18. Duplicate genes controlling long grain of a rice variety IRAT13

1) Research Institute for Bioresources, Okayama University, Kurashiki, 710 Japan

A long-grained rice variety IRAT13 (9.2 mm in grain length) was crossed with a Japanese cultivar Gimbozu (5.8 mm) with the view to analyze the inheritance of grain size. A total of 625 F2 plants and 171 randomly selected F3 lines, 15 plants each, were examined.

The F2 population showed a continuous distribution of grain length, but transgressive segregation was not recognized, suggesting that the long-grain character of IRAT13 was controlled by multiple factors (Fig. 1). F3 lines were

Fig. 1. Distribution of grain length in F2 plants. Arrows show parental means (P1: Gimbozu, P2: IRAT13) and F2 mean.

each examined for the distribution of grain length. The distribution within lines was continuous in 78 short- and 15 long-grained lines, but was discontinuous in 78 segregating lines (Fig. 2).

Fig. 2. Distribution of within-line variation in grain length in F3 lines of IRAT13 X Gimbozu.

When duplicate genes are assumed, F3 lines are expected to segregate in 3: 1 and 15: 1 segregating lines, plus non-segregating short-grained lines and long homozygous (double recessive) lines in a ratio of 4: 4: 7: 1. As the number of plants per line was 15 only, lines segregating in 3: 1 and 15: 1 were not distinguishable. The F3 lines observed, 78 non-segregating short grained: 78 segregating: 15 non-segregating long grained-lines, showed a ratio close to the expected 7: 8: 1 ratio (X²=2.5, P=0.2-0.3).

Takamure and Kinoshita (1986, 1987) observed monogenic segregation for grain length in the F2 and F3 progenies from IRAT13 X H- 165, and detected a recessive gene lk-i for the long-grain character of IRATI3. The newly detected gene for long grain, one of the duplicate genes segregating in Gimbozu X IRAT13 may be symboled lk-i-2.

Comparison between non-segregating short-grained lines (6.65 mm in mean length) and long-grained lines (7.45 mm) shows that the duplicate gene lk-i and Ik-i-2 increase grain length by 1.12 times of the normal counterpart.

Takamure, I. and T. Kinoshita 1986. inheritance of a long grain gene derived from IRAT13 in rice. Jpn. J. Breed. 36 (Suppl 2): 270-271. (in Japanese)

____and ____, 1987. Progeny tests for the gene action of the recessive long kernel gene derived from IRAT13 in rice. Jpn. J. Breed. 37 (Suppl 2): 306-307. (in Japanese)