Clonal variation in phenological synchronization and cone production in a Pinus patula seed orchard

Abstract Synchronization between female receptiveness and pollen dispersal, and fecundity of clones influence effective population size and genetic diversity of germplasm produced in seed orchards. Our objective was to determine clonal variation in phenological synchronization and in cone production in a Pinus patula seed orchard. Two-year phenology data of female and male strobili from a sample of 31 clones, and of male strobili in trees from neighboring natural stands of the same species were used. Synchronization indices between female receptiveness and pollen release of the same clone (O̅iP̅i), of other clones (O̅i P̅j), and of natural stands (O̅i P̅NS) were calculated for each clone and averaged per precocity group (early, intermediate, and late). Genetic parameters for cone production of clones during three consecutive cone harvests were estimated, as was their relationship to precocity and synchronization index O̅i P̅NS. Cone production showed a broad variation among clones and between years, with strong genetic control (H2c ≥ 0.80) and stable (rB ≥ 0.79) between yeas. There was wide clonal variation in synchronization indices, but no significant variation was found in most cases among precocity groups, neither were they consistent between years. Negative correlations [rp = -0.37 and -0.40 (P < 0.05)] in cone production per clone in two years with the O̅i P̅NS index in the first year, indicated that the most prolific clones had lower synchronization with pollen release in natural stands in the orchard’s vicinity, and thus less risk of genetic contamination.