Biological control of toxigenic citrus and papaya‐rotting fungi by Streptomyces violascens MT7 and its extracellular metabolites

Abstract

An Indian indigenous, Loktak Lake soil isolate Streptomyces violascens MT7 was assessed for its biocontrol potential both in vitro and in vivo against toxigenic fruit-rotting fungi. Strain MT7 exhibited broad-spectrum antifungal activity against various pathogenic postharvest fungi of citrus and papaya. In shake-flask fermentation, antagonist S. violascens MT7 highly produced extracellular antifungal metabolites in early stationary growth phase in glucose-yeast extract-malt extract (M93) broth. Both extracellular culture fluid (ECF) and its n-butanol extract showed significant broad-spectrum fungal mycelial inhibition of several tested fruit-rotting fungi. Antifungal metabolite was found to be heat stable, nonpeptidic, and polyene type antibiotic. The lowest minimum inhibitory concentration (MIC) of n-butanol extract against Colletotrichum gloeosporioides MTCC 9664 and Aspergillus niger MTCC 281 was 0.0312 and 0.0625 mg/ml, respectively. Purification of n-butanol extract through silica gel chromatography resulted in partial purification of bioactive metabolite and the TLC autobiography revealed the presence of single antifungal metabolite with Rf value of 0.755. In vivo bioassays demonstrated the biocontrol potential of tested biocontrol agents on fruit-rotting fungi. Use of cell suspension of S. violascens MT7, extracellular metabolite(s), and n-butanol extract significantly (p < 0.05) reduced sour-rot development on Citrus reticulata Blanco (oranges) and soft-rot development on papaya fruits. Therefore, these results strongly suggest a high potential for application of S. violascens MT7 and its extracellular metabolites as an effective eco-friendly alternative to synthetic fungicides for controlling toxigenic citrus and papaya-rotting fungi.

Biocontrol potential of Streptomyces sp. CACIS-1.5CA against phytopathogenic fungi causing postharvest fruit diseases

“…Also, Streptomyces alboflavus strain TD-1 produced volatiles that inhibited in vitro the storage fungi Fusarium moniliforme, Aspergillus flavus, A. ochraceus, A. niger, and Penicillium citrinum (Wang et al 2013). An indigenous soil isolate, Streptomyces violascens MT7 was assessed for its biocontrol potential under both in vitro and in vivo against various pathogenic postharvest fungi of citrus and papaya, Colletotrichum gloeosporioides, and A. niger (Choudhary et al 2015). Inhibition of mycelial growth of Botrytis cinerea, a major causal fungus of postharvest root rot of ginseng and strawberry gray mold disease, was induced by Streptomyces sp.…”

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“…24 However, the deterioration of the fruit could be delayed if conservation treatments are carried out during its pre and post-harvest. 25 There are technologies in post-harvest management of other fruits that are difficult to extrapolate to management of the papaya fruit, due to the fact that their genetic characteristics limit it. 26 The shelf life of papaya depends largely on post-harvest treatments, storage, packaging, and transportation.…”

“…Chemical fungicides are the most used to fight diseases due to their high effectiveness and low cost. 25 Prochloraz and Propiconazolebased fungicides have shown their effectiveness for that reason they are widely used to combat anthracnose. 37 The immersion of papayas in cinnamaldehyde with calcium chloride has been effective in protecting the fruit against Salmonella and Escherichia coli.…”

“…Some of the organisms used successfully as biological control are Pseudomonas syringae, Bacillus subtilis, Candida oleophila, Cryptococcus albidus and Streptomyces griseoviridis. 25 The use of Bacillus amyloliquefaciens PPCB004 in combination with 1-methylcyclopropane reduces significantly the incidence of disease and extends the shelf life of papaya. This last treatment could be used in the market of organic products.…”

Antagonistic microorganisms efficiency to suppress damage caused by Colletotrichum gloeosporioides in papaya crop: Perspectives and challenges

“…Extraction of antifungal compounds was carried out with five organic solvents, with n-butanol being the best at percentage of extraction and antifungal activity. Further analysis demonstrated that this antifungal compounds are of polyene nature (Choudhary et al, 2015). Landero-Valenzuela et al (2016) compiled information with different methods for controlling C. gloeosporioides in different fruits.…”