1) Agricultural Experimental Farm, Hokkaido University, Sapporo, 060 Japan
2) Hokkaido Green-Bio Institute, Naganuma, 069-13 Japan
An Indonesian variety, Silewah was reported to show a high cold resistance and F1 fertilities with Japonica rices (Satake and Toriyama 1979). However, Ikehashi and Araki (1984) reported partial F1 sterilities between Silewah and Japonica as well as Indica varieties. We found that the F1 hybrid between Silewah and Hayakogane, a Hokkaido variety, was highly sterile although its pollen fertility was normal and that the spikelet sterility was caused by anther indehiscence (Maekawa et al. 1991).
To analyse genes for this sterility, an F2 population from Hayakogane/Silewah (1988) and a B1F1 population of Hayakogane/Silewah//Hayakogane (1989) were tested in a vinyl-house at Sapporo and spikelet fertility was observed. Both populations showed segregation for fertility although the distribution was continuous (Table 1). In view of the pattern of fertility variations observed in segregating populations and variety Silewah (lower than normal possibly due to some
Table 1. Distributions of spikelet fertility observed in F1, F2 and other
cross populations involving varieties Hayakogane, Silewah and Norin 20
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Parent and cross Generation Spikelet fertility, (%) No. of Ratio X2
============================== plants
5 15 25 35 45 55 65 75 85 95
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1988 experiment
Hayakogane(H) 1 5 6
Silewah(S) 1 2 1 2 6
H/S F1 3 3
H/S F2 57 4 4 5 6 9 14 19 31 61 165 9;7 1.50
_________________ ___________
85 80
1989 experiment
Hayakogane(H) 12 12
Silewah (S) 5 5 10
Norin 20(N) 2 8 2 12
H/S F1 6 6
N/S F1 1 2 2 5
H/N F1 2 1 5 6 14
H/S//H B1F1 31 18 5 6 3 4 6 15 24 33 145 1;1 0.01
____________________ ________
73 72
H/S//N 1 4 4 6 4 14 33 32 98 1:3 1.65
_____________ ________
19 79
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All chi-square values are non-significant.
environmental factors), plants showing fertilities higher than 65% in 1988
and higher than 75% in 1989 may be taken as fertile and those lower as
sterile. Thus, the segregation pattern in F2 is regarded as 9 sterile: 7
fertile and that in B1F1 as 1: 1. This suggests that a set of complementary
dominant genes controls the nondehiscence of anthers, although the
penetrance of the genes can be lowered by modifiers in segregating
populations. Our tentative gene model is that the interaction of genes A
and B brings about non-dehiscence, and that Silewah has AAbb and
Hayakogane has aaBB. These genes may be designated by S-A(t) and S-B(t),
respectively.
Furthermore, a triple cross, Hayakogane/Silewah//Norin 20 was observed (Table 1). The segregation pattern was judged to be 1 sterile: 3 fertile. This is explained by assuming the genotype of Norin 20 be aabb or s-A/s-A(t) s-B/s-B(t). Sterility of hybrids between normal parents is always due to interaction of parental genes. But, complemetary genes causing sterility do not seem to have been reported in the past.
References
Ikehashi, H. and H. Araki, 1984. Varietal screening of compatibility types revealed in F1 hybrids of distant crosses in rice. Jpn. J. Breed. 34: 304-313.
Maekawa, M., T. Inukai and N. Shinbashi, 1991. Spikelet fertility in F1 hybrids bteween rice varieties Silewah and Hayakogane. Jpn. J. Breed. 41: 359-363.
Satake, T. and K. Toriyama, 1979. Two extremely cool-tolerant varieties. Intern. Rice Res. Newsl. 4: 9-10.