The different origins of artificially-induced unreduced female gametes and their effect on transmitted parental heterozygosity in Populus

The induction of unreduced gametes via chromosome doubling is an effective way to produce triploids. During this process, the transmitted parental heterozygosity varies by different origins of unreduced gametes. In this study, a total of 110 allotriploid individuals from two cross combinations who shared only one male parent were obtained by chromosome doubling of megaspore via high temperature treatment in Populus tomentosa . Twenty-six SSR loci, at which the allelic configurations of the female parents ‘MC1’ and ‘MC2’ were heterozygous and different from male parent ‘YX1’, were screened. Among them, five pairs of pericentromeric SSR primers were selected to identify the origins of unreduced female gametes. Our results showed that 30 individuals from 110 allotriploids derived from the first division restitution (FDR), and 80 allotriploids from the second division restitution (SDR) in these two cross combinations. The transmitted parental heterozygosity of unreduced female gametes via FDR were 0.824 and 0.769 in two cross combinations, respectively, which was significantly higher than that of SDR (0.395 and 0.396, respectively). The FDR type unreduced gametes with higher heterozygosity transmitted from parents may be more desirable in triploid breeding. However, no significant difference in transmitted parental heterozygosity was found between the two FDR groups and two SDR groups. Correct elucidation of the origins of unreduced gametes may be conducive to their effective utilization for further sexual hybridization in triploid poplar breeding.