S. FUKUOKA and K. OKUNO
Laboratory of Plant Genetic Diversity, National Institute of Agrobiological Resources, Kannondai 2-1-2, Tsukuba, Ibaraki. 305 Japan
Hybrid breakdown, which is one of the reproductive barriers found in cultivated rice, was found in the progeny of the crosses between the Thai and Japanese rice varieties. A pair of complementary recessive genes control the hybrid breakdown in rice (Okuno 1985). This report deals with the chromosomal location of complementary genes controlling hybrid breakdown in Asian cultivated rice using restriction fragment length polymorphism (RFLP) markers.
Rice varieties with dominant alleles at either of complementary loci, Siborunauli 1 from Indonesia and Co1.No.15 from Thailand, were crossed to a tester line, W26, with four recessive alleles. A tester line was selected in F3 generation from the cross between Co1.No.15 and the Japanese variety, Sasanishiki which was homozygous for weakness. Two hundred and twentyfive F2 plants of the cross between W26 and Siborunauli 1 segregated into 52 normal and 173 weak plant types. Ninetytwo F2 plants of the cross between Co1.No.15 and W26 segregated into 34 normal and 58 weak plant types. DNA was extracted from leaves of each F2 plant and was used for RFLP analysis. Linkage analysis and interval mapping were performed using MAPMAKER (Lander et al. 1987).
Linkage between hybrid weakness genes and RFLP markers located on chromosome 10 was detected in F2 plants from the cross between W26 and Siborunauli 1. Interval mapping using 9 RFLP markers located near the terminal end of chromosome 10 indicated that one of the complementary genes, hwd1, was located between C701 at a distance of 0.9cM and R2309 at a distance of 0.6cM (Fig. 1). Linkage between weakness gene and RFLP markers located on chromosome 7 was found in F2 plants from the cross between Col.No. 15 and W26. Mapping of the other complementary gene, hwd2, was undertaken using 18 RFLP markers in the middle region of chromosome 7 (Fig. 2). Eight RFLP markers in this region cosegregated with hybrid weakness and were mapped in two sites at a distance of 1.1cM. The results showed that the chromosomal location of hwd2 should be more precisely determined.
Lander, E.S., P. Green, J. Abrahamson, A. Barlow, M.J. Daly, S.E. Lincoln and L. Newburg, 1987. MAPMAKER: an interactive computer package of constructing primary genetic linkage maps of experimental and natural populations. Genomics 1: 174-181.Okuno, K., 1985. Complementary recessive genes controlling hybrid breakdown found in a varietal cross of rice. RGN 2:52-54.