16. Molecular mapping of a gene for resistance to a Korean isolate of rice blast

Sang Nag ahn', Yeon Kyu kim', Seong Sook han, Hae Chime choi, Hun Pal moon and Susan R. McCouch

1 ) National Crop Experiment Station, RDA, Suweon, Korea

2) National Agricultural Science and Technology Institute, RDA, Suweon, Korea

3) Department of Plant Breeding, Cornell University, Ithaca, NY 14853, USA

 We report the tagging of a blast (Pyricularia grisea) resistance gene, designated Pi-18 (t), in rice using DNA markers. This gene confers complete resistance to Korean isolate Kl-313 of the blast pathogen which is genetically stable and routinely used for genetic studies in Korea (Lee and Cho 1990).

Major genes for blast have been tagged and mapped previously (see McCouch et al. 1994 for review). To know whether there is a relationship among genes conditioning resistance to location-specific isolates of the blast pathogen and thereby to identify linked markers to resistance genes for isolate KI-313 isolated in Korea, RFLP markers previously reported to be linked to major blast resistance genes in different rice germplasm and other markers mapped to nearby regions (24 in total) were surveyed for polymorphism between a resistant (Suweon 365) and a susceptible (Chucheongbyeo) parent. The resistance of Suweon 365 to isolate Kl-313 is controlled by single dominant gene (Kim et al. 1995). Eight enzymes were used in the parental survey and the percentage of clones detecting polymorphism between the parent was low (33 %), due to the fact that both were Japonica varieties.

Research Notes 75

An F2 population was derived from a cross between Suweon 365 and Chucheongbyeo. DNA was extracted from F2 plants and each individual was given a score for eight RFLP markers showing polymorphism between the parents. F2 plants were ratooned and 69 F3 families were test-inoculated with isolate KI-313 21 days after sowing (at least 15 plants per family) and disease was evaluated 7 days after inoculation.

Linkage analysis was performed using MAPMAKER software (Lander et al. 1987). Marker order was determined with a LOD score >2.0 and map distance were estimated using the Kosambi function. Results showed that the resistance gene to blast isolate Kl-313 was linked to a single-copy DNA marker RZ536 on chromosome 11 at a distance 5.4 cM. Five additional RFLP markers (RG, RZ, and CD) and two microsatellite markers (RM224 and RM21) from Cornell University, U.S.A. and one RFLP marker (C82) from National Institute of Agrobiological Resources, Japan were mapped to better define the location of the gene (Fig. 1). Previous studies by other workers (Mew et al. 1994, Yu et al. 199) reported that Pi-1 on chromosome 11 is flanked by two markers RZ536 and RG303. However this study suggests that a different gene governs resistance to isolate Kl-313. Based on these results, we report the existence of a resistance gene Pi-18(t), in Suweon 365 that is linked to, but different than, Pi-1.

Additional markers are being surveyed in the targeted region in an attempt to Find makers flanking the gene. Microsatellite markers, such as RM224 offer a more efficient and economical screening tool than RFLP markers though RM224 is located farther from Pi-18 (t) than RZ536 (10.2 cM compared to 5.4 cM). (Gene symbol: Old system)

Fig. 1. RFLP map of long arm of rice chromosome 11 showing the location of a gene from Suweon 365 conferring resistance to blast isolate KI-313 (The gene has been tentatively designated Pi-18(t) and is indicated by an arrow). 76 Rice Genetics Newsletter Vol. 13

References

Lee, E.J. and S.Y. Cho, 1990. Variation in races of rice blast disease and varietal resistance in Korea. Paper

presented at the Focus on Irrigated Rice. pp.27-31, August 1990, Seoul, Korea. Kim, Y.K., Y.J. Kim, H.C. Choi and S.S. Han, 1995. Inheritance of leaf blast reactions to four races of blast

fungus in segregating populations of eight rice crosses. RDA J. of Agric. Science 37(2): 283-298. 

Lander, E.S., P. Green, J. Abrahamson, A. Barlow, M.J. Daly, S.E. Lincoln and L. Newburg, 1987. MAPMAKER: an interactive computer package for constructing primary linkage maps of experimental and natural populations. Genomics l: 174-181.

McCouch, S.R., R.J. Nelson, J. Thome and R.S. Zeigler, 1994. Mapping of blast resistance genes in rice. In R.S. Zeighler, S.A. Leong, and P.S. Teng (eds.). Rice Blast Disease. Cab Intl. and IRRI, Wallingford, Oxon, UK, pp. 167-186.

 Mew, T.V., A.S. Parco, S. Hittalmani, T. Inukai, R. Nelson, R.S. Zeigler and N. Huang, 1994. Fine-mapping of major genes for blast resistance in rice. RGN 11: 126-128.

Yu, J.H., D.J. Mackill, J.M. Bonman, S.R. McCouch, E. Guiderdoni, J.L. Notteghem and S.D. Tanksley, 1996. Molecular mapping of genes for resistance to rice blast (Pyricularia grisea Sacc.). Theor Appl Genet, (in press)