8. Heading-time genes of rice, E\1\, E\2\ and E\3\


H.YAMAGATA

Faculty of Agriculture, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto, 606 Japan


The three heading-time genes, E\1\, E\2\, and E\3\, independent of one another and delaying the heading time of rice, were detected 30 years ago through the intercrosses among three varieties, Gimbozu, Aikoku and Kyotoasahi (Syakudo et al. 1954; Kawase 1961). From those varieties and intercrosses, seven lines possessing different genotypes for the three genes, EG1 to EG7, were then developed (Table 1).

Making use of these lines as testers, the three genes have been studied on their attribues, and the genes responsible for heading dates of many Japanese varieties have been genetically analysed and identified. The recent experimental results are summarized as follows:

1) Growth-cabinet experiment clearly showed that each of E\1\, E\2\ and E\3\ was a photoperiod-sensitivity gene which did not affect basic vegetative growth. It also showed that the degree of photo-sensitivity, which evenually determined the magnitude of delay in flowering under natural conditions, was ranked as E\1\ >> E\3\ > E\2\ (Table 1).

2) The response of E\1\ to a light break (1 hour, over 300 lux) during short-day treatment far exceeded those of the other two genes.

3) The heading-delaying effects of E\2\ and E\3\ under natural condition were significantly lower than that of E\1\. However, E\3\ showed a synergistic effect when it coexisted with E\1\, and E\2\ also did when it coexisted with both E\1\ and E\3\ (Table 1).

4) So far as the 15 varieties tested are concerned, all varieties grown south of Tohoku district possessed E\1\ (Yamagata 1984).

5) Yokoo et al. (1980) reported the presence of a photo-sensitivity gene, Lm (late maturity), belonging to linkage group I. In spite of its similarity in action, this gene was found to be independent of E\1\, indicating the necessity for further studies of the genetic mechanisms controlling heading time in rice.



Table 1. Basic vegetative growth (BVG), photoperiod sensitivity, and days to heading under natural condition of seven lines having different genotypes for E\1\, E\2\ and E\3\

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Line   Genotypea    BVGb    Photoperiodc         Days to headingd
                            sensitivity          in natural daylength
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EG  1  E\1\e\2\e\3\   37          58                   112
EG  2  e\1\E\2\e\3\   38          46                    97
EG  3  e\1\e\2\E\3\   38          52                   101
EG  4  E\1\E\2\e\3\   40          60                   117
EG  5  e\1\E\2\E\3\   39          54                   105
EG  6  E\1\e\2\E\3\   37          81                   121
EG  7  E\1\E\2\E\3\   41          92                   131
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a)    Genotype for E\1\ E\2\ and E\3\, all lines being homozygous.
b)    Days from sowing to heading under short day (10 h) at 30deg.C.
c)    Difference in days to heading between a long day (14 h) and a short day 
      (10 h) at 300C.
d)    Sown on May 6, 1980.

References

Kawase, T., 1961. Studies on the inheritance of heading time and the response of heading-time genes to environments in rice. (in Jap.) Doctoral thesis submitted to Kyoto University, 246pp.

Syakudo, K., T. Kawase and K. Yoshino, 1954. Studies on the quantitative inheritance, 13. Jpn. J. Breed. 4: 83-91.

Yamagata, H., 1984. Genetical analysis of heading date in rice. Report of research project supported by research-aid fund from the Ministry of Education, Science and Culture, 24pp.

Yokoo, M., F. Kikuchi, A. Nakane and H. Fujimaki, 1980. Genetical analysis of heading date by aid of close linkage with blast resistance in rice. Bull. Nat. Inst. Agric. Sci. D 31: 95-126.