SEED PRODUCTIVITY AND POPULATION GENETIC STRUCTURE IN HYBRID ZONE BETWEEN SIBERIAN STONE PINE AND SIBERIAN DWARF PINE

IN NORTHEASTERN PART OF BAIKAL REGION

Petrova E.A. ¹, Goroshkevich S.N. ¹, Politov D.V. ², Belokon M.M. ²,

Popov A.G. ¹, Vasilieva U.V. ¹

Institute of monitoring of Climatic and Ecological systems, Tomsk, Russia, petrova@imces.ru

N.I. Vavilov’s Institute of general genetics, Russia, Moscow

Natural hybridization is thoroughly studied in forest tree species. In Russia, natural hybridization between different species within genus Picea, and Larix, that similar in morphological and ecological traits, was investigated and reported. For Russian Stone pines that ranges are overlapped the ecological and morphological differences more expressed. The aim of the study is comparative analysis of seed productivity, genetic variation and mating structure in Siberian Stone Pine, Siberian Dwarf Pine and natural hybrids in northeastern part of Baikal region. Two sites in Baikal lakeside were examined in this study: Barguzin Biosphere Natural Reserve, Davsha bight (BR) (P. sibirica forest stand with scattered P. pumila), and delta of Upper Angara (DUA) (swamped area, P. pumila dominated and P. sibirica occurred rarely). In both studied sites there was natural hybridization between the stone pine species, the number of hybrids was approximately 5 plants per hectare. Cone and seed sizes in hybrids were intermediate relative to parental species. At all stages of generative cycle from seed scale differentiation to embryo differentiation the hybrids had sufficiently higher rate of mortality and underdevelopment of reproductive structure compare to pure species. At the same time, fertility of hybrids in DUA was some higher than it was previously determined - according to our data approximately 25% of ovules developed into valid seeds with differentiated embryos. Genotypes of adult trees and their embryos, including 48 interspecific hybrids were determined by means of 31 allozyme loci controlling 18 enzyme systems. For most loci the hybrids had intermediate allele frequencies relative to P. pumila and P. sibirica samples that confirmed hybrid nature of these trees. All hybrids were heterozygous at diagnostic Skdh-2 locus. In the site where P. sibirica dominated 27% of P. pumila seeds were sired by P. sibirica but no P. pumila specific alleles were found in Siberian Stone Pine seeds embryos genotypes. In the site with alternative ratio of pure species only 1,4% of P. sibirica seeds had P. pumila paternal contribution, all P. pumila seeds were sired by the same species pollen. Studying of hybrids mating structure demonstrates that main portion of their embryos had paternal contribution from parental species dominated in the site and second species sired 13-14% of embryos. Portion of hybrid pollen in effective pollen pool of hybrid seeds in DUA was 13% that is fourfold compare to BR. It was shown that hybrids take part in pollination of pure species rarely occurred in the sites. We conclude that natural hybrids are fertile and produced seeds and pollen in different types of mixed P. sibirica - P. pumila stands. Our results confirm the possibility of backcrosses and F2 hybrids existence and demonstrate that at least initial stages of introgressive hybridization take place in the studied mixed stands of the two stone pine species. Sufficient fertility of hybrid plants in some sites of hybrid zone attests of its fitness and allows supposing an evolutionary perspective of the novelty in plant kingdom.