33. A new tester line for analyzing heading-time genes in rice

Yutaka OKUMOTO, Takatoshi TANISAKA and Hirotada YAMAGATA

Laboratory of Plant Breeding, Faculty of Agriculture, Kyoto University, Sakyo-ku, Kyoto, 606-01 Japan

We have carried out analysis of heading-time genes in Japanese varieties and induced mutants of rice (Yamagata and Ikeda 1974; Tanisaka et al. 1990; Okumoto et al. 1991), using seven tester lines, EG1 to EG7 which have different combinations of three genes for late heading-time, E1, E2 and E3. These three genes confer photoperiod sensitivity (Yamagata 1984).

The series of our tester lines (EG lines) did not include the genotype, recessive for all relevant loci, e1e1 e2e2 e3e3. This has often made it difficult to estimate the action of each of the three dominant genes and to identify the heading-time genes of early-maturing varieties and mutants. Therefore, we planned to raise a new tester line having genotype e1e1 e2e2 e3e3 through the cross between EG4 (E1E1 E2E2 e3e3) and EG3 (e1e1 e2e2 E3E3). By selecting a few earliest plants in F2, F3 and F4, a line fixed for an early heading time was obtained in the F5. This line, coded EG0, was crossed with the seven EG lines to identify its genotype. Fig. 1 shows the frequency distributions of F2 plants derived from crosses with EG1 (E1E1 e2e2 e3e3) and EG6 (E1E1 e2e2 E3E3)- In EG1 x EGO, early-heading and late-heading plants were found in a 1 : 3 ratio, indicating segregation for E1. In EG6 x EGO, four types of segregants, early, middle I, middle II and late, were observed in a 1 : 3 : 3: 9 ratio, indicating the segregation for E1 and E3. Crosses with other five testers also supported that EG0 had genotype e1e1 e2e2 e3e3.

Line EG0 now shows fixation also for agronomic characters other than head- ing time. The heading time of EG0 is shown in Table 1 along with those of other EG lines.

Fig. 1. Frequency distributions of heading date in F2 populations derived from crosses of EG0 with EG1 and EG6 (observed in 1988).

Table 1. Genotypes and heading dates of eight tester lines, EG0~EG7
Tester line        Genotype                         Days to heading1)  
EG0                e1e1 e2e2 e3e3       82.5±1.37
EG1                E1E1 e2e2 e3e3      101.7±0.85
EG2                e1e1 E2E2 e3e3       90.0±2.79
EG3                e1e1 e2e2 E3E3       94.5±1.31
EG4                E1E1 E2E2 e3e3      106.6±0.80
EG5                e1e1 E2E2 E3E3       99.0±1.30
EG6                E1E1 e2e2 E3E3      113.0±1.18
EG7                E1E1 E2E2 E3E3      123.1±0.95
1)Sown on May 17, 1988


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