Virulence analysis of Rhizoctonia solani Kuhn and evaluation of resistance in Rice
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Date
2021-12-18
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Palampur
Abstract
Sheath blight of rice caused by Rhizoctonia solani is the second most important
production constraint after blast in rice-growing regions of India. The investigation on
“Virulence analysis of Rhizoctonia solani Kuhn and evaluation of resistance in rice” was
undertaken during 2020-2021 in the Department of Plant Pathology, CSKHPKV, Palampur
and RWRC, Malan. The fungal organism was confirmed as Rhizoctonia solani on the basis of
its morphological and cultural characteristics. In all, twenty isolates were collected from
different rice growing areas of Himachal Pradesh. Among twenty isolates studied, colony
colour varied from cream to dark brown while hyphal cell size ranged from 102.90 x 4.20 µm
to 220.50 x 5.95 µm. All the isolates except RS-2 produced light to dark brown, small to large
sclerotia of varying intensity ranging from low to high. Isolates were placed into different
groups based on colony colour, sclerotial colour, sclerotial size and sclerotial intensity.
Growth rate of isolates ranged from 0.10 to 2.08 mm/h and 1.20 to 2.98 mm/h at 25⁰C and
30⁰C, respectively with maximum rate (2.98 mm/h) exhibited by isolate RS-5 and the least by
RS-2 at both the temperatures. Isolates were further grouped into slow, medium and fast
growing groups based on growth rate at 30⁰C temperature. Studies on pathogenic variability
among R. solani isolates carried out on seven different rice cultivars showed that incubation
period of all the isolates on the cultivars varied from two to four days. The relative lesion
height (RLH) caused by the isolates also varied as in cultivar HPR 2880, it ranged from 26.83
to 55.71per cent, in TN1 from 23.44 to 54.76 per cent, in HPR 2612 from 27.27 to 54.69 per
cent, in IR50 from 31.63 to 54.76 per cent, in HPR 1068 from 23.10 to 53.73 per cent, in HPR
2143 from 15.38 to 54.10 and in HPU 2216 from 32.38 to 52.82 per cent. On the basis of
RLH induced on different cultivars, ten R. solani isolates were classified as highly virulent
(>45 % RLH), seven as moderately virulent (35-45% RLH) and three as less virulent (<35%
RLH). Out of sixty seven genotypes evaluated, seven genotypes showed resistant, seventeen
moderately resistant, twenty nine moderately susceptible and fourteen genotypes showed
susceptible reaction on the basis of disease severity while, no genotype was found immune.