The Anatomical Study On Seed Abortion Of Syringa Villosa And S.Microphylla In Cultivated Sites In Beijing

Syringa spp are famous for their ornamental value at garden throughout the world. Syringa villosa Vahl, flowering late and shade tolerance and S.microphylla Diels with twice flowering one year are not only excellent ornamental plants, but also play the important role on lilac hybridization breeding. However, They have very low fruit sets and completely aborted seeds in cultivated conditions in Beijing,which becomes the barrier to crossbreeding. The author has measured the fruit sets and seed sets from different pollination methods in S.villosa and S.microphylla in Beijing botanical garden,conducted morphological and anatomical observation on flower organs and embryo development sequentially, and compared climatic conditions in S.villosa in different habitats in order to better understand the aborted seeds,speculate the reason for abortion and provide the reference for embryo culture.The results are as follows:1、The average fruit sets of S. villosa from artificial cross pollination and open pollination in cultivated conditions were31.86%and8.32%respectively while artificial self-pollination and controlled emasculation was0%, four kinds of pollination didn’t produce any seeds and the seed set was0%; While the seed set of S.villosa from open pollination in comparison site of Dongling mountain was25.55%, and the fruit set was21.35%which was more than8.32%in cultivated site, while the method of artificial cross pollination increased the fruit set to31.86%. The average fruit sets of S.microphylla from artificial cross pollination and open pollination in Beijing botanical garden were20.37%and9.13%while artificial self-pollination and controlled emasculation was0%, none of these ways produced viable seeds. The results showed that two kinds of lilac were self-sterile plants without apomixia in cultivated conditions, the lack of pollination vectors may lead to the low fruit set in cultivated conditions.2、The fluorescence microscope test showed that when3-6d after open pollination and artificial cross pollination in S. villosa and2-8d in S.microphylla, pollens germinated on the stigma and pollen tubes growed toward the ovary. The results indicated that the pollens germination on their stigmas and growth along the styles of two lilacs in cultivated site were normal, pollens and stigmas were compatible with each other, they could pollinate and be fertilized normally. Therefore this stage can not lead to the seed abortion.3、The study on embryology of S.villosa and S.microphylla showed that the embryological characters of two plants were simular. The anther wall conformed to be the basic type and glandular tapetum. The cytokinesis of the microspore mother cells in meiosis was the simultaneous type. And microspore tetrad was tetrahedral shape,the mature pollens were of2-celled type; The ovule was anatropous,unitegmic and tenuinucellate, megaspore tetrad was linear shape. The development of the embryo sac was polygonum type; The endosperm developed to be the nuclear type and the embryo the asterad type,The globular embryo, heart-shaped embryo, torpedo embryo and cotyledonal embryo were formed sequentially. The development of the cotyledonal embryo in S.villosa and S.microphylla in cultivated conditions stopped since3rd August and1st September respectively, all cells degraded gradually at later stages and seeds were aborted.4、The morphological and anatomical observation showed that when40-50d after pollination in S.villosa, corresponding to the fruit length of13-20mm, and3months after pollination in S.microphylla, the fruit length of9-14mm, the end of the reflorescence, cotyledons primordia had developed to be mature,organs had been differentiated and cotyledonal embryo had not degraded, This period may be the suitable stage for embryo culture in order to rescue later aborted embryo on time.5、S.villosa can produce normal seeds in Dongling mountain.Comparing the growing environments of cultivated site and original habitat in S. villosa during the embryo development stage, the author supposes that summer high temperature and rainfall fluctuation in large range in cultivated conditions may be some factors that lead to stagnation of the later embryo development and seed abortion.The research indicated that two lilacs, growing and blossoming normally in Beijing, could increase the fruit sets well not produce any seeds by artificial cross pollination. The reproductive biology research showed that microspore and megaspore, male and female gametophytes, pollination fertilization and early embryo development of S. villosa and S.microphylla in cultivated conditions were normal, but the later embryo development stagnation and cell structure degradation led to the seed abortion. We try to solve the problem by the embryo culture or providing the suitable environments for later embryo development.