Physio‐biochemical and histological alterations in response to sheath blight disease of rice ( Oryza sativa L.)

Sheath blight caused by Rhizoctonia solani is one of the most destructive rice diseases, leading to serious economic yield losses all over the world. The present studies were conducted to assess the impact of sheath blight infection on biochemical and anatomical attributes of a susceptible rice cultivar, i.e., PR 121. Post infection, an increase in endogenous salicylic acid (+97.93), phenols (+74.32%), flavonoids (+32.34%), proline (+74.03%), MDA (+28.78%), POD (+63.57%), CAT (+65.38%), PAL (+90.56%), SOD (+87.04%) and PPO (+53.25%) was due to a possible secondary defence response of the host plant. A significant decline of 61.77% in the total chlorophyll content was observed in the infected leaves over the healthy leaves, whereas lignins (-88.94%) were found to escalate upon infection. SEM observations of infected leaves revealed that the fungal hyphae could intercept surface structures like trichomes and rely on chemotaxis for the infestation. Depositions of phenolic substances might have resulted in the plugging, which caused the disorganization of vascular bundles and disruption of water channels, leading to the cellular collapse, indicating wilting of susceptible rice plants at later stages of infection. The presence of silica on an infected leaf surface indicates the occurrence of a stronger defence response during the early infection phase. The pathogen exhibited increased hyphal colonization, making intimate contact with the host tissues post infection. Hence, it can be concluded that sheath blight infection caused significant metabolic changes in the most efficient antioxidant system of the plant that could limit the cellular damage caused by R. solani. The information obtained by investigating the ultrastructural and metabolic events of healthy and diseased plant parts can assist in the development of effective sheath blight management strategies, thereby reducing the impact on the rice crop.