Influence of temperature and inoculum density of Fusarium oxysporum f. sp ciceris on suppression of fusarium wilt of chickpea by rhizosphere bacteria

The effects of temperature and inoculum density of Fusarium oxysporum f. sp . ciceris race 5 on suppression of Fusarium wilt in chickpea (Cicer arietin um) cv. PV 61 by seed and soil treatments with rhizobacteria isolated from the chickpea rhizosphere were studied in a model system. Disease developmen t over a range of temperatures (20, 25, and 30 degreesC) and inoculum densi ties (25 to 1,000 chlamydospores per gram of soil) was described by the Gom pertz model. The Gompertz relative rate of disease progress and final amoun t of disease increased exponentially and monomoleclarly, respectively, with increasing inoculum densities. Disease development was greater at 25 degre esC compared with 20 and 30 degreesC. At 20 and 30 degreesC, disease develo pment was greater at 250 to 1,000 chlamydospores per gram of soil compared with 25 to 100 chlamydospores per gram of soil. At 25 degreesC, increasing inoculum densities of the pathogen did not influence disease. Nineteen Baci llus, Paenibacillus, Pseudomonas, and Stenotrophomonas spp. out of 23 bacte rial isolates tested inhibited F: oxysporum f. sp. ciceris in vitro. Pseudo monas fluorescens RGAF 19 and RG 26, which did not inhibit the pathogen, sh owed the greatest Fusarium wilt suppression. Disease was suppressed only at 20 or 30 degreesC and at inoculum densities below 250 chlamydospores per g ram of soil. Bacterial treatments increased the time to initial symptoms, r educed the Gompertz relative rate of disease progress, and reduced the over all amount of disease developed.