Abstract
This experiment was carried out to clarify the inter-population variation of intra-plant variations and to investigate the relationship of intra-plant variation with forage yield in timothy (Phleum pratense L.). Thirteen natural populations collected from the eastern district of Hokkaido and three cultivars were grown under spaced planting conditions for four years. In the seeding year, heading date of each tiller within plant was recorded, and it was found that there was a large variation among natural populations for the inter-tiller variation of heading date. In the second and third years, plants were cut in early July (first cut) and in mid-September (second cut). At each cut, the number of heading tillers and green yield per plant were measured. Heding ratio, which stands for the number of heading tillers in the 2nd cut relative to the total heading tillers of two cuts, and total green yield (1st cut+2nd cut) were closely associated with. For these two characters there were significant differences between natural population and cultivar, and among natural populations. The inter-tiller variation of heading date in the seeding year was correlated positively with heading ratio and negatively with total green yield in the second and third years. In the fourth year, four lines of which two had higher and the other two had lower heading ratio in the previous years were examined on inter-tiller variation within plant for six characters as well as total green yield and heading ratio. Consequently it became evident that the former lines had larger inter-tiller variations on vegetative organs but less total green yield than those of the latter. Experimental results suggested that heading ratio was a reflection of a intraplant variation in tiller elongation and that high heading ratio was a factor which decreased forage yield. Cultivars had more synchronous heading, lower heading ratio and smaller inter-tiller variations on vegetative organs than natural populations.
