Prospect of the QTL-qSB-9Tq utilized in molecular breeding program of japonica rice against sheath blight.

The major QTL-qSB-9(Tq) conferring partial resistance to rice (Oryza sativa L.) sheath blight (Rhizoctonia solani Kühn) has been verified on chromosome 9 of the indica rice cultivar, Teqing. In this study, the prospect of this QTL utilized in molecular breeding program of japonica rice for sheath blight resistance was investigated. Most of the japonica rice cultivars showed lower level of sheath blight resistance than the indica rice cultivars. At the corresponding site of qSB-9(Tq), nine typical japonica rice cultivars from different ecological regions or countries proved to possess the susceptible allele(s). Introgression of qSB-9(Tq) into these cultivars enhanced their resistance level by decreasing sheath blight score of 1.0 (0.5-1.3), which indicated that qSB-9(Tq) had a large potential in strengthening the resistance of japonica rice to sheath blight. The use of the three molecular markers, which were polymorphic between Teqing and many japonica rice cultivars, promotes the application of qSB-9(Tq) in a concrete molecular breeding program.