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

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 (H_O) and expected heterozygosity (H_E) 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.

Keywords

Genetic diversity / Juglans regia / Mating patterns / Microsatellites / Pollen flow

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