Influence of inoculum density of races 0 and 5 of Fusarium oxysporum f. spciceris on development of fusarium wilt in chickpea cultivars

Artificial inoculation experiments were carried out at 25 degrees C to dete rmine the effects of inoculum density of Fusarium oxysporum f.sp. ciceris r aces 0 (Foc-0) and 5 (Foc-5) and susceptibility of chickpea cultivars P-224 5 and PV-61 on development of Fusarium wilt. Foc-5 proved much more virulen t than Foc-0. Increasing the inoculum density of F. oxysporum f.sp. ciceris caused an exponential reduction in disease incubation period and a monomol ecular increase of disease incidence and the area under the disease intensi ty progress curve. The extent of these effects was highest in the most cond ucive 'P-2245'/Foc-5 combination and decreased in the less susceptible 'PV- 61' and for the less virulent Foc-0, in that order. For 'P-2245'/Foc-5, the highest disease intensity was attained with 6 chlamydospores g(-1) of soil , the lowest inoculum density in the study. One thousand chlamydospores g(- )1 of soil of the same race were needed to attain a comparable disease inte nsity in 'PV-61'. Twenty thousand chlamydospores g(-1) of soil of Foc-0 wer e required for maximum disease intensity in 'P-2245'. The disease intensity curves were adequately described by the Gompertz mode l. Using this model, a response surface for disease intensity was developed , in which the model parameters are expressed as a function of both time fr om inoculation and inoculum density. This response surface confirmed that t he final amount of disease intensity increases in a monomolecular relations hip with increasing inoculum density and showed that the relative rate of d isease progress increases exponentially with increasing inoculum density of the pathogen.