Rai, MayankDebnath, Ashim2023-01-272023-01-272018-11https://krishikosh.egranth.ac.in/handle/1/5810192829Rice blast is one of the most devastating biotic stresses that limits rice productivity in NE region and causes yield loss from 40 to 46 %. The NEH region is considered to be the centre of diversity for both rice and Magnaporthe grisea. Here, host resistance is short-lived in the disease-prone environments because of high level of variability in the pathogen population. Therefore, the present study was carried out to elucidate the genetic basis of leaf and neck blast resistance under Meghalaya conditions in terms of genes and loci associated with resistance to the local patho types, and intra and inter allelic interactions, if any, that play a role in the expression of the resistance pathotype and other related yield contributing traits. The field experiments involved a set of 80 genotypes and six generations of a cross between LR-5 (Lal Jangali) and Sambha mahsuri SUB 1. The study involved association analysis of reported major gene linked markers with leaf and neck blast resistance in natural and F2 populations to identify effective genes under local conditions; and generation mean analysis to understand the genetic components of mean and variance for resistance and other yield related traits. A set of 80 genotypes were screened across two seasons, under two different rice ecosystems (upland and lowland) and a panel of 43 tolerant and susceptible genotypes was identified for marker trait association study. Marker trait association studies revealed seven different loci to be associated with blast resistance. These genes/loci were Pi54, Pi2, Pib, Pi2/9 locus, Pi5, Pb1/qPbm locus and Pi20(t). Genes Pi5 and Pi54 were found to be associated with leaf blast resistance in both, natural population and biparental F2 population. Pib and qPbm showed some degree of association with neck blast resistance in natural population. Generation mean analysis revealed that dominance genetic variance was higher than additive variance for majority of the traits under study. It also suggested that the epistatic interaction model was found adequate to explain the gene action in the blast resistant related traits like Leaf Blast Score, Percent Infected Leaf, Neck Blast Percentage and Spikelet Fertility Percentage. Narrow sense heritability was found to be moderate for Leaf Blast Score and Neck Blast Percentage indicating that marker assisted selection would be an effective way to augment phenotypic selection for blast resistance. The study indicates that leaf and neck blast resistance is primarily governed by dominant alleles of multiple genes that interact with each other to impart resistance. The markers and genes identified in this study can be used for marker assisted selection of breeding material to increase the frequency of favourable alleles at these loci in the elite rice breeding populations so that varieties with durable resistance can be developed.EnglishRice blast diseaseGenetic markersThesis