Yield loss in chickpeas in relation to development of Fusarium wilt epidemics

Development of 108 epidemics of Fusarium wilt of chickpea caused by Fusariu m oxysporum f. sp. ciceris were studied on cvs. P-2245 and PV-61 in field m icroplots artificially infested with races 0 and 5 of F. oxysporum f. sp. c iceris in 1986 to 1989. Disease progression data were fitted to the Richard s model using nonlinear regression. The shape parameter was influenced prim arily by date of sowing and, to a lesser extent, by chickpea cultivars and races of F. oxysporum f. sp. ciceris. Fusarium wilt reduced chickpea yield by decreasing both seed yield and seed weight. These effects were related t o sowing date, chickpea cultivar, and virulence of the prevalent F. oxyspor um f. sp. ciceris race. Regression models were developed to relate chickpea yield to Fusarium wilt disease intensity with the following independent va riables: time to initial symptoms (t(is)), time to inflection point (t(ip)) Of the disease intensity index (DII) progress curve, final DII (DIIfinal), standardized area under DII progress curve (SAUDPC), and the Richards weig hted mean absolute rate of disease progression (rho). Irrespective of the c hickpea cultivar x pathogen race combination, the absolute and relative see d yields decreased primarily by delayed sowing. The relative seed yield inc reased with the delay in t(is) and t(ip) and decreased with increasing DIIf inal, SAUDPC, and rho. A response surface was developed in which seed yield loss decreased in a linear relationship with the delay in t(is) and increa sed exponentially with the increase of rho.