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

Artificial inoculation experiments were carried out at 25°C to determine the effects of inoculum density of Fusarium oxysporum f.sp. ciceris races 0 (Foc-0) and 5 (Foc-5) and susceptibility of chickpea cultivars P-2245 and PV-61 on development of Fusarium wilt. Foc-5 proved much more virulent than Foc-0. Increasing the inoculum density of F. oxysporum f.sp. ciceris caused an exponential reduction in disease incubation period and a monomolecular increase of disease incidence and the area under the disease intensity progress curve. The extent of these effects was highest in the most conducive '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^sup -1^ of soil, the lowest inoculum density in the study. One thousand chlamydospores g^sup -1^ of soil of the same race were needed to attain a comparable disease intensity in 'PV-61'. Twenty thousand chlamydospores g^sup -1^ of soil of Foc-0 were required for maximum disease intensity in 'P-2245'. The disease intensity curves were adequately described by the Gompertz model. Using this model, a response surface for disease intensity was developed, in which the model parameters are expressed as a function of both time from inoculation and inoculum density. This response surface confirmed that the final amount of disease intensity increases in a monomolecular relationship with increasing inoculum density and showed that the relative rate of disease progress increases exponentially with increasing inoculum density of the pathogen.[PUBLICATION ABSTRACT]