Improvement of a RD6 Rice Variety for Blast Resistance and Salt Tolerance through Marker-Assisted Backcrossing

RD6 is one of the most favorable glutinous rice varieties consumed throughout the north and northeast of Thailand because of its aroma and softness. However, blast disease and salt stress cause decreases in both yield quantity and quality during cultivation. Here, gene pyramiding via marker-assisted backcrossing (MAB) using combined blast resistance QTLs (qBl 1, 2, 11, and12) andSaltolQTL was employed in solving the problem. To pursue our goal, the RD6 introgression line (RGD07005-12-165-1), containing four blast-resistant QTLs, were crossed with the Pokkali salt tolerant variety. Blast resistance evaluation was thoroughly carried out in the fields, from BC(2)F(2:3)to BC4F4, using the upland short-row and natural field infection methods. Additionally, salt tolerance was validated in both greenhouse and field conditions. We found that the RD6 "BC(4)F(4)132-12-61" resulting from our breeding programme successfully resisted blast disease and tolerated salt stress, while it maintained the desirable agronomic traits of the original RD6 variety. This finding may provide a new improved rice variety to overcome blast disease and salt stress in Northeast Thailand.