Rice is not only one of major crops grown in the world but also the staple food in Asia. However, in modern agriculture, the genetic diversity in rice gene pool is diminishing by selection breeding. Hence, rice is readily threatened by biotic and abiotic stresses. Rice blast is one of the major threats to stable rice production. The best approach to prevent rice blast is development of rice cultivars harboring resistance gene against blast disease. National Institute of Crop Science (NICS) in Korea developed a mutant line, Namil(SA)-bl5, which has inherited short culm and rice blast resistance by treatment of sodium azide (SA). To localize favorable mutated allele types, two mapping populations were constructed by using F2 progenies derives crosses between Namil(SA)-bl5 and Milyang23 and Namil (wild type) and Milyang23. Each F2 progenies were evaluated in terms of culm length and resistance level against a rice blast isolate, 94-254 along with their parental lines. Association analyses between marker genotype on 68 SSR anchor markers and evaluated phenotype of progeny lines were adopted to localize the putative chromosomal locations involved to culm length and blast resistance. Association analyses localized two major loci on the chromosomes of middle-low region of 6 (R2=15.8%) and the distal region of 7 (R2=20.0%), and a major locus on the middle of chromosome 12 (R2=46.6%) for the reduced culm length and increased resistance level against rice blast, respectively.

Rice is a source of food supply as the staple food. The narrow genetic diversity of Korean Japonica cultivars is prone to be susceptible to abiotic and biotic stresses such as rice blast, bacterial blight, and brown planthopper (BPH). The best approach for prevention of the breeding and extermination of disease and insect pest would be the development of rice cultivars harboring multiple disease and insect pest resistance genes. National Institute of Crop Science (NICS) in Korea developed a mutant line, Namil(EMS)-bl10,bph1, by using ethyl-methane-sulfonate (EMS) as the chemical mutagen on the wild type, Namil. The mutant line exhibits strong resistance levels against rice blast and brown planthopper. To localize favorable mutated allele types, two mapping populations were constructed by using F2 progenies derives crosses between Namil(EMS)-bl10,bph1 and Milyang23 and Namil (wild type) and Milyang23. Each F2 progenies were evaluated in terms of DNA marker genotype as well as agronomic traits measured, and for rice blast and BPH resistance, virulent blast isolate 94-254 and Korean biotype of BPH were used to screen F2:3 seedlings to conduct association analysis between marker genotype and evaluated phenotype of progeny lines. Through comparisons on major loci between two mapping populations, the putative major loci for rice blast resistance (RM1337, R2=54.4%) and BPH (RM0277, R2=55.1%) were primarily localized on chromosome 12.

Rice blast is one of the major threats to stable rice production. In modernized rice breeding system, development of rice cultivars harboring resistance gene is one of the most efficient approaches against blast disease. Wild rice species, to the context, have been recognized as valuable genetic resources in improving resistance or tolerance level of modern commercial rice cultivars against biotic or abiotic stresses. National Institute of Crop Science (NICS), Korea developed an introgression line, ‘Suweon 506’, which has inherited the rice blast resistance from a BBCC genome wild Oryza species, O. minuta (Acc. 101141). Genetic analysis was carried out to localize the chromosomal region responsible for the rice blast resistance of ‘Suweon 506’ by using F2 progenies from ‘Suweon 506’ × ‘Milyang 23’. Association analysis between marker genotypes and their inferred resistance levels of F2 progenies against a Korean blast isolate, ‘93-072’ localized the target genetic region on rice chromosome 12. Further association analysis with increased number of DNA markers, and e-Landings on the rice pseudomolecule 6, the segment of ‘RM101-S10704-RM1337’ was identified to be tightly linked to the rice blast resistance gene from O. minuta at the 8.8~11.9 Mbp physical region of rice chromosome 12, where at least 9 rice blast resistance genes have been also identified. The 3.1 Mb equivalent virtual contig, composed with 31 BAC/PAC clones will be further analyzed for fine mapping and gene identification.