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Comparative epidemiology of three maize viruses in Reunion Island in relation to the population dynamic of their vectors Cicadulina mbila and Peregrinus maidis

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Academic year: 2021

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Agricultural Entomology

15-121

COMPARATlV~

EPIDEMIOLOGY OF THREE MAIZE VIRUSES IN"

RE'UNION ISLAND IN RELATION Ta

TIŒ

POPULATION DYNAMIC OF

THEIR VEcrORS.CfCADULINA MBfLA ANDPEREGRfNUS MArDIS

B.Reynaud(1) D.Fargette (2) M. Petersehmitt(3)

(1) Centre de Coopération Internationale en Recherche Agronomique pour le Développement. départementdesCultures Annuelles, St Pierre, La Réunion. France - (2) LPRC (Laboratoire de Phytovirologie des Régions Chaudes). Orstom/Cirad Montpellier. France· (3) Cimd CA (Cullures Annuelles), Cirad.

Montpellier, France. .

The simullaneous presence of maize streak virus (MSV). maize stripe virus ~lpV)and maire mosaic virus (MMY) in Réunion bas enabled us to study tbeircomparative epidemiology. .

Symptomatelogical ratings were Laken through three years

oC

culture on weelc1y soWings of!he temperate hybrid INRA 508 and the compOsite variety [RAT 297. Fluctuations of emigrant populatiOns of C. mbi/aand ./:' maidisand climatic faclors(lemperaWIe,rninfaUandrelative humi<fity) were measured and analysed by ûme series and slepwise regression analyses. Streak is the dominant disease. particularly during the

wann

rainy season and MMV was less frequent. Highest autocorrelations were observedwitha time-Iag of ,12 months, confirming the annual periodicity of the fluctuation.

Pattern of change of insect numbers was positively correlated with the change in disease incidence (correlations ranging from 0.65 to 0.87). Disease incidence and vector numbers always remained constant or increased slowly with temperature up

1024°C and increased rapidly above 24°C. The relationship between rainfall. relative humidity. disease incidence and vector nwnbersisless cleàr.

Depending on the series, from63%toSO%of the variance of disease incidence was explained by the stepwise regression with vector nurnbers.and (sometimes) temperamre. rainfall or relative hurnidity. Therefore. the close adjustement found between observed and data calculaled with the resulting regression allowed us to propose a simple epidemiological mode!.

Epidemiological data especially from Africa are compared in arder to better understand the epidemiology of these viroses. Further work is needed te confum the validity of the mode!. The rate of plants infected by the three viroses and the numberof P. maidis per plant were significantly lower (P=0.0001) on lRAT 297 than on INRA 50S. The resistance behavior of IRAT 297 under natura! conditions points to its utilization as resistance donorinbreeding program geared toward obtaining multi-resistance maize genotypes.

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