COMPLETION OF THE JUVENILE STAGE IN ORCHARDGRASS

Abstract

Three orchardgrass strains of different origins were used to determine the stage at which seedlings become capable of responding to induction treatment. The seedlings were grown under long photoperiods and warm temperatures after emergence until the sixth to ninth leaf appeared on the main tiller (shoot), and were then exposed to the induction conditions (10 hr photoperiod at 10 C) for 6 weeks. The juvenile stage in all three strains was completed at the eighth to ninth leaf stage. From the practical point of view, the eighth leaf stage can be used as an indicator of the completion, since about 90% of the seedlings induced at this stage subsequently developed heads, compared with 100% at the ninth leaf stage and 30–60% at the seventh leaf stage. Different photoperiods (14, 17, 24 hr) and different temperatures (15.5, 21 C), prior to the induction treatment, influenced the rate of leaf appearance, but did not affect subsequent heading. The maximum rate of leaf appearance occurred under long photoperiods (17 and 24 hr) and a warm temperature (21 C). Under these conditions, seedlings reached the eight-leaf stage in 3–4 weeks after emergence. The number of tillers was not as good a criterion of the completion of the juvenile stage as was the number of leaves on the main tiller.