17. An allele for long grain found in a mutant line of cultivar Gimbozu

1) School of Bioresources, Hiroshima Prefectural University, Shobara, 727 Japan

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

A mutant line having large grains (7.4 mm in length), IMR39 was obtained from gamma-ray irradiation of seeds of a Japanese cultivar Gimbozu (5.8 mm in length; Yamagata 1964; Kato 1990). In the cross IMR39 X Gimbozu, the F2 plants segregated into short-grained (Gimbozu type), medium-grained (F1 type) and long-grained group (IMR39 type) in a 1 : 2: 1 ratio (Fig. 1a; X² =4.1, P>O.1), indicating that the mutant allele for long grain was incompletely dominant over its normal allele of Gimbozu.

An allelism test of this gene was conducted by Kato (1990) with Lk-f, which is present in cultivar Fusayoshi and also conditions long grains (Takeda and Saito 1980). The test demonstrated that the IMR39 gene for long grains was non-allelic to Lk-f (Fig. 1b). Allelism tests of the IMR39 gene were also made with other two genes for long grain, lk-i (Takamure and Kinoshita 1987) and lk-i-2 (Takeda and Kato, this issue of RGN), both being present in cultivar IRAT13. The grain length in the F2 and F3 of IMR39 X IRAT13 was distributed widely exceeding the range of parental extremes, especially in the downward direction (Figs. lc and 2). No frequency peak was apparent in the distributions. These segregation patterns suggest that the IMR39 gene is non allelic to Ik-i as well as Ik-i-2.

Thus, we can consider the incompletely dominant allele of IMR39 as a new gene causing long grain, about 1.2 times longer than that of Gimbozu. It was designated as Lk-g(t), Gimbozu long kernel. This allele is expected to be useful for increasing grain size or sink capacity in rice.

Fig. 1. Distributions of grain length in three crosses. Arrows show parental means (P1 and P2) and F2 means.

Fig. 2. Distribution of F3 line means in IRAT13 (P1)XIMR39 (P2). Arrows show parental means.

References

Kato, T., 1990. Genetic analysis on the mutant alleles for long grains induced in a rice cultivar, Gimbozu. SABRAO J. 22: 123-129.

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

Takeda, T. and K. Saito, 1980. Major genes controlling grain size of rice. Jpn. J. Breed. 30: 280-282. (Japanese)

Yamagata, H., 1964. Thremmatological studies on the utility of artificial mutations in rice. Dr. Thesis. Kyoto Univ., Kyoto. (Japanese/English)