Oat species and interspecific amphiploids show predominance of diploid nuclei in the syncytial endosperm

Apart from apomictic types, the Polygonum-type eight-nuclear embryo sac is considered to be dominant in grasses. A triploid endosperm is formed as a result of double fertilisation. This study showed, for the first time, the dominance of diploid nuclei in the syncytial stage of the central cell of embryo sac in oat species and amphiploids. The dominance of diploid nuclei, which were the basis for the formation of polyploid nuclei, was weaker in amphiploids due to aneuploid events. The genomic in situ hybridisation method applied in the study did not distinguish the maternal and paternal haploid nuclei of embryo sac. However, this method demonstrated the lack of a set of genomes of one haploid nucleus. It can be assumed that the formation of diploid oat endosperm occurred after the fusion of one polar nucleus and the nucleus of a sperm cell, while the second polar nucleus formed 1n nuclei. The levels of syncytial ploidy were not influenced by both aneuploid events and correlated with pollen developmental anomalies. The differences in the analysed cytogenetic events distinguished amphiploids and their parental species in the ordination space.