Targeting xa13 , a recessive gene for bacterial blight resistance in rice
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Bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most serious diseases of rice worldwide. Thirty bacterial blight resistance (R) genes (21 dominant genes and 9 recessive genes) in rice have been identified. They are the main sources for the genetic improvement of rice for resistance to Xoo. However, little is known about the recessive R genes. To clone and characterize the recessive R genes, we fine-mapped xa13, a fully recessive gene for Xoo resistance, to a DNA fragment of 14.8 kb using the map-based cloning strategy and a series of sequence-based molecular markers. Sequence analysis of this fragment indicated that this region contains only two apparently intact candidate genes (an extensin-like gene and a homologue of nodulin MtN3) and the 5' end of a predicted hypothetical gene. These results will greatly facilitate the isolation and characterization of xa13. Four PCR-based markers, E6a, SR6, ST9 and SR11 that were tightly linked to the xa13 locus, were also developed. These markers will be useful tools for the marker-assisted selection of xa13 in breeding programs.
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