Seasonal development of lesions caused by Hymenoscyphus fraxineus on young Fraxinus excelsior trees in Latvia

AbstractSince the early 1990s, ash dieback due to the invasive ascomycete Hymenoscyphus fraxineus is threatening Fraxinus excelsior in most of its natural range. Previous studies reported significant levels of genetic variability for susceptibility in F. excelsior either in field or inoculation experiments. The present study was based on a field experiment planted in 1995, fifteen years before onset of the disease. Crown and collar status were monitored on 788 trees from 23 open-pollinated progenies originating from 3 French provenances. Susceptibility was modeled using a Bayesian approach where spatio-temporal effects were explicitly taken into account. Moderate narrow-sense heritability was found for Crown Dieback (CD, h2=0.42). This study is first to show that Collar Lesions are also heritable (h2=0.49 for prevalence and h2=0.42 for severity) and that there is significant genetic correlation (r=0.40) between the severities of both symptoms. There was no evidence for differences between Provenances. Family effects were detected, but computing Individual Breeding Values (IBV) showed that most of the genetic variation lies within families. In agreement with previous reports, early flushing correlates with better crown status. Consequences of these results in terms of management and breeding are discussed.

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Estimating mortality rates of European ash ( Fraxinus excelsior ) under the ash dieback ( Hymenoscyphus fraxineus ) epidemic

Plants People Planet ◽

10.1002/ppp3.11 ◽

2018 ◽

Vol 1 (1) ◽

pp. 48-58 ◽

Cited By ~ 27

Author(s):

Tim L. R. Coker ◽

Jiří Rozsypálek ◽

Anne Edwards ◽

Tony P. Harwood ◽

Louise Butfoy ◽

...

Keyword(s):

Mortality Rates ◽

Fraxinus Excelsior ◽

Ash Dieback ◽

Hymenoscyphus Fraxineus ◽

European Ash

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Rising Out of the Ashes: Additive Genetic Variation for Crown and Collar Resistance to Hymenoscyphus fraxineus in Fraxinus excelsior

Phytopathology ◽

10.1094/phyto-11-15-0284-r ◽

2016 ◽

Vol 106 (12) ◽

pp. 1535-1543 ◽

Cited By ~ 22

Author(s):

Facundo Muñoz ◽

Benoît Marçais ◽

Jean Dufour ◽

Arnaud Dowkiw

Keyword(s):

Genetic Variation ◽

Health Status ◽

Fraxinus Excelsior ◽

Narrow Sense ◽

Narrow Sense Heritability ◽

Ash Dieback ◽

Family Effects ◽

Hymenoscyphus Fraxineus ◽

Natural Range ◽

Crown Dieback

Since the early 1990s, ash dieback due to the invasive ascomycete Hymenoscyphus fraxineus is threatening Fraxinus excelsior in most of its natural range. Previous studies reported significant levels of genetic variability in susceptibility in F. excelsior either in field or inoculation experiments. The present study was based on a field experiment planted in 1995, 15 years before onset of the disease. Crown and collar status were monitored on 777 trees from 23 open-pollinated progenies originating from three French provenances. Health status was modeled using a Bayesian approach where spatiotemporal effects were explicitly taken into account. Moderate narrow-sense heritability was found for crown dieback (h2 = 0.42). This study is first to show that resistance at the collar level is also heritable (h2 = 0.49 for collar lesions prevalence and h2 = 0.42 for their severity) and that there is significant genetic correlation (r = 0.40) between the severities of crown and collar symptoms. There was no evidence for differences between provenances. Family effects were detected, but computing individual breeding values showed that most of the genetic variation lies within families. In agreement with previous reports, early flushing correlates with healthier crown. Implications of these results in disease management and breeding are discussed.

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Growth and wood anatomical adjustments of Fraxinus excelsior to the infestation of the invasive fungus Hymenoscyphus fraxineus

10.5194/egusphere-egu2020-22520 ◽

2020 ◽

Author(s):

Stefan Klesse ◽

Georg von Arx ◽

Martin Gossner ◽

Christian Hug ◽

Andreas Rigling ◽

...

