MESTA, RAGHAVENDRA K.N., ROHAN HUNDEKARK. C., Kiran kumarKurubetta, KrishnaTanveer AhmedHire math, Veeresh2020-10-192020-10-192017-12UHS14PGM479https://krishikosh.egranth.ac.in/handle/1/5810153326The present investigation on the epidemiology and management of purple blotch of onion was conducted at Collage of Horticulture, Bagalkot during 2015-16. The survey carried out in major onion growing districts of northern Karnataka during 2015-16, revealed that the highest incidence of the disease was in Haveri district (37.00 %) and least in Koppal district (19.00 %). Over all disease severity was higher in irrigated crop than rain fed crop. Among the eight isolates collected from different locations during the survey, the isolate API-7 has found to have bigger size of conidia with more number of septa. Among the eight solid and liquid media tested, pathogen showed the maximum growth and sporulation on potato dextrose broth. A temperature of 35 oC, pH of 6.0, RH of 90 per cent and incubation of 12 days on potato dextrose broth were found best for the growth and sporulation of A. porri. The experiment on transplanting at different days revealed that PDI (36.00 %) was lowest when onion was transplanted on 2nd July with highest yield of 23.91 t/ha. The epidemiological studies revealed that per cent disease index was progressing at linear rate throughout the crop growth and it was negatively correlated with relative humidity (morning and evening) and maximum temperature. It was positively correlated with minimum temperature, while non significant with rain fall. The PDI at all stages were highly and positively correlated with thrips incidence and wind speed. Multiple linear regression analysis revealed that weather parameters influenced to the extent of 35 to 88 % on per cent disease index. Fifty five genotypes were screened to identify the resistance source, among which the genotype DOA-24 was found moderately resistant to purple blotch of onion. Among the 12 different fungicides tested in vitro, tebuconazole + trifloxystrobin completely inhibited (100 %) the mycilial growth of the fungus at 0.15 per cent, followed by propiconazole @ 0.15% (90.37 %). In the field experiment two sprays of tebuconazole + trifloxystrobin @ 0.1 per cent at 15 days interval recorded maximum disease control with highest yield and net returns.EnglishThesis