Canadian Forest Service Publications
When exotic poplars and native Populus balsamifera L. meet on the Canadian Prairies: Spontaneous hybridization and establishment of interspecific hybrids. 2012. Talbot, P.; Schroeder, W.R.; Bousquet, J.; Isabel, N. For. Ecol. Manag. 285:142-152.
Available from: Laurentian Forestry Centre
Catalog ID: 34078
Available from the Journal's Web site. †
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As the interest in plantations of fast-growing tree species increases, concerns regarding the possibility of gene flow between plantations of exotic trees and their wild relatives are being raised. In Canada, the Prairie ecozone provides a unique opportunity to examine spontaneous hybridization and the spread of exotic genetic material because of the historical introduction of large numbers of exotic poplar species and their hybrids. In this region, poplar shelterbelts bearing exotic components such as Populus laurifolia Ledeb. and Populus nigra L. have been in contact with the native populations of Populus balsamifera L. since the 19th century. Given the ability for poplar species to hybridize, the objective of this study was to estimate the rates of spontaneous hybridization between one common poplar cultivar planted in shelterbelts, ♂‘Assiniboine’ (♀‘Walker’[♀Populus deltoides Marsh. x ♂(P. laurifolia x P. nigra)] x ♂P. deltoides), and its neighbouring native congener, ♀P. balsamifera, on two study sites. To distinguish the genetic contributions of the species under study, a set of 26 diagnostic single nucleotide polymorphisms (SNPs) representative of 23 genes was used. We genotyped 2116 seeds sampled from P. balsamifera and identified paternal alleles specific to P. laurifolia, P. nigra and P. deltoides, which are typical genetic components of poplar shelterbelts. Surprisingly, the highest hybridization rate (2.3%) was observed at the site where 100-year-old Russian poplar shelterbelts (P. laurifolia x P. nigra) were found. A preliminary study of the P. balsamifera stands established in an 8 km radius around the study site confirmed introgression of P. laurifolia and P. nigra alleles at a rate of 4.6%. These results indicate that spontaneous hybridization between shelterbelts of exotic cultivars and native P. balsamifera does occur in the Canadian Prairies and that interspecific hybrids can establish and survive in this landscape. This study suggests that biological factors such as the genetic composition of the native population and the gender of the exotic cultivars should be taken into consideration in the management strategies of this ecozone.
Plain Language Summary
In the Canadian Prairies, balsam poplars grow in patches, and this habitat fragmentation affects the ecology of the species. Do these native poplars naturally cross with the exotic poplars often used as windbreaks? Because genetics make it possible to identify the parents of a hybrid, researchers were able to answer this question and determine that the rate of hybridization between native and exotic poplars is 2% or less.
The researchers extended their work to other populations and discovered that the success of hybridization is largely attributable to the seeds of female exotic poplars. The potential hybridization zone is therefore reduced, as the pollen from male trees has a higher dispersion capability than the seeds of the female.
Studying herbarium specimens has confirmed that exotic characteristics have been present in Western Canadian balsam poplars for 40 years.
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