Assignment testing reveals multiple introduced source populations including potential ash hybrids (Fraxinus excelsior × F. angustifolia) in Ireland

Lack of genetic structure and evidence for long-distance dispersal in ash (Fraxinus excelsior) populations under threat from an emergent fungal pathogen: implications for restorative planting

“…However, such replanting should be carried out using native material from long-established, unplanted / unstocked woodlands, since recent studies have shown that material used for replanting in Ireland often contains individuals that possess alleles introgressed from the congeneric F. angustifolia (Thomasset et al 2013). …”

Thank you for not flowering: conservation genetics and gene flow analysis of native and non-native populations of Fraxinus (Oleaceae) in Ireland

“…The trees in each plantation were designated as F. angustifolia, F. excelsior or hybrid groups. Designation was based on previous multivariate morphological and molecular classification (Thomasset et al, 2013). Finally, we applied a non-parametric w 2 test to compare the numbers of seeds that were sired by plantation trees classified either as F. excelsior or as hybrid type.…”

“…Trees were sampled following transects that started at a random corner in each plantation, with trees that were closest to grid points spaced 30 m apart along the transects being sampled, in accordance with the sampling design described by Thomasset et al (2013). The position of each tree was recorded using GPS coordinates and leaf samples were excised as discs (1 cm diameter) and placed in 1:1 ethanol and acetone solution for 48 h. The leaf samples were drained and then air-dried in a laminar-flow cabinet, and finally stored in microcentrifuge tubes before DNA extraction.…”

“…Native trees were pollinated by both native and plantation trees, which included pollen donors that were assigned as hybrids (Thomasset et al, 2013). Trees identified as hybrids within the plantation sired 9 out of 19 offspring (47.4%) collected from native mother trees at Clonee.…”

“…In addition, the terminal buds were often pale in colour, brown rather than black and hence were more characteristic of the narrow-leaved ash, Fraxinus angustifolia. The ash plants that had been introduced into Ireland and that showed unusual morphology were identified using several molecular and morphological criteria as follows: (a) hybrid trees between F. excelsior and F. angustifolia, (b) pure F. angustifolia and (c) pure F. excelsior (Thomasset et al, 2013). Today, there are an unknown number of afforested sites in Ireland with suspected alien ash from the plantings made between 1992 and 2000.…”