Studies on Ecotypic Variations among Natural Populations of Timothy (Phleum pratense L.) : VI. Seasonal growth pattern of tiller

Abstract

This experiment was carried out to investigate the variation of seasonal growth pattern among the natural populations of timothy (Phleum pratense L.). Seven and ten populations which were collected from the northern and southern areas of Hokkaido respectively, were grown in the experimental field at Sapporo. In the fourth year after seeding, from the restarting of growth in early spring to seed maturing in mid-summer, two vigorous tillers on each of ten plants per population were cut off at one week interval at the soil surface and their dry weight was measured. Logistic equation, w=A/[1+κ・exp (-λt)], was fitted to a series of observed values of weight of a tiller between May 12 and July 28 and three parameters characterizing growth pattern, intrinsic growth rate (λ), maximum growth rate (MGR) and the time at which growth rate reaches the maximum (T at MGR), were estimated in each population (Table 1). The MGR and λ tended to be larger in the southern group than in the northern group. Furthermore, except for one population of the southern group, all populations of that group reached the maximum growth rate earlier than any population of the northern group. The growth rate approximated by logistic equation was higher in the southern group during the early half of the growing period, but in the northern group during the late half of the growing period (Fig.3). From May 12 to May 19, leaf weight increased in the southern group but did not in the northern group (Fig.1) and thus their relative growth rates differed significantly in this period (Table 3, Fig.4). Allometry coefficient of stem and leaf development was not different among the populations and stem weight increased in proportion to about a square of leaf weight (Fig.5). It was suggested by these results that the differences in seasonal growth pattern of tiller between northern and southern populations were largely due to the time lag of developmental stage resulting from the difference in the time of leaf growth commencement under low temperature conditions in early spring.