Studies on variability and anastomosis among the potato and rice isolates of Rhizoctonia solani Kuhn
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Date
2017
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CCSHAU
Abstract
Sheath blight of Rice and black scurf of Potato caused by Rhizoctonia solani has emerged as a serious problem in
majority of rice-potato growing states of India, leading to considerable yield loss in both rice and potato crops. The present
investigation on variability, anastomosis and cross infectivity was carried out with eighteen rice and eleven potato isolates of R.
solani collected from different locations. Based on the radial colony growth rate, all the isolates from both the crops were
categorised in to three groups as slow, medium and fast growing. Majority of rice isolates showed medium colony growth rate,
while, most of the potato isolates showed slower growth rate. Potato isolates had colony texture either appressed or raised,
whereas rice isolates had either raised or fluffy growth. Colony colour in all isolates was varied from pale yellow to very pale
brown, while whitish color was appeared in rice isolate R16. Sclerotia were found aggregated at the centre of the colony in potato
isolates, whereas it was scattered on colony surface in rice isolates. Colour of sclerotia in all rice isolates was dark brown while it
was brown in Kurukshetra (R4) and black in Dapoli isolate (R18), however, it was varied from light brown to dark brown in
potato isolates. Moderate to profuse sclerotial intensity was observed in rice isolates whereas it was scanty to moderate in potato
isolates. Among the rice isolates, mean maximum lesion length was recorded in isolate R14 (Ludhiana isolate) which indicated
strong pathogenic nature towards all four cultivars while lowest mean lesion length was observed in isolate R12 (Gurdaspur
isolate) which indicated the least virulent nature.. Among the potato isolates, isolate P5 was found highly pathogenic to all the
four varieties while the isolate P10 was found least pathogenic. On the basis of mean lesion length in rice and per cent disease
severity in potato, all isolates from both hosts were categorized into three virulent groups viz., VG-I (less virulent), VG-II
(moderately virulent) and VG-III (more virulent). Majority of rice isolates were moderately virulent while most of the potato
isolates were less virulent. The diversity analyses using ISSR primers, exhibited genetic relatedness among the eighteen rice
isolates ranged from 61 to 82 per cent with an average similarity of 70 per cent. The ISSR analyses differentiated R. solani
isolates into two major clusters at similarity coefficient of 0.61. The maximum genetic similarity (82%) among all rice isolates
was observed between isolate R4 and R5 while minimum genetic similarity (66& 66.5%) with all other isolates was observed by
isolates R11 and R2, respectively. Similarly, the genetic relatedness among eleven potato isolate ranged from 63 to 86 per cent
with average similarity of 70 per cent. On the dendrogram, two main clusters viz., group A and group B, were produced at 0.63
similarity coefficient. The highest genetic similarity (86%) was observed between isolate P1 and P2, whereas minimum (69.5 %)
with all other isolates was shown by isolate P9. The present investigation on cross-infectivity of rice and potato isolates indicated
that none of the potato isolates were able to infect all four rice cultivars. On the other hand, rice isolates showed varied degree of
virulence on three potato cultivar. In anastomosis interaction studies, majority of isolates showed compatibility with isolates with
those belonged to same host with few exceptions. There was no compatible reaction occurred between rice and potato isolates
indicated that both the isolates belong to different and distinct groups within same species.
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