Abstract
In this study, twenty marine-derived fungi were evaluated for their antagonistic activities against 10 economically important plant pathogenic fungi and investigated for their halo tolerance on potato dextrose agar (PDA) amended with 1%-25% NaCl. The results of dual culture tests showed that the marine Trichoderma species, T. asperellum and T. harzianum exhibited higher antagonistic effects against all plant pathogens than the other tested fungi, causing percentages of mycelial growth inhibition ranging from 59.31-100%. The results of dilution plate assays revealed that crude extracts of marine-derived fungi in the genera Emericella, Myrothecium, Neocosmospora, Penicillium and Talaromyces displayed great antifungal activity against plant pathogenic fungi at a low concentration of 1 g/L. However, the crude extract of Myrothecium verrucaria showed the best antifungal activity: more than 52% inhibition of five of the tested species of plant pathogenic fungi and complete mycelial growth inhibition of Bipolaris oryzae and Lasiodiplodia theobromae at 1 g/L. All of the tested marine-derived fungi were tolerant to NaCl at concentrations up to 7%. These results revealed marine-derived fungi possess exploitable antagonistic activities against plant pathogenic fungi through antibiosis, competition for nutrients and space and halo tolerance. Moreover, the results from this study showed their potential as novel BCAs for supporting crop production under climatic changes in the future.
Highlights
The disadvantages of commercial synthetic fungicides in both organic and conventional farming have led to attempts to find new strategies for controlling plant diseases[1,2]
Seven of these pathogenic fungi belonged to Ascomycetes (Alternaria brassicicola, Bipolaris oryzae, Colletotrichum capsici, C. gloeosporioides, Fusarium oxysporum, Lasiodiplodia theobromae and Pyricularia oryzae), one to Oomycetes (Phytophthora palmivora) and two to Agonomycetes (Rhizoctonia solani and Sclerotium rolfsii)
The results on the antagonistic effects of the rest of the selected marine-derived fungi against plant pathogenic fungi belonging to Ascomycetes revealed that ten of the tested fungi displayed potent (> 50% inhibition) antagonistic effect against at least one pathogen belonging to this class
Summary
The disadvantages of commercial synthetic fungicides in both organic and conventional farming have led to attempts to find new strategies for controlling plant diseases[1,2]. Biological control agents are currently held to be a very promising strategy for plant disease management due to their being eco-friendly and non-toxic to consumers and farmers[3,4]. Finding novel BCAs is required to combat plant disease outbreaks and over come plant pathogen resistance to fungicides. Marine invertebrates present a rich source of bioactive metabolites[5,6]. They are the major hosts of symbiotic microorganisms such as actinomyces, bacteria and fungi[7,8]. Marine-derived fungi are often associated with marine organisms and substrata such as sponges, corals, tunicates, higher algae, sea grasses, mangroves, molluscs, woody substrates and drift wood . 9,10
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