Role of Root and Stem Base Fungi in Fraxinus angustifolia (Vahl) Dieback in Croatian Floodplain Forests

Abstract

Large-scale ash (Fraxinus spp.) dieback caused by the fungus Hymenoscyphus fraxineus has been a major concern throughout Europe for more than two decades. Most of the related research has been focused on Fraxinus excelsior L., and there is still little information on fungal involvement in the dieback of Fraxinus angustifolia Vahl, especially in roots and stem bases, which play an important role in decline progress and tree stability. The objectives of this study were to identify fungi present in visually healthy and symptomatic wood tissues in basal parts of narrow-leaved ash trees in different decline phases, in order to determine the possible role of these fungi and their importance in the dieback process. The stem bases and roots of 90 trees in three different health categories, determined based on crown defoliation, were sampled in natural stands affected by ash dieback. Isolated fungal cultures were identified based on the rDNA ITS (Internal transcribed spacer) region and their association with tree health status was analyzed. In total, 68 different fungal taxa were confirmed, including Hymenoscyphus fraxineus and Armillaria spp., which were mainly present in roots, although overall in lower frequencies than on common ash in other studies. Most frequently isolated fungal taxa, which encompassed 51% of all obtained isolates, were Trichoderma spp., Ilyonectria robusta, Fusarium solani, Cladosporium cladosporioides, and Diaporthe cotoneastri. Their associations with tree health categories and presence in both symptomatic and visually healthy wood indicate that they act as opportunistic pathogens and early colonizers of weakened ash tissues. Research also revealed that, although the extent of crown defoliation and presence of root and stem necroses were associated, basal symptoms occurred on a number of trees with healthy looking crowns, meaning they can develop independently.

Development of Neonectria punicea Pathogenic Symptoms in Juvenile Fraxinus excelsior Trees

“…To our knowledge, this is the first report of N. punicea on common ash trees in B&H. N. punicea has a wide host range, and it was previously reported in multiple hosts in Europe, Asia, and North America ( Booth, 1959 ; Hirooka et al, 2013 ; Langer, 2017 ). This fungus has also been reported in common ash in Germany ( Langer, 2017 ; Meyn et al, 2019 ) and recently in the narrow-leaved ash in neighboring Croatia ( Kranjec Orlović et al, 2020 ). In B&H, N. punicea ( Nectria punicea var.…”

Pathogenic fungi and oomycetes causing dieback on Fraxinus species in the Mediterranean climate change hotspot region

“…Other studies have shown a frequent association of declining ash trees with secondary root pathogens such as Armillaria spp. (Lygis et al, 2005;Skovsgaard et al, 2010;Langer, 2017;Kranjec Orlović et al, 2020;Peters et al, 2023).…”

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

“…However, more recent studies have revealed that ash decline is more probably driven by a complex of multiple interacting factors, including other fungal species, which contribute to and accelerate this process [5,6]. Ash trees are asymptomatically colonized by a variety of endophytic fungi, which can become opportunistic pathogens and spread in weakened tissue, especially when the host undergoes vitality loss caused by biotic or abiotic stresses [7][8][9][10][11].…”