Variability in rhizoctonia solani kühn, the causal agent of sheath blight of rice and its management
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Date
2013
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UAS Dharwad
Abstract
The sheath blight of rice caused by Rhizoctonia solani (Kuhn.) is considered as major
bottleneck in successful production of rice in irrigated tract of Tungabhadra Project area of
north eastern zone of Karnataka.
The study comprising survey on prevalence and incidence of sheath blight of rice,
collection of sheath blight pathogenic isolates for exploring cultural, morphological and
molecular variability, evaluation of rice genotypes, influence of planting density, nitrogen
level, botanicals and biocontrol agents and IDM against sheath blight of rice was also
attempted.
The study identified pockets in Bellay, Koppal and Raichur districts under TBP area
affected by moderate to severe incidence of sheath blight compared to Cauvery belt areas in
Mysore, Shimoga and Mandya during kharif 2006 and kharif 2007. The diversity with respect
to morphological and cultural characters of 32 isolates of R. solani on PDA revealed that the
maximum radial growth of mycelia was noticed in isolates RS-14, RS-16 and RS-18 each
with 89.33 mm. Based on the morphological and cultural characteristics, the isolates of R.
solani were grouped into four and designated as G1, G2, G3 and G4 where as the molecular
analysis of variability using RAPD primer indicated two major clusters such as C1 and C2
comprising 15 and 17 isolates, respectively. Among 139 rice genotypes screened under field
condition, Aditya, Ajaya, Swarnadhan, Nidhi and Vikramarya were found resistant by
registering 1 grade. In the management of disease with fungicides, botanicals and bioagents,
Hexaconazole, Validamycin and Carbendazim, Tricure (Azadirachtin 0.03%), P. fluorescens
(Pfr-l) were found effective in managing sheath blight. Application of 200 kg N per ha
recorded higher disease severity (40.37%) and increased further with higher levels of
nitrogen (350 kg/ha) when compared to plots with recommended nitrogen and zero nitrogen
fertilizer applications. Among different planting densities, the Systematic Rice Intensification
(SRI) method was found effective in reducing severity of sheath blight (5.00 PDI) when
compared to other planting (16.12 PDI). In IDM trial, use of moderately resistant cultivar IR
64 with spray of hexaconazole @0.1% was found effective in managing sheath blight disease
as compared to Samba mahsuri.