<i>Xa39</i> , a novel dominant gene conferring broad‐spectrum resistance to <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> in rice

Abstract

Bacterial blight ( BB ), caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most devastating rice diseases worldwide. In this study, a rice introgression line ( IL ), FF 329, which was identified from a BC 1 F 4 population derived from the cross between donor PSBRC 66 (P66) and recipient Huang‐Hua‐Zhan ( HHZ ), exhibited a typical hypersensitive response ( HR ) when inoculated with all 21 representative Xoo strains, consisting of 14 Philippines races and seven Chinese pathotypes. By contrast, the parents were highly susceptible to 10 of the tested strains and resistant or moderately susceptible to 11 strains, but without HR symptoms. Genetic analysis of the F 2 population derived from the HHZ / FF 329 cross with virulent Philippines race 6 (P6) and Chinese pathotype V (CV) revealed that BB resistance in FF 329 was controlled by a single dominant gene. Because FF 329 showed broad‐spectrum BB resistance, different from both parents, the gene identified was novel and was designated Xa39 . Two SSR markers, RM 21 and RM 206, located on rice chromosome 11, were linked to the target gene by bulked segregant analysis. A further six markers linked to Xa39 were identified in the region between RM 21 and RM 206 for fine gene mapping, and the Xa39 locus was refined to a 97·4 kb interval flanked by markers RM 26985 and DM 13 using a large F 2 population. This gene provides rice breeders with a new option to incorporate BB resistance into newly developed cultivars.