1) National Institute of Genetics, Mishima City, 411 Japan
2) Institute for Genecology, Tohoku University, Katahira, Sendai, 980 Japan
Gene gl-1, controlling glabrous or hairless kernel and leaf blade (chromosome 5), is widely distributed among japonica upland cultivars grown in monsoon Asia. Segregation distortion is frequently observed at this locus in indica X glabrous japonica crosses. In this paper, segregation ratios for this locus observed in the F2 and B1F1 populations from a cross are reported.
In the F2 populations from a cross of Ac 130 (non-glabrous Taiwan indica) X Ac221 (glabrous Philippine japonica), the frequency of gl/gl homozygotes was 14.7% to 18.6%, significantly lower than expected 25%. The frequency of gl/gl homozygotes differed in F2 populations grown in different conditions, but not significantly. In the B1F1 populations derived from Ac221 X F1, non-glabrous and glabrous plants were 24 and 21, fitting the expected 1:1 ratio. In the B1F1 population from F1 X Ac221, where the F1 plant was used as the female parent, the ratio of non-glabrous and glabrous segregants was 41:21, being distorted from the 1:1 ratio significantly (Table 1). The data suggest that the female gametes with +g1 and gl have unequal chance of being fertilized by the pollen with gl. On the assumption that female gametes having +g1 and gl are fertilized in a 41:21 ratio, while pollen grains with +gl and gl participate in fertilization in a 1:1 ratio, the F2 frequency of gl/gl homozygotes is expected to be 16.9%, which is very close to the observed mean frequency of 16.8%.
The differential ability of megaspores with different genes to be fertilized by the same pollen appeared to be affected by the growing conditions of the F1 plants, although it was little affected by the growing conditions of F2 populations. When the F1 plants were grown in a phytotron, seeds from those grown in an upland condition without standing water in pots gave normal 3:1 F2 ratios. When the F1 plants were grown in standing water under a low temperature (22 deg in day, 17 deg in night), the deficiency of gl homozygotes in the F2 was observed clearly (Table 2). How the megaspores with gene gl and +gl are influenced by growing conditions remain as an unanswered question.
Table 1. Segregation patterns for normal vs. glabrous plants observed in F2and B1F1 populations grown in different conditions
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Population and growing No. of plants %, glabrous X2 from
condition =========================== homozygotes expected
Normal Glabrous Total ratio
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F2 (Ac13O X Ac221) (3:1)
Mishima, rice field 177 39 216 18.1 4.5*
Mishima, short days 262 53 315 16.8 11.2**
Mishima,greenhouse(winter)127 29 156 18.6 3.4
Taichung, winter crop 197 40 237 17.2 8.3**
Taichung, summer crop 238 41 279 14.7 15.8**
Total 1001 202 1203 16.8 43.7**
B1F1 (1: 1)
Ac221 X F1 24 21 45 46.7 0.2
F1 x Ac221 41 21 62 33.9 6.5**
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* P<0.05, ** P<0.01.Note: The F1 plants were grown in a rice field at Mishima and headed in summer normally. Heterogeneity chi-square for differences in segregation pattern among F2 populations (X2 =1.45, df =4) was not significant.
Table 2. F2 segregation for normal and glabrous plants derived from F1 plants grown in different conditions in a phytotron
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Condition at No. of F2 plants X2 from
flowering ============================= %, glabrous
of F1 plants Normal Glabrous Total homozygotes 3:1
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Without standing water,
30 deg-25 deg C 121 50 171 29.2 1.6
22 deg-17 deg C 99 34 133 25.6 0.02
With standing water,
30 deg-25 deg C 148 38 186 20.4 2.1
22 deg-17 deg C 110 13 123 10.6 13.7**
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P<O.O1