Introgressive hybridization of Populus laurifolia Ledeb. and Populus nigra L. in the Tom river basin: scale, direction and significance

Studies of natural hybrid zones of Populus L. in Western Siberia have shown that the observed hybridization is asymmetric and introgressive. However, its phenotypic manifestation has not been sufficiently studied, which makes it difficult to create effective programs for the selection of valuable forms and subsequent selection work. The purpose of this study is to analyze the results of studying the populations of P. nigra L., P. laurifolia Ledeb. and P. irtyschensis Ch. Y. Yang in the Tom River basin, according to some qualitative anatomical and morphological characteristics, to show phenotypic manifestations of introgressive hybridization, to reveal its scale, direction and significance. Studies of a complex of qualitative morphological characters were carried out in 23 populations on 684 individuals. It was found that hybridization of P. laurifolia and P. nigra in the Tom River basin is not observed everywhere. Clusters of hybrids (foci of hybridization) stand out only in areas where the optimal combination of factors promoting hybridization develops. The morphological characters we selected allow us to reliably identify the parental taxa and P. irtyschensis. Additional use of the features of petiolar anatomy makes it possible to study the diversity of individuals within the identified taxa. The study of P. laurifolia in both mixed and pure (monospecific) plantations did not reveal any signs indicating the penetration of P. nigra genes into its gene pool. On the contrary, in the populations of P. nigra, phenotypic manifestations of introgression were found in both morphological and anatomical characteristics. It has been suggested that the asymmetric introgressive hybridization between two poplar species observed in the Tom River basin is apparently a fairly widespread phenomenon within the genus Populus. The studies performed demonstrate the adaptive role of introgression in the colonization of suboptimal habitats.