Characteristics of the soil nematode populations from the ...

Characteristics of the soil nematode populationsfrom the peanut cropping area of Senegal, WestAfrica

Pierre BAUJARD & Bernard MARTINY

Baujard, P. & Maniny, B. 199'5. Characteristics of the soil nematode populations from thepeanut cropping area of Senegal, West Africa. I Afr. Zool. 109: '51-(>9.

The ecology of soil nematode populations in the peanut cropping area of Senegal was studiedbv surveys, population dynamics and vertical distribution. The structure of the populationscorresponds to those identified in the other countries of the Sahclian zone of West Africa andmight he under the dependance of two main factors: the rainfall which clcrcrmincs the soilmoisture level and the tloristic diversity, and the soil temperature which increases from theWest to the East of this area. The dry season is considered to he the more appropriate s.uuplingtime for the comparison of populations since the numerical variations of population dcnsirk-sremained lower th:1I1 during the rainy onc.

Caractcristiqucs des j)ojJ1llafiolls de nematodes du sol dans If'bassin arachidier dt! SC'negal. ­L'ecologie des populaiions (le nematodes du sol clans la zone arachidiere du Senegal estabordce par des prospect ions, l'ctud« de la dvn.uniquc cl de la repartirion vcrtkale despopulations. Lacomposition spccifique ct l'ahondancc (Ies popularions correspondent acellescnregisrrccs clans d'autrcs regions de lAfriquc (le l'Ouest. Deux principaux facteurs sernblcntregir la structure des populations du sol clans lcs regions semi-arides d'Afrique de I'Ouest: legradient pluviomctrique nord-sud qui conditionne les taux cl'humidire des sols cl la divcrsitchotaniquc, le gradient tdlurique thermique ouest-cst. L\ periocle optimalc de prclevcmcntpour des etudes comparatives des peuplcmcnts de nematodes clans ccrte region est la saisonsechc pendant laquelle les variations des taux (le population resrenr faibles.

Keys words: Ncmata, soil, ecology, semi-arid tropics, West Africa.

P. Baujard ' & B. Martiny, ORSTOM, Laboraroire de Ni:'matologie, B. P. 13H6, Dakar. Senegal.

INTRODUCTION

The role played by plant-parasiticnematodes in cropping systems of semi­arid tropics is studied since more thantwenty years in West Africa, mainly inSenegal and Hurkina Faso where,respectively, the nematodes Scutellone­ma cauenessi Sher, 1964 and Apbasma­tylencbus straturatus Germani, 1970were suspected to he one of the most

CO) Present address: Museum national d'I Iistoircnaturcllc, Laboraroire de Biologic parasitairc,Protistologie, Helminthologie, 61 rue Buffon,F-7'5005 Paris, France.

© 1995 AGAR Publishers

important factors limiting the yield ofpeanut (Baujard & Martiny, 1991a;Germani et al., 198'5; Germani & Luc,1982a, b). More recently, other studieshave been developped in the peanutcropping areas of Mali (Baujard &Martiny, 1994a, b) and Niger (Sharma etal., 1988, 1990, 1992; Sharrna, 1990;Sharrna & Siddiqi, 1990) and in some aridregions of Mauritania and Niger (Baujardet al. 199'5).

Although soil nematodes com­munities of these countries are com­posed of numerous plant-parasitic andfree Jiving species (Baujard, 1986;Sharrna, 1990; Baujard & Martiny, 1994a;

52 fOURNAL OF AFRICAN 7,OOLOGY f()'J( 1)

Baujard et al., 1995), liule is knownabout their distribution and ecology.

Ecological studies were undertakenin Senegal by surveys and fields trials toprecise soil nematodes communitystructure in the peanut cropping area ofSenegal.

MATERIAL AND METHODS

Study site and its ecologicalcharacteristics

The peanut cropping area of Senegalis located between latitudes 13.5 and 16°North (Fig. n The year is divided in twoparts: the dry (November to May) andthe rainy (June to October) seasons;rainfall level increases from North toSouth, precipitations varying from 200 to700 mm during the 3 to 4 months of therainy season; the annual meantemperatures ranges from 25 to 3üoC(Leroux, 1980). The soil are mainly sandy(Michel & Sali, 1980). Pluvial croppingsystems are mainly based on biannualpeanut-millet crop rotation; cowpea iscropped as food crop on small fields;sorghum is cropped only in more clayersoils or in lowlands (Lericollais, 1980).Vegetables are cultivated in smallgardens or fields always under irrigationand mainly during the dry season.

Nematode extraction

Nematodes were extracted from soil(250 cm') by elutriation (Seinhorst, 19(2)and from roots in a mist chamber(Seinhorst, 1950). Elutriates were placedon Baermann trays and the nematodeswere counted 7 and 14 days after.

Nematodes surveys

The nematodes were collected from1981 to 1990 on experimentation sites ofthe laboratory or during surveys (Fig. 1).Sampling was done during both rainyand dry seasons.

