GENIC ANALYSIS FOR HEADING TIME IN WILD-RICE STRAINS

Rice cultivars so far examined mostly had the early-heading gene, Ef-1 . Their wild progenitor, Oryza rufipogon Griff., was examined in respe ct to the genes for heading time in the present study. Of three strain s tested, W593 from Malaysia and W1623 from Tauyuan, Taiwan produced n o panicles when planted in the first crop season at Taichung, suggesti ng their strong sensitivity to photoperiod, while W630 from Burma was practically insensitive to photoperiod and produced panicles. In the s econd crop season, the wild strains headed several days later than Tai chung 65. When they were crossed with Taichung 65, the heading dates o f the F-1 plants were similar to, or a few days earlier than that of T aichung 65. In the B1F1 (T65 X F-1) populations, early-heading plants like Ef-1 carriers were found. They were backcrossed to Taichung 65 se veral times and true-breeding early-heading lines were obtained. When they were crossed with T65(20)E(a) carrying Ef-1(a), the heading dates of the F-2 plants varied within the parental range, suggesting that t he wild strains had similar alleles at the Ef-1 locus. Regarding genes controlling photoperiod sensitivity W593 and W1623 were found to have recessive ones denominated as se-7 (t) and se-6 (t), respectively. Th e effect of these genes can be suppressed by Ef-1 when combined togeth er.