A Study On Breeding System And Disseminule Germination Of Viola Tuberifera

The plant breeding system has become the most active area among the recent evolutionary studies, in which the mating system is the most critical. The different mating systems will produce different disseminule. The characteristics of disseminule germination represent the mechanism to adapt to the environment. The plant breeding system and characteristics of disseminule are ecologically significant, which play an important role in the maintain and update of the plant populations.Viola tuberifera endemic to Qinghai-Tibet Plateau, can produce open,chasmogamous(CH) flowers and closed, obligately self-pollinating aerial and subterranean cleistogamous(CL) flowers. The species has an extremely unique breeding system, not only can carry out clonal growth through bulbs, but also has sexual reproduction through CH and CL seeds. In this paper, floral morphology,breeding system, pollen viability, stigma receptivity, characteristics of disseminule germination were researched. The results will help us to realize the adaptive significance of Viola tuberifera at high elevation environment of Qinghai-Tibet Plateau. The main results are as follows:(1) The CH flower is bisexual, it belongs to bilaterally symmetry and approach herkogamy. The process of flower anthesis is last about ten days. The flower has five green calyx, white petals and stamens. The stigma is above anther. Anthers ring around the ovary, which shows 1-locules and 3-carpels. When excluded from floral visitors,duration of the monitored flowers prolonged distinctly, and pollination did not induce floral closures, which together suggested the plasticity of the floral longevity of this species and their special contributions to ensure reproductive success. The main pollinators of flowers are Apis cerana(Apidae), Abia sp.(Cimbicidae) and Vespa sp(Vespidae).(2) During the flowering phase, the pistil matured before stamens. There is a 6days overlap between high stigma receptivity and pollen dehiscence. On the day of anthesis, the stigma and anther change from light green and pale yellow to brown. In the first day of flowering, the stigma has no receptivity, but then not. On the day of anthesis, the pollen vitality was more than 80 % in the first four days.(3) The result of OCI and P/O ratios suggested that the breeding system of Violatuberifera is facultative outcrossing, self-compatible and pollinator depended. The tests of reproductive systems of Viola tuberifera indicate that the species is self-compatible but has not autonomous self-pollination and apogamy. To sum it up,under artificial pollination and bagging, we can draw a conclusion that there is obvious outcrossing advantage and passive selfing phenomena exist in CH flowers of Viola tuberifera. In addition, we have supplementary pollination experiments in four natural populations, finding pollen limitation exists only at the highest altitude of3292 meters.(4) The bulbs and seeds of Viola tubeirfera germinated for 60 d with a 12 h photoperiod and 12 h thermoperiods(dark / light) of 5/15?, 5/20? and15/25?. The germination percentages of freshly bulbs are high(>85 %), on the contrary the germination percentages of three types of freshly seeds are very lower, especially the subterranean CL seeds. Extending the storage time can significantly increase germination percentage of aerial CH and CL seeds, but have no significant effect on subterranean CL seeds. 1, 2, 4 months of cold stratification significantly increased the germination of aerial CH seeds, aerial CL seeds and subterranean CL seeds,respectively. In addition, scarification on covering layers can significantly increase the germination percentage of these heteromorphic seeds. Results indicated that subterranean CL seeds have deep physiological dormancy and two types of aerial seeds have non-deep physiological dormancy.