Temporal and spatial variation of pollen dispersal in a seed orchard and nearby natural stands of Pinus patula

Abstract

Pollen flow from natural populations towards seed orchards has a negative effect on the genetic quality of germplasm produced. The objective of the study was to evaluate the potential gene flow into a Pinus patula clonal seed orchard from nearby natural stands. In 2014 and 2015, pollen traps were established at the center and periphery of the seed orchard and in nearby natural stands along an altitudinal transect in Aquixtla, Puebla, Mexico. With the pollen capture curves, total pollen dispersal (pollen grains cm^-2), dates and extent of the dispersal period were estimated. The relationship of the dispersal period with temperature, rainfall and degree-days was also analyzed. Pollen captured in the seed orchard was 1.5 times higher and dispersal started one week earlier than in natural stands in both years. In 2015, the amount of pollen dispersal doubled and the dispersion period was delayed. The pollen captured at the center of the orchard was 74 % higher than in the periphery, and the dispersal period started one to three days later. No altitudinal trend in the dispersal period was observed in natural stands. Phenology differences between years in pollen dispersal were related to cumulative degree-days and to variation in maximum temperature and rainfall. Results reveal risks of genetic contamination in the seed orchard, though these are lower in the center than in the periphery.