Delineation of Purple Blotch Disease Hotspots Caused by Alternaria porri in Key Onion Cultivation Regions of Southern Karnataka, India

Onion (Allium cepa L.) stands as a crucial bulb crop and a primary commercial vegetable crop in India. Among the various maladies affecting bulb and seed development, purple blotch, caused by Alternaria porri, stands out as one of the most devastating. This ailment inflicts extensive damage on both bulb and seed crops. Through an extensive roving survey, we have unveiled the disease's prevalence, enabling the identification of disease hotspots in the major onion cultivation regions of southern Karnataka. A total of 28 hotspot regions were identified in the eight districts surveyed for purple blotch disease severity in onions. Notably, the highest mean of percent disease index (PDI) was recorded in Chikkamagaluru (51.12%), while Chamarajanagara showed the lowest mean PDI (23.35%). Among all surveyed villages, the most severe disease prevalence was observed in Koverahatti village within Hiriyur taluk of Chitradurga district, with a PDI of 64.47%. On the other hand, the lowest disease severity was noted in Uttamballi village (16.89%) in Kollegala taluk, Chamarajanagara district.