Genetic improvement of resistance to blast and bacterial blight of the elite maintainer line Rongfeng B in hybrid rice ( Oryza sativa L.) by using marker-assisted selection

Rice blast caused by the fungus Magnaporthe grisea and bacterial blight (BB) caused by Xanthomonas oryzae pv. Oryzae ( Xoo ) are two major rice diseases in the world. An elite, early maturing maintainer line of hybrid rice, Rongfeng B hybrid rice is susceptible to both blast and BB. For improving its diseases resistance, BL122 and CBB23 were used as the donors of blast resistance genes Pi1 and Pi2 and BB resistance gene Xa23 , respectively. These resistant genes were introgressed into Rongfeng B by using a marker-assisted backcross breeding programs, and two improved lines D521 and D524 with Pi1 , Pi2 and Xa23 were developed. The results indicated that both improved lines showed high resistance to leaf and neck blast and BB. The resistance frequencies for the rice blast and the length of lesions resulting from BB ranged from 96.7 to 100% and 0.77 to 1.18 cm, respectively. The two improved lines showed the desired variation in the majority of evaluated agronomic traits, including the number of grains per panicle, the grains weight, plant height, and seed setting rate. A new cytoplasmic male sterile line, Rongfeng 3A, with Pi1 , Pi2 , and Xa23 , was successfully developed through successive backcross breeding. Keywords: Gene pyramiding, marker-assisted backcross breeding, rice blast, bacterial blight