Survey for purple blotch of onion (Alternaria porri(Ellis) Cif.) in northern parts of Karnataka

Onion (Allium cepa L.) is one of the important bulb crop and most important commercial vegetable crops cultivated extensively in India and it accounts for 90 per cent of the exported vegetables from India in terms of value. The production ofbulbs and seeds is limited by certain diseases. The most serious one is the purple blotch caused by Alternariaporri (Ellis) Cif. The disease causes extensive damage to bulbs as well as seed crop and also a major limiting factor in cultivation of onion. In view of the destructive nature of purple blotch of onion the present investigation was conducted through survey to know the disease incidence or severity and collection of infected samples. A survey was conducted during kharif 2013–2014 in onion growing areas of Northern Karnataka viz., Bijapur, Bagalkot, Gadag and Dharwad districts. The highest per cent disease index was noticed in Ilkal village of Bagalkot district. While, the lowest per cent disease index was noticed in kerur village of Bagalkot district. Among the districts, severity of disease was more in Bijapur and less in Gadag. Isolation was made from onion leaves showing typical purple blotch symptoms. Pure culture of A. porri was obtained and its pathogenicity to onion plants was proved. On the basis of isolation and morphological studies, the pathogen was identified as Alternariaporri (Ellis) Cif.