Taichung 65 (abbr. T65) is a representative Japonica (Ponlai) rice cultivar in Taiwan, which has been used as a recurrent parent in repeated backcrosses to establish isogenic or near-isogenic lines having early-heading gene, Ef-l. The early heading gene, Ef-1, is known to be present in various cultivars and wild strains (Tsai 1985; 1986a, b; 1986b; 1992; 1995; 1996), and is located on Chromosome 10 (Sato et al. 1988). T65 has its recessive allele, ef-l. The different Ef-l alleles were considered to be isoalleles (Tsai 1976; Tsai and Oka 1968). Among Ef-I alleles, Ef-l r was derived from a Northern Chinese variety Tatung-tsailai, Ef-Ib from a Hokkaido variety Bozu 5, while Ef-lr and Ef-Ix were mutants of T65 induced by gamma-rays and x-rays, respectively. When repeated backcrosses were made the heading-advancing effects of Ef-la, Ef-lr and Ef-lx were reduced, while that of Ef-Ib was increased significantly (Tsai 1976; Tsai and Oka

Table 1. Distribution of heading days in selfed progenies of early-heading offtype plants occurred

T65(7), (20) indicate backcrosses repeated 7 and 20 times with T65, respectively.

Research Notes 79

Table 2. Variation of heading days in succeeding progeny lines produced from offtype plants

1968), suggesting that some element weakening the early-heading effect was combined with Ef-1^b gene.

In the winter crop (1st crop) season, an early heading line, T65(20) Ef-I^b, headed several days earlier than line T65 (7) Ef-I^b, although both had the same earliness gene, Ef-I^b, as shown in Table 1. Two early offtype plants out of twenty, unexpectedly occurred in a line of T65 (7) Ef-I^b in an experiment. The selfed progenies of these offtypes were raised and heading time variations are shown in Table 1. These two Ef-I^b lines show transgressive variation. From the first progeny of the offtypes, some early and late heading plants were selected to raise their successive progeny lines. They produced early-heading ((20) Ef-I^b like) and segregating lines raised from early-heading parental plants while the late-heading plants produced late-heading ((7) Ef-1^b-like) lines (Table 2). The F2 population from the cross of (7) Ef-I^b and (20) Ef-1^b lines produced an amount of genetic variance (VF2 4.24 > VE 1-20) indicating their genetic differences (Tsai 1987a). One of the (20) Ef-71^b-like lines (Table 2) was selected to cross with (20) Ef-I^b line. The F2 population of this cross showed the heading-variation within the parental range with smaller variance (VF2 : 2.08 ; ve : 1-77) somewhat differed with that of the cross, (7) Ef-1^b x (20) Ef-l^b.

Thus, the early-heading line, T65(7)Ef-1^b, seemed to have Ef-1^b gene and its weakening gene w-Ef-I. The w-Ef-I gene could have been eliminated by crossing-over in the process of repeated backcrosses or mutation, and the effect of Ef-I^b would have then inforced. (Gene symbol: Old system)

Sato, S., I. Sakamoto, K. Shirakawa and S. Nakasone, 1988. Chromosomal location of an earliness gene Efi of

Tsai, K.H., 1976. Studies on earliness genes in rice, with special reference to analysis of isoalleles at the E

80 Rice Genetics Newsletter Vol. 13

Tsai, K..H., 1985. Further observations on the Ef-I gene for early heading. RGN 2: 77-78.

Tsai, K.H., 1986a. Genes controlling heading time found in a tropical Japonica variety. RGN 3: 71-73.

Tsai, K.H., 1986b. Genes at the Ef-I locus found in Fujisaka 5 and two Chinese Indica varieties. RGN 3:

Tsai, K.H., 1987a. Interaction between an early-flowering gene. E, and its emphasizing gene, m, in rice and

Tsai, K.H., 1987b. Genes for early heading found in tropical late heading rice varieties. RGN 4: 85-86.

Tsai, K.H., 1992. A T651ike line obtained from Kameji x Shinriki cross. RGN 9:71-73.

Tsai, K.H., 1995. Genic analysis for heading time in wild rice strains. Jpn. J. Genet. 70: 555-562.

Tsai, K.H., 1996. Genic analysis for heading time in tropical rice strains. Chinese Agron. J. 6: 91-100. (in