Flowering and cone production variability and its effect on parental balance in a Scots pine clonal seed orchard

Abstract

Clonal variation in flowering characteristics and cone production was investigated in a Scots pine (Pinus sylvestris L) clonal seed orchard consisting of 32 clones. At the time of observations, the orchard was 17-19 years old. It was found that on average, within a clone, female flowers were receptive about 1 day before the beginning of pollen shedding and there was a significant correlation between the ranks of clones according to their onset of flowering in 2 consecutive years. Male and female flowering periods were synchronized among the majority of clones and the index of phenological overlap was over 0.41. Significant variations among clones were found for male and female cone production as well as for some selected pollen-related characteristics. On average, individual clones in the orchard produced in total from 0.4 to 4.5 kg of pollen and from 900 to 6500 cones a year. It was found that 25% and 50% of clones produced 46% and 72% of pollen, respectively. Analogous numbers for cone production were 35% and 63%. Some patterns of sexual asymmetry among clones were detected; however, genetic correlations between pollen and cone productions were positive. Effective population sizes were generally high, but the estimate was lower for pollen (75.9%) than for cone production (95.9%). The expected outcrossing rate, based on effective population size calculated using both male and female contribution and background pollination, was high (0.977). The efficiency of the orchard and its potential use for reforestation purposes is discussed.