL D. M. Mukunya, Dr A. W. Mwang'ombe (Univers.ty 01

Naírobl) and Dr R. Buruchara (CIAT) lor their suggeslíons.

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