Floral Induction by Natural Daylength in Rice Plants

[摘要] Present experiment was conducted to clarify the effect of natural daylength on the floral induction of rice plants, using four Japanese cultivars : Sasanishiki (less sensitive to photoperiod), Tosan No.38 (moderately sensitive to photoperiod), Hatsushimo (photoperiod-sensitive) and Zuiho (photoperiod-sensitive). The plants sown on two different dates were treated by natural day length or short day 1 or 10 days at 10 days intervals (Table 1, Fig. 1). The dates of young panicle initiation and heading were compared with those of the plants grown under long day condition. In Sasanishiki sown on 1 May, short day effect was obtained by the natural daylength treatment for 10 days started from 2O June when astronomical daylength is the longest in ycar. In Tosan No. 38 sown on 1 May, the time of earliest natural daylength treatment showing short day effect was not claified. The earliest natural daylength treatment showing short day effect started on 30 June in Sasanishiki sown on 22 May, on 10 July in Tosan No. 38 sown on 31 May, on 20 July in Hatsushimo sown on 1 May and sown on 10 June, on 30 July in Zuiho sown on 1 May and on 9 August in Zuiho sown on 10 June, respectively (Figs. 2, 3, 4 and 5). From these results, the dates when rice cultivars begin short day response to natural daylength in Osaka can be estimated as fellows : 28 June in Sasanishiki sown on 22 May, 15 July in Tosan No. 38 sown on 31 May, 20 July in Hatsushimo sown on 1 May, 25 July in Hatsushimo sown on 10 June, 28 July in Zuiho sown on 1 May and 7 August in Zuiho sown on 10 Junc (Table 3). It is discussed that critical daylength is the daylength controlling heading date of Japanese rice cultivars.

[学科分类] 农业科学（综合）