Prashanthi S. K.Lavale, Shivaji Ajinath2020-02-272020-02-272016-02http://krishikosh.egranth.ac.in/handle/1/5810143746Sheath blight (ShB) caused by Rhizoctonia solani Kuhn. is one of the most important rice diseases worldwide. It has been difficult to generate ShB resistant rice varieties by relying on traditional breeding because resistance to rice ShB is a quantitative trait. Marker-assisted backcross breeding approach was adopted for introgression of ShB QTL qSBR11-1 into an elite rice variety Samba Mahsuri (BPT5204) which is already introgressed with Pi2 gene conferring blast resistance. Tetep was used as the donor line for QTL qSBR11-1. Tightly linked polymorphic markers viz. RM224 and Sbq33 flanking QTL region (~0.85 Mb) were used to confirm hybridity in F1 plants. These plants were screened against R. solani by artificial inoculation by following microchamber method. The F1 plants were resistant to ShB with less relative lesion height than the recipient parent. These plants were further backcrossed and BC1F1 plants were generated. Foreground selection for QTL qSBR11-1 was done using polymorphic RM224 and Sbq33 marker. Phenotypic evaluation of 134 rice landraces was carried out for identification of new resistance sources for sheath blight. Seven landraces were found to be resistant to sheath blight. Genotyping was done using 63 RM markers representing all the linkage groups of rice crop. Population structure analysis divided the mapping panel into two subgroups. Marker trait association study was carried using phenotypic and genotypic data of all the 134 rice landraces. Twenty one marker loci were identified to be significantly associated with the sheath blight resistance at significance level of 0.05 with phenotypic variation ranging from 3.02 per cent to 22.71 per cent. Thirteen new markers (viz. RM206, RM231, RM337, RM5556, RM295, RM72, RM3628, RM163, RM320, RM247, RM508, RM246 and RM583) were identified for sheath blight resistance. This study validated the previously identified markers (viz. RM5919, RM85, RM551, RM335, RM169, RM7488, RM287 and RM224) flanking different sheath blight resistance QTLs. Since, marker interval RM337 and RM5556 on chromosome 8 are not yet reported to posses any QTL for sheath blight resistance, this may be a novel region governing ShB resistance in Tetep.ennullThesis