Fields experiments

Ali the field studies were conductedin a field previously cropped with milletin 1983, and localized in the center of thepeanut cropping area, at Nebe 5 kmSouth to Diourbel CExperiment site n° 6on Fig. 1).

Biotope characteristics

Rainfall was recorded on the field;soil moisture was measul'ed for eachsampling date from 08.05.86; data on soiltemperature originate from theexperimental station ofI .S.R.A., Bambey,located at 25 km West to Nebe; soilcharacteristics were measured at theLaboratoire de Pédologie, ORSTOM,Dakar, Senegal.

PojJlllation dynamics

The population dynamics wasstudied in field plots (6 x 6 m) separatedby 3 m wide, non cropped, and weeklywceded alleys. The field was constitutedby 42 plots: seven treatments (Table 1)with six replications per treatment(monocultures of peanut IArachishypogea L. cv 55 437), millet rPennise­tum typhoides Rich. cv Sou na III),sorghum rSorghum lIulgare L. cv 51 (9),cowpea rVigna unguiculataJ (L.) Walp. cvN58 571, biannual peanut-millet rotationwithout nematicidal tl'eatment, biannualpeanut-millet rotation with a nematicidaltreatment and permanent fallow) werearranged in a completly randomizeddesign. Peanut and millet were croppedrespectively in 1984 and 1986, and in1985 and 1987 in the plots constitutingthe two rotation treatments. Sorghumexhibited a very poor growth in ] 984 anddid not developp during the followingyears. Nematicidal treatment wasachieved by the injection of metamsodium (31.25 kg/ha a. i.) at 15 cm deepat the beginning of the experiment. Alithe plots except those constituting the"fallow" treatment were weekly weeded.Sixty six soil samples series were taken

(

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14'

17"1

16'1

15'1

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112'

n;~ ~...,.-200

o'.:.... ~100km 1

27° ···l.. 28°

fig. 1. - Lüctiiz;trion üf rhe slLldies and dilll;tric characrerisrics (doned lines. - annual l11ean jsotherr"s ,conrinllolls lines. - annllal mean isohyer,;).

'54 JOURNAL OF AFRICAN LOOLOGY I09( 1)

Table 1. - Characteristics of the treatments in the field experiment conducted at Nebe.

Treatment Plant crorred uuring the rainy seasonscode cultural I\ematicide

practice arrlication 19H4 198'; 1986 19H7

A monoculture no peanul reanul peanut pelnutTI rotation no peanut millet peanut milletC rotation yes peanut millet peanut milletD monoculture no millet millet millet milletE monoculture no s()rghum sorghum sorghu1l1 s()rghuITIF monoculture no C()\vpc-a cowpea cowpea cowpeaG fallow no

from 04.02.1984 to 06.08.1988 on eachplot, monthly during the dry season andevery two weeks during the rainyseason. Samples were constituted bythrcc 250 cm; soil samples per plot thatwere thoroughly mixed and one 250 cm3

subsample was extracted for nematodecounting.

The structure of the soil nematodepopulations on the different treatmentswere compared at the heginning and theend of the rainy Se;IS(ln for the years 1985and 1987: importance (number ofnematodes per dm; of soil) and diversity(nematode orders present and speciespresent for the order Tylenchida) werecompiled. Multiplication rates during theyear were calculated from countingsregistered at the end of each dry season(initial population) and at the beginningof each following dry season (finalpopulation); survival rates du ring the chyseason were calculated from countingsregistered at the beginning of the dryseason (initial population) and at the endof the same dry season (final popu­lation).

Vertical distrihution

Two studies on the vertical distri­bution of nematode population wereconducted: the first cluring the dryseason (December 1984-January 1985).and the second cluring the rainy season(September-October 1987). Twotrenches were dug in the alleys alongeach plot; two samples were taken ineach trench at 5,10,1'5.20,25.30,35,40,

45,50 cm deep during the dry season andat 5.10,15,20,30,40,50,60,70,80 cmdeep cluring the rainy season. The foursamples collected for cach depth werethoroughly mixed and one 2'50 cm;suhsample was extracted for nematodecounting.

RESULTS

Nematodes identified

Three nematodes orders (Tylenchi­da, Rhabclitida and Dorylaimida) arealways predominant in the peanutcropping area of Senegal either becauseof the abundance of some species, orbecause of the specific diversity (seetable 2).

The orcier Tylenchicla is mainlycomposecl hy two families that are weilc1iversifiecl: Belonolaimiclae with at leastthree different species of the genus'(ylenchorhynchus and the familyHoplolaimiclae with the genera Scutel­IOl/ema, Hoplolaimus, Aorolaimus ancllJelico(ylenchus. The other Ltmilies ofthe order Tylenchida (Tylenchidae,Anguinidae. PratyJenchiclae, Hetero­deridae, Criconematiclae, Tylenchu li­dae, Aphelenchiclae) are composecl ofonly a few species. more often in lownumhers in these soils. Only species ofHoplolaimidae were found in the motsystems of both cultivated ancl noncultivated plants.

