Quantitative genetic parameters of heartwood and its chemical traits in a black pine (Pinus nigra J.F.Arnold) clonal seed orchard established in Greece

Background: Black pine (Pinus nigra J.F.Arnold) is one of the most productive conifers species for timber production in southern Europe, the Mediterranean region and Greece. Recently, the interest for its heartwood extractives content due to their medicinal properties has been renewed. Black pine can be used to produce high added value products, such as bioactive compounds produced from wood and wood waste materials. Methods: Quantitative genetic parameters were estimated for heartwood chemical traits and heartwood percentage in a 44-year-old Pinus nigra clonal seed orchard, established in Peloponnese, Greece. Results: Significant variation was found among clones and among provenances for all studied traits. Heritability on a clone mean basis was extremely high for total acetone extractives, total resin acids as for all resin acids (≥0.85), except levopimaric acid (0.47) and very high for total stilbenes, pinosylvins as for dehydroabietic acid and heartwood percentage (0.69-0.79). On an individual basis, the genetic control was moderate to high (0.53-0.62) for total acetone extractives, total resin acids as for most of resin acids (≥0.85) with dehydroabietic acid presenting low value (0.39) while levopimaric acid very low (0.15). Total stilbenes, pinosylvins and its ether derivatives as heartwood percentage exhibited low values of heritability on individual basis (0.31-0.43). The phenotypic correlation (rp) between total acetone extracts and total stilbenes was negatively weak (≤-0.173) and significant (p≤0.01) while the genetic correlation (rg) was moderate to strong (≤-0.502). The rp values between several pinosylvins were significantly (p≤0.01) moderate to strong (0.529-0.975) as were genetic correlations (0.583-0.975). Between the studied resin acids, both rp and rg values were mostly medium to strong (rp≥0.8 and rg≥0.7) and significant (p≤0.01) in the case of phenotypic correlations, with minor exceptions (levopimaric acid). Phenotypic and genetic correlations between heartwood percentage and its chemical traits were positive (being in most cases significant), except for dehydroabietic and levopimaric acid. Conclusions: The studied clones, comprising the clonal seed orchard, can be used in clonal forestry and subsequent breeding cycles, indicating high potential for advanced breeding, especially for heartwood extractives that are of high pharmaceutical and economic value.