Molecular markers and their use in marker-assisted selection in rice

Increasing world population, shrinking cultivable rice (Oryza sativa L.) land area, water scarcity and excess, evolution of new biotypes of pests and diseases, and climate change pose serious challenges to rice breeders to increase production and productivity with multiple resistances to biotic and abiotic stresses. Recent advances in rice genomics research and completion of the rice genome sequence have made it possible to identify and map precisely a number of genes through linkage to DNA markers. Noteworthy examples of some of the genes tightly linked to markers are resistance to or tolerance of blast, bacterial blight, virus diseases, brown planthopper (Nilaparvata lugens), drought, submergence, salinity, and low temperature and improved agronomic and grain quality traits. Marker-assisted selection (MAS) can be used for monitoring the presence or absence of these genes in breeding populations and can be combined with conventional breeding approaches. Marker-assisted backcross breeding has been used to effectively integrate major genes or quantitative trait loci with large effect into widely grown varieties. Pyramiding different resistance genes using MAS provides opportunities to breeders to develop broad-spectrum resistance for diseases and insects. The use of cost-effective DNA markers derived from the fine mapped position of the genes for important agronomic traits and MAS strategies will provide opportunities for breeders to develop high-yielding, stress-resistant, and better-quality rice cultivars.