Ecological Studies of Heading of Rice : IV. Heading of phto-sensitive paddy rice under the condition of 24-hr illumination.

[摘要] For investigation of heading habits of so-called photoperiod-sensitive rice varietis under long-day conditions, the two following experiments were conducted in 1966. (1) Ten sensitive japonica varieties including Zuiho, one of the most sensitive varieties, were cultured in pots under 24-hr daylength in greenhouse. (2) The variety Norin No. 29 grown under long-day (24-hr) condition was treated with different number of photo-inductive cycles (8-hr) at different stages. In the first experiment, though the days to heading or the shape of ears were different with varieties, all the ten varieties could come into ears within 114-200 days. So it may be concluded that photo-sensitive japonica rice varieties can shift from vegetative phase to reproductive phase under 24-hr daylength condition. In the second experiment, the authors found the three limiting photo-cycles specific for each age, the plant of higher age needs less cycles. According to cycles given more or less than the limiting one for some age, the heading habit of the plant is distinguished as follows: (A) When treated with enough cycles for the age, the plant will come into ears in fewer days and with normal shape. (B) With less cycles than that for (A), premature death or mal-formation of ears is expected. (C) Cycles more insufficient for the age result in delayed emergence of the normal ears. (D) Cycles under the lower-most limiting ones produce almost little of the stimulus and let the plant come into ears almost at the same time as the untreated plants. The authors clarified in the first experiment that short-day condition isn't essential for heading of japonica varieties, but with reference to the fact of (B), it seems that the plant given some photo-inductive cycles requires short-day condition for some while after floral differentiation also, and that short-day condition given after floral differentiation accelerates ear-emergence. In case of tillers, their heading is independent of primary culms; that is, in relation to the time of tiller-sprouting and the time of short-day, treatment, some of four above-mentioned aspects of heading can be expected.

[学科分类] 农业科学（综合）