Abstract
The ten most frequently isolated fungi from the wood of the dead branches of Acer pseudoplatanus L. were tested in dual cultures to evaluate their in vitro antagonistic activity against Eutypella parasitica R.W. Davidson and R.C. Lorenz, the causative agent of a destructive disease of maples in Europe and North America. The tested fungi, treated also as challenge isolates, were Diaporthe sp., Eutypa sp., Eu. maura, E. parasitica, Fusarium avenaceum, Neocucurbitaria acerina, Neonectria sp., Peniophora incarnata, Petrakia irregularis, and Phomopsis pustulata. The antagonistic ability of each challenge isolate was evaluated by calculating an index of antagonism (AI) based on the interaction type in the dual cultures. The results of competition between the fungal isolates were quantified after re-isolations from the interaction zone (s). The dual cultures revealed two main types of competitive interactions: Deadlock, consisting of mutual inhibition after mycelial contact or at a distance, and replacement, reflecting in the inhibition of E. parasitica, followed by partial overgrowth by the replacing fungus. Statistical analysis showed significant differences in average AI and s of challenge isolates between different dual culture assays. Based on the results of the antagonism index, Eutypa sp., Eu. maura, Neonectria sp., and P. incarnata had the highest inhibitory effect on E. parasitica growth and were recognized as the most promising candidates for further biocontrol studies of E. parasitica. The mycelium of E. parasitica at the interaction zones remained mostly viable, except in dual cultures with Eutypa sp., F. avenaceum, and Neonectria sp., where re-isolations did not yield any colony of the E. parasitica isolate. Based on the results, we assume that E. parasitica is a weak competitor, which invests less energy in direct mycelial competition. We discuss the potential of the observed antagonists as a possible biocontrol of Eutypella canker of maple. Nevertheless, additional experiments should be performed for a solid conclusion about competitive ability of E. parasitica and usefulness of antagonists as biocontrol.
Highlights
Interactions play a significant role in shaping the community structure of fungal organisms [1].They are an important determinant of the distribution, growth pattern, and abundance of fungal species in any natural fungal community [2,3] and can be used for developing biocontrol strategies.Interactions in the natural environment are complex [1] and have been studied using a variety of Forests 2020, 11, 1072; doi:10.3390/f11101072 www.mdpi.com/journal/forestsForests 2020, 11, 1072 techniques, including observations of hyphal interactions, tests of inhibition on hyphal growth, and examination of reaction types [3]
Macroscopic examination of dual cultures revealed that almost all challenge isolates made hyphal contact with the response isolate, i.e., E. parasitica, within the time of the experiment
In four assays we found an interaction in which Eutypa sp., Eu. maura, Neonectria sp., and P. incarnata partially replaced E. parasitica after initial deadlock with mycelium contact (Figure 2b,c,f,g)
Summary
Interactions play a significant role in shaping the community structure of fungal organisms [1].They are an important determinant of the distribution, growth pattern, and abundance of fungal species in any natural fungal community [2,3] and can be used for developing biocontrol strategies.Interactions in the natural environment are complex [1] and have been studied using a variety of Forests 2020, 11, 1072; doi:10.3390/f11101072 www.mdpi.com/journal/forestsForests 2020, 11, 1072 techniques, including observations of hyphal interactions, tests of inhibition on hyphal growth, and examination of reaction types [3]. Interactions play a significant role in shaping the community structure of fungal organisms [1]. They are an important determinant of the distribution, growth pattern, and abundance of fungal species in any natural fungal community [2,3] and can be used for developing biocontrol strategies. The outcome of interspecific fungal interactions depends on species compatibility [11], as well as the microclimate and physio-chemical structure of the substrate [12]. The fungal interaction outcome is a complex phenomenon and may be one of the following: (1) Deadlock, i.e., neither isolate enters the territory of the other, or (2) replacement, i.e., one isolate is partially or entirely replaced by the other [13]. Deadlock usually occurs due to each isolate excreting and/or detecting "non-native"
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