Temporal quantification of mating system parameters in a coastal Douglas-fir seed orchard under manipulated pollination environment

Jiayin Song,Yousry A El-Kassaby,Tony Kess,Ben S Lai,Blaise Ratcliffe,Jiří Korecký

doi:10.1038/s41598-018-30041-4

Abstract

Seed orchards main function is delivering breeding programs’ gains in the form of genetically improved seedlings. They are unique experimental populations, perfectly suited for studying various pollination environments (natural or otherwise), affecting their mating system parameters. Here, under different pollination environment (natural and intrusive (pollen augmentation and/or bloom-delay)), the mating system of a second generation, wind-pollinated, coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) seed orchard was evaluated over four years. Using DNA microsatellite markers and bulk seed samples, we conducted pedigree reconstruction to assign each seed’s male and female parents, followed by determining the extent of pollen contamination (external gene flow), selfing rate, and, parental gametic contribution for each year. Overall, external pollen contamination rates ranged between 10 and 28%, selfing rate varied between 12 and 17%, and 80% of the seed crops were produced by 37–64% of the orchard’s parents. Pollination environment and seed crop size substantially influenced the observed results, particularly for small crops as pollen contamination was high in natural (28%) vs. intrusive pollination (10%). Generally, irrespective of the crop size, seed produced under natural pollination had higher pollen contamination, confirming the role of pollination environment manipulation in improving seed crops’ genetic quality.

Highlights

Tree selective breeding programs are designed to increase the economic values of future forests through planting superior stock with the highest genetic gain and diversity[1]
The present study presents a complex situation where all these factors are interacting and effectively influencing the pollination dynamics of the studied Douglas-fir seed orchard
In the Saanich Peninsula where the seed orchard is located, Douglas-fir reproductive bud development under natural conditions is characterised by a protracted pollination season[13]

Summary

Introduction

Tree selective breeding programs are designed to increase the economic values of future forests through planting superior stock with the highest genetic gain and diversity[1]. In order to fulfil this role, seed orchards are expected to function as closed, perfect panmictic populations[2], an ideal scenario that is hardly met due to the commonly observed variation in reproductive success and phenology among parents as well as external gene flow (pollen contamination) from the ambient environment[1,3,4] These factors could lead to reducing the genetic worth and diversity as well as harbouring higher levels of inbreeding in the resulting seed crops[5,6,7]. Self-fertilization, as well as parental gametic contribution are reported and compared across years to evaluate the pattern of gene flow and parental reproductive success under different conditions To our knowledge, this is the first temporal variation study of Douglas-fir seed orchard pollination dynamics while considering both natural and intrusive pollination practices and seed crop sizes variability

Methods

Results

Conclusion