Natural hybridization is widely distributed and has important role in micro- and macro-evolutional processes of plants. Natural hybridization is possible when 3 conditions keep, namely contact of areals, overlapping of flowering times and species compatibility (Grant, 1981). All these conditions for Siberian stone pine P. sibirica Du Tour and Japanese pine P. pumila (Pall.) Regel take place in the territory contiguous to Baikal Lake (Goroshkevich, 2004). To novel species establish it is necessary to hybrids are isolated from both parental species because isolation in different its displays ensures species discreteness (Zavadskiy, 1961).

In general, hybrids between Siberian stone pine and Japanese stone pine are result from pollination of Japanese stone pine’s ovules by Siberian stone pine’s pollen (Politov, 2007). The hybrids are fertile, however, their seed efficiency reduced compared with parental species. For example, hybrid seed efficiency was 25% in the delta of the Upper Angara River and 3% in the north-eastern Baikal coast territory of the Barguzinskiy reserve. The hybrids were characterized increased loss of their ovule during whole period of the development ovules in viable seeds. Ability of the hybrids to seed reproduction allows them relatively quickly to achieve species level or can provide gene introgression from one species to another. It was revealed that hybrids could intercross with other hybrids under natural conditions and the portion of such embryos was significantly higher than portion of hybrid pollen in total pollen pool in air. However, among hybrid embryos predominated backcrosses to the species that was dominate in the given stand (Petrova et al., 2006).

Test crossing of Siberian stone pine and the hybrids shown the hybrids as maternal plants had significantly reduced seed efficiency than Siberian stone pine pollinated hybrid pollen. In the former case portion of full seed was 1.7-17.1% and in the last case it was 36.7-66.7%. Hence it appears that quality of the hybrid ovules is the most important cause of decrease of their seed efficiency. Moreover, test crossing of the hybrids shown they are capable for high seed efficiency, portion of the full seeds was 62.8% at the best case.

Thus, the hybrids between Siberian stone pine and Japanese stone pine has required features in order to become isolated from parental species and to give rise novel species in the future.

Grant V. Plant speciation. Moscow.: Mir, 1984. 528 p. (in russian)

Zavadskiy K.M. Theory about species. Leningrad: Publishing of Leningrad’s university, 1961. 255 p. (in russian)

Petrova E.A., Goroshkevich S.N., Politov D.V., Belokon M.M., Popov A.G., Vasilieva G.V. Seed productivity and population genetic structure in the hybrid zone between Siberian stone pine and Japanese stone pine // Hvoinie borealnoi zoni. – 2007. – V. 24. – № 2–3. – P. 329–335. (in russian)

Goroshkevich S.N. Natural hybridization between Russian stone pine (Pinus sibirica) and Japa-nese stone pine (Pinus pumila) // Breeding and genetic resources of five-needle pines: growth, adaptability, and pest resistance. Proceedings of the IUFRO Five-Needle Pines Working Party Conference, July 23-27, 2001, Medford, Oregon, USA – 2004, p. 169–171.

Politov D.V. Population genetics and evolutional relationship between pine species (Pinacea) of Northern Eurasia. Dissertation abstract. Moscow., 2007. – 47 p. (in russian)

Note. Abstracts are published in author's edition