Weedy rices possess genes useful under adverse environmental conditions, because they are adapted to natural growing condition. They are genetically more similar to cultivars than wild rices. Despite the relatively easy crossability with cultivars, weedy rices have not been extensively exploited by rice breeders, partly because of their recent discovery.

To use the weedy rice in rice breeding and genetic studies, a set of introgression lines (ILs) were developed, each containing a few independent chromosomal segments from the japonica weedy accession of O. sativa L. "Hapcheonaengmi3" in the background of Tongil-type rice cultivar "Milyang23". Each of the introgression lines is nearly isogenic to Milyang23. These lines provide complete coverage of the Hapcheonaengmi3 genome.

Milyang23 was crossed to Hapcheonaengmi3 using Milyang23 as the female parent. F₁ plants were backcrossed to Milyang23 to produce 98 BC₁ plants. These BC₁ plants were analyzed for 135 genetic markers covering 1,640 cM of the rice genome for QTL mapping (Suh et al.1999). The plants contained on the average 2.6 independent introgressions per line. Based on the molecular map, 80 BC₁ plants with desired genotypes were selected for the ILs development. This population and the following five generations of selfing were grown in the field and subjected to phenotypic selection favoring the phenotype of the recurrent parent by single

seed descent.

To select the lines having genotypes at target loci, the SSR genotypes of the BC₁F₅ plants were determined using 85 SSR markers evenly distributed along the 12 rice chromosomes (Temnykh et al. 2001). Fig. 1 shows the introgressed chromosome segments in a sub-set (45 plants) of the candidates for ILs. Most parts of the genome were covered by ILs.

ILs reported in this study would be effective as a tool for finemapping, evaluation and characterization of QTLs underlying the traits of agronomic importance because genetic differences between the recurrent parent and introgression lines can be associated with the introgressed segment. Additional backcrosses and selections are currently being made to purify the candidate ILs with a few independent introgressions and to construct a complete set of ILs.

Acknowledgements

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

References

Suh, J.P., S.N. Ahn, H.P. Moon and H.S. Suh, 1999. QTL analysis of low temperature germinability in Korean weedy rice. Kor. J. Breed. 31: 261-267.

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.