Long-term study of a subdioecious Populus ×canescens family reveals sex lability of females and reproduction behaviour of cosexual plants
Cosexual Populus ×canescens plants are inconstant females with life course plasticity of sex phenotype and can reproduce by selfing.
Populus species are dioecious, but deviations from dioecy are reported in some cases. The objectives of this study were to investigate the phenotypic expression and the inheritance of subdioecy in a Populus ×canescens pedigree. The F1 progeny was monitored for sex during 14 years. Thirty per cent of individuals expressed deviations from dioecy and long-term plasticity of sex. Some plants started flowering as male, then became cosexual, and finally turned female. Two cosexual individuals were self-pollinated and generated a selfed progeny markedly impaired by inbreeding depression, but able to reproduce by outcrossing. Sex segregation of the F1 progeny statistically fitted the expected ratio 1:2:1 (female:male:cosexual). By analysis of DNA markers, the cosexual individuals were genetically clustered with the females. The segregation ratio and the genetic profile indicated that cosexual plants were female with altered sex phenotype. Linkage analysis identified a putative sex-determining region with suppressed recombination on chromosome 19 of the male Populus tremula parent. The male sex trait was linked to the pericentromeric region of the P. tremula chromosome 19, whereas the cosexual trait was linked to chromosome 19 of the female Populus alba parent. A genetic model is proposed to explain inheritance and phenotypic expression of sex.
KeywordsCosexuality Poplar Self-compatibility Sex-determining region Sex plasticity Subdioecy
The authors thank S. Khoury for photographs of P. tremula flowers, K. Groppe and M. Will for technical assistance with the laboratory work, B. Pakull for helpful discussions, and the Experimental Farm of University of Tuscia for hosting the experiments. We gratefully thank R. Stettler for his meaningful support and discussion during the whole study and the anonymous reviewers for the detailed and constructive comments. The maintenance of the field trials was managed by F. Ferri and funded by the University of Tuscia (AZAGR 2017—Promotion of Poplar germplasm collections. CF_40507).
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