Asymmetrical natural hybridization betweenPopulus deltoidesandP.balsamifera(Salicaceae)This note is one of a selection of papers published in the Special Issue on Poplar Research in Canada.

Abstract

Natural hybridization has long been recognized as a means for gene flow between species and has important evolutionary consequences. Although hybridization is generally considered to be symmetrical, with both hybridizing species being equally likely to be the male or female parent, several studies have demonstrated the presence of asymmetrical hybridization and introgression from one species to the other. We investigated the direction of natural hybridization between two sympatric forest tree species in North America ( Populus deltoides Bartr. ex Marsh. and Populus balsamifera L.) using species-specific single nucleotide polymorphism (SNP) markers in both the nuclear and chloroplast genomes. All natural hybrid individuals, identified from morphological traits, had nuclear alleles corresponding to both parental species, while the chloroplast genotypes showed similarity to P. deltoides, indicating asymmetrical hybridization with P. deltoides as the maternal and P. balsamifera as the paternal donor species. This observed asymmetrical hybridization may be attributable to cytonuclear interactions.

Trees of the people: the growing science of poplars in Canada and worldwideThis commentary is one of a selection of papers published in the Special Issue on Poplar Research in Canada.

“…Developing cost-effective, efficacious molecular markers to reliably distinguish species and their hybrids is an important first step to enable studies of systematics, taxonomy, population genetics, and evolutionary ecology. Contemporary molecular genetics approaches that take advantage of the P. trichocarpa genome sequence are shedding new light on hybridization in Populus and gene flow between species and populations, as described in Meirmans et al (2007) and Hamzeh et al (2007). In their article, Temmel et al (2007) also take advantage of the genome sequence to examine the genomic region in P. trichocarpa that corresponds to a putatively sex-linked locus in Salix.…”

Variation of Traits on Seeds and Germination Derived from the Hybridization between the Sections Tacamahaca and Aigeiros of the Genus Populus

“…Intersectional hybridization plays an important role in the genetic improvement of the species of the genus Populus and wide hybridization easily contributes to hybrid incompatibility and hybrid sterility, but it is a way to produce transgressive hybrids. Cross-incompatibility usually occurs in wide hybridization and it generally takes place as the dropping of flowers and fruits, low seed set, shriveled seeds, and low seed formation percentage [66][67][68]. In our study, the combinations which had P. deltoides as the male parent had a low seed formation percentage and seed set, shriveled seeds, and low seed germination rate, some having no collected seed.…”

“…Meanwhile, Mahama et al [68] pointed out that the crosses involving male P. deltoides and female P. maximowiczii were less successful and rarely acquired seedlings. However, when P. deltoides was taken as the female and some species of section Tacamahaca were taken as male, the crosses showed a high success rate, obtaining many seedlings [33,66,67]. The results in our research suggested that cross-incompatibility was occurring.…”

A second-generation diagnostic single nucleotide polymorphism (SNP)-based assay, optimized to distinguish among eight poplar (Populus L.) species and their early hybrids

“…Adding to this complexity, trihybrids (crosses involving three different species) and more complex combinations have been developed and deployed in Populus-breeding programs (e.g., Meirmans et al 2010;Talbot et al 2011) and have been detected in nature (Thompson et al 2010;Talbot et al 2012;Williams et al, unpublished). Molecular diagnostics, including AFLP (Cervera et al 2005), DNA sequencing (Hamzeh and Dayanandan 2004) combined with RFLP , microsatellites (Liesebach et al 2010), and mediumthroughput single nucleotide polymorphism (SNP)-based genotyping assays (Hamzeh et al 2007;Meirmans et al 2007; Thompson et al 2010;Talbot et al 2011) have been used to diagnose poplar species and hybrids with success.…”