| In the new list of rare and endangered plant drafted by the State Forestry Bureau, all species of Chinese cycas were classified as grade one protected species. There are three main problems confuse us in sexual reproduction Cycas. They are: "the pollinator of Cycas, low percentage of pollination and low percentage of seed set in nature, and cycas seed take long time to germinate and grow, as well as seedlings not come out evenly". For confirm the pollinator of Cycas, an exclusion experiment, brought insects from male cones to female cones was conducted for the first time; To develop the reliable method of storage of cycas pollen, the germination test (hanging drop) was used to estimate its viability of Cycas debaoensis, C. micholitzii, C. parvulus and C. elongata; An investigation was made at different grads of temperature and humidity on longevity of pollen storage. Besides, to explore the effect of integument on seed germinating, an experiment of removing sclerotesta of cycas seeds was conducted, and at last the seeds were cultured at different temperature to find the suitable temperature for seeds germinating. All the results of experiments as follows:1. The male cone shed pollen from the base of the cone to the top, and the period of shedding pollen will last for about 20d before the cone collapse. It is a good time to collect very much of high viability pollen when the shedding period come to the 5th days. The result of airborne pollen calculated at different sampling points showed that the amount of airborne pollen was always aboundent within a 3m radius of male cones but descreased markedly beyond this distance. The female cone excluded insects by mesh bags, bring in insects and natural pollination got average percentage of seed set of 55.3%,57.2%,63.5% respectively. There is no significant difference with each others. It means that both wind and insect are efficient pollinator of cycas elongata. This species has the same mode of pollination as cycas revoluta reported by Kono in 2007, opposed to the host-specific insect pollination observed in most Zamiaceae. It may be conclude that Cycas is more original than Zamiaceae in evolution which involve an analogous evolution of plant-insect interaction.2. The best germination condition of Cycas pollen is on a medium containing 2.5%sucrose, 100 mg/L -500 mg/L boric acid and pH 6.5-7.0. Cycas pollen stored over silica gel at room temperature maintained some viability up to one month. The pollen stored in container without desiccant maintain considerable viability more than 4 months in 0℃. Pollinating with the pollen of C. elongata stored in liquid nitrogen presented similar percentage of seed set comparable with fresh pollen. They got average percentage of 90.3 and 90.0 seed set respectively. Pollen of C. elongata can be stored in liquid nitrogen without any considerable loss of germinability. The water content of the pollen decreased to below 15.5% is good for the liquid nitrogen storage. It is the first time to report that pollen of Cycas can be stored in liquid nitrogen.3.The suitable temperature for Cycas seed germinating is culturing in 30℃. The seeds of Cycas revoluta which integument were removed begin to germinate when they were cultured in 30 for 8 days, the highest germination percentage, nearly 100% (except the abortive seeds); Contrary, the seeds with which no treatment did not germinate when cultured in 30℃even after 20 days. The seed which integument was removed absorb more 5 times water than the seeds which have not been treated. It can be concluded that a large number of Cycas seedlings can be obtained by removing the integument of seeds and then cultured in 30℃. The method can be applied in commercial seeding production.
|
PDF Full Text Request