K.H. TsAI

      Department of Agronomy, National Chung-Hsing University, Taichung, 40227 Taiwan

     The Aman type of rice cultivar for winter cropping, Naizar Shail Aman (abbr. Aman) from India, and 1R4227-18-23-2 (1R4227) from Philippines were genetically examined regarding heading time in the present study. The dominant gene for early heading, Efi (= Ea), is located on chromosome 10 with recombination value of 27% with pgl (Sato 1976,Tsai 1986). Efi accelerates floral initiation and heading by about 10 days (Tsai and Oka 1968) and is distributed in many cultivars of the Indica and Japonica types (Tsai 1985, 1986, 1987; Tsai and Oka 1966) as well as in common wild rice strains of Oryza rufipogon (Tsai 1995). The Efi seems to be one of basic loci controlling the heading behavior of rice (Tsai 1995). A near isogenic line carrying Efi (= E2), T65 (20) Ea, was established after 20 backcrosses to T65 (Taichung 65 from Taiwan) by using the northern Chinese early variety Tatung-tsailai as a donor. T65 carries a recessive allele efi and the Aman and IR4227 similar alleles to Eli (Tsai 1992).

     Aman showed a strong photopenod sensitivity (Yamada 1968) and it did not flower in the first crop season in Taiwan. The TDM (tangent-day-minute) degree which is an estimate of photoperiod-seflsitivity was examined in 6 lines including Aman, according to Oka (1954) as shown in Table 1. The F2 populations between T65 and Aman showed a continous variation from early-heading (Eli-like) to late-heading (Aman-like). The F2 plants showing late-heading were backcrossed to T65 to obtain a near isogenic line of T65 which was designated (3)AmanL-2. (3) indicates three backcrosses. The F1 plants between T65 and (3) AmanL-2 showed T65 type in the second crop season, and the F2 population segregated T65-type and AmanL-2 type into a 3: 1 ratio. Thus, the late- heading time gene involved in (3) AmanL-2 was assumed to be recessive. The photopenod sensitivity gene was tentatively named as se(A), which was independent of Efi. The genotypes of T65, (3)AmanL-2 and T65(20)Ea were assumed to be ef Se(A), efi se(A) and Efi Se(A), respectively. The F plants from a cross of T65(20)E’2 x (3)AmanL-2, whose genotype was expected as Efi/efi, Se(A)lse(A). showed the T65(20)E2 type, suggesting that Efi was epistatic to se(A). As shown in Table 2, the F2 population of the cross showed an observed segregation ratio of 12 early-type: 3 T65-type: 1 AmanL-2 type as expected from the above assumption.