Although the flowering of facultative biennials is size-dependent, flowering size varies markedly within a single population as well as among populations. In this study, 15 half-sib families of the facultative biennial Aster kantoensis were grown from seeds at three nutrient levels (low, medium, and high). A significant nutrient × family interaction effect was found for bolting size, and among-family variation in bolting size increased with decreasing nutrient level. Growth from bolting to flowering tended to be greatest at the high nutrient level. Such responses of bolting size and growth from bolting to flowering resulted in an increase in flowering size at the high nutrient level and a significant variation in its reaction norm among families. For flowering age, there was a significant interaction of nutrient × family, and its among-family variation increased with decreasing nutrient levels, as was the case with bolting size. These results indicate that genetic variation in phenotypic plasticity of bolting size with nutrient availability was one cause of the variation in flowering size and age in the A. kantoensis population on the floodplain with the spatially heterogeneous nutrient availability. Moreover, responses of growth from bolting to flowering to nutrient availability could enhance the variation in flowering size.
In plant species producing non-dormant seeds, the germination time (from the start of imbibition to radicle emergence) is the main factor determining the timing of seedling emergence. We investigated maternal and paternal genetic effects on the germination time of non-dormant seeds of a monocarpic perennial, Aster kantoensis Kitamura (Compositae). Three sets of reciprocal diallel crosses among five plants were conducted to produce genetic variation in seeds, and the germination time of the progeny of each parent was determined. The effects of the maternal parent and the interaction of maternal and paternal parents on the germination time of progeny were significant in all sets, and the effect of the paternal parent was significant in two of the three sets. This result means that the germination time of the progeny of a maternal or paternal parent can vary with the genotype of its mating partners. Because variation in the emergence time of seedlings contributes to avoiding seedling loss owing to unpredictable environmental changes, genetic variation in the germination time among the progeny of each parent mating with multiple partners could contribute to the establishment of the parent's seedlings in species producing non-dormant seeds in the field.
Seeds of Aster kantoensis Kitamura (Compositae) were experimentally exposed to different cycles of hydration and dehydration: 3H1D (cycles of 3-d hydration and 1-d dehydration periods), 2H3D, 2H1D, 1H3D, 1H2D, and 1H1D. Under continuous hydration (control), all viable seeds germinated within 9 d. However, all viable seeds exposed to the 3H1D, 2H3D, and 2H1D cycles germinated within 36, 50, and 36 d of the start of the experiment, respectively. Not all viable seeds exposed to the 1H3D, 1H2D, and 1H1D cycles germinated during the experimental period. Compared with the control, the number of days required for 50% germination increased in seeds exposed to the hydration-dehydration treatments except for those seeds exposed to the 3H1D and 2H1D cycles. In addition, seeds treated with a 1-d hydration period required a larger number of cumulative hydration days for 50% germination than those seeds exposed to one of the other three treatments or the control. These results indicate that sporadic germination of A. kantoensis seeds during an extended period of several months in the gravelly flood plain where they are found results because the dispersed seeds are exposed to various cycles of hydration and dehydration depending upon the rainfall pattern and spatial heterogeneity of evaporation rates at the sand surface resulting from shading by gravel.Key words: Aster kantoensis, dehydration tolerance, gravelly flood plain, hydration-dehydration cycles, seed germination.
Résumé : Des graines de l'Aster kantoensis
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