Chloroplast DNA variation and pollen contamination in a Pinus brutia Ten. clonal seed orchard: implication for progeny performance in plantations

Pollen contamination is one of the important factors affecting the yield, adaptability, and genetic quality of the seed produced from seed orchards in forest tree breeding programs. Incoming pollen from the forests surrounding the seed orchard is a major concern in tree breeding because it contributes to losses in the expected genetic gains from seed orchard crops. The genetic variation and the level of pollen contamination in a 16-year-old Pinus brutia Ten. first-generation clonal seed orchard was studied using chloroplast microsatellite markers (cpSSRs). In total, 23 alleles and 36 unique allelic combinations (haplotypes) were detected based on the 6 cpSSR loci analyzed. The haplotypic diversity of the clones in the seed orchard was found to be 0.849. Out of 300 embryos analyzed, 87 were not compatible with any male parent within the seed orchard. Thus, 29% of the embryos were sired by pollen sources outside the orchard (i.e. apparent contamination). Microsatellite-based analysis revealed that the estimated contamination rate was 39.3%. Background pollination at this level will cause losses of 20% in the expected genetic gains. Our findings are valuable for the assessment of the intended seed orchard function, i.e. provision of genetically improved seed. It may be worthwhile to use pollen management strategies like strobilus stimulation, controlled pollination, and supplemental mass pollination to decrease pollen contamination and increase the genetic quality of the seeds produced.