The effect of temperature during cone and seed development on primary dormancy of Scots pine (Pinus sylvestris L.) seeds

Abstract

Scots pine (Pinus sylvestris L.) seeds have variable levels of primary dormancy which reflect within-species adaptation to local environments. The objective of this study was to use a thermal time approach to determine whether primary dormancy levels in seeds were correlated with mean ambient temperature during temperature-sensitive phases of the reproductive cycle. Seedlots were obtained from a single open-pollinated clonal seed orchard in five crop years and germinated over a wide temperature range (7–35 °C) to calculate base temperature for germination with and without pre-chills (4 and 8 weeks). Primary dormancy levels varied amongst seedlots collected in different crop years (CY). Unchilled seeds were the most dormant for CY2007 (Tb = 10.9 °C) and least dormant for CY2012 (Tb = 5.6 °C). Base temperatures for germination were correlated with mean ambient temperature during different phases of the reproductive cycle. There was a strong positive correlation between base temperature for germination of unchilled seeds and mean temperature during pollination and early pollen tube growth. This suggests that maternal environmental effects during this phase could potentially select for dormant or non-dormant seeds, which has implications for tree breeding and seedling production in forest nurseries.