ABSTRACT
This chapter focuses on the origin and spread of apomixis in populations of sexually or vegetatively reproducing plants depend on the views of genetic regulation of apomixis. Even if apomixis is genetically regulated, reproductive behavior is variously influenced by environmental conditions such as temperature and daylength, at least in facultative apomicts. Origin of genetic variants in plant tissue culture, or somaclonal variation, has been demonstrated in several plant species. Some tissue culture experiments with apomicts have been performed. Mutagen treatment increased the number of sexually formed aberrants in offspring. In several cases, mutagen treatment has been carried out in apomictic plant species. The aim has partly been to increase genetic variation, partly to try to achieve a breakdown of apomixis and induce sexual reproduction. In sexual plants, distant hybridization, as well as pollination with irradiated or chemically treated pollen, enforces haploid formation by parthenogenetic development of reduced egg cells. Traces of sexuality are difficult to detect in highly apomictic taxa.
