Regarding the effect of day length on the expression of cloning gene, results of some previous studies (Singleton, J. Hered. 37, Shaver, J. Hered. 58) varied. In order to make further investigation on this effect, two dozen plants from a cross between a plant heterozygous for Clg and a plant homozygous for clg, were grown in the greenhouse last March. In June all of these plants were transplanted to the field and 22 of them survived. Among them, 10 vigorous plants were selected in July and treated with short-day illumination daily (8-hour light, 16-hour dark) for four weeks. The other plants, 12 in number, grew under long-day illumination (16-hour light, 8-hour dark). One month after the treatment, the treated plants had flower-induction for all of them but there was no evidence of the expression of the cloning gene despite the expected frequency of 50% that should have manifested the gene. On the other hand, three of the control-plants regenerated plantlets on their tassels. This number is much less than the expected 6, if the cloning gene is a responder to long-day illumination. Furthermore, the number of plantlets on the responder plants ranged from three to five per tassel. Comparing with the previous results reported by the senior author, the gene was only weakly activated. With the objective of clarifying this phenomenon, further studies are planned.
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