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National Institute of Genetics, Mishima, 411 Japan
To examine the genetic basis of photoperiod sensitivity in the wild rice, Oryza rufipogon, its five strains from India, Malaysia and China were crossed with a tester strain, Taichung 65 Ef-1b Mb (designated as T65Em in this paper), which showed insensitivity and a short basic vegetative phase. The F2 and backcrossed generations with T65Em were planted under natural daylengths at Mishima (35 deg N) in summer.
In the F2s derived from Em/W106, Em/W1827, Em/W1954, and Em/W1961, segregation for heading date was discontinuous showing a bimodal pattern. In the former three populations, segregation into early and late groups fitted a 7 : 9 ratio, suggesting the presence of two independent complementary genes (Table 1). Their B1F1s (Em//Em/wild) showed a 3 early: 1 late ratio expected from complementary regulation (Table 2).
The Em//Em/W1961 population showed a 3 early : 1 late segragation although its F2 did not show a 7 early : 9 late pattern. In the cross with W589, expected ratios were observed after two backcrosses (Table 2). Perhaps, other genes were also involved in its B1F1 population.
The photoperiod sensitivity of wild-rice strains examined appears to be controlled at least partly be a set of complementary genes.
Table 1. Segregation of days to heading in F2 populations derived from 5
crosses
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Days to heading
Cross =======================================================================
86 90 94 98 102 106 110 114 118 122 126 130 134 138 142 146 Latera
===============================================================================
Em/W106 3 8 6 14 1 6 1 1 6 2 11 6 10 8 6 2 0
(N=91) _____________________________ ___________________________________
40 51
Em/W589 8 8 14 0 6 6 2 3 99
(N= 158)
Em/W1827 3 5 6 11 8 5 2 0 6 0 1 3 11 4 8 12 25
(N=110) _________________________________ ______________________________
46 64
Em/W1954 4 9 11 10 4 3 1 1 4 2 6 13 23 7 13 9
(M=116) _________________________________ _________________________
47 73
Em/W1961 2 3 5 9 6 8 11 4 6 0 2 4 4 4 5 6 76
(N=155) _________________________________ _____________________________
54 101
===============================================================================
a-Heading later than 150 days or no heading.
Table 2. Segregation of days to heading in backcross populations
===============================================================================
Cross Days to heading Number X2
_______________________________
86 94 102 110 118 126 134 142 of plants (3:1)
===============================================================================
Em//Em/W106 2 5 3 3 1 1 2 2 19 0.24n.s.
_________________ ________
14 5
Em//Em/W1823 6 7 9 2 0 3 3 4 34 0.35n.s.
_________________ ________
24 10
Em//Em/W1954 3 4 7 0 1 0 3 3 21 0.01n.s.
_________________ ________
15 6
Em//Em/W1961 2 8 9 10 2 4 4 4 43 0.19n.s.
_________________ ________
31 12
(3:1) (7:9)
Em//Em/W589 5 25 19 4 2 2 3 3 63 - -
B\1\F\2\ad(W589) 5 24 17 4 0 18 54 25 147 6.37* 5.65*
____________ _________
50 97
B\2\F\1\a(W589) 6 38 2 0 0 14 2 62 0.02n.s. -
____________ _________
46 16
B\2\F\2\a(W589) 8 31 14 3 1 27 46 18 148 - 2.10n.s.
____________ ____________
56 92
===============================================================================
* Significant at 5% level.
a- Each population was derived from a late-heding plant selected.
