Plant & Animal Genome VI Conference

P24

CONSTRUCTION OF A BAC CONTIG CONTAINING THE XA5 LOCUS IN RICE

1. Plant Breeding, Genetics, and Biochemistry Division, the International Rice Research Institute, P. O. Box 933, 1099 Manila, Philippines
2. College of Life Sciences, Wuhan University, Wuhan, 430072, P.R. China

The recessive gene, xa5, confers resistance to bacterial blight in rice. To generate a physical map of the xa5 locus, three RFLP markers, RG556, RG207 and RZ390, closely linked to xa5, were used to screen a rice bacterial artificial chromosome (BAC) library. BAC clones were identified forming two small contigs. The contigs were extended on both sides by chromosome walking and merged into one contig by DNA fingerprinting. The final physical map consists of 14 BAC clones and covers 580 kb. Genetic analysis with an F₂ population showed that two Tail-PCR markers, 28N22R and 40F20R, derived from the BAC clones flanking the xa5 locus, indicated that the contig encompasses the xa5 locus. To further delimit the location of the xa5 locus, the RFLP markers, RG556 and RG207, were converted to sequence tag sites and used to perform genetic analysis. The results indicated that the xa5 locus is located between RG207 and RG556. Among the BAC clones in the contig, one BAC clone, 44B4, hybridized to both marker RG207 and RG556. Therefore, we conclude that BAC clone, 44B4, carries the xa5 locus. The physical map of the xa5 locus is being used for map-based cloning of the xa5 resistance gene.