Tadashi Takita1, and Norindo Takahashi2
1) Kyushu National Agricultural Experiment Station, Chikugo, Fukuoka-ken, 833 Japan
2) 17-12, Minami 1-chome, Nankodai, Sendai, 980 Japan
Line SLG12 with an extraordinarily large size of grains was obtained from a series of crosses of lines selected for larger grain size. Its grain length and width reached 12.8 mm and 4.9 mm, respectively, and its single grain weight was 77.9 mg (Table 1). It could be the largest of the world, as the world collection of 14,128 rice cultivars kept in the IRRI showed a range from 6 to 52 mg of single grain weight (IRRI 1976).
The pedigree of this line is shown in Fig. 1. BG1 (Big Grain 1) was selected from Taiho-Cho-ko-to as the first large-grain line which weighed more than 50 mg. Next, SLG1 (Super large grain 1) with a single grain weight of more than 70 mg was developed from BG1/813042 (Takita 1983). The latter parent which also had more than 50 mg grain weight had been developed by Takeda and Saito (1980). Finally, SLG12 was obtained from SLG1/Hao-Gang, the latter being a Chinese cultivar having a very large grain width.
Genes controlling grain size so far reported have been reviewed by Takeda (1986). The large grain size of IR8 was, in its cross with IR42 (having a small grain) found to be controlled by two major genes, one for grain length and the other for grain width, whose effects were additive (Takita 1986). In the present experiment, the genes concerned are not identifiable, but it may by inferred that major genes with additive effects similar to those detected previously, have been accumulated during the course of crosses. One of the genes may be Lk-1 as Fusayoshi is involved in the pedigree (Takeda 1984). As the grain length and width of SLG12 both exceed those of its parents, it seems that the parents of this line, SLG1 with longer grain and Hao-Gang with wider grain had partly different genes controlling grain size. Analysis of the genes for grain size accumulated in this line will be carried out in the future.
This line may be profitably used in studies of genetic control of yield potential. An examination of yield characters showed that the very large grain size was obviously associated with high yield, as will be reported elsewhere.
Table 1. Grain size of SLG12 and some other varieties
=============================================================================== Variety Heading 1-grain weight Grain length Grain width time* (mg) (mm) (mm) =============================================================================== Koganebare Aug 24 27.3 5.9 3.6 Nishihomare Sep 4 28.4 6.3 3.5 BG1 Aug 18 56.4 9.7 4.3 SLG1 Sep 1 76.8 12.2 4.4 Hao Gang Sep 13 47.9 8.6 4.6 SLG12 Sep 9 77.9 12.8 4.9 =============================================================================== *Seeded on May 22, 1986 at Kyushu National Agricultural Experiment Station. ===============================================================================
Fig. 1. The ancestry of SLG12.
*Strain with single grain weight exceeding 50 mg.
IRRI, 1976. Annual report for 1976, p. 22-23.
Takeda, K., 1984. A big-grain gene, Lk-f, found in a Japanese local variety Fusayoshi and its character expression. RGN 1: 108-109.
Takeda, K., 1986. Gene symbols for grain size and shape. RGN 3: 14-15.
Takeda, K., and K. Saito, 1980. Major genes controlling rice grain size. Jpn. J. Breed. 30: 280-282. (in Japanese)
Takita, T., 1983. Breeding of a rice line with extraordinarily large grains as a genetic source for high yielding varieties. JARQ 17: 93-97.
Takita, T., 1985. Inheritance of grain size and the relationship between grain size and other characters in rice. Bull Natl. Agr. Res. Center 3: 55-71. (Japanese/English)
Takita, T., 1986. Two major genes controlling the large grain size of IR8. RGN 3: 67-68.