Abstract
Relatively few attempts have been made to define the relationships between stage of seed development and germination capacity in pasture grasses. In the second report of this series, the germination behaviour in relation to seed development of Rumex obtusifolius L. was investigated and three developmental phases could be recognized during seed development after flowering. The present experiment was carried out to make clear the changes in dry weight, % moisture content and germination behaviour during seed development of Aonami orchardgrass (Dactylis glomerata L.), and moreover to evaluate the effect of prechilling treatment on the dormancy-breaking of the seeds at various stages of the development. The results obtained were as follows ; 1. Immediately after harvest of mature orchardgrass seeds, the germination rate under continuous light condition was high in low temperature range (18℃-23℃), but decreased in high temperature range (28℃). Under continuous dark condition, the germination scarcely occurred at any constant temperature. Such light-sensitive and temperature-dependent germination was induced regardless of the varieties and the locations where the seeds were harvested. 2. Three developmental phases during seed maturation could be recognized as follows ; The first phase lasted for about 7 days after flowering. During this stage, dry weight increased gradually and moisture content was above 60%. The seeds harvested during this stage were not viable. The second phase lasted for end of the first phase to 28 days. During this period, dry weight increased rapidly and moisture content decreased gradually. The seeds during this stage could not germinate immediately after removing from plant. However, with the lapse of the period of air-drying at room temperature, the light-dependent germination occurred within the limited range of temperature (18℃ to 23℃). Especially, the seeds stored at laboratory conditions for 2 to 3 months after harvesting showed almost the same germination behaviour as the seeds at the third phase. The third phase covered the period after 28 days. From this time on, dry weight and moisture content became equilibrium and the appearance of the seeds got complete. During this stage, immediately after harvesting, the light-dependent germination within the limited range of temperature occurred apparently, and scarcely changed during air-drying period following the harvest. 3. The dormancy of the seeds harvested on the 30th day from flowering could not be broken by any period of prechilling treatment when the moisture content was high (39.5%) immediately after removing from plant. The dormancy, however, was noticiably broken by prechilling for 10 days when the moisture content decreased to 9.7% after air-drying at room temperature for 7 days. After air-drying for 3 to 4 months following the harvest, the seeds in any developmental phase, except the first phase, markedly responded to prechilling treatment, and consequently high germination occurred even in high temperature range under continuous light condition.
