Abstract
In most cases of Japanese grass cultivars, certified seed is increased in the western coast of USA, and population shifts are sometimes at issue. To investigate the population stability, characteristics of Breeder Seed (BS), Foundation Seed (FS) and Certified Seed (CS) of three and two Italian ryegrass cultivars were evaluated in 1985 at Saku and at Nishinasuno, respectively. Differences of characteristics between two locations were larger in 'Nasuhikari' in almost of all characters than in 'Minamiwase' (Table 3). The number of characters, in which significant differences were found among generations, was less in 'Minamiwase' than in 'Nasuhikari' or in 'Yamaaoba'. It was assumed that population was more stable in cultivars with less variability than in cultivars with greater variability. Among characters, the difierences were observed more frequent in date of heading. No consistent change in the date of heading was observed in 'Minamiwase' with advancing generation, but 'Nasuhikari' and 'Yamaaoba' markedly shifted toward earliness (Fig. 1). In some characters concerned with grass height, tendency toward higher with advancing generations was observed in most experiments with the exception of 'Minamiwase' at Saku (Fig. 2). Two BS lots differed in harvesting year were also compared using 'Nasuhikari' (Table 4). Significant differences were observed in several characteristics including the date of heading at both locations. Difference of characteristics at two locations, characteristics change between BS and FS, and differences between two BS lots suggest need to pay attention to population stability even if the seed would be multiplied in our country.
