Effect of temperature on growth and sporulation of Botrytis fabae, and resistance reactions of Faba Bean against the Pathogen

Abstract

Chocolate spot (Botrytis fabae) is a devastating disease of faba bean and reduces its production and productivity. Three controlled condition experiments were conducted to assess the effect of temperature on growth and sporulation of B. fabae, and faba bean resistance reaction against the pathogen using a single B. fabae isolate and Degaga and Bulga-70 faba bean varieties. For cultural experiment, a circular block of actively growing B. fabae mycelia was placed on faba bean dextrose agar medium and arranged in a completely randomized design (CRD) with four replications. For resistance reaction evaluation, fresh culture of isolate suspension was prepared (2 × 105 spores ml-1) and inoculated on to three weeks-old faba bean seedling detached leaves and the whole plant. Inoculated leaflets and seedlings were factorial arranged in a CRD with four replications. Both sets were incubated at 20, 22, 24 and 26°C. The maximum (84.00 mm) radial growth on 5 days after inoculation (DAI); average conidial size (24.86 × 16.32 μm), sporulation (2.48 × 103 conidia ml-1) on 12DAI and growth rate (1.058 mm day-1) were recorded at 22°C. The least values of these parameters and nil sporulation were obtained from 26°C. The highest average lesion size (17.67 mm in Degaga and 22.83 mm in Bulga-70), AUDPC for lesion sizes (30.92 mm in Degaga and 42.08 mm in Bulga-70) and severity (2.13 score) values were recorded at 22°C on 5DAI in detached leaf test. Infection and disease development was reduced at 26°C. The trend was similar in the whole plant test. Such parameters were linearly increased with temperature to maximum and declined progressively in both reaction evaluation tests. The two evaluation experiments indicated that the optimum temperature for B. fabae growth, sporulation, infection and disease development was at 22°C.