The relationship between natural rain intensity and Ascochyta blight in chickpea development.

Ascochyta blight management strategy in chickpea standing crops in Australia is solely based on applying protective fungicides before a forecast rainfall event. Despite this, studies on the likely interaction between natural rain (as well as simulated rain) amount, duration and Ascochyta blight development are rare. This study was conducted to investigate the relationship between natural rain intensity (mm/h) and Ascochyta blight development. Infested chickpea residue were placed at the soil surface, and three pots of a susceptible chickpea cultivar were randomly placed on each side of the plot (total 12 pots and 36 plants), preceding a forecast rainfall event. Trap plants were transferred to a controlled temperature room after rain events. After a 48 h incubation period, trap plants were transferred to a glasshouse to allow lesion development. The number of lesions on all plant parts were counted after two weeks. Lesions developed in rain amounts as low as 1.4 mm and rain durations as short as 0.7 h. The number of lesions significantly increased with increasing rain amount. There was a positive effect of increasing rain duration and a negative effect of increasing wind speed. This study suggests that small rain amounts, shorter duration rains or a limited amount of primary inoculum are not barriers to conidial dispersal or host infection, and that the current value of a rainfallthreshold (2 mm) for conidial spread and host infection is not accurate for susceptible cultivars.