IDENTIFICATION OF RAPD MARKERS LINKED TO A MAJOR BLAST RESISTANCE GENE IN RICE

Rice blast, caused by Pyricularia grisea, is a major production constraint in many parts of the world. The Korean rice variety Tongil showed high levels of resistance for about six years when widely planted under highly disease-conducive conditions, before becoming susceptible. Tongil was found to carry a single dominant gene, designated Pi-10t, conferring resistance to isolate 106 of the blast pathogen from the Philippines. We report here the use of bulked segregant RAPD analysis for rapid identification of DNA markers linked to Pi-10t. Pooled DNA extracts from five homozygous blast-resistant (RR) and five susceptible (rr) BC3F2 plants, derived from a CO39 x Tongil cross, were analyzed by RFLP using 83 polymorphic probes and by RAPD using 468 random oligomers. We identified two RAPD markers linked to the Pi-10t locus: RRF6 (3.8 +/- 1.2 cM) and RRH18 (2.9 +/- 0.9 cM). Linkage of these markers with Pi-10t was verified using an F2 population segregating for Pi-10t. The two linked RAPD markers mapped 7 cM apart on chrome some 5. Chromosomal regions surrounding the Pi-10t gene were examined with additional RFLP markers to define the segment introgressed from the donor genome. Pi-10t is likely to be a new blast-resistance locus, because no other known resistance gene has been mapped on chromosome 5. These tightly linked RAPD markers could facilitate early selection of the Pi-10t locus in rice breeding programmes.