Mapping quantitative trait loci controlling sheath blight resistance in two rice cultivars (Oryza sativa L.)

Rice sheath blight, caused by Rhizoctonia solani Kuhn, is one of the three major diseases of rice. The present study was conducted with an F-2 clonal population of Jasmine 85/Lemont. The F-2 population, including 128 clonal f amilies, was inoculated by short toothpicks incubated with a strain, RH-9 o f the fungus. Based on field disease evaluations in 2 years and a genetic m ap with 118 evenly distributed molecular markers, we identified six quantit ative trait loci (QTLs) contributing to sheath blight resistance. These QTL s, qSB-2, qSB-3, qSB-7, qSB-9-1, qSB-9-2 and qSB-11, were located on chromo somes 2, 3, 7, 9 and 11, respectively. The respective alleles of qSB-2, qSB -3, qSB-7, and qSB-9-2 from Jasmine 85 could explain 21.2%, 26.5%, 22.2% an d 10.1% of the total phenotypic variation, respectively; while the alleles of qSB-9-1 and qSB-11 from Lemont could explain 9.8% and 31.2% of the total phenotypic variation. Of these qSB-2 and qSB-11 could be detected in both years, while remaining loci were detected only in a single year. Furthermor e, four QTLs (qHD-2, qHD-3, qHD-5 and qHD-7) controlling heading date and t hree QTLs (qPH-3, qPH-4 and qPH-11) controlling plant height were also iden tified. Though rice sheath blight resistance may be influenced by morpholog ical traits, such as heading date and plant height, in the present study mo st detected resistance loci were not linked to the loci for heading date or plant height.