The order Rhabcliticla IS composecl

I3AI!!A/W ,e; ,HA/(I1NL S()fr N/MA 7'()f)/,S PNOM S/,Nh'(,'Ar

Table 2. - Nematodes identified in the peanut cropping area of Senegal

Tylenl'hida Thortll', l 'Ji9Tylenl'hidae {)lTley, IHHO

Fi/l'I/l'hl/s cf. ji/cII//a/i/'lIs' (Szl'zygiel, 1970)HasJ,;j <'(; Ceraert, 191'17

C(j>ha/l'I/chlls /ohlls Dhanal'hand <'(;

Jairajpuri. 19HO/IIl'o/hada callc<!l/a/a ' (Thome, 1941) Khan,

1975FljJhyat!0l'hora sI'.

Anguinidae Nicol!, 19Y5 ( 1926)ni/Y/I'nchlls sI'.

Bdonolaimidae Whitehead. 19(,0TY/I'nchorhynchlls am1ll/a/lls (Cassidy,

1930) Golden. 1971T. liermanii' Fommer & Luc 191'17T. g/ae/io/a/us ' Fortuner '" Amougou, 1974T. indicus (Siddiqi, 19()0) Fortuner '" Luc,

19H7T. Sil/ca/lis de Guiran, 1967T. œll/ralis' (Lour, 19(5) Fortuner '" Luc

19H7Tricho/Y/l'nchllsjà/cifimJlis Wilitehead,

19()()l'ratylenchidae Thome, 19-19

/'mY/l'lIchlls hrachY"rlls «(;odfrey. 1929)Filip'ev '" Schuurmans Stekhoven,1941

/'m/v/el/chlls /oosi Inof, 19()Ol', se!uellsis' Fortuner, 197·i

Ilopiolaimidae Filip'ev, 19YiAoro/aill/Ils II/ache/hi' (Sher, 1961i)

Fortuncr, 19H7Aphasma/y/enchus l'ariahilis Cermani '"

Luc, 191'14f/l'iicu/I'/enchus dihys/I'ra' (Cobb, IH93)

Sher, 1961Hop/o/aimlls pl/rl/rohlls/IIS' (Schuurmans

Stekhoven '" Teunissen, 1931'1) Sher,1961

RO/I'/enchu/us reniJ(mllis Lindford &Oliveira, 1940

SCII/I'/lonema cavene"s; . Sher, 1964Sl'/lI'ga/onema sorghi . Germani, Luc &

Baldwin. 1984HeteroderiliJe Filip'ev '" Schuurmans

Stekhoven. 1941//l'!l'rodera sI'JlsJl/a/o (only second stage

juveniles identified)MI'/oidogYlle sp.

Crilonematidae Taylor, 1936Cricollell/e/la clm'a/a' ([{aski, 19';2) Luc ,'(

Raski, 191'11

• ~ species present Olt Nehe

C sphal'roœpha/a (Taylor, 1956) Luc &Haski, l ')H 1

Tylenchulidae Skarhilovitch, 19,17(,'mci/I/ClIS sp./'ara/Y/l'Jlchlls !,er!lOxizls . Siddiqi. Ilaujard

& Mounport. 19')5Aphelenchillae (Fuchs. 1957) Steiner, 1949

Al'hl'il!Jlchlls {1I'l'//{/l" Bastian. IH(,';Aphdenchoididae (Skarhilovitch. 1947)

l'aramonov, 19';5Aphl!/l!nchr,ides sp.Paurouot/lllS sp. ": Menus i1lceJ1ae sedis

(Fortuner, 19H7)

Hhabditida Chitwood, 1933l'en unidentified species . helonging to the

suborder Cephalohina Andra'ssy,1974

Dotylaimida l'earse, 1942Dorylaimoidea De Man, IH76

Carcharolainllis sp.niscolaimlls sp..l'lInlil!u/IlS sI'..+ ten species . unidenlified at l'l'nus Ievd

Longidoridae <Thome, 195';) Meyl, 19(,1l'aralonliidon/s hu/la/Ils . Shallll:! '" Siddiqi.

1990/) dlllicl/ni' Siddiqi, Baujard & Mounport,

1995XiJ,hilll'lI/{/ l'iUJllia/llm . Schuurtnans

Stekhoven '" Teunissen, 193HX. parase/ariae' Luc, 19';HXiphillema sp..

Leptonchoidea Thome, 193';Lep/ollehlls seNSIl la/o'

llelondiroidea Thome, 1939Dury/aimel/lls seusu la/o'

Triplonchida Cohh, 1920Trichodoridae Thome, 193';

Para/r/chodonts minor (Colbran. 19';6)Siddiqi.1974

P. nanus (a!en, 19';7) Siddiqi. 1974P. rhodesiensis' (Sidùiqi & Brown. 19';6)

Siddiqi, 1974Tr/ehudorus ehu rneus' De Wade &

Carhonell, 19k2

Mononchida Siddiqi, 19k3llathyodontidae Clark, 19h 1

!3{//hj'ut!(I11/us cvliliuriclls' Fielding, 19';0

56 JOURNAL OF AFRICAN ZOOLOGY 1GY(1)

only by nematodes of the suborderCephalobina; this group is weil diver­sified and constitutes frequently morethan 40% of the soi! population.

