MOLECULAR MAPPING OF GENES FOR RESISTANCE TO RICE BLAST (PYRICULARIA-GRISEA SACC)

Two dominant genes conferring complete resistance to specific isolates of the rice blast fungus, Pyricularia grisea Sacc., were located on t he molecular map of rice in this study. Pi-l(t) is a blast resistance gene derived from the cultivar 'LAC23'. Its map location was determine d using a pair of nearly isogenic lines (NILs) and a B6F3, segregating population from which the isoline was derived. RFLP analysis showed t hat Pi-l(t) is located near the end of chromosome 11, linked to RZ536 at a distance of 14.0+/-4.5 centiMorgans (cM). A second gene, derived from the cultivar 'Apura', was mapped using a rice doubled-haploid (DH ) population. This gene was located on chromosome 12, flanked by RG457 and RG869, at a distance of 13.5+/-4.3 cM and 17.7+/-4.5 cM, respecti vely. The newly mapped gene on chromosome 12 may be allelic or closely linked to Pi-ta (=Pi-4(t)), a gene derived from 'Tetep' that was prev iously reported to be linked to RG869 at a distance of 15.4+/-4.7 cM. The usefulness of markers linked to blast resistance genes will be dis cussed in the context of breeding for durable blast resistance.