B.C. KamannaRavichandran S.2016-11-162016-11-162012http://krishikosh.egranth.ac.in/handle/1/85965Onion (Allium cepa L.) (2n=16) one of the most important commercial vegetable crops of India belonging to the family Alliaceae. Purple blotch caused by Alternaria porri (Ellis) Cif. is a destructive disease and causes extensive damage to bulbs as well as seed crop. Survey during kharif 2011, revealed that, highest per cent disease index (69.33) was noticed in Vonnali village in Uttara Kannada district. While the lowest (17.33) was recorded in Annigeri village in Dharwad district. On the basis of morphological and pathological studies, the pathogen was identified as Alternaria porri (Ellis) Cif. The pathogen was grouped into six isolates viz., Dharwad, Gokak, Savanur, Navalgund, Mundargi and Kumta isolates. The cultural and morphological characters were studied on different media where the growth was fast in Czapeks Dox medium and slow growth in the Corn meal agar. The weather studies revealed that PDI was progressing at linear rate throughout the plant growth and it was negatively correlated with minimum temperature, relative humidity (morning and evening). While, positively correlated with maximum temperature and negatively non significant with rainfall. Out of twelve different fungicides tested in vitro, Zineb 68% + Hexaconazole 4%WP, Mancozeb 75%WP at all the concentrations completely inhibited the mycelial growth of Alternaria porri. Among the six plant extracts, garlic clove extract and NSKE extracts were highly inhibitory to Alternaria porri, while periwinkle leaf extract proved to be least inhibitor. Among six bioagents, Trichoderma harzianum was most effective. In case of field evaluation field evaluation of different fungicides botanicals and bioagents indicated that, lower disease index (30.66), high bulb yield (20.60 t/ha) and maximum B:C ratio (5.30) was recorded in plots receiving three sprays of Avatar (0.15%). In botanicals and bio agents Garlic clove extract @ 5 per cent recorded highest yield of (16.13 t/ha) and incremental B:C ratio of 4.07.Thesis