The order Dorylaimida is as weildiversified than the orderTylenchida butless abundant; it constitutes in mean lessthan 10% of the total soil population.

Ecological trends

Ecological trends concern thefrequency and the abundance of thespecies and the localization in depth forthe soi!s without irrigation during the dryseason. The surveys having been con­ducted at different times along the yearand during several years, numerical data(abundance, frequency) can not be com­pared since they are strongly dependentfrom several biotic and abiotic factors:time of sampling, vegetation, rainfall(see below). The soil nematocies com­munities showed a tendancy to anincrease of the specific diversity andabundance for the Tylenchida, Rhabdi­tida and Dorylaimida i) from the North tothe South ofthe studied area, probably inrelation to the inCl-ease of rainfall (Fig. 1)and ii) in relation to the vegetation,sorghum and fallow appearing "besthosts" than other c:rops.

These trends are weil marked for theplant-parasitic species of the ordersTylenchida, Dorylaimida and Triplon­chida.

Tylenchidae

C. lobus is a rare species, found onlyat two times in uncropped lowlands withwet soils. N. cancellata is a commonspecies localized in the upper layer ofthe soil (between 0 and S-1 Cl cm deep)occurring most often during the dryseason.

Anguinidae

Ditvlenchlls sI'. is common.

Belonolaimidae

T germanii, T sulcatus and T. ven­tratis are three very common speciesalways present in the soi!s. T.gladiolatusis a species absent from the northern partof the area, rare and in low number in thecenter and frequent in the South. T. an­nulatus appeared to be more frequent inthe South of the area; it is found in thenorthern part only in sorne lowlandscropped with sorghum. T. indicus is arare species, mostly found around rootsof Euphorbia balsamifera Ait., a plantused as green fence in this area. T. falci­formisis generally absent in the northernpart of the area, becoming more frequentand abundant progressively to the South.

PraZvlenchidae

P. hrachyurus and P. loosi are twovery rare species, the last one beingfound only once. P. se/àensis is morecommon, but rarely abundant in theNorth and the center of the area.

Hoplolaimidae

Two species, A. variahilis and S.sorghi are found only from the center tothe South of the area, mostly deeperduring the dry season. A. machethi is acommon species, in low density, like H.pararobustus and H. dihystera. S. cave­nessi is always present, with populationsincreasing from North to South, rangingl'rom 500 to more than 60000 specimensper dm' of soil.

Heteroderidae

Only J2 of one undetermied speciesof Heteroderinae have been found, veryrarely and in low numbers du ring the dryseason. Members of the gemls Meloi­dogyne have never been found in thesesoils.

Criconematidae

Only one species, C. curuata has

IJAI 7//1 Nf) (. ,HART/NL SOir NI:'MA rOD!:S FNOM S/:'NI:'C;AI. '57

h<::cn identifieu in the soi!; it is a commonSIWClCS, always in very low numh<::rs.

7)J/eilchulidae

Gracile/CilS sp. is velY rare; P. per­noxius is a common species, always inlow numhers, except in the lowlands ofthe area Waujaru & Martiny, 1994c).

Aphelenchidae

A. avenae is a very common species.

Aphelenchoididae

Specimens of the genus Aphelen­cboides are very rarely found in the soi!sof the area. Paurodontus SI'. is a com­mon species occurring in the upperbyers of the soi!, more frequently e11­countereu during the ury season thanuuring the rainy one.

Longidoridae and Trichodoridae

Memhers of these two families can

he, at first view. con.sidered as very raretaxa, occurring only cJuring the rainyseason. mostly in velY lo\v numhers.Recent investigations (Baujard &Martiny, 1993,199'5; lbujarcJ etaI., 1993)have shown that species ofthese familiesare localizecJ deeper (helow '50 cm)during hoth dry anu rainy seasons and50, uifficult ta ohserve hy usual samplingprocedures (0-30 cm e1eep).

The use of irrigation during the e1ryseason for cropping vegetabJesprovokes some impoI1ant changes in thenematode populations: the diversity andabunelance are reuuced for the threeoruers. The most important changes arenoteu for the Tylenchiua where most ofthe species e1isappeared completely;three species rarely or never found in thenon irrigatccJ fielus, are common anuabundant: Rotylenchulus reniformis,lvleloidogyne SI'. Jnel PamtrichodorusminaI'. C. sphaerocephala is a rarespecies, only founu in gardens in thenorthern part of the a reJ.

40

45

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Depth-::" 10 cm -'/ - 20 cm

35

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EUJ

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Fig 2 - Annll;ll e\'olLition of the soil temjJcr:ltllre in rel"riuD tu deprh ;lnd rime of mClsuremenr in 19H3 "ml19H4

58 JOURNAL OF AFRlCAN LOOLOCV 109( 1)

-~---- -..-1l' __

~--, ..-;--.

