genetic strategy of adaptation and the prospects of pine selection for intensive growth in optimal conditions*

¹Tarakanov V., ²Demidenko V.P., ³Bushkov N.T., ¹Rogovtsev V.V.

¹ West-Siberian Office of the Forestry Institute, Russia, vvtarh@yandex.ru

² Regional State Agency «Berdsk seed forestry», Russia, berdskleshoz@mail.ru

³ Krai State Agency «Larichikha forestry», Russia, larles@yandex.ru

In the populations of forest-forming plant species in the optimum of their area natural selection favours the genotypes with increased growth, providing advantage in the intraspecies competition for light and nutrition. In West Siberia in the Middle Ob basin favourable years see as much as 1 mln of pine seedlings per hectare. In a mature forest less than 1,000 trees are left. Under such high pressure of natural selection, which surprisingly coincides with the tasks for selectionists, can one be sure in successful selection for intensive growth? Theoretical considerations and experimental data about “selection plateau” suggest that under maximal adaptation due to intensive growth the additive variance of the variables describing growth intensity, should be reduced in natural populations. Because of it, mass and individual selection can be less effective. However, to make final conclusions about it we needed information about the genetics of productivity traits.

The available information, on one hand, confirms the above-mentioned hypothesis, but on the other hand, raises new questions. The hereditability coefficient in its narrow sense h² is much lower than 0.20 for variables describing pine growth intensity. Genetic estimation of plus-trees by their seed offspring often revealed low efficiency of mass selection, as well as low frequency of “elite” trees. Our estimates showed that the number of outstanding semi-sib families of plus-trees vary between 0-25%. Considering the genotype-environment interactions, the share of “elite” trees does not exceed 10%. However, the high interclonal variability in growth intensity contradicts these data, which suggest essential non-additive effects. What are their mechanisms?

Recent information about allozymic variability of the coniferous plants offers different approach to the problem. The Scots pine is one of the most polymorphic species of the globe, having high heterozygosity. Moreover, some researchers showed positive correlation between heterozygosity and growth intensity. Pooled together, the information inevitably leads to the question whether the observed phenomenon is the result of adaptive genetic strategy of pine, i.e. selection in favour of heterozygotes with increased growth intensity? Such “heterosis” adaptation strategy suggests regular elimination of significant “segregation load”. Under tough intraspecies competition and the need to create “forest environment” to suppress herbs and grasses and interspecies competition, this “segregation load” may paradoxically be of adaptive importance. Some experimental data showed single-digit percentage frequency of heterosis under random pairing of pine trees. Taking into account self-thinning, we may conclude that this can be enough to ensure the dominance of “heterosis” trees in mature plantations, where of special significance are individuals with high seed production.

Thus we believe that the most perspective selection technique for intensive growth of the Scots pine is heterosis. We suggest to distinguish “natural” (self-thinning) and “cultivar” models for future selectionally improved tree plantations, using different selection techniques and approaches and further detailed research.

*The study was carried out with financial support of SB RAS Integration 5.23.