27. Complementary genes responsible for photoperiod sensitivity in the common wild rice

Yo-Ichiro SATO

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°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
===============================================================================
                                    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           -     -
B1F2a(W589)          5  24  17  4    0  18  54 25         147        6.37* 5.65*
                    ____________       _________
                          50               97

B2F1a(W589)          6  38   2  0    0  14   2             62        0.02n.s.  -
                    ____________    _________
                        46             16

B2F2a(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.