Embryological Study On Facultative Apomixis And Cytological Observation On Male Sterility Of Taraxacum Species

The paper explored the types and the developmental process of embryos of Taraxacum liaotungense Kitag. and Taraxacum mongolicum Hand.-Mazz. by using Ovule Clearing Technique. Seed sets of the two species of Taraxacum were detected by bagging treatments in the fields. To investigate the relationship between the normal fertile Taraxacum junpeianum Kitam and the male sterile mutant, paraffin sections were used for observing microsporogenesis and male gametes development. The results are as follows:1. The bagging treatments resulted in 53.71% of apomictic frequency of Taraxacum liaotungense Kitag. and 54.05% of Taraxacum mongolicum Hand.-Mazz, which resulted in facultative apomixis.2. By observing embryos development of Taraxacum liaotungense Kitag. and Taraxacum mongolicum Hand.-Mazz, we found two reproductive ways within one capitulum, corresponding to apomixis and sexuality. The development of apomictic embryo could be divided into 7 stages, which had abnormal meiosis reflecting in first division while forming dyad, then one of dyad megaspores at micropylar end degenerated leaving the functional one at chalazal end, which undergo three karyokinesis. The egg cell could develop into embryo autonomously. Sexual reproduction embryo underwent tetrad more than apomictic embryogenesis, i.e. resulting into a total of eight stages. Three megaspores of tetrad at micropylar end would degenerated leaving a large decreasing functional megaspore. Neither embryo nor endosperm development was observed before flowering.3. Both Taraxacum liaotungense Kitag. and Taraxacum mongolicum Hand.-Mazz were facultative apomixes including two patterns of reproduction. The two species resulted in same Polygonum-type. Apomictic embryogenesis underwent abnormal meiosis resulting in unreduced megaspore, which called Taraxacum-type while sexual embryogenesis going through two divisions of meiosis. The dyad of apomixes would degenerated leaving a functional one at chalazal end. Apomictic embryogenesis was autonomous development without fertilization.4. In the development of Taraxacum junpeianum Kitam. mutant, abortion stage arose during tetrad to early mononuclear microspore, induced unusual decomposition of tapetum, and mutual adhesion of microspores. Lagged micronucleus was observed during dyad phase of microsporocyte meiosis in male sterile mutant, few tetrads of abounding chromosome bridges were emerged, loss of nutrients happened, leading to abortion of microspore eventually.Taraxacum liaotungense Kitag. and Taraxacum mongolicum Hand.-Mazz is facultative apomixis with different meiosis. The male sterile Taraxacum junpeianum Kitam. had a speciality like a species.