Abstract
To investigate population stability with advancing generation, characteristics of Breeder Seed (BS), Foundation Seed (FS) and Certified Seed (CS) of two orchardgrass cultivars were evaluated at Saku and at Nishinasuno in 1985-86 and in 1985, respectively. Number of characters in which significant differences were found among generation, was less in 'Okamidori' than in 'Aonami' (Table 3). It was assumed that population was more stable in a cultivar with less variability in heading date than in a cultivar with greater variability. The heading date tended to shift toward earliness with advancing multiplication genarartions in both cultivars (Fig. 1). The difference between BS and CS was smaller at Nishinasuno than at Saku, and in the year after the next of planting than in the next. Length to top of head exhibits a tendency toward higher with advancing generation (Fig. 2). Characteristics of two BS lots differed in harvesting year were compared using 'Okamidori'. Large population shift was not occured except for the length of flag leaf (Table 4). Significant differences among generations were hardly observed in common with locations and years. This indicates that data with more than one year or one location are required to evaluate population stability of orchardgrass cultivars, especially in the area where orchardgrass is seeded in fall. Furthermore, there is a possibility that putting too much importance on statistical analysis induces wrong results.
