|WOESTE, KEITH - Purdue University|
Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2017
Publication Date: 2/6/2017
Citation: Alexander, L.W., Woeste, K.E. 2017. Distance and phenology influence pollen gene flow, male reproductive success, and female mate choice in a northern red oak (Quercus rubra L.) seed orchard. PLoS One. 12(2):e0171598.
Interpretive Summary: Northern red oak (Quercus rubra L.) is a species that has long been valued for its hard and attractive wood, acorn production, large size, and deep red autumn foliage. While northern red oak has historically been harvested from natural stands, increased habitat pressure and poor long-term natural regeneration have resulted in large-scale plantations of oaks and other hardwoods to meet the needs of hardwood industries. A 2005 survey of forest tree nurseries in the eastern United States showed that 7% of hardwood seedlings were from genetically improved sources; northern red oak consisted of only 6.8% of improved hardwoods. In the same survey, 77% of nursery managers felt that improved hardwoods were beneficial to forestry in their region, and 64% desired to use more genetically improved hardwood material in the next 10 years. However, there is a lack of detailed information about northern red oak seed orchard pollination dynamics. In particular, the parental reproductive success and level of pollen contamination is essential for the correct determination of both the genetic gain and diversity of seed crops. To fill that knowledge gap, we used eleven microsatellite markers to investigate pollen gene flow, female mate choice, and male reproductive success in a clonal seed orchard of northern red oak based on paternity analysis of seed orchard offspring planted in replicated progeny tests. The results showed that about half of the trees in the orchard served as male parents each year. Distance between trees and flowering time were the two largest drivers of male reproductive success, and early-flowering trees had more contamination from pollen outside the orchard than later-blooming trees. These results will help seed orchard managers make decisions about keeping or removing trees based on distance and flowering time to retain goals of genetic gain and genetic diversity.
Technical Abstract: Northern red oak is a high-value hardwood used for lumber, furniture and veneer. Intensively managed northern red oak orchards require genetic gain for trait improvement. Data from conifer seed orchards and natural and managed stands of hardwood trees have shed light on the distance over which pollen can move, and underscore the need for managerial attention to seed orchard placement and maintenance. We used eleven microsatellite markers to investigate pollen gene flow, female mate choice, and male reproductive success in a clonal seed orchard of northern red oak based on paternity analysis of seed orchard offspring in progeny tests. The objectives of the study were to determine i) the percentage of clones acting as pollen parents each year and the factors influencing male reproductive success, ii) the influence of maternal clone genotype, year, female phenology, and DBH on female mate choice, and iii) the average genetic correlation among offspring. Microsatellite-based paternity analysis showed that 93% of offspring were sired by a male parent within the seed orchard. The mean number of male parents per year was 69.5, or 47.6% of all clones in the seed orchard. Female clones in the early phenology group had more offspring sired from extra-orchard pollen (13%) than clones in the intermediate (5%) and late (1%) phenology groups. Distance was the largest influence on pollination success, and pollination occurred most often by male trees in the same subline as the maternal tree. Males in the early phenology group sired more offspring in the overall progeny pool and more offspring per mother tree than males in the intermediate or late phenology groups. Average genetic correlations among all OP progeny ranged from 0.26 to 0.35 with a mean of 0.28 ± 0.01. The importance of progeny test genotyping for northern red oak improvement likely is increasing with the demand for improved varieties. The current study demonstrated the feasibility of post hoc assembly of full-sib families for genetic analysis of important traits for seed orchard management.