Identification of quantitative trait loci (QTL) associated with sheath blight tolerance in rice

Sheath blight, caused by the pathogen Rhizoctonia solani Kuhn, is one of the most serious diseases of rice and leads to severe yield losses worldwide. A recombinant inbred line (RIL) population consisting of 122 lines was constructed from a cross between Danteshwari a high yielding popular rice cultivar but moderately susceptible to water stress, susceptible to sheath blight and Dagad Deshi a tall deep rooted poor yielder and tolerant to water stress and sheath blight. Five traits, namely infected tillers per hill, lesion size (total coalescing lesions) and individual lesion (one spot) and lesion's length and width) were used to evaluate sheath blight resistance. Using the RIL population and 162 molecular markers, 11 quantitative trait loci (QTLs) were identified for the five traits. Identification of map position was accomplished by identifying BAC or PAC clones that simultaneously contained a hit from the microsatellite / HvSSR marker further helped us to generate a high resolution molecular marker map of the identified QTL region. Identified QTLs were located on seven chromosomes. A major QTL for infected tillers per hill on chromosome 1 was identified with phenotypic variance of 18.02%. Six QTL's with positive additive effect and one with negative additive effects was identified indicating alleles at these loci are being contributed by either of the parents respectively.