-,-------- ------ ---1-----

~'--.--- _._-

t--- ----1-'-

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a

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: ri-------+-- ---"1" '-1,-'---l .\_.2 !~,---+----+- rk-I - ~jj---, >--- ------t- - ---- - -- ,~ r-a ! , 0"',=,"-,=,~c.L ~:;~......=;n>--.",=,~~==

1984 1985 1966 1967 1988

II~--- -I_'-_u! ~--: J~--I. ~ 3= Crh 'n-~,~;;i"J,===n~~grJ:!"'~. ---'== 1

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-----+----+I\'l--\-~ 1. ~---t'----}----- ---+--- -'-1-- . --i

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:~ ~i ~+-----+--or.-jl'-:-:-c--=: -_-::--_-_---'-+_-_-_-_-_-_-_----:----t-C-=-=--=--=--=-~~-=--=--==.~~~~.,...:.,:-- ...==:-JL-:":-_••-,~=<-"'-...-'"---:~.:~-~_=~I~"' -'-'::-===="

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a

Fig. 3. - !binfall and cvo!ution of the soil'l1oistUl'e in relation lU the cultur,l! praetices (arrows show droughtperiods during the raillY scason and their dTl'ets on soilll1ol.<lurc Icvl'I ; A, D. E. f. G. - cultural practices).

Field studies

HA li/ANI) 0- MAltlYNL son M!MA 101)/,S l'NOir/ SI!NH;AI.

Population strllctllre

';9

Characteristics (!l the hiotope

Soi! characteristics: 2.H'% clay; 1.(YJ;iJfine loam; 4.6%J coarse loalll; 61.71YtJ finesand; 30.4°/(J coarse sand: pH

lll() ';.3; pHK<I

4.9; 0.21% total carhon; 0.019% totalnitrogen.

Soil temperaturcs valY between 2';and 3HoC depending on the depth, andduring the day and the year; the warmestperiod occurred each year at thebeginning of the rainy season, inJune orJuly (Fig. 2).

The length of the rainy season variedfrom 104 days 09H,;) to 122 days 09H7);rainfall and its periodicity is abo variable:420 mm in 23 days in 19H4, 473.'; mm in30 days in 19H';, 32'; mm in 37 days in19H6 and ';33 mm in 34 days in 19H7(Fig. 3).

The soi! moisture 1cvel dependedfrom the alllount and periodicity of therainfall. During the dry season, soilmoisture is constant around 0.1% in thetop 30 cm of the soi!; it remains aboconstant below 1.';-2% in depth. Duringthe rainy season, soi! moisture levelinCl-eases up to 7%. Variations in soi!llloisture occured during the rainyseason following the rainfall periodicityand the crop: each drought perim]during the rainy season provoked a more(2-2.5% in 1986) or less (0.5-1% twice in1987) deerease of the soi! moisture level(Fig. 3); soi! moisture levels are lowerunder fallow and higher under peanutthan under the other crops (Fig. 3). Afterthe last rainfall of the rainy season, soilmoisture decreased up to 0.1% in 60-13'idays, the speed of drying dependingfrom previous moisture level and fromthe l'roI', bcing faster in 19H6 than in19H7 and faster on fallow and cowpeathan on other crops (Fig. 3).

The soil nematodes identified in thefield (sec tahle 2)be!ong to three mainorders characteristic of the area:Tylenchida, Rhabditida, Dorylaimida.The relative importance of each ordervaries fo]jowing the time of sampling(rainy season vsc!Jy season): 64-H7 vs 39­Hl % for the Tylenchida, 10-29 vs lH-'i9%for the Rhabiditida, and 0.2-1. 'i us 0.4­10% for the Dorylaimida. The ahsoluteand relative importances valY followingthe yeu and time of sampling and thel'roI' (Figs. 4, H).

S. cavenessi is the more abundantspecies, representing 2'i-70% of the totalpopulation du ring the dlY season and 60­H4% during the rainy one; the three othermore abundant species are T germanii(respectively 0-';% and 1-9%), A. avenae(rcspectively 3-11 % and 0.2-3°/t,) andDi~ylenchusSI'. (respectively 0.6-H'lfo andO-'i.'i%) (Figs. 'i, 6).The other species ofthe order Tylenchida are less ahundantand frequent (Figs. 'i, 6). As for the()[CIers, the year and time of sampling asthe crop affected the absolute andrelative importances of the speciespopulation (Figs. 'i, 6).

