Abstract
An actinomycete strain, CB-75, was isolated from the soil of a diseased banana plantation in Hainan, China. Based on phenotypic and molecular characteristics, and 99.93% sequence similarity with Streptomyces spectabilis NBRC 13424 (AB184393), the strain was identified as Streptomyces sp. This strain exhibited broad-spectrum antifungal activity against 11 plant pathogenic fungi. Type I polyketide synthase (PKS-I) and non-ribosomal peptide synthetase (NRPS) were detected, which were indicative of the antifungal compounds that Streptomyces sp. CB-75 could produce. An ethyl acetate extract from the strain exhibited the lowest minimum inhibitory concentration (MIC) against Colletotrichum musae (ATCC 96167) (0.78 μg/ml) and yielded the highest antifungal activity against Colletotrichum gloeosporioides (ATCC 16330) (50.0 μg/ml). Also, spore germination was significantly inhibited by the crude extract. After treatment with the crude extract of Streptomyces sp. CB-75 at the concentration 2 × MIC, the pathogenic fungi showed deformation, shrinkage, collapse, and tortuosity when observed by scanning electron microscopy (SEM). By gas chromatography-mass spectrometry (GC-MS) of the crude extract, 18 chemical constituents were identified; (Z)-13-docosenamide was the major constituent. Pot experiments showed that the incidence of banana seedlings was reduced after using Streptomyces sp. CB-75 treatment. The disease index was 10.23, and the prevention and control effect was 83.12%. Furthermore, Streptomyces sp. CB-75 had a growth-promoting effect on banana plants. The chlorophyll content showed 88.24% improvement, the leaf area, root length, root diameter, plant height, and stem showed 88.24, 90.49, 136.17, 61.78, and 50.98% improvement, respectively, and the shoot fresh weight, root fresh weight, shoot dry weight, and root dry weight showed 82.38, 72.01, 195.33, and 113.33% improvement, respectively, compared with treatment of fermentation broth without Streptomyces sp. CB-75. Thus, Streptomyces sp. CB-75 is an important microbial resource as a biological control against plant pathogenic fungi and for promoting banana growth.
Highlights
Phytopathogenic fungi are most worrying, resulting in significant crop yield losses
The following test phytopathogenic fungi were used in the experiments: Fusarium oxysporum f. sp. cubense Race 1 (ATCC 76244); F. oxysporum f. sp. cubense Race 4 (ATCC 76255); Colletotrichum gloeosporioides (Penzig) (ATCC 58222); Colletotrichum fragariae Brooks (ATCC 58718); Colletotrichum acutatum Simmonds (ATCC 56815); Botrytis cinerea Persoon (ATCC 11542); Colletotrichum musae (ATCC 96167); Curvulatia fallax (ATCC 38579); