Defense reaction and biochemical interpretation of rice genotypes to sheath blight, Rhizoctonia solani Kuhn

Abstract

Rice (Oryza sativa L.) is one of the most important cereal crops in the world. Sheath blight disease of rice caused by Rhizoctonia solani Kuhn AG-1 IA (Telomorph, Thanatephorus cucumeris Frank. Donk) is a devastating disease in all rice-growing regions of the world. The yield losses ranging from 4-50% have been reported depending on the crop stage at the time of infection, the severity of the disease, and environmental conditions. Landraces are valuable genetic resources to explore novel genetic variations and they are highly adaptive. Considering the significance of this disease the present study was conducted at College of Agriculture, V.C. Farm, Mandya during Kharif 2021 and Summer 2022. Ninety landraces and ten popular varieties of rice were screened against sheath blight disease by artificial inoculation method. Disease scoring was done by the standard evaluation system (SES) as per IRRI (2002). The mean percent disease index (PDI) ranged from 11.11 to 79.56%. Based on AUDPC values, rice genotypes were categorized into 5 groups i.e., resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible. Further to know the resistance mechanism, 34 selected genotypes were analyzed for biochemical constituents by using standard procedure and protocols and it was found that phenol (-0.79), total soluble sugar (-0.84), reducing sugar (-0.87), crude protein (-0.84), tannin (-0.91), peroxidase (-0.67), polyphenol oxidase (-0.83), and phenylalanine ammonia lyase (-0.84) was negatively correlated with sheath blight disease severity and these biochemicals were higher in resistance genotypes viz., Kalanamak and Sidda sanna compare to susceptible genotypes.