Fungi Detected in the Previous Year’s Leaf Petioles of Fraxinus excelsior and Their Antagonistic Potential against Hymenoscyphus fraxineus

Abstract

Studies on fungal communities in the previous year’s leaf petioles of Fraxinus excelsior found in litter in five ash stands in southern Poland were made in 2017. Fungi were identified on the basis of isolation from 300 surface sterilized leaf petioles and by in situ inventory of fruit bodies (on 600 petioles, in spring and autumn). Identification was based on morphology of colonies and fruit bodies, and sequencing of ITS region of the rRNA gene cluster. In total, 2832 isolates from 117 taxa (Ascomycota—100; Basidiomycota—15; Mucoromycota—2 taxa) were obtained with the isolation method. The most frequent taxa (with frequency >10%) were: Nemania serpens, Hymenoscyphus fraxineus, Alternaria sp. 1, Boeremia sp., Helotiales sp. 1, Epicoccum nigrum, Venturia fraxini, Fusarium sp., Fusarium lateritium, Nemania diffusa, Typhula sp. 2 (in descending order). In total, 45 taxa were detected with the in situ inventory method. Eleven taxa were classified as dominant: Hymenoscyphus fraxineus, Venturia fraxini, Leptosphaeria sp. 2, Cyathicula fraxinophila, Typhula sp. 2, Hypoderma rubi, Pyrenopeziza petiolaris, Cyathicula coronata, Hymenoscyphus scutula, Leptosphaeria sclerotioides and Hymenoscyphus caudatus. Among 202 leaf petioles colonized by H. fraxineus, 177 petioles also showed fructification of 26 other fungi. All the isolated saprotrophs were tested in dual-culture assay for antagonism to two strains of H. fraxineus. Three interaction types were observed: type A, mutual direct contact, when the two fungi meet along the contact line (occurred with 43.3% of test fungi); type B, with inhibition zone between colonies (with 46.9% of test fungi); type C, when the test fungus overgrows the colony of H. fraxineus (with 9.8% of test fungi). The possible contribution of the fungal saprotrophs in limiting of the expansion of H. fraxineus in ash leaf petioles, which may result in reduction in the inoculum of ash dieback causal agent, is discussed.

Priming of Resistance-Related Phenolics: A Study of Plant-Associated Bacteria and Hymenoscyphus fraxineus

“…Recent studies have reported ash endophytes that may contribute to tree vitality through antagonisms against H. fraxineus in vitro [21,36,53,69,70].…”

Fungal Communities in Re-Emerging Fraxinus excelsior Sites in Lithuania and Their Antagonistic Potential against Hymenoscyphus fraxineus

“…Cladosporium sp. in our tests was not only among the fungi showing the strongest reaction of inhibition of H. fraxineus , but it also was able to show the overgrowth of H. fraxineus , suggesting the potential antagonism in nature [ 9 ]. On the other hand, A. pullulans and Cladosporium sp.…”

“…Antagonistic reaction of isolated fungi against H. fraxineus strains, which were also isolated during this study, was assessed using dual-culture assays and by evaluating the pattern and growth rate of H. fraxineus [ 9 , 10 ]. Petri dishes containing Hagem agar medium were pre-inoculated with an agar plug (5 × 5 mm) of respective H. fraxineus strains and left for 5 days at room temperature in the dark.…”

Culturable Endophytic Fungi in Fraxinus excelsior and Their Interactions with Hymenoscyphus fraxineus

“…An endophytic isolate of Trichoderma koningiopsis from Hevea guianensis inhibited the causal agent of Corynespora leaf fall disease (Corynespora cassiicola), both in culture and in plants [26]. Several studies have already been published on the endophytic microbiome of ash in recent years, and the protective effects of some endophytic fungi against the ash dieback pathogen have also been studied [27][28][29][30][31][32][33][34]. Although endophytes that inhibit H. fraxineus in vitro (e.g., Boeremia exigua, Botrytis cinerea, Clonostachys rosea, Epicoccum nigrum, Nemania diffusa, N. serpens, Peniophora cinerea, Phoma macrostoma, Rosellinia corticium, Setomelanomma holmii, and Xylaria polymorpha) [28,29,34] are promising candidates for a biocontrol agent for ash dieback, their efficacy should be verified by in planta tests because the in planta situation is more complex [35].…”