New insights in the recognition of the European ash species Fraxinus excelsior L. and Fraxinus angustifolia Vahl as useful tools for forest management

Abstract

Common ash (Fraxinus excelsior L.) and narrow-leaved ash (F. angustifolia Vahl) are the most common ash species in Western Europe. The former is considered to be a highly valuable timber tree and contamination of its seed lots by the latter is strongly undesirable. We studied molecular, physiological and morphological characteristics that can help to detect the presence of F. angustifolia at the population level, either in seed and/or seedling samples, or in adult ash leave samples from natural or managed populations. First we developed two molecular markers, which correspond to a RAPD-SCAR marker and a nuclear microsatellite-derived marker. Results indicate that these markers are almost specific to one or the other species for a set of populations sampled across Europe. Second, first year dormancy was studied using germination tests without stratification. F. excelsior seeds did not germinate at all, while germinations were observed in samples of F. angustifolia and introgressed populations after 16 weeks. In addition, F. angustifolia embryo/seed length ratios at the dispersal stage were significantly higher than those from F. excelsior populations. This study provides straightforward and robust tools for avoiding commercial problems of impurity of seed lots and can help forest managers to certify common ash stands. © INRA, EDP Sciences, 2006.