Progression of Alternaria blight on different varieties of rapeseed- mustard in relation to weather parameters

Prediction model for Alternaria blight of rapeseed and mustard was developed for adopting better disease management Four cultivars each of Brassica juncea (RH-30, RH-8113, RH-8695, RH-8546) and B. campestris (YSPb-24, BSH-1, Candle, Shiva), two of B. carinata (HC-2, HC-9001), one each of B. napus (GSH-1) and B. alba (local) were monitored for the development and progression of Alternaria blight for three consecutive crop seasons (1998–99 to 2000–01). Each cultivar was inoculated with Alternaria brassicae (Berk.) Sacc. spores when the crop was about two months old. The progression of Alternaria blight was recorded in terms of lesion size on every alternate day till the maturity of leaf. The data on disease progression in relation to corresponding weather variables were subjected to step-wise multiple regression analysis. There were significant variations in the development of Alternaria blight during all the three crop seasons. The progression was much less during 2000–2001 as compared to other two crop seasons. The rate of disease development was faster on B. juncea and B. campestris groups as compared to B. carinata, B. napus and B. alba. Further during the crop year 1998–99, Temp, (min), RH (E) and Sun-shine played significant role whereas, Temp, (max), Temp, (min), RH (M) and RH (E) contributed largely towards the disease development during 1999–2000. Studies conducted revealed that Temp, and RH had prominent role in Alternaria blight development in addition to varietal behaviour. The prediction equations so developed were at par with observed values. It will help to formulate suitable chemical spray schedule to check the disease more efficiently.