Crossability of Pinus sibirica and P. pumila hybrids and their parental species was studied using the controlled pollination method. Pinus sibirica and its hybrids were represented by grafts at the “Kedr” field station southeast of Tomsk Oblast, Russia; the parental species was of local provenance, with its hybrids obtained from the Southern Baikal region. In the case of P. pumila, trees were pollinated in a wild stand located in the Upper Angara River delta. Parental species had the highest number of filled seeds under open pollination. When they were pollinated with hybrid pollen, the trees showed nearly two-fold reductions in the number of filled seeds. Hybrids tended to abort most ovules during the first year of female cone development, resulting in a high seed abortion rate and consequent low seed production. The number of filled seeds obtained from hybrids was low, with levels ranging from 8.2 to 24.3%. Because of weak reproductive isolation between hybrids and parental species, crosses are inevitable and lead to species introgression. The hybrids probably contribute to interspecies genetic exchange both through hybrid seed production following pollination by parental species and by hybrid pollen distribution.

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The capability of conifers for interspecific hybridization is well known. Five-needle pines from the section Quinquefoliae of the subgenus Strobus play an important role in ecosystems and have great economic significance. Interspecific hybridization that occurred in nature or under controlled pollination suggests that reproductive isolation is relative, being expressed to different degrees. Controlled pollination allows us to gather knowledge about reproductive compatibility and provides valuable material for breeding work. Artificial crosses of five-needle pines began with a purely practical purpose to increase blister rust resistance and it was subsequently suggested that species crossability should be taken into account in their classification. We carried out a number of controlled pollinations using Pinus sibirica, P. koraiensis and natural P. sibirica × P. pumila hybrid clones as maternal trees along with pollen of 11 species and four hybrids of the five-needle pines. For the first time, seeds were obtained from the interspecific crosses P.

Pinus sibirica and P. pumila are Asian five-needle pines with vast geographic distributions that are partially overlapping. Natural hybrids with intermediate morphology have been found previ­ously, but there is a lack of evidence of ongoing introgression. The goal of our study was to elucidate the genetic structure of P. sibirica and P. pumila populations growing in the north-east of their sympatry zone (Aldan plateau) using cytoplasmic DNA markers. All studied P. sibirica and P. pumila trees had usual spe­cies-specific growth habits. Using nad1 intron2 of mitochond­rial DNA (mtDNA) and trnV of chloroplast DNA (cpDNA) we found that trees morphologically identified as P. sibirica had pumila-specific mtDNA. Moreover, some of them also had pumila-specific cpDNA. P. pumila trees were typical and had pumila-type cytoplasmic DNA markers. These results suggest that interspecific hybridization took place long ago and lead to introgression and cryptic hybrids with P. sibirica appearance and P. pumila mtDNA

Application of amplified fragment length polymorphisms markers to study the hybridization between Pinus sibirica and P. pumila Abstract. The genetic diversity of Pinus sibirica, P. pumila, and their hybrids, in a mixed natural stand was studied using amplified fragment length polymorphisms (AFLP). The stand was situated in the northern slope of the Khamar-Daban Ridge. Hybrid trees were determined by their morphological traits in the field. Three AFLP primer combinations detected 167 bands in 35 putative hybrids, and in 25 P. sibirica and 26 P. pumila individuals. Genetic variation in the hybrids was the highest, and was the lowest in P. sibirica. Principal coordinate analysis clustered P. sibirica, P. pumila and the hybrid genotypes into three distinct groups. Nei's distance between the species was 0.193, whereas that between the hybrids and P. sibirica was 0.047, and between hybrids and P. pumila it was 0.074. Application of AFLP in the future studies promises to increase our knowledge of P. sibirica and P. pumila hybridization.