Survey for purple blotch [Alternari porri (Ellis) cif.] on onion (Allium cepa) in northern parts of Karnataka

Onion (Allium cepa L.) is most important commercial vegetable crop cultivated extensively in India, accounting for 90% of the exported vegetables from India. The production of bulbs and seeds is limited by certain diseases. The most serious is purple blotch caused by Alternaria porri (Ellis) Cif. The disease causes extensive damage to bulbs as well as seed crop and also a major limiting factor in its cultivation. Therefore, 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, 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 Alternaria porri (Ellis) Cif.