Wild species of rice are valuable source for improving traits of agronomic importance and broadening genetic diversity in rice breeding. For those reasons, the use of wild species is gradually increasing in rice breeding.

In order to use novel genes, both qualitative and quantitative, of wild species in rice breeding and genetic studies, a set of introgression lines (ILs) were developed each containing a few independent chromosomal segments from a strain of Asian wild rice (Oryza rufipogon Griff.), W1944 in the background of a Korean elite cultivar, "Hwayeongbyeo" (O. sativa ssp. japonica). Each of the introgression lines is nearly isogenic to Hwayeongbyeo and these lines provide nearly complete coverage of the O. rufipogon genome.

Hwayeongbyeo was crossed to W1944, using Hwayeongbyeo as a female parent. F₁ plants were backcrossed to Hwayeongbyeo to produce 120 BC₁ plants. This population and the following 5 generations of selfing were grown in the field and subjected to phenotypic selection favoring the phenotype of the recurrent parent via single seed descent. In the field trial, the population showed significance amount of variation for evaluated traits including days to heading, culm length, panicle number, shattering, grain characters, and more (Lee et al. in preparation)

To select the lines having genotypes at target loci, whole genome survey was conducted in BC₁F₅ generation by using 124 SSR markers evenly distributed along the 12 rice chromosomes (Temnykh et al. 2001, McCouch et al. 2002). Figure 1 represents the genome constitution of candidates for ILs (36 selected lines). Most part of the O. rufipogon genome were covered by these ILs except for several regions on chromosomes 2, 4, 6, 7, 9, and 10 (marked with arrows in Fig. 1). The lack of introgression segments in these genomic regions might be due to gene(s) related to sterility and gametophyte. Also, selection against extremely late flowering, sterility,
tall plant height, and other deleterious traits during the generation advancement contributed to the lack of the introgressions. On the average, each line has 6.3 segments and 13.2 percent

genome from O. rupifogon. The mean size of introgressed segments is 43.2 cM.

These ILs can not only facilitate the utilization of novel traits of O. rufipogon, but also allow identification and fine mapping of QTLs by eliminating epistatic effects. Additional backcrosses and selections are underway to purify the candidate ILs with a few independent introgressions and to construct a complete set of ILs including lines with uncovered regions.

Acknowledgement

This research was supported by a grant (CG3121) from Crop Functional Genomics Center of the 21st Century Frontier Research Program funded by the Ministry of Science and Technology, Republic of Korea. Seeds of O. rufipogon Griff., W1944 was kindly provided by the National Institute of Genetics through Dr. H.S. Suh, Yeungnam University, Korea.

References

Temnykh, S., G.. DeClerck, A. Lukashova, L. Lipovich, S. Cantinhour and S.R. McCouch, 2001. Computational and Experimental Analysis of Microsatellites in Rice (Oryza sativa L.): Frequency, Length Variation, Transposon Associations, and Genetic Marker Potential. Genome Res. 11: 1441-1452.

McCouch, S.R., L. Teytelman, Y. Xu, K.B. Lobos, K. Clare, M. Walton, B. Fu, R.Maghirang, Z. Li, Y. Xing, Q. Zhang, I. Kono, M. Yano, R. Fjellstrom, G. DeClerck, D. Schneider, S. Cartinhour, D. Ware, and L. Stein, 2002. Development and Mapping of 2240 New SSR Markers for Rice (Oryza sativa L.). DNA Res. 9: 199-207