Gene flow among wild and cultivated common walnut (Juglans regia) trees in the Qinling Mountains revealed by microsatellite markers

Huijuan Zhou,Peng Zhao,Shuoxin Zhang,Keith Woeste

doi:10.1007/s11676-020-01254-z

Abstract

Patterns of gene flow and gene introgression can be used to assess the risk of genetic pollution of wild forest trees from widespread cultivated trees. A comprehensive understanding of the genetic relationships and levels of gene flow among wild and cultivated common walnut (Juglans regia) has become an urgent issue. Using twelve microsatellite markers, we investigated the genetic diversity and gene flow between cultivated and wild trees of J. regia in the Qinling Mountains, China. A high level of genetic variation was detected in both cultivated and wild trees. The mean number of alleles per locus was 17.5. Observed heterozygosity (HO) and expected heterozygosity (HE) were 0.777 and 0.800, respectively. Pollination of mother trees was not by nearest neighbors, and a paternity of 60.7% of offspring evaluated could not be assigned to a local, sampled tree. Pollen flow from cultivated trees to wild trees was infrequent (5.4%), and selfing rates ranged from zero to 25.0%. Male parents were located from 0 to 1005 m from their female partners, with an average pollination distance of 285.1 m. These results are discussed in light of the cultivated species' diversity, outlining the frequent spontaneous genetic contributions from the wild to the cultivated compartment. In addition, the pollen flow parameters provide useful information about the dynamics of pollen movement within J. regia populations.

Highlights

Mating patterns, including pollen dispersal, gene flow, and the movement of genes among lineages, play an important role in the evolution of organisms by shuffling the genetic diversity and structure within species (Jones et al 2008)
We investigated gene flow between wild and cultivated common walnut trees in the Qinling Mountains of China, a region believed to contain an ancient population of J. regia (Cheng et al 2013; Guo et al 2013)
To characterize the genetic diversity of cultivated common walnuts, we sampled seeds from trees planted by farmers in 16 locations around the Qinling Mountains, Shaanxi province, China (Table 1, Fig. 1)

Summary

Introduction

Mating patterns, including pollen dispersal, gene flow, and the movement of genes among lineages, play an important role in the evolution of organisms by shuffling the genetic diversity and structure within species (Jones et al 2008). Genetic invasion between wild species and cultivars by pollen dispersal, seed dispersal, and hybridization has played an important role in plant evolutionary history, especially the domestication of trees as crops (Miller and Gross 2011; Delplancke et al 2013). In other cases, cultivated plant species have been selected for non-competitiveness or are less robust because of genetic bottlenecks caused by long-term cultivation (Miller and Gross 2011; Delplancke et al 2012), but these phenotypes and domestication bottlenecks are often much less pronounced in perennial tree crops

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