Purple Blotch of Onion and Its Management.प्याज का बैंगनी धब्बा और उसका प्रबंधन.پیاز کی پرپل بلاچ

Purple blotch in onion is caused by the fungus Alternaria porri. A fairly common disease of onions, it first manifests as small, water-soaked lesions that rapidly develop white centers. As the lesions progress, they turn from brown to purple with a halo of yellow. Often the lesions merge and girdle the leaf, resulting in tip dieback. Less commonly, the bulb becomes infected through the neck or from wounds. Fungal growth of spores of A. porri is fostered by temperatures of 43-93 F. (6-34 C.) with the most optimal temperature of 77 F. (25 C.). Cycles of high and low relative humidity encourage spore growth, which can form after 15 hours of relative humidity greater than or equal to 90%. These spores are then spread by wind, rain, and/or irrigation. Both young and mature leaves affected by thrip feeding are more susceptible to purple blotch in onions. Onions with purple blotch present symptoms 1-4 days after infection. Onions infected with purple blotch become defoliated prematurely which compromises bulb quality, and lead to storage rot caused by secondary bacterial pathogens.

Read more at Gardening Know How: Purple Blotch On Onions: Dealing With Purple Blotch In Onion Crops https://www.gardeningknowhow.com/edib...