Histopathological patterns and differential behavioural of Rhizoctonia solani causing sheath blight in rice (Oryza sativa L.)

Abstract

AbstractSheath blight of rice caused by Rhizoctonia solani Kuhn [teleomorph: Thanatephorus cucumeris (Frank) Donk] is a significant threat to rice cultivation, accounting for up to 50% yield losses. The present investigation demonstrates the early pathogenesis events and R. solani pre‐ and post‐penetration activities on moderately resistant (MR) and highly susceptible (HS) lines under field conditions. A pure culture of R. solani isolate (R1965) was inoculated inside the sheath at the maximum tillering stage for different time intervals (24, 48, 72 and 96 hpi). R. solani exhibited more profuse, dense, closely contact around surface grooves, lobate appressoria‐like structures and greater microsclerotia development on the HS line compared to the MR one. Using fluorescent, optical, and scanning electron microscopy, it was noticed for the first time that R. solani could intercept sheath papillae and employ them for attachment or penetration in two ways: (a) direct penetration by lobate or runner hyphae, appressorium and infection cushion and (b) indirect stomatal penetration. Assays using in vivo plant inoculation showed that disease lesion length was higher in the HS line than the MR line. Intraxylary hyphal colonization could be seen using microtomy to understand the cellular spatial dynamics of xylem colonization by R. solani. The penetration mechanism along with penetration hyphae of the R. solani inside HS rice lines describe in this paper for the first time using optical ultrastructure. These results supported for better understanding of host–pathogen interaction, penetration mechanism and colonization of R. solani in rice.