Reproductive System Of Three Invasive Alien Plants In Asteraceae

Biological invasion has become a global problem,and China is also one of the countries most affected by biological invasion.The invasion of alien species,especially the invasion of alien plants,has caused a serious harm to agricultural production,development of social economy and ecosystem diversity in China.In our study,the seeds and capitula at different developmental stages of Ageratum conyzoides L.,Praxelis clematidea(Griseb.)R.M.King et H.Rob.,and Erigeron annuus(L.)Pers.selected from different regions of China were used as experimental materials.Here,flow cytometric seed screening(FCSS)and artificial controlled pollination experiments were used to study the reproductive system of A.conyzoides,P.clematidea and E.annuus,and cytoembryological development of the ovule and anther was observed by differential interference contrast(DIC)microscopy after the application of whole clearing technology.The main results were obtained as follows:(1)The results of FCSS showed that A.conyzoides was facultative apomixis,while P.clematidea and E.annuus were diploid apomixis without pseudogamy;(2)The results of artificial controlled pollination showed that there was no significant difference in seed set between the open pollination and bagging of A.conyzoides,and they were(88.01 ± 1.19)% and(86.18 ± 1.67)% respectively,but significant differences were found among seed set under emasculation and the other two treatments,and the seed set of emasculation was(2.68 ± 0.81)%,this indicated that A.conyzoides has high self-compatible and facultative apomixis.There was also no significant difference in seed set between the open pollination and bagging of P.clematidea and both were very high,which were(98.65 ± 0.20)% and(97.73 ± 0.35)% respectively.There was significant difference between the seed set of the emasculated and the other two treatments of P.clematidea,but the seed set was also very high,which was(93.58 ± 0.38)%,this proves that the P.clematidea is highly apomixis.(3)The results of embryological observation showed that A.conyzoides was facultative apomixis and the embryo sac development under sexual reproduction was Polygonum type,whereas the apomixis embryo sac was Hieracium type.Reproductive mode of P.clematidea was diplosporious apomixis without pseudogamy and the type of embryo sac development was Antennaria type of diplospory.Reproductive mode of E.annuus also was diplosporious apomixis without pseudogamy and the type of embryo sac development was Ixeris type of diplospory.According to the results of FCSS,cytoembryological observation and artificial controlled pollination,it is concluded that A.conyzoides has both sexual reproduction and apomixis,which is facultative apomixis,and both P.clematidea and E.annuus are apomixis without pseudogamy.Self-compatible and facultative apomixis characteristics of A.conyzoides can not only makes it capable of autonomous seed set which through self-fertilization or asexual propagation under the condition of unsuitable pollination but also can ensure the populations variability through open pollination under the condition of suitable pollination to achieve the purpose of constantly adapting to the environment.The apomixis characteristic of P.clematidea and E.annuus allows them to reproduce independently of suitable mates and pollinators.In conclusion,the autonomous self-fertilization and apomixic characteristics of A.conyzoides,P.clematidea and E.annuus can enable them to efficiently complete the reproductive mission in the invasion area and increase the possibility of naturalization and invasion in the new habitat.Moreover,apomixis has the advantages both of seed reproduction and asexual reproduction,which directly leads to the increase in the distribution and richness of species with apomixis characteristic.It can be seen that the characteristics of the reproductive system of invasive alien plants are closely related to their invasiveness.In-depth research on the reproductive system of invasive alien plants and analysis of the relationship between their reproductive characteristics and invasiveness can take scientific and reasonable prevention and control measures of invasive alien plants.