Keyword(s):

Turgor Pressure ◽

Ring Width ◽

Late Summer ◽

Mortality Rates ◽

Fraxinus Excelsior ◽

Climate Conditions ◽

Vessel Size ◽

Hymenoscyphus Fraxineus ◽

Crown Health ◽

Crown Dieback

Since the 1990s the invasive fungus Hymenoscyphus fraxineus has led to severe crown dieback and high mortality rates in Fraxinus excelsior in Europe. In addition to a strong genetic control of tolerance to the fungus, previous studies have found high landscape variability in the severity of dieback symptoms. However, apart from heat and humidity-related climate conditions favoring fungal development the mechanistic understanding of why smaller or slower growing trees are more susceptible to dieback remains less well understood.Here, we analyzed three stands in Switzerland with a unique setting of eight years of intra-annual diameter growth and annual crown health assessments, together with ring-width and quantitative wood anatomical measurements preceding the monitoring, to investigate if wood anatomical adjustments can help better explaining the size-related dieback phenomenon.We found that slower growing trees or trees with smaller crowns already before the arrival of the fungus were more susceptible to dieback and mortality. We show that defoliation directly reduces growth as well as maximum earlywood vessel size, and that the positive relationship between vessel size and growth rate causes a positive feedback amplifying crown dieback. Because leaf necrosis happens during late summer when ring formation has already finished, photosynthesis is heavily reduced during a time when non-structural carbohydrates (NSCs, sugars and starch) are stored. Thus, we hypothesize that a lack of NSCs (mainly sugars) leads to lower turgor pressure and smaller earlywood vessels in the next year impeding efficient water transport and photosynthesis, and is responsible why smaller and slower growing trees show stronger symptoms of dieback and higher mortality rates.

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Amplifying feedback loop between growth and wood anatomical characteristics of Fraxinus excelsior explains size-related susceptibility to ash dieback

Tree Physiology ◽

10.1093/treephys/tpaa091 ◽

2020 ◽

Cited By ~ 1

Author(s):

Stefan Klesse ◽

Georg von Arx ◽

Martin M Gossner ◽

Christian Hug ◽

Andreas Rigling ◽

...

Keyword(s):

Landscape Heterogeneity ◽

Turgor Pressure ◽

Ring Width ◽

Mortality Rates ◽

Data Availability ◽

Fraxinus Excelsior ◽

Ash Dieback ◽

Vessel Size ◽

Hymenoscyphus Fraxineus ◽

Crown Dieback

Abstract Since the 1990s the invasive fungus Hymenoscyphus fraxineus has caused severe crown dieback and high mortality rates in Fraxinus excelsior in Europe. In addition to a strong genetic control of tolerance to the fungus, previous studies have found landscape heterogeneity to be an additional driver of variability in the severity of dieback symptoms. However, apart from climatic conditions related to heat and humidity influencing fungal infection success, the mechanistic understanding of why smaller or slower-growing trees are more susceptible to dieback remains less well understood. Here, we analyzed three stands in Switzerland with a unique setting of 8 years of data availability of intra-annual diameter growth and annual crown health assessments. We complemented this by ring width and quantitative wood anatomical measurements extending back before the monitoring started to investigate if wood anatomical adjustments can help better explain the size-related dieback phenomenon. We found that slower-growing trees or trees with smaller crowns already before the arrival of the fungus were more susceptible to dieback and mortality. Defoliation directly reduced growth as well as maximum earlywood vessel size, and the positive relationship between vessel size and growth rate caused a positive feedback amplifying and accelerating crown dieback. Measured non-structural carbohydrate (NSC) concentrations in the outermost five rings did not significantly vary between healthy and weakened trees, which translate into large differences in absolute available amount of NSCs. Thus, we hypothesize that a lack of NSCs (mainly sugars) leads to lower turgor pressure and smaller earlywood vessels in the following year. This might impede efficient water transport and photosynthesis, and be responsible for stronger symptoms of dieback and higher mortality rates in smaller and slower-growing trees.

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