Abstract
The purpose of our research series is to elucidate the individual and varietal differences in concentrations and characteristics of nonstructural carbohydrate (NSC), and the relationships of NSC concentration to some morphological and physiological traits in Italian ryegrass at vegetative phase grown in fall. In the present paper, differences of concentrations and characteristics of nonstructural carbohydrate between 1) tetraploid strains and thier parental diploid varieties and 2) diploid and tetraploid groups each of which is composed of 10 varieties with different maturities and origins, and also relationships between NSC concentrations and some traits were investigated. 1) NSC percentages of dry matter were distinctly higher in tetraploid strains than their parental diploid varieties at the early growth stage in the experiment, i.e. up to about 35 days in stem and 45 days in leaf blade after emergence. But the differences decreased as the time goes and, on the contrary, the diploid varieties showed clearly higher values than their tetraploid strains at the later growth stage in the experiment. 2) Mean NSC percentages of fresh matter was significantly higher in diploid group than tetraploid group. And it is recognized that the result described above was due to the difference in fructosan, especially in percentage of the low molecular weight component of fructosan. No clear inter group difference in mono- and oligosaccharide percentage was obtained. Although no significant difference was obtained, mean NSC percentage of dry matter was also higher in the diploid group than tetraploid group. 3) Under the space-planted condition, NSC percentages of the tetraploid strains were equal to or slightly less than those of their diploid parental varieties. But under the condition of community, NSC percentages were distinctly lower in the tetraploid strains than their diploid parental varieties. It is considered that under the community condition the heavier mutual shading due to more drooping leaf blade of plants resulted in lower NSC percentages in the tetraploid strains. 4) In inducing tetraploid varieties from diploid varieties, it is necessary not only to keep the ability of reserving carbohydrate physiologically but also to improve the canopy form for light-interception morphologically. 5) Highly significant positive linear regressions between dry matter contents and NSC percentages were shown both in diploid and tetraploid groups, which may indicate that the dry matter content is possible to be used as the criterion of NSC concentration. But diploid and tetraploid varieties must be dealt with separately because of their significantly different intercepts.
