Molecular genetic methods were used to study all wild poplar species (Populus L., Salicaceae), which belong to the subgenus Tacamahaca (Spach) Penjkovsky, i.e. representatives of section Aigeiros Duby (black poplars, 29 specimens) and section Tacamahaca Spach (balsamic poplars, 100 speci-mens), as well as their natural and cultivated hybrids (186 specimens), including intersectional hybrids (180 specimens); hybrids involving American poplar Populus deltoides s.l. cultivated in Russia were also considered. In 7 cases, 2 possible definitions are given. Another 57 specimens were not identified to species, but their gender was taken into account. In total, the studied collection is represented by 379 specimens. Targeted deep sequencing of sequences of NTS 5S rDNA, ITS, DSH 2, DSH 5, DSH 8, DSH 12, DSH 29, 6, 15, 16, X18, trnG-psbK-psbI, rps2-rpoC2, rpoC2-rpoC1, as well as sites of the gender locus (for the first time!) and ARR17 gene for all specimens (partial repeats of this gene are located in the gender locus) was performed. The sites of the gender locus and ARR17 gene together with the traditionally used multicopy and single-copy nuclear and chloroplast DNA sequences allowed us to obtain the clustering most consistent with the systematics of poplars based on morphological data, as well as to test a number of controversial hypotheses about the origin of the studied taxa. The results indicate genetic closeness or even identity of Populus suaveolens and later described
P. maximowiczii and P. koreana. P. nigra and its hybrid with P. pyramidalis (northern variant of raina) are also very close. The balsam poplar P. laurifolia is closer to the black poplar P. nigra than to the balsam poplar P. suaveolens, because the range of P. laurifolia is located within the range of P. nigra and is less in contact with the range of P. suaveolens. P. talassica and P. afgha-nica are also genetically close, although they belong to different sections; at the same time, they are significantly distant genetically from the more northern P. nigra and P. laurifolia. The combined analysis of sequencing data of the sex locus and chloroplast genome sequences made it possible to determine the origin of P. × petrovskoe – P. laurifolia (female tree) × P. × canadensis (male tree), and P. × rasumovskoe – P. nigra (female tree) × P. suaveolens (male tree). P. × rasumovskoe (cultivar) is represented by one male clone; P. × petrovskoe (also cultivar) by several male and two female clones, but all are very close to each other. P. nigra (especially large participation), P. laurifolia, and possibly some other species of balsam poplar took part in the formation of P. × sibirica, but it is not yet possible to state unequivocally that it is P. suaveolens on the basis of our molecular genetic data. P. × sibirica is represented predominantly by female clones, but there are also male clones, and the molecular-genetic distances between them are greater than in P. × petrovskoe, and P. × sibirica itself is intermediate in its status between a hybrid cultivar and a hybridogenic species. In addition, the conceptual statements made earlier by the authors [Nasimovich and Vasilieva, 2019; Nasimovich et al., 2019] were confirmed: 1) all balsam and black poplars of Eurasia are connected by powerful gene flows, have a common gene pool and represent a single superspecific system (syngameon); 2) the opposite “poles” of this system are P. suaveolens (the most mountainous and easternmost poplar in the harshest climate) and P. nigra (the most plain and the most western poplar in temperate climate); the other Eurasian species occupy one or another intermediate position; 3) sections in the subgenus Tacamahaca are ecological (mountain and plain poplars); belonging of a species (race) to balsam (mountain) or black (plain) poplars is in no way related to the origin and kinship of this species; 4) relative genetic similarity between species (races) is determined by interspecific gene flows, and it is the greater the geographically closer the ranges of these species are; 5) species in the syngameon can be viewed as dynamic states existing in equilibrium between natural selection adapting to local conditions and gene flows equalizing gene composition within the entire syngameon; 6) new dynamic states continue to be formed at present; example – Populus longifolia (new dynamic state of poplar in the northern half of the Russian Plain, formed in the last two-three centuries by a native of the harsh climate mountains); 7) poplars of urban landscaping can participate in the formation of new dynamic states. The position of Chinese authors [Wang et al., 2019] that samples are distributed into higher-order clusters not only according to species affiliation, but also by alleles due to the genetic proximity of all species and high polymorphism of each of them was also confirmed. In our case, the distribution took into account gender dimorphism and other forms of polymorphism: samples of the same species or close species appeared in elementary clusters, but samples of the same species formed such elementary clusters in several high-order clusters at once, i.e. many species are represented by several compact groups of samples in different parts of dendrograms. When analyzing the simultaneous whole population of the studied loci, this tendency is weakened, that is, the distribution is carried out in the first approximation by species.
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