Sobrizal, K. IKEDA, P.L. SANCHEZ and A. Yoshimura

       Plant Breeding Laboratory, Faculty of Agriculture, Kyushu University,
       Fukuoka, 812-8581 Japan.

     

     As in other wild rice species, a high rate of seed shattering was also observed in a wild rice, Oryza glumaepatula (Acc. IRGC 105668). During the process of development of 0. glumaepatula introgression lines (Sobrizal eta!. 1999), we found that some lines having Taichung 65 cytoplasm and genetic background segregated for highly seed shattering. Seed shattering is characterized by the shedding of seeds as soon as the spike- lets mature.

     In developing 0. glumaepatula introgression lines, F, seeds were obtained through reciprocal crosses between the 0. glumaepatula and Taichung 65. The resultant F1 plants served as female parents and were repeatedly backcrossed with Taichung 65. Out of 83 BC3F, plants, six plants showed a high rate of seed shattering. The genotyping survey of the six plants revealed that the alleles were beterozygous for 0. glumaepatula and Taichung 65 at the RFLP1oci C1016 and C445 in the end of long arm of chromosome 4. Moreover, a non-shattering plant having the heterozygous allele of 0. glumaepatula and Taichung 65 at these RFLP loci was not observed. These results indicate that the gene controlling seed shattering is located in this region of chromosome 4.

     For further analysis, a BC4F, population derived from BC3F, plants showing seed shattering was used as a mapping population. This population consisting of 43 plants was classified into two groups; shattering and non-shattering. The numbers of plants in each group were 22 and 21 plants, respectively, suggesting that the seed shattering was controlled by one dominant gene (Sh(t)). The dominat allele from 0. glumaepatula caused seed shattering.

     The results of linkage analysis indicated that the Sh(t) was located between RFLP markers R1427 and C107 on the long arm of chromosome 4. The Sh(t) was linked to R1427 and C107 with map distances of 2.3 cM and 2.3 cM, respectively (Fig. 1).

     Eiguchi and Sano (1990) reported a seed shattering gene, Sh3(t) found in the progenies from the crosses between an isogenic line of Taichung 65 with morphological markers and the Indian wild strains, W107 (0. ruflpogon), Wl49 (0. rufipogon) and Wi 192(0. glumaepatula). The Sh3(t) was located between the liguleless (ig) and phenol staining (Ph) genes on chromosome 4. The ig and Ph flanked the RFLP markers XNpb267 and XNpbl77(G267 and G177) as reported by Saito et al. (1990). Harushima eta!. (1998) confirmed that G267 and G177 are situated at end of the long arm of chromosome 4 where the Sh(t) found in this study was also located. Therefore, there is high possibility that the Sh(t) mapped in this study is an allele of Sh3(t).

     This study was supported in part by Bio-oriented Technology Research Advancement Institution (BRAIN), Japan. Sobrizal and K. Ikeda were supported by postdoctoral fel