A mutagenic factor, mutator, that was detected in the progeny from a γ-ray irradiated M1 seed of a japonica rice variety Gimbozu, generated novel mutations at many different loci, when activated by the reversion of a mutable slender-glume gene slg, which was induced by γ rays in the above identical M1 seed. For the effective utilization of the mutator in plant breeding, the reversion mutability of slg was analyzed for its genetic behavior and relationship with the mutator activity. First, changes in the reverse mutation frequency of slg (RMF) were traced among several generations, using 39 slender-glume lines which originated from a single slender-glume mutant but were more or less different from each other in background genotype. The results revealed that the mutability of slg was essentially an inherited character, but that it often increased or decreased. Secondly, eleven of the 39 slender-glume lines were each estimated for the mutator activity by examining the frequency of mutator-induced heading-date mutations that appeared in the progenies of non-slender-glume plants from the slender-glume lines, using 424 sublines derived from the 11 lines. As a result, it was found that the mutability of slg did not influence the mutagenic activity of the mutator.

View full abstract

Life history characteristics including energy allocation as well as tiller formation were investigated in 7 lines of 3 Lolium species, namely L. perenne, L. multiflorum and L. temulentum. Annual types tended to show a higher value of reproductive effort which was estimated from the proportion of seed weight to total biomass above ground. The variation in energy allocation suggested that adaptive strategies differentiated in association with breeding systems within the genus Lolium. Among the various traits related to seed production, the proportion of heading tillers at maturity showed the highest correlation with reproductive effort. Since reproductive effort may thus be regulated through developmental changes in tiller formation in Lolium, the development of tillers was compared among them. The results indicated that the developmental fate of tillers markedly depended on the nodal position on the mother stem, as reported in rice. Namely, above the node from which the tiller emerged, both the tiller and the mother stem produced almost the same number of phytomers until floral initiation. However, perennial types tended to produce more phytomers on the tiller than on the mother stem. The intensity of the perennial character varied among the 5 lines except for annual types. After maturity, non-productive tillers continued to grow and new tillers grew from dormant tiller buds. Weakly perennial lines tended to produce more tillers from dormant buds. Furthermore, the developmental fate of tillers markedly differed among them. A weakly perennial line continued to produce inflorescences depending on the nodal position on the mother stem, while the growth of highly perennial lines changed to the vegetative type. Thus, changes in the developmental fate of tillers may play a significant role in adaptive strategies in Lolium.

View full abstract