Pyramiding of Four Blast Resistance QTLs into Thai Rice Cultivar RD6 through Marker-assisted Selection

Thai rice cultivar RD6 is well known for its cooking and eating qualities. However it is susceptible to blast disease, a major rice disease caused by the fungus Magnaporthe oryzae. This study focused on the pyramiding of four QTLs for blast resistance located on chromosomes 1, 2, 11 and 12, from two RD6 introgression lines. Marker-assisted selection was performed and facilitated the selection with 8 microsatellite flanking markers to enable the selection in BC2F2:3 lines. All possible combinations of the four QTL alleles were assessed for blast resistance by artificial inoculation using 8 diverse isolates in a greenhouse and under field conditions using the upland short row method. The results showed that the RD6 introgression lines carrying a high number of QTLs for blast resitance achieved from pyramiding have high levels of blast resistance and broad spectrum of resistance to the blast pathogens prevalent in the region. Only one of the M. oryzae isolates, THL185, was virulent to all the breeding lines, suggesting that the identification of new blast resistance genes or QTLs and pyramiding them into RD6 for durable blast resistance and no yield penalty should be the focus of further research.