Variation in reproductive phenology in a Pinus patula seed orchard and risk of genetic contamination from nearby natural stands

Abstract

Genetic variation in reproductive phenology among clones in a seed orchard affects the genetic efficiency of the orchard. Our objective was to evaluate genetic variation in reproductive phenology of Pinus patula clones in a seed orchard and the amount of overlap with pollen dispersal in natural stands. In 2014 and 2015, phenology of female and male strobili was recorded on 31 clones in the orchard, and phenology of male strobili was measured on 10 trees in each of four nearby natural stands along an elevational transect. Onset and end dates, and length of female receptivity (F_onset, F_end and F_length) and pollen dispersal (M_onset, M_end and M_length) were calculated, and genetic parameters were estimated. Differences between years in M_onset were larger in the natural stands than in the orchard, but there was a large overlap between the orchard and natural stands. A negative linear relationship with elevation was found for M_end and M_length in natural stands along the elevation transect. Genetic variation was detected for most reproductive phenology traits in the orchard. Genetic control was stronger for M_onset and M_length ( $$H_{c}^{2}$$  ≥ 0.54) than for female receptivity traits ( $$H_{c}^{2}$$  ≤ 0.38). Most phenological traits showed high genetic stability in both years (rB ≥ 0.76). We found a positive genetic correlation (r = 0.67) between F_onset and M_onset, suggesting there is a risk of selfing among clonal ramets. Moreover, the overlap between female receptivity in the orchard and pollen dispersal in neighboring natural stands indicates a risk of genetic contamination in the orchard, particularly for late-phenology clones.