Rice Genetics Newsletter, Vol. 18

Rgn18

36.	Oryza meridionalis *chromosomal segment introgression lines in cultivated rice, O. sativa* L.**
	T. KURAKAZU¹, SOBRIZAL¹, K. IKEDA¹, P. L. SANCHEZ¹, K. DOI¹, E.R. ANGELES², G.S. KHUSH² and A. YOSHIMURA¹ 1)Plant Breeding Laboratory, Faculty of Agriculture, Graduate School, Kyushu University, Fukuoka, 812- 8581 Japan. 2)International Rice Research Institute, MCPO Box 3127, Makati City 1271, Philippines.

The wild species Oryza meridionalis Ng is distributed in north Australia. This species is found at edges of freshwater lagoons, temporary pools and swamps in 15 - 20 cm of water (Vaughan 1989). O. meridionalis differs from cultivated rice in morphology, environmental adaptability and growth habit. Doi et al. (2000) reported that O. meridionalis is a distant species in O. sativa complex. To analyze the genetics of traits specific to O. meridionalis and to exploit its genetic potential, we developed a series of O. meridionalis chromosomal segment introgression lines (merILs) with reciprocal cytoplasms of O. sativa L. cv. Taichung 65 and O. meridionalis with genetic background of O. sativa L. cv. Taichung 65.

To develop merILs, F₁ plants obtained by reciprocal crosses between O. meridionalis (W1625) and Taichung 65 which served as female parents, were continuously backcrossed with Taichung 65 to generate BC₄F₁ populations. To select plants of desired genotypes, whole genome survey was conducted in BC₄F₁ generation using 105 RFLP markers scattered in 12 chromosomes.

Out of 160 BC₄F₁1 plants having O. meridionalis cytoplasm, 35 were selected as candidates of merILs with O. meridionalis cytoplasm based on the introgressed segment in the target regions and the homogeneous genetic background. Likewise, out of 170 BC₄F₁ plants having Taichung 65 cytoplasm, 26 plants were selected as candidates of merILs with Taichung 65 cytoplasm. The selected 35 and 26 candidate lines carried entire chromosome segments of O. meridionalis (Fig. 1). Most parts of the O. meridionalis genome were covered, except for regions marked with arrows. The lack of introgression segments in the introgression lines may be due to a random selection during the development of introgression lines. Uncovered regions are now under reconstruction by transferring the introgressed segments from the lines with different cytoplasm.

To obtain the homozygous O. meridionalis introgressed segments in the target regions, selected BC₄F₁ plants were self-pollinated before selecting single homozygous introgression lines. Using a complete set of merILs with overlapped homozygous introgression chromosomal segments, it is possible to estimate the contribution of chromosome regions to certain traits in replicated trials.

This study was supported by Bio-oriented Technology Research Advancement Institution

(BRAIN), Japan.

References

Doi, K., M.N. Nonomura, A. Yoshimura, N. Iwata and D.A. Vaughan, 2000. RFLP relationships of A-genome species in the genus Oryza J. Fac. Agr., Kyushu Univ. 45: 83-98.

Vaughan, D., 1989. The genus Oryza L. current status of taxonomy. IRRI Research Paper Series No. 138. The International Rice Research Institute, Manila, Philippines.