Purple blotch disease of onion in punjab

Summary

Alternaria porri, the causal organism of Purple Blotch disease, lives over from one season to the next as mycelium and spores in onion leaves and seed stalks left as debris on the surface of the soil from the last harvest. The diseased debris loses its viability when buried two inches or more, deep in the soil, but diseased debris retains its viability for eight and nine months when exposed to the weather and kept in the laboratory rooms.

The viability and infectivity tests with dried cultures and test-tube cultures have shown that fungus can be kept pure as dried cultures for a period of 12 months or more.