Plant & Animal Genome VI Conference

P30

PROGRESSES IN MAP-BASED CLONING OF Xa22(t), A NEW GENE FOR BACTERIAL BLIGHT RESISTANCE IN RICE

National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China

Bacterial blight is one of the most devastating diseases of rice worldwide. We previously identified an indigenous rice variety, Zhanchanglong, from Yunnan Province, a center of diversity for cultivated rice, showing resistance against a wide range of bacterial blight strains. Allelism and inoculation tests determined that this variety carried a gene for bacterial blight resistance that is distinct from all the genes identified previously. RFLP analysis located this gene to the distal end on the long arm of chromosome 11, a location that is also different from all previously identified genes. We thus designated this gene as Xa22(t). To clone this gene following a map-based cloning approach, we fine mapped the gene using 13 RFLP markers within a region of less than 7 cM on the distal end of this chromosome arm. Six markers were identified in a segment of about 2 cM bracketing the Xa22(t) genomic region, and one marker (R1506) cosegregated with the resistance! in a random sample of 248 plants from a very large F₂ population. The cosegregation was further confirmed by analyzing 300 highly susceptible F₂ plants from this same population. These six markers were used as probes to screen a BAC library kindly provided by Dr. Hongbin Zhang of Texas A&M University, resulting in 12 positive clones. We are now constructing the physical map of this genomic region. The details and progresses will be reported in the meeting.