Abstract
In the previous paper, it was clarified in orchardgrass that juvenile stage was completed within 5 to 6 weeks after sowing under continuous light and warm temperature. The study reported here was carried out to investigate the influence of plant-age after juvenile stage on the responsiveness to floral-induction treatment. The 7-weeks-old seedlings and the aged tillers were used. Seedlings were grown under continuous light in a warm (25℃ in day/15℃ at night) glasshouse after sowing. Aged tillers were obtained by dividing clonal materials which had been grown under the same condition for about 6 months. These materials of each age were subjected to floral-induction treatments for 2 to 6 weeks. After the treatments, their heading behaviour was observed under continuous light in a warm glasshouse (Fig.1 and Table 1). The results are summarized as follows: In Experiment I, 7-weeks-old seedlings and aged tillers of "Aonami" were subjected to floral-induction treatment of natural short-day-lengths and low temperatures for 2, 3, 4, and 5 weeks. From the heading behaviour, it was clarified that the number of weeks required for floral-induction was considerably shorter in aged tillers than in 7-weeks-old seedlings (Table 2). In Experiment II, 7-weeks-old seedlings of "Aonami", "Aberystwyth S143" and "Nakei EV-No.1" were subjected to floral-induction treatments of continuous light with two different temperatures (natural low temperature and controlled warm temperature) for 6 weeks. The results showed that floral-induction was almost entirely prevented by continuous light independently of temperature conditions in seedling of all materials tested (Table 3). In Experiment III, aged tillers of "Aonami", "Aberystwyth S143" and "EV-700" were subjected to floral-induction treatments of continuous light with the two different temperatures as mentioned in Experiment II for 6 weeks. From the results, it was recognized in all materials tested that floral-induction scarecely occurred under both conditions of continuous light and warm temperature but was brought about only by low temperature even under continuous light in aged tillers (Table 4). From the above results, it was suggested that the responsiveness of orchardgrass to short day-length and low temperature increased with the advance of plant-age after juvenile stage and that the short-day requirement for floral-induction became lower in the aged-plants than in the seedlings immediately after juvenile stage.
