AbstractsBiology & Animal Science

Growth chamber and field experiments were conducted to investigate the effects of different temperature levels and durations on floral induction and vegetative growth in orchardgrass. Propagules of two clones, XLI-8 (clone R) and MID-5 (clone 0), from the synthetic variety Pennlate, were used in all experiments. Clone R plants were less dependent than clone 0 plants on extended low temperature exposure for floral induction. Temperature regimes in the growth chambers, where daily maxima were above 65°F for the durations of exposure used in these experiments, did not induce clone 0 propagules. However, clone R plants were induced to some degree with all temperature regimes except where the maximum temperature reached over 90°F for 10 hours each day. The longer the exposure periods of inductive regimes, the higher the percentage of plants initiating an inflorescence and the larger the number of tillers induced. Clone R plants were usually induced in a shorter time than was true for clone 0. A positive linear relationship between floral induction and exposure time through the longest duration of 10 weeks suggests that the optimum duration of exposure under growth chamber conditions was not reached. Constant 38°F and alternating 38°-60°F induced the highest percentage of plants of both clones. Cyclic daily temperatures of 15 hours at 38°F and 5 hours at 60°F temperatures gave the highest number of inflorescences per plant for clone 0. This effect appeared to be due in part to the more favorable conditions for tillering with alternating temperatures, which resulted in more potentially inducible tillers. Alternating temperatures of 38°-60°F did not show a similar advantage over 38°F constant in number of inflorescence per plant for clone R, but did increase the number of tillers per plant. Cyclic temperatures with high temperature maxima usually favored tiller development, both in the controlled environment chamber and after they had been transferred to the greenhouse. Constant 38°F temperatures were less promotive to tillering and reduced leaf development on the main tiller. Leaf development was accelerated by high temperatures with response related to the duration of high temperature received in each cyclic regime. Field results indicated that the earlier the plant were transplanted to the field, the larger were the number of inflorescences. Differences in the number of floral primordia were more pronounced for clone 0 than they were for clone R plants. Earlier planting dates for either clone resulted in earlier inflorescence exsertion. Inflorescence exsertion started about a week earlier for clone 0 than for clone R. Clone 0 plants were superior to clone R plants in number of reproductive primordia, as well as in the total number of tillers developed in the field for early dates of planting. These differences were smaller or nonexistent with the later planting dates.