7. Development of a series of introgression lines of Japonica in the background of Indica rice

Y. AIDA, H. TSUNEMATSU, K. DOI and A. YOSIMURA

Faculty of Agriculture, Kyushu University, Fukuoka, 812-81 Japan

We have constructed a series of introgression lines (ILs) of rice using marker-aided selection to locate quantitative trait loci (QTLs) and measure their effects. ILs were nearly isogenic to a recurrent Indica parent IR24. Each IL was selected so as to carry a single homozygous introgressed chromosome segment from Japonica variety Asominori. A series of ILs covers entire genome with overlapping introgressed segments of each line.

RI (Recombinant Inbred) lines derived from the cross between Asominori and IR24, which were previously utilized for RFLP map construction (Tsunematsu et al. 1996b) and QTL analysis (Yoshimura et al. 1996; Tsunematsu et al. 1996a), were used for the original crosses. Eighteen lines with desirable genotypes which involve more than 60% of recurrent parent genotypes, were crossed three times to the recurrent parent IR24. BC1F1, and BC2F1 plants were genotyped using RFLP markers giving an evenly spaced coverage of the genome and promising plants retaining the entire donor segments were selected. Out of 888 BC2F2 plants from 65 BC2F1, plants, 70 plants were selected using 87 RFLP markers (Fig. 1).

Most parts of genome were covered by ILs. In 70 selected BC2F2 plants, the ratio of recurrent parent genome ranged from 84.9% to 98.7% with an average of 92.7% (Fig. 2). The ratio of heterozygous regions ranged from 0.0% to 14.8% with an average of 4.6% (Fig. 3). Four regions on chromosomes 2, 3 and 6 were not included in any of the 70 lines. Three regions on chromosomes 3 and 6 were not covered by overlapping introgressed segments.

ILs are effective as a tool for genetic analysis of QTLs. Any differences between ILs and their parents must be due to a QTL located in the introgressed region. These ILs series help fine mapping of QTLs as well as precise estimation of the effect of each QTL which are likely to be affected by environment. Further backcrossing and selection are underway to obtain a complete set of ILs.

References 

Tsunematsu, H., A. Yoshimura, M. Yano and N. Iwata, 1996a. QTL analysis using RI lines in rice. In Rice Genetics III, pp.619-623. Proc. 3rd Intl. Rice Genet. Symp., IRRI, Manila, Philippines.

Tsunematsu, H., A. Yoshimura, Y. Harushima, Y. Nagamura, N. Klirata, M. Yano, T. Sasaki and N. Iwata, 1996b. RFLP framework map using recombinant inbred lines in rice. Breeding Science 46: 279-284.

Yoshimura, A., J.X. Lei, T. Matsumoto, S. Yoshimura, N. Iwata, M.R. Baraoidan, T.W. Mew and R.J. Nelson, 1996. Analysis and pyramiding of bacterial blight resistance genes in rice by using DNA markers. In Rice Genetics III. Proc. 3rd Intl. Rice Genet. Symp., pp.577-581, IRRI, Manila, Philippines.

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