Morphotypic diversity in populations of Populus nigra L., P. laurifolia Ledeb. and P. x jrtyschensis Ch. Y. Yang. in the zone of natural hybridization

Natural interspecific hybridization provides extensive opportunities for the selection of valuable forms and serves as a base for the selection of forest tree species. The purpose of this study was to investigate the polymorphism of qualitative characteristics and the isolation, on their basis, of morphotypes in P. nigra, P. laurifolia and their spontaneous hybrid P. x jrtyschensis. The knowledge of morphotypes will simplify identification of pure species and hybrids and selection of valuable forms in the zone of natural hybridization of the Tom River basin. The Tom is the right tributary of the Ob river (estuary: height 68 m, coordinates: 56°50'00''N; 84°29'20''E). It originates in the south of the Kuznetsk Alatau in the area of its articulation with the Abakan ridge (source: height 903 m, 53°39'05"N; 89°45'50"E). The river basin is located on the border of the West Siberian Plain and the Altai-Sayan mountainous country, in temperate latitudes. For the upper and middle reaches of the Tom River, the flood plain multi-face is typical. The river branches, forming islands occupied by poplar forests. Morphotypic diversity was studied in 432 individuals from 15 populations of P. nigra, P. laurifolia and P. х jrtyschensis. Populations of P. х jrtyschensis in the Tom River basin are confined to disturbed habitats, whose occurrence is associated with the dynamics of channel processes, or with human economic activity in the floodplain. We carried out these studies using a comparative morphological method. Each complex studied the set of qualitative characteristics: the shape of the surface of elongated shoots, the types of truncated shoots of the crown, the pubescence of the shortened shoot, the leaf petiole, the underside and the edge of the leaf blade, on the basis of which the morphotypes were isolated. Qualitative characteristics were selected in such a way that they met the criteria of "fen": 1) discreteness - alternative; 2) genetic conditioning. Study of the shape of the surface of elongated shoots of the examined species showed that in P. nigra they are always cylindrical, and P. laurifolia is ribbed. In hybrids, there are shoots typical of parent species, but the intermediate ones with ribbing in the upper part predominate, which disappears down to the base. All the P. х jrtyschensis specimens studied, even with the external similarity of P. nigra leaf blade, always show shortened rosette shoots characteristic of P. laurifolia. In parent species and hybrids, the nature of pubescence and trichome length varies, although the latter are always hiding, unicellular, simple hairs. In general, the pubescence is not typical of P. nigra. However, in populations of the Tom River in the foci of hybridization, individuals with developed pubescence are found. In P. laurifolia shoots and leaves are of different pubescence degree. Among the individuals of P. х jrtyschensis, plants with developed pubescence also predominate. The studied qualitative characteristics of shoots and leaves are only found in certain combinations, which form a series of morphotypes. Morphotypes for P. nigra, P. laurifolia and P. х jrtyschensis in 2, 3 and 3, respectively, were detected in single-species and hybrid populations. They are found in all studied populations, in different ratios, but one morphotype always prevails. In P. х jrtyschensis populations, most individuals have intermediate qualitative characteristics of the leaf. Given the differentiation of shoots, an asymmetry towards P. laurifolia is observed for the crowns of hybrids. The presence of a morphotype not typical of P. nigra with pubescent petiole and the base of the leaf blade is explained by introgression. The article contains 5 Figures, 2 Tables, 21 References.