Cryptostroma corticale and fungal endophytes associated with Fraxinus excelsior affected by ash dieback

Abstract

While assessing the filamentous fungi associated with woody tissues of stem collar rots, necroses, and lesions of European ash trees (Fraxinus excelsior) presenting symptoms of ash dieback in Germany, Cryptostroma corticale was recovered from three different ash trees. These isolated strains were the first report of C. corticale on ash and the first proof of an association of this plant pathogen with woody tissues of other tree species than Acer spp. in Germany. To test the pathogenicity of C. corticale against F. excelsior and to fulfil Koch’s postulates, inoculation tests in planta with strains isolated from Acer pseudoplatanus and F. excelsior were conducted according to Henle–Koch’s postulates in a greenhouse located in Göttingen. The pathogenicity tests were performed with apparently healthy ash saplings from June 2021 until January 2022. After three and seven months, neither necroses or lesions due to C. corticale nor disease symptoms were observed. Mostly, the inoculation wounds healed over, and C. corticale could not be re-isolated from the ash woody tissue. In an attempt to re-isolate the inoculated strains, the filamentous fungal endophytes of the ash woody tissues were isolated and identified. A total of 32 taxa of the Ascomycota were found, where the most common species was Boeremia exigua. Most frequently observed orders were Pleosporales (58.4%), followed by Sordariales (13.5%), Hypocreales (9.4%), and Diaporthales (8.7%). On average, 3.7 endophytic species were recorded on each sapling.

Fungal Presence and Changes of Wood Structure in Bark Stripping Wounds Made by Red Deer (Cervus elaphus L.) on Stems of Fraxinus angustifolia (Vahl)

“…The most frequently isolated taxa which colonized more than two stems were Boeremia spp., Clonostachys rosea, Fusarium spp., and Trichoderma spp., all of which are reported to be endophytes and potential opportunistic pathogens of ash. Boeremia isolates were found to be the most abundant fungi in necrotic common ash lenticels in [66], with the species B. lilacis and B. exigua reported to be endophytes with an ability to become pathogenic and cause minor damage to the host [8,66,67]. Clonostachys rosea has been isolated from both healthy and necrotic wooden tissues of common and narrow-leaved ash in previous studies [9,68], confirming its ability to spread in symptomatic tissue.…”