Purple blotch disease in onion: Management through biological agents

Abstract

Alternaria porri (Ellis) Cifferi, a Deuteromycetetious fungus, is the most critical pathogens causing Purple Blotch disease in onion. The paper reveals symptomatology, microscopic studies, seed treatment experiments and management of Purple Blotch disease in onion. It was observed that the spread of disease caused due to the presence of Thrips tabaci Lind. In the initial stage of infection the disease symptoms appeared as tiny, water-soaked, orange coloured lesions encircled by yellow hallow. As, the disease progressed the lesions enlarged and became elliptical with concentric rings, turning into necrotic patches. Under the cultural conditions, the fungus showed white fluffy growth of mycelium producing dark orange to purple pigmentation. The seed treated with Trichoderma harzianum and Pseudomonas fluorescens @ 10g/kg of seed gave the best results to increase germination % and yield of onion bulbs. The prophylactic spray of Neembicidine @ 0.3% and T. harzianum @ 1% was observed as the most effective in the management of disease or thrips and was the most efficient in prolonging the disease occurrence respectively under field conditions.