Abstract
We compared the performances of 18 local strains collected from old pastures and roadsides in Hokkaido with those of 27 verieties from overseas. From these results, the magnitude and the nature of shift caused by natural selection during the domestication. of timothy of Hokkaido local strains were estimated. Hokkaido local strains possess character combinations biased towards the hay type. The following conditions were considered to be responsible for this phenomenon. (1) The original introductions from the United States seemed to have the characteristics of the hay type. (2) Agronomic selection, especially seed production, favored the development of hay type. (3) Climatic conditions, daylength and temperature of early spring, favored hay type. Because of these conditions we suggested that the shift which could be expected during domestication might not be a conversion of major-genic construction but polygenic adjustment. Namely, natural selection favored plant types that produced more seed, while the main agronomic characteristics remained relatively constant. Because most causative factors appeared to be daylength and temperature, the Hokkaido local strains will be a climatic ecotype rather than an agronomic ecotype.
