Abstract
Influences of low-temperature immediately after floral-induction treatment on heading responses were investigated to establish the program of accelerating generation time in orchardgrass. Seedlings of "Nakei EV-No.1", "Aonami" and "Later" were grown under continuous light in a high-temperature (25℃ day/15℃ night) glasshouse for 42 days after sowing. Thereafter, they were subjected to floral-induction treatments of 9-hour day-length under natural low-temperatures in autumn for 26 and 40 days in "Nakei EV-No.1", and for 33 and 54 days in "Aonami" and "Latar" (Table 1). After the treatments, their heading responses were observed under continuous light with two temperature regimes: (1) Control regime, 35 days of high temperature ; (2) Low-temperature regime, 7 days of low-temperature (10℃ const.) followed by 28 days of high-temperature (Fig.1). For all the materials, the percentages of plants with heading tillers were markedly higher under low-temperature regime as compared with control regime after the short periods of floral-induction treatments. Almost all the plants, however, reached heading regardless of temperature regimes after the long periods of treatments. Heading tillers increased as the periods of treatments became longer, and still more increased under low-temperature regime (Table 2). Heading began one to two days later in "Aonami", three to four days later in "Nakei EV-No.1" and "Latar" under low-temperature regime than under control regime. But under low-temperature regime, heading tillers increased promptly after the onset of heading and the periods of heading were apparently shortened in all the materials tested (Fig.2 and Fig.3). On the other hand, there were large variations in the number of heading tillers per plant among individual plants within each material, and the variations were scarecely influenced by temperature regimes (Table 3). From the above results, it is considered to be able to decrease the percentage of nonheading plants, to increase the number of heading tillers and to synchronize their flowering in orchardgrass by promoting inflorescence differentiation under low-temperature immediately after floral-induction treatment.
