Identification and Molecular Mapping of Xa32(t), a Novel Resistance Gene for Bacterial Blight (Xanthomonas oryzae pv. oryzae) in Rice

The rice bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is the most devastating bacterial disease of rice worldwide. Because of the rapid changes in the pathogenicity of the pathogen (Xoo), novel BB-resistance genes are always needed for rice (Oryza sativa L.) breeding. In this article, a novel BB-resistance gene was identified from a wild rice (Oryzae ustraliensis) introgression line, C4064, and its chromosomal location was reported. On the basis of the resistance spectrum analysis, C4064 presented resistance to Xoo strains P1 (PXO61), P4 (PXO71), P5 (PXO112), P6 (PXO99), P7 (PXO145), P8 (PXO280), P9 (PXO339), and KX085, but susceptible to P2 (PXO86) and P3 (PXO79). Therefore, the resistance gene harbored in C4064 was a novel BB-resistance gene and tentatively designated as Xa32(t). Furthermore, the chromosomal position of this gene was located using bulked segregant analysis with the help of simple sequence repeat and expressed sequence tag markers. Of the 299 markers tested, 6 markers, i.e., RM27256, RM27274, RM2064, ZCK24, RM6293, and RM5926 on the long arm of chromosome 11, were linked with Xa32(t) with genetic distances of 2.1, 1.0, 1.0, 0.5, 1.5, and 2.6 cM between the resistance gene and the markers, respectively. The resistance gene was located between markers RM6293 and RM5926 at the end side of long arm and the other 4 markers at the centromere side. Finally, Xa32(t) was mapped within a length of 2.0 cM on the long arm of rice chromosome 11.