Stdies on Variability, Epidemiology and Management of Soybean Rust in Northern Karnataka
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Date
2012
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Publisher
UAS, Dharwad
Abstract
Rust 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.