THE ROLE OF THE HISTORY OF DISSEMINATION AND INTROGRESSION IN THE MORPHOLOGY OF POPULUS NIGRA L. IN THE NORTH-WESTERN PART OF ALTAI-SAYAN MOUNTAIN COUNTRY

Abstract

Introduction. The morphology of P. nigra remains poorly studied in the northwestern part of the Altai-Sayan mountainous country. Field studies of populations in the basins of the Tom, Biya and Katun rivers showed that there are individuals with a translucent edge of the lamina and leaf pubescence. It is difficult to consider the indicated signs as the manifestation of exclusively intraspecific variability of P. nigra in the indicated part of the range. Since here is a zone of its joint growth and natural crossing with P. laurifolia (Tacamahaca section), and some of them may be the result of introgressive hybridization. The goal of this study is to examine some of the morphological features of P. nigra in the zone of natural hybridization in the northwestern part of the Altai-Sayan highland, to identify the nature of their occurrence and practical value. Material and methods of study. The studies were performed in nine populations of P. nigra in the floodplain of the Tom river, in two - of the Katun river and in one - of the Biya river. Signs of vegetative organs were investigated using comparative morphological and anatomical methods. Results and discussion. In the studied plantations of the Katun river all the trees have leafy plates with a well-defined translucent edge, on the Biya river the number of such trees is slightly reduced, and they are not observed in the Tom river populations. The leaves do not differ in the anatomical structure of the leaf edge, however, the process of formation of the cuticle layer by the cells of the epidermis is different. The nature of the development of the cuticle and, as a result, a different refraction, create the effect of visibility of the border of the hypodermis along the edge of the plate in Altai plants. The symptom of pubescence in P. nigra is expressed in all the populations confined to the foci of hybridization. Conclusions. The studies have shown that in the zones of natural hybridization of species of the Populus genus, qualitative morphological features may have a different nature. The differences in severity of the semitransparent edge of the lamina in P. nigra observed in the areas of its spontaneous crossing with P. laurifolia in the river basins of the Katun, Biya and Tom can be considered as intraspecific taxon variability unrelated to hybridization and due to different paths of recolonization of territories after the Pleistocene- Holocene glaciation. The presence of pubescent forms of P. nigra is a phenotypic manifestation of introgression. The part of individuals with pubescence is characterized by a high rooting rate of woody cuttings. Therefore, the use of this visual feature will allow adjusting the program for the selection of its economically valuable forms.