12. Inheritance of amylose content in crosses of low amylose mutants

Toshiro KINOSHITA1 and Harumi KIKUCHI2

1) Plant Breeding Institute, Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan

2) Kamikawa Branch, Hokkaido Agricultural Experiment Station, Asahikawa, 078-02 Japan

The preference for amylose content in rice differs from region to region in the world. In Japan, a low amylase rice is preferred as delicious, as represented

Table 1. Segregation for amylose content in F2 and F3 of
         Shiokari X SM-1 

a) F2 populations
______________________________________________________________
          Amylose content*           Goodness of fit (3: 1)
          ________________           ______________________
Cross      High    Low       Total       X2         P
______________________________________________________________               
A          63      23         86        0.14      0.7-0.8
B          65      17         82        0.80      0.3-0.5
______________________________________________________________
*Demarcation by 17%.

b) F3 lines
______________________________________________________________
                      Amylose content   Goodness of fit (3: 1)
                      _______________   ______________________
#of lines  F2 genotype  High  Low   Total   X2       P
______________________________________________________________                     2       +    +       46    0    46
   10       +  lam(t)   183   69   252     0.76   0.3-0.5
    7    lam(t)lam(t)     0  166   166
______________________________________________________________

Fig. 1. Frequency distributions of amylose content in the F2 of a cross, SM-1 (lam(t))x E-84268 (du(t)) and the parental strains.

by Koshihikari having approximately 15% amylose. In Hokkaido, even newly improved varieties show higher amylose content than this, as amylose increases due to low temperatures during the maturing period. Therefore, low amylose is an important breeding objective in Hokkaido.

To elucidate the mode of inheritance of amylose content, crosses were made with two lines of low-amylose mutants, SM-1 ftom Shiokari and NM-391 from Nihonmasari which is a dull-endosperm mutant. The amylose content of SM-1 was 80% of that of Shiokari. Observations of the F2 and F3 populations of its cross with Shiokari revealed that its low amylase content was controlled by a recessive gene symbolized lam(t) (Table 1). This gene was independent from wx (glutinous endosperm). Search for its linkage relationships by crossing it with different marker lines showed that lam(t) was linked with I-Bf+ (inhibitor for brown furrows) and belonged to the fifth linkage group.

Line SM-1 also carried a mutant gene Ef(t) which hastened heading time for about one week. This gene produced pleiotropic effects to reduce amylose content by about 10% and to increase protein content. Ef(t) and lam(t) were independent, and reduced amylose cumulatively when combined in the genetic background of Shiokari.

Line NM-391 had a recessive dull-endosperm gene, du(t), which reduced amylose content to about half of Nihonmasari. In the F2 populations of several crosses involving du(t), a deficiency of its homozygotes was often observd. When NM-391 was crossed with BC-17 which had a high-amylose gene Wxa (Sano 1984), the F2 showed an anomalous segregation pattern possibly because of an interaction between du(t) and Wxa. Three dull-endosperm genes, du-1, du-2 and du-3, are known as mutants of cultivar Kinmaze (Okuno et al. 1983; RGN 2, p. 21). Allelism tests of du(t) with these genes are necessary.

Genes du(t) and lam(t) are independent. In the cross of their carriers, SM-1 with lam(t) X E-84268 with du(t), the F2 showed a wide range of variation in amylose content which masked the expected 9: 3 :3: 1 segregation (Fig. 1).

References

Okuno, K., H. Fuwa and M. Yano, 1983. A new mutant gene lowering amylose content in endosperm starch of rice, Oryza sativa L. Jpn. J. Breed. 33: 387-394.

Sano, Y., 1984. Differential regulation of waxy gene expression in rice endosperm. Theor. Appl. Genet. 68: 467-473.