Abstract
In the previous paper, it was suggested in orchardgrass that the low temperature and short-day requirement for floral-induction become lower with the advance of plant-age after the juvenile stage. The study reported here was carried out to clarify the effective range of temperature and day-length on floral-induction in aged plants. Clonal plants of "Aonami", "Latar", "Aberystwyth S143" and "EV-700" were grown under continuous light in a warm (25℃ day/15℃ night) glasshouse for longer than 6 months before being separated into individual tillers, from which aged tillers were chosen for the experiments. Then, the tillers were subjected to floral-induction treatment of outdoor- or unheated glasshouse-temperatures with natural day-lengths for five weeks. The experiments were conducted with intervals of 2-month from October, 1976 to August, 1977 (Fig.1 and Table 2). After the treatments, they were retransferred to a warm glasshouse under continuous light, and their heading behaviour was observed. Floral-induction was promoted in the range of mean temperature from 5.3 to 15.8℃ in "Aberystwyth S143" and 5.3 to 19.0℃ in "Aonami" and "Latar", and retarded when mean temperature was higher than those ranges described above in these three materials. While the whole range of mean temperature used in this study (5.3 to 22.9℃) was effective on floral-induction in "EV-700". Day-length changed seasonally from the minimum of 9hr., 37min. to the maximum of 14hr., 43min. This range of day-length was shorter than the critical day-length for floral-induction in all the materials tested (Table 3). As the day-length during floral-induction treatments became longer, the number of days from the beginning of treatment to heading became smaller (Table 4). From the results of the treatment in "June" during which day-lengths were longer than 14hr., 32min. and temperatures were moderately high (mean temperature ; 19.0℃), it was estimated that 15.2, 21.8, 21.3 and 11.5 days were required for floral-induction in "Aonami", "Latar", "Aberystwyth S143" and "EV-700", respectively (Table 5 and Fig.2). These estimated values suggested that, in aged plants, the period required for floral-induction under fairly long day-length and high temperature was almost similar to that under short day-length and low temperature. From the above results, it may be concluded that the effective range of temperature and day-length on floral-induction is markedly wider in aged plants than in seedlings.