Population dynamic

Nematode population increasedconstantly during the rainy seasonexcept if a drought period occurred(years 1986 and 1987, Fig. 7); higherlevels were reached after the end of therainy season, from 15-30 days up to twomonths later; during the dry season,nematodes population level decreasedcontinuously up to the next rainy season(Fig. 7); ail the species identified in thetop soi! are anhydrobiotic stages. Thispattern did not vary with the crop norwith the taxonomical groups consideree!(Fig. 8). The monoculture of peanutinduced a regular decrease of the plant­parasitic nematodes population. Thenematicidal treatment provoked adecrease of the population for ail the

60 .I0llNNAL OF AFRlCAN ZOOLOCY 1090)

-1

oIIIU­a

M~orrwa.rrwCD~::lZwo~ 10000

<~wZ

2000

1985 TOTAL POPULATION

RHABDITIDA

1987

DORYLAIMIDA20000 V

1000o-V i---

A B c o E F G

CULTURAL PRACTICES

l'ig. 4. - Nematode densities numl)L'r.s in Ihe soil during Ihe ury (h;Hcheci coluonn) and Ihe "liny (bhlCkeolullln) seasons at two differenr ye;rrs. - IOlal population, Tyknchid;l, Hhallditida and Porylaionida (A-G.- euhural rraclices).

/JAU/ANf) & MAltUNY- son NEMA'IODFS FROM SI:N/:GAI. 61

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Filenchus sp.

HA------- - 1985.

O~ Tylenchorhynchus gladlolatus J2°:U~;--~!'~i::::::::q::qszz::.-::;:::=:::;~~~) ~~i~::::;::::::::::

Tylenchorhynchus ventralis

20

200

60

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120()-

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CULTURAL PRACTICES

Fig. 'i. - Nel11alode cicnsilie, in the ,(lil dllring Ihc dry (h'lIcil<'ci clllllmn) <Inti thc "liny (black colllmn)sc,{S(.n, <II twO diff<:renl years. - Tylenchid<le. Angllinid'le, i-lelonol"il11ici;lC, i\phelenchiLiac, Paurodon/ussr. (A-G. - ClIitlll'"t Ix"crices).

62 ./OURNAL Of' AfRICAN ZOOUX;}' lU,)( 1)

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100

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60

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- AOrOlaimus racbethi _. -- --;

îf#;--qz~1) i 4'P~t??<p';:;;JSenegaJonema sorghi -

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CULTURAL PRACTICES

fig. 6.. Nemaroue densilic' in Ille soi! c1l1ring Ihe dry (J"ltchec! l'()lumn) ;1ml the r:lin)' (h!:Ick colllilln)seasons ar tW() c1iffercnr years_ . lloplol;limid:lc (A-C .. nilrllr,,1 pracrices) ..

HAll/ANf) (, MAlrnM.· SOIL NF.MA?Of)f:S NWM SI:NI:(;AI 63

. G' Ir .. 1praclic"" . hatchcd. . . ". .. l' 'to the cultural praclI('c~ (A- . - cu lll.1 ..Fig. 7. - 1'01,11 populatIon dynallllcs aculr<lngareas. - rainy sC'ason~).

64 JOURNAL OF AnaCAN7.00WGY I09( 1)

species; this effect remaineù visibledu ring the year following the treatmentand disappeared afterwards. The nondevelopment of sorghum induced aregular decrease of the soi! population.

The multiplication rate of the soilpopulation during the rainy seasonvaries hetween 0.6 and R following theyear and/or the crop; the highest ratesare recorded for millet in 1985 in theplots under monoculture and in 1985and 1987 in the plots under rotation withor without nematicide (Fig. 9). Study ofthe multiplication rate in relation to theorders show that the highest multiplica­tion rates are recorded for the Dorylai­mida.

The survival rate of the soil popu­lation during the dlY season varies from3 to R7°/(, follO\ving the year and/or thecrop; the highest rates are recorded in19R4 for peanut in the plot unùermonoculture and rotation. For ail cropsexcept sorghum and fallow, a tendancyto a decrease of the survival rate is tè)Undfrom 19R4 to 19RR (Fig. 9J.

Vertical distrihution

COlilparison of the patterns of thevertical distribution of nematodespopulations during the dry and the rainyseasons shows no differences; the mostimpot1ant part of the population (80%) islocalized between 0 and 20 cm deepwithout any effect of the crop on thedistribution pattern (Fig. 10). During therainy season, the soi! moisture levelappeareù constant up to RO cm deep.There was no eviùence of a verticalmigration of nematodes in ùepth at theenù of the rainy season.

S. sorp,hi showed a different palternwith highest populations in depth ùuringboth the rainy anù dry seasons; H.pararohustlls is deeper localized underpeanut anù millet than unùer fallowplants ùuring the ùry season; A. avenaewas more predominant (50-60% of the

population) in the top ofthe soi! (0-5 cm)'during the chy season. Nematodes of thefamilies Longidoridae and Tricho­ùoridae were never present in the top ofthe soil; they remaineù always helow 40cm where soil moisture never was below1.5%).

DISCUSSION

Nematological studies in the arachidhasin of Senegal revealed the presenceof a polyspecific falma. Most of thesespecies seem to he weil adapted toecological conditions of this region: theyare able to reproduce at high soi!temperature levels, low soi! moisturelevels; they are polyphagous, most of theplants cropped in this area being hostsfor them; at least two behaviores havebeen developped to support the long dryseason, anhydrohiosis and localizationin depth.

