Guifu Liu, Shaohong Qu, Guodong Lu, Guo-liang Wang

Department of Plant Pathology, The Ohio State University, Columbus, Ohio

Rice blast, caused by fungal pathogen Magnaporthe grieas, is the most devastating disease of rice and causes about US$ 5 billion yield loss per year in rice production worldwide. Host resistance is the only practical means currently available to effectively control the disease. Through wide hybridization and repeated backcrossing, the resistance gene Pi9 was transferred from tetraploid wild rice Oryza minuta (BBCC genome) into elite breeding lines. We tested the resistance spectrum by inoculating the Pi9 introgression line with more than 50 isolates from 7 countries. The Pi9 plants were resistant to all isolates tested, suggesting that it is a unique resistance gene with broad-spectrum resistance. We have identified three RAPD markers tightly linked to Pi9. One of the markers (pB8) has no recombination with the gene in over 1200 F2 plants, suggesting that the marker may be within the gene or located very close to the gene. A bacterial artificial chromosomal (BAC) library of the Pi9-introgression line has been constructed. Twelve positive BAC clones hybridizing with pB8 have been identified and construction of a contig spanning the Pi9 region is in progress. After sequencing one of the BAC clones containing pB8, we identified a candidate gene with a nucleotide-binding site (NBS) and leucine rich repeats (LRRs), which are the common features of many cloned resistance genes in plant species. Complementation of the candidate gene in rice is in progress.