Development of purple blotch incited by Alternaria porri and its losses in seed crop of onion (Allium cepa)

Abstract

Purple blotch of onion (Allium cepa L.) caused by Alternaria porri (Ellis) Cif. is serious bottleneck in onion seedproduction. This disease reaches epidemic proportion every year during March. The purple spots/blotches were observedsupernumerary on older leaves and scapes when fortnightly dew fall is > 1.0 mm, mean maximum relativehumidity >75% and mean maximum temperature 20-30°C with >18 hr favourable temperature (lO-30"C) duration.Exposure of 1eaf anO/or scape wetness lor 8 hr was pre-requisite for conidial germination. With the inrease in intensityof infection, every yield component was adversely affected. Severe most infection reduced number of scapes/plant, height of scape, number of umb1ets/umbel, number of seeds/umblet, 1 OOO-grain weight, number of seeds/plantand seed yield/plant to the tune of28.7, 74.5, 89.9,41.7/,35.7,95.7 and 97.3% respectively compared to healthy plants.