Comparison with faunistical datafrom arid and semi-arid West At'ricaCBaujard & Martiny, 1994a; Baujard et al.,1995; Sharma, 1990; Sharma et al., 19RR,1990, 1992) showed the great uniformityof the soi! nematode fauna of this area:most of the species identified in Senegalare present in Mauritania, Mali, Niger andBurkina Faso. The main differences arc iJthe replacement of S. cavenessi hy S.c/athricaudatum between the West andthe East of West Africa CBaujard &Martiny, 1994 a), ii) the diminution ofpopulation levels from Senegal to Nigerwhere plant-parasitic populations arcalways helO\v 2500 nematodes per dm1

of soil (Sharma, 1992; Shanna et al.,1990), hi) the decrease of populationdiversity and abundance from the Southto the North of the area, most of thespecies idenlified in tlie Soutli and thecenter of the area disappearing on thenorthern margin of the Sahel (Baujardet a/., 1995 J.

Three main hypothesis concerningthe characteristics of soi! nematode

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l'i,'(. H. - P0l'lIl,"ioll dYIl;lInic~ ;lCcordiog ro rhl' clIllllr,I! pr;·lnicl's. - Tylcochid:l (."III:,re). Hh:lI>Liilid" lx) ;JoLiDorylaillKb (Iri:loglc) (A-C - clIlllIr;I! rraCliccs : h"rchl'd "rc,,'. - r<liny .'l':\SOOS).

66 .lOu/mAL OF AFRICAJV ZOO/OGY J09( /)

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TOTAL POPULATION100

GD

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Fig. 9. - Mulripliearion r'Hc~ during the rain)' scasons and surviv,i1 rates during rhe dry scasons (A-(J. -l'uluralpracriecs).

ilA iJjAIW (- MA I(IINL SO/!, Nhl1A TOOhS Ff(OM ,\FNI"(;AL 67

DRY SEASDN

•• 1

'..:

,~~1

••'.•r

1..J,

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RAINY SEASON

F

fig, lU, - Vl'r1ic;ti distrihutiun Pl' the tul:,1 pUIJulaliun dlll'ing Ihl' dry :Jnd rhl' rainy S":lsons "ncl vui"liuns,l spi! 111< ll,slUrc' 111 rl'I:ttiun tu c1Cplh during the rainy ,casun CA, D-C : l'ultur,,1 practices),

68 jO{If(NAL OFAFR[CAN ZOOLOGY [09(1)

c+-

populations in semi-arid regions of WestAfrica have been elaborated: i) thespecifie diversity and abundance ofpopulation increase from the N011h tothe South of the stutied area in relationwith the increase of rainfall along thesame axis which determines in part theimportance of root masses and length ofnematode activity period; ii) the specifiediversity and abundance of populationsincrease with the increase of plantdiversity which is in relation with rainfallincrease; iii) the increase of soi!temperature from the West to the East ofWest Af'rica influences negatively theabundance and diversity of the soilnematode populations. In order to testthese hypothesis, 39 species of plant­parasitic nematodes identified in thesoils from semi-arid West Africa havebeen reared in the lahoratory for theevaluation of the effects of soi!temperature, soil moisture and hostplants on their multiplication rate and theevaluation of their ability to enteranhydrobiosis (Baujard, 1995; Baujard &Martiny, 1991 b, c, 1993, 1994 c, 1995;Baujard et al., 1993).

Observations of the populationdynamics showed that the variations ofpopulation levels remained lower duringthe dry season which appeared thereforethe more appropriate sampling time forthe comparison of population structurein these countries.

REFERENCES

I:3aujard, p. 1986. Ecologie des nématodesdans le hassin arachidier du Sénégal.Reulle Nématol., 9: 288 (abstr.),

I:3aujard, P. 199'5, Lahoratory methods usedfor the study of the ecology andpathogenicity of Tylenchida, Longi­doridae and Trichodoridae fromsemi-arid tropics of West Africa.Fundam. appl. Nematol., 18: 63-66.

I:3aujard, P. & Martiny, B. 1991a. Dommagescausés par des nématodes auxarachides et aux cultures de rotationdans la région sahélienne de l'Afriquede l'Ouest. Comptes renellls de laDeuxième réunion régionale del'ICR/SA Tsurl'arachide en Afrique de

l'Ouest, 11-14septemhre1990, Centresahélien de l'fCR/SA T, Niamey, Niger,43-44.

---. 1991b. Données nouvelles sur lenématode Tylenchorhynchus ger­manii (Germani & Luc, 1984)Fortuner & Luc, 1987 (Nemata:Be!onolaimidae). 1. Etudes au champ.A.,/j'o-Asian]. Nematol., 1: 94-100.

---. 1991e, Données nouvelles sur lenématode Tvlenchorhynchus ger­manii (Germani & Luc, 1984)Fortuner & Luc, 1987 (Nemata: Be­lonolaimidae). II. Etudes au labora­toire. Alro-Asianf, Nematol.. 1: 135­142.

