Drought Stress Can Induce the Pathogenicity of Cryptostroma corticale, the Causal Agent of Sooty Bark Disease of Sycamore Maple

Abstract

Reports of sooty bark disease of maples caused by the fungus Cryptostroma corticale have recently been emerging from across Europe. The aims of our study were to describe the first report of sooty bark disease in Slovenia, to determine the pathogenicity of C. corticale, to confirm the optimum temperature for the growth of the fungus, and to determine the mass loss of Acer pseudoplatanus wood inoculated by C. corticale. We confirmed the presence of C. corticale on A. pseudoplatanus via morphological and molecular analysis. The optimal growth of C. corticale was measured in vitro on potato dextrose agar and was determined to occur at 25 °C. Pathogenicity tests were performed on 30 saplings of A. pseudoplatanus under two treatments, humid and drought stress, and the fungus was pathogenic in both treatments. The mean length of bark lesions and wood discoloration of the drought-stressed saplings was significantly greater than that in the humid treatment. Re-isolations of C. corticale were successful from all inoculated saplings, and thus Koch’s postulates were confirmed. The mass loss of A. pseudoplatanus wood was determined by mini-block test in a period of 10 weeks and was observed as minimal. Based on the results, we conclude that C. corticale is a weak and opportunistic pathogen that most likely expresses itself intensively under hot and dry conditions.

Fungi associated with woody tissues of Acer pseudoplatanus in forest stands with different health status concerning sooty bark disease (Cryptostroma corticale)

“…Our result that 26% of all studied, apparently healthy sycamores, harboured C. corticale non-symptomatically, regardless of the occurrence of external symptoms in the studied forest stands or area, lead to the assumption that latent infection with C. corticale is widespread in Germany. Therefore the risk of mortality due to C. corticale for apparently healthy sycamore trees rises with the increase of years with drought and extraordinary high temperatures, since SBD is triggered by drought and hot temperatures (Dickenson 1980;Ogris et al 2021). Even though only vital trees with no signs of distress or injury were chosen for our sampling, 35% of the increments exhibited wood discoloration and/or wood rot.…”

Applications of a conceptual framework to assess climate controls of forest tree diseases

“…Similar dual effects of climate influence on the host and pathogen could be anticipated for many stress‐related diseases (e.g. some Armillaria root diseases (Sturrock et al, 2011; Wargo & Harrington, 1991), sooty‐bark disease of maple ( Cryptostroma corticale , Ogris et al, 2021), pitch canker ( Fusarium circinatum , Elvira‐Recuenco et al, 2021; Swett et al, 2016), Hypoxylon canker of poplar, and bacterial leaf scorch, caused by Xylella fastidiosa . For insects, bark beetles are known to increase their populations and related damage during the combination of warm conditions that enhance overwintering success (in some cases, number of generations per year) and periods of increased vulnerability of trees facilitated by drought or other stress (Bentz et al, 2010).…”

Endophytic community in juvenile Acer pseudoplatanus and pathogenicity of Cryptostroma corticale and other associated fungi under controlled conditions

“…Ju family (Ju et al 1998;Koukol et al, 2014). As expected from a xylarialean fungus, C. corticale also shows a potential for wood degradation (Ogris et al 2021). The closest relatives are species of Biscogniauxia Kuntze and Graphostroma Piroz.…”

“…In comparison, in our study 22% of the re-isolates were identified as C. corticale. Additionally, Ogris et al (2021) isolated Fusarium sp. (13.7%) and Alternaria sp.…”