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-lOt, 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-lOt. Pooled DNA extracts from five homozygous blast-resistant (RR) and
five susceptible (rr) BC3F 2 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-lOt locus: RRF6 (3.8 + 1.2 cM) and RRH18 (2.9 + 0.9 cM). Linkage of these markers
with Pi-lOt was verified using an F2 population segregating for Pi-lOt. The two linked RAPD markers
mapped 7 cM apart on chromosome 5. Chromosomal regions surrounding the Pi-10 t 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-lOt locus
in rice breeding programmes