Present Status and Future Prospects of Marker Assisted Selection for Sheath Blight Resistance Breeding in Rice (Oryza sativa L.)

Sheath blight is one of the destructive diseases of rice, caused by the fungus Rhizoctonia solani Kuhn (Teleomorph: Thanatephorus cucumeris (Frank) Donk.). Rice resistance to sheath blight (ShB) is controlled by polygenes or quantitative trait loci (QTLs) and affected by plant morphological traits. Breeding and use of varieties resistant to ShB is crucial in controlling the disease, but the advances achieved have been limited due to the lack of highly ShB-resistant rice germplasm. Although many QTLs conferring resistance to ShB have been identified in recent years, most of the QTLs only showed small effects and few of them have been evaluated for utilization potential. Many R. solani-resistant resources have been found in wild rice species, microorganisms and other plant species. To develop ShB-resistant rice varieties, it is important to develop and explore new resistant rice germplasms, fine map and evaluate resistance QTLs, and also to pay attention to various bio-resources showing resistance to R. solani. With the rapid development of molecular markers, the use of QTL in breeding practice by marker-assisted selection (MAS) has become feasible. MAS provides opportunities for enhancing the response from selection because molecular markers can be applied at the seedling stage, with high precision and reduction in cost. In quantitative disease resistances, MAS would be very useful, but the individual QTL often have small effects.