Effect of drought stress on Fusarium root rot severity of white bean (Phaseolus vulgaris L.) genotypes

Root rot caused by Fusarium solani f.­sp. phaseoli is an important disease of beans in Iran. It causes considerable damages to bean production in Markazi Province. Unfavorable conditions such as drought stress can enhance disease severity. In this research, reaction of 100 white bean genotypes to Fusarium solani f.­sp. phaseoli in drought stress condition was evaluated. Drought stress was applied at V4 growth stage (third trifoliate leaf) and continued until harvest. Irrigation was done after 50 and 100 mm evaporation from evaporation pan (A class) for optimum and stress conditions, respectively. Disease severity was rated on a scale of 1 (immune) to 5 (very susceptible). The experiment was carried out in augment design. Bean genotypes yield under normal irrigation and drought stress conditions was calculated with tolerance indices such as mean value of production (MP), geometric mean value of production (GMP), stress tolerance index (STI), stress susceptibility index (SSI) and tolerance index (TOL). Fusarium root rot severity was greater in drought stress condition. In drought condition, growth parameters viz yield, plant height, 100-seed weight, number of pods in plant and number of seeds in pod were significantly decreased. There was a negative and significant correlation among disease severity and yield in drought stress condition and tolerance indices including STI, MP and GMP. At the same time susceptibility to Fusarium root rot of bean genotypes increased with decreasing of tolerance levels and tolerance indices in drought stress condition.