Survival of Alternaria brassicae in seeds and crop debris of rapeseed and mustard in Nepal

Alternaria brassicae, the causal organism of leaf blight of rapeseed and mustard survived in seeds stored in room temperatures (11-25°C) for 10 months and at 30°C in an incubator 6 months. These storage temperatures are found respectively in the midhills and terai regions of the country during storage of seeds. The fungus survived in the seeds at least one year at 5 and 10°C but it was eliminated after 2 months of storage at 40°C. The fungus did not survive for more than one month in the crop debris buried under soil. However, it was isolated after 3 months from the debris placed on soil and room temperatures at two locations, Khumaltar and Nawalpur. After 6 months of storage in the room temperatures, the fungus was found to survive in the debris at Khumaltar only. The importance of the survival of the fungus in the seeds at low temperatures is discussed. It is concluded that infected seeds act as the primary source of inoculum in Nepal.