Adaptive potential of ash (Fraxinus excelsior) populations against the novel emerging pathogenHymenoscyphus pseudoalbidus

Abstract

An emerging infectious pathogen Hymenoscyphus pseudoalbidus has spread across much of Europe within recent years causing devastating damage on European common ash trees (Fraxinus excelsior) and associated plant communities. The present study demonstrates the presence of additive genetic variation in susceptibility of natural F. excelsior populations to the new invasive disease. We observe high levels of additive variation in the degree of susceptibility with relatively low influence of environmental factors (narrow-sense heritability = 0.37–0.52). Most native trees are found to be highly susceptible, and we estimate that only around 1% has the potential of producing offspring with expected crown damage of <10% under the present disease pressure. The results suggest that the presence of additive genetic diversity in natural F. excelsior populations can confer the species with important ability to recover, but that low resistance within natural European populations is to be expected because of a low frequency of the hypo-sensitive trees. Large effective population sizes will be required to avoid genetic bottlenecks. The role of artificial selection and breeding for protection of the species is discussed based on the findings.

Impacts of climate change on plant diseases—opinions and trends

“…Genetic analyses will be instrumental in devising strategies to cope with an increased pressure from established and new diseases as a result of better suitability of the climatic conditions and/or more intense and farreaching trade (Bawa and Dayanandan 1998;Archie et al 2008;Jombart et al 2011). For example, there is genetic evidence that some ash trees (Fraxinus excelsior) in Denmark are resistant against the emerging fungal pathogen Chalara fraxinea (McKinney et al 2011;Kjaer et al 2012), which is now reported to cause ash dieback throughout Europe, from Poland to France and from Sweden to Switzerland (Bengtsson et al 2012;Gross et al 2012). For this pathosystem, there are also data on the genetic variability of the pathogen in lowland vs. highland Poland (Kraj et al 2012) and in the Åland islands, mainland Finland, Estonia and Latvia (Rytkönen et al 2011).…”

The susceptibility of Asian, European and North American Fraxinus species to the ash dieback pathogen Hymenoscyphus fraxineus reflects their phylogenetic history

“…European ash shows evident genetic variation in the level of susceptibility to shoot damage caused by H. fraxineus (Kirisits and Freinschlag 2012;Lobo et al 2014;McKinney et al 2011;Stener 2013), a feature that is inherited from parents to offspring (Kjaer et al 2012;Lobo et al 2015;Pliura et al 2011). The genetic mechanisms behind the differential field performance of individual trees in stands with epidemic levels of disease remain unknown.…”

Genetic analysis of European common ash (Fraxinus excelsior L.) populations affected by ash dieback

“…Within clonal trials in Sweden (STENER, 2013) and Denmark (MCKINNEY et al, 2011a;KJAER et al, 2011) strong genetic control of resistance against ash dieback was found. This was based upon the observation of artificially or naturally infected trees in common garden experiments that have shown clonal differences in infection intensity (MCKINNEY et al, 2011b).…”

“…After observing that some individuals were less affected by the disease than others systematic investigations on the resistance against the disease were started (MCKINNEY et al, 2011a;PLIURA et al, 2011;KJAER et al, 2011;STENER, 2013). Such investigations include the question whether the lower susceptibility of certain individuals might be in relation to genetics.…”