IDENTIFICATION OF AN EARLY HEADING TIME GENE FOUND IN THE TAIWANESE RICE CULTIVAR TAICHUNG-65

An early heading time gene tentatively designated as 'v' and nonalleli c to E-1, E-2, E-3 and Ef-1 was detected in the Taiwanese rice cultiva r Taichung 65 (T65) (Okumoto et al. 1992b). This gene remarkably accel erated heading time. The allelism test of this gene to a photoperiod i nsensitivity gene Se - 1(e) at the Se - 1 locus was per formed using t he progenies from reciprocal crosses between T65 and a heading time te ster line ER. The role of this gene in the rice cultivation in Taiwan was also discussed on the basis of photoperiod responses of T65: ER an d a heading time tester line LR. T65 was found tee have the genotype E 1E1E2E2E3E3 vv ef - 1ef - 1, while ER and LR had the genotypes E(1)E(1 )e(2)e(2)E(3)E(3)Se - 1(e)Se - 1(e)Ef-1Ef-1 and E(1)E(1)e(2)e(2)E(3)E( 3)Se - 1(u)Se - 1(u)Ef - 1Ef - 1, respectively. ER also carried a rice blast resistance gene Pi - z(t) closely linked to Se - 1(e) on chromo some 6. E-1, E-2, E-3 and Se -1(u) were all photoperiod sensitivity ge nes, and ef - 1 at the Ef - 1 locus remarkably increased the duration of the basic vegetative growth period (BVG). In the F-2, no distinct t ransgressive segregants appeared, and the three genotypes (Pi - z(t) P i - z(t), Pi - z(t) +, ++) for the Pi-z locus in the Fa exhibited almo st the same range and the same mean for heading time. These facts impl y that 'v' is identical with Se - 1(e). T65 exhibited a far longer BVG than the two tester lines. The critical day-lengths (CDLs) of T65 and ER were longer than 16 h, while the CDL of LR ranged between 14 h and 15 h : the CDL of LR was shorter than those of T65 and ER. When compa red to LR, T65 and ER exhibited a small retarding effect under super o ptimum photoperiod (RES), and did not differ in RES. These results ind icate that the low photoperiod sensitivity of T65 is due to the action of 'v' (=Se - I-e). Since the long BVG of T65 is attributed to the ac tion of ef - 1, it is considered that 'v' (=Se - I-e) and ef - 1 are v ery important genes for rice cultivation in Taiwan, where natural day- length is short even in summer and seasonal changes are negligible.