Shamarao JahagirdarDevaraj L.2016-11-212016-11-212012http://krishikosh.egranth.ac.in/handle/1/86786Rust caused by Phakopsora pachyrhizi Syd. is the major constraint of soybean production in northern Karnataka. Survey conducted during kharif 2011 revealed the average severity of 67.46 Percent Disease Index in northern Karnataka. The maximum rust severity was observed in Dharwad taluk (95.16 PDI) followed by Bailhongal (88.61 PDI) and Chikkodi (74.50 PDI) talukas. The study on variability of Phakopsora pachyrhizi indicated variability of all isolates in spore shape, colour and size. Among 25 isolates, the maximum uredospore size was recorded with Ugarkhurd isolate (90.93 × 70.05 μm).Cultural studies on thirteen differentials revealed that JS-335 reacted to maximum of eight isolates. The Rayanal isolate produced both Reddish Brown (RB) and TAN lesions on most of the differentials. Twenty five different isolates were grouped into three different pathotypes such as Pathotype I (RB lesion producing pathotypes), Pathotype II (TAN lesion producing pathotypes) and Pathotype III (No lesion producing pathotypes) based on their with 13 international set of differentials. The study described the presence of three pathotypes in causing soybean rust in northern Karnataka. Minimum temperature ranging from 18.6 to 20.70C, maximum relative humidity between 87.9 percent to 97 percent and the spore load ranging from 4.56 to 27.51 spores/ microscopic field were favourable for disease development and spread. Irrespective of date of sowing, the variety DSb 21 showed highly resistant reaction. While, development of rust was relatively slow in VLS 58 when compared to JS 335 and JS 93-05 recording highly susceptible reaction. The management of soybean rust through fungicides and botanicals revealed that two sprays of hexaconazole @ 0.1% was found effective followed by kresoxim methyl @ 0.1% - azadirachtin @ 0.5%, two sprays of kresoxim methyl @ 0.1% in reducing disease severity and increasing the seed yield with better economic returns.Thesis