Phenotyping and marker assisted screening of rice (Oryza sativa L.) germplasm for sheath blight(Rhizoctonia solani kuhn) resistance

Abstract

The study entitled “Phenotyping and marker assisted screening of rice (Oryza sativa L.) germplasm for sheath blight (Rhizoctonia solani Kühn) resistance” was carried out at the Department of Genetics and Plant Breeding, College of Agriculture, Vellayani during 2022 to 2024 with an objective of artificial screening and identification of rice genotypes for sheath blight resistance and validation with molecular markers linked to reported QTLs of sheath blight resistance. The phenotypic screening for sheath blight resistance was conducted, using thirty rice genotypes and different biometric, biochemical and computed parameters were analysed. Analysis of variance revealed significant difference for all the biometric characters except number of tillers per plant. All the biochemical parameters such as peroxidise, catalase, polyphenol oxidase and phenylalanine ammonialyase showed an increase in biochemical activity in genotypes under stress but only phenylalanine ammonialyase showed significant difference among them. Studies on phenotypic coefficient of variation and genotypic coefficient of variation revealed high variation for lesion height, number of grains per panicle, number of unfilled grains per panicle and grain yield per plant. In general, PCV values were higher than GCV for all characters indicating the influence of environment towards total variance. High heritability with high genetic advance was noticed for days to heading, days to 50 per cent flowering, number of productive tillers per plant, stem thickness, panicle length, number of grains per panicle, thousand grain weight and grain yield per plant indicating the influence of additive gene action and suitability of these traits for selection. Panicle length, days to 50 per cent flowering, number of tillers per plant and thousand grain weight had significant positive correlation with grain yield per plant where as plant height and lesion height were negatively correlated with grain yield per plant. The days to 50 per cent flowering has a strong positive direct effect on grain yield per plant and days to heading through the days to 50 per cent flowering showed a strong indirect effect on grain yield per plant. Based on genetic divergence analysis 30 genotypes were grouped into four clusters. Cluster III with nine genotypes was the largest followed by cluster I (eight genotypes) and cluster IV (seven genotypes). The clusters II had the least number of genotypes (six). Based on the inter-cluster distances, clusters III and IV had the lowest divergence (6.50) while clusters I and IV recorded the highest divergence (11.41). The highest intra cluster distance was noticed among genotypes of cluster IV (6.32) and the lowest was noticed among genotypes of cluster II (5.36). The genotypes Remanika, Chenthadi, Krishnanjana, Panchami, Karishma, Revathy, White Ponni and Bhadra in the cluster I had the highest mean value for days to heading, days to 50 per cent flowering, number of tillers per plant, number of productive tillers per plant, stem thickness, panicle length, number of grains per panicle, thousand grain weight and grain yield per plant. Based on scoring of sheath blight severity and percentage disease index the genotypes Gouri, Chenthadi, Krishnanjana, Panchami, White ponni, VYT-1, Chenkayama and Onam were found to be resistant for sheath blight. Moderate resistance to sheath blight was shown by the cultivars Karishma, Revathy, Bhagya, VYT-7, Karuna, Sreyas, Prathyasa, Karthika, Chettivirippu, Makom, Uma and Bhadra. The 15 SSR markers linked to the reported sheath blight QTLs used for validation were polymorphic with the PIC value ranging between 0.17 (RM16200) and 0.63 (RM71). RM105 linked to qShB9-1 had the maximum number of alleles (4). The cluster analysis for marker data grouped the rice genotypes into two major clusters with cluster II having the highest number of genotypes. The high yielding rice genotypes Chenthadi and Krishnanjana were identified as resistant to sheath blight based on phenotypic and genotypic data. These genotypes can be used as donors for sheath blight resistance in future breeding programmes.