Investigations concerning the role of Chalara fraxinea in declining Fraxinus excelsior

Abstract

A study was carried out to clarify the role of the fungus Chalara fraxinea in decline of Fraxinus excelsior , which is observed on a large scale in central and northern Europe with high incidence of tree mortality. The aims of this work were: (i) to check for the presence of C. fraxinea in various tissues of declining F. excelsior by agar culture isolations and by direct analysis of plant tissues using molecular techniques (DNA extraction, ITS-PCR, cloning, ITS sequencing and T-RFLP); (ii) to study fungal communities inhabiting tissues with symptoms; and (iii) to test the pathogenicity of C. fraxinea to F. excelsior . Chalara fraxinea was isolated from 93% of stem cankers, 91% of necrotic leaf stalks, 27-28% of bark wounds and 30% of visually healthy leaf stalks. Molecular analyses of necrotic leaves, leaf stalks and bark revealed the presence of 25 different fungal taxa, 14 of which were detected in all three types of tissue sample. Chalara fraxinea was the second most common species (61% of samples), and only Cryptococcus foliicola occurred more often (70%). All eight of the tested C. fraxinea isolates induced necroses in bark and cambium on each of 86 inoculated trees, and all controls remained healthy. Average length of necroses caused by different C. fraxinea strains varied from 4·2 to 8·9 cm, but the differences were statistically insignificant. Instead, differences in resistance of individual trees to C. fraxinea were observed.

Fungi on stems and twigs in initial and advanced stages of dieback of European ash (Fraxinus excelsior) in Poland

“…Its role as the main pathogenic agent of the current ash dieback epidemic in Europe has been confirmed in this and several other studies and is beyond dispute (Kowalski 2006;Kowalski and Holdenrieder 2009b;Bakys et al 2009b;Husson et al 2011;Gross et al 2014). The necrotic lesions formed in the initial stage of disease on twigs and young side branches were typical, and similar to those described for H. fraxineus after natural infections (Kowalski and Holdenrieder 2008) and artificial inoculations (Kowalski and Holdenrieder 2009b;Bakys et al 2009a, b).…”

Chalara fraxinea - ash dieback in the Czech Republic

“…The pathogenicity of C. fraxinea has been demonstrated by inoculation experiments Bakys et al 2009;Kowalski & Holdenrieder 2009a). However, the ecological behavior of this pathogen and the process of canker formation are still enigmatic.…”

“…However, single genotypes of ash are tolerant against the infection (Bakys et al 2009). Therefore ash will probably survive in the long term, but its population may be significantly reduced over the course of several generations.…”

“…Many fungi occur on declining ash trees (e.g. Lygis et al 2005;Cech 2006), but the hyphomycete Chalara fraxinea has been recently determined to be the causal agent of this disease (Kowalski 2006(Kowalski , 2007Kowalski & Holdenrieder 2008, 2009aBakys et al 2009).…”

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

“…As a consequence of the increasing damage the research dealing with ash has also increased. The causative agent was identified in 2009 (KOWALSKI and HOLDENRIEDER, 2009;BAKYS et al, 2009b;QUELOZ et al, 2011) and methods to describe the disease stages in ash were developed later on (MCKINNEY et al, 2011a;LENZ et al, 2012a;. LENZ et al (2012a) described the status and the distribution of the disease for Bavaria.…”