---. 1993. Ecology and pathogenicity ofParalongidol7ls dlll/cal/i (Nemata:Longidoridae) from Senegal. WestAfrica. Alro-Asial/]. Nernatol., 3: 177­181.

---, 1994a, Etudes nématologiques auMali, Afrique de l'Ouest. 1. Prospec­tions de deux zones arachidières. ].A/j'. ~oo!, 108: 217-224.

---. 199'tb. Etudes nématologiques auMali, Afrique de l'Ouest. II. Effets destraItements nématicides sur l'arachIdeet le mil.]. Afr. Zool., 108: 329-334.

---. 1994c. Ecology anJ pathogenicity ofParatylenchus pernoxius (Nemata:Tylenchulidae) from Senegal, WestAfrica. Alro-Asian]. Nematol., 4 7-10.

---. 199'5. Eeology and pathogenicity offour trichodorid speeies from thesemi-arid region of West Afriea.Nematologica, 41: in press.

Baujard, P., Martiny, B & Tostain, S. 1995.Nématodes associés à Pennisetumglallcum L. dans les zones arides deMauritanie et du Niger, Afrique del'Ouest. .f. A/i', L.ool., 109 (in press).

Baujard, P., Martiny, B, & Traore, A. 1993.Ecology ami patllOgenicity of thenematode Parulollgidorus hul/atus(Nemata: Longidoridae) in semi-aridtropies of West Africa. Nematropica,23: 149-1 '57

Fortuner, R. 1987. A review of Neotylen­chidae Thome, 1941 (Nemata:Tylenehida). Reuue Némato!, 10: 2'57­267.

Germani, G., I:3aujard, P. & Luc, M. 198'5.Control ofphytoparasitic nematodesin the Bassin Arachidier (Jl Senegal.ORSTOM, Paris, 16 pp.

Germani, G. & Luc, M. 1982 a. Etudes sur la"chlorose voltaïque" des légumi­neuses due au nématode Aphasma­tylenchus strature/tus Germani. I.ReUlle Nématol., '5: 139-146.

---. 1982 b. Etudes sur la "chloros­voltaïque" des légumineuses due au

}JAl IfAR}) ,"- J/ARnVL SOlL Nl:MA1U})FS FROM SFN!!(;Al 69

•

n0malodt: Aphasnla/ylellchlls s/ ra/lI­ra/lis Gt:rmani. II. Rel'Ile Nénla/ol., 'i:19'i-199.

Ll'ricollais, A. 19HO. k Bassin dt: l'Arachide.111: Atlas dit Sénégal, Editions Jt:unt:Afrique, Paris, 50-'i3.

Leroux, M. 19HO. Climat. 111: Atlas dit Sénégal,Editions Jt:unt: Afriqut:, Paris, 12-17.

Michel, P. & Sali, M. 19HO. Modd0 d sols. 111:Atlas dll Sénégal, Ed itions ,ku neAfrique, Paris, 4-7.

Seinhorst, j. W. 1950. 1k hdt:kt:nis van degro'nd voor het optrt:dt:n van aan­statsting door hl't stl'ngt:iaatje(fJitylellchlls dljisaci (Kühn) Filip­jt:v). 7ïjdschr. 1'1. 7-iekt., 56: 291-349.

Seinhorst. j. W. 1962. Modifications of theduiriation ml'thod for extractingnl'l11arodt:s l'rom soi!. Nell1atologica,H: 117-12H.

Sharma, S. B. 1990. Furthl'r investigations ontlle roil' of plant parasitic nl'matodesin (TOP growth variahility of ground­nut in Niger. Legumes Pathology Pro­gress Report, ICmSAT, India, H: 61 p.

Sharma, S. B. &. Siddiqi, M. R. 1990. Para­IOl/giC!orlls hill/atits n. sp. fromgroundnul soiis in Niger and com­ml'l1ls on Xiphillema pamse/ariaeLuc. f. il/ellla/ol., 22: 579-5H4.

Sharma, S. 1\., Suhrahmanyam, P. &. Sarr, E.1990. Planl parasitic nematodt:sassociatt:d with groundnut in Niger.7hipical l'es/ Management, 36: 71-72.

Sharma, S. B., Suhrahmanyam, P., Sarr, E. &Van Riel, H. 19H8. Plant parasilicnematodes associatt:d with ground­nut at Sadoré in Niger. InternationalA rachis il/eU'sletter, 4: 10-11.

Sharma, S. B., Waliyar, P., Suhrahmanyam, P.& Ndunguru, B. J. 1992. Roll' ofScu tel!onema c/ath rica Ildat Ilni inetioiogy of groundnut growth varia­hility in Nigt:r. Plant alld Soi!, 143:133-139.

(ManI/script received 4 Octoher 1993, rel'ised16 il/ouemher 1994, accepted 28 il/ol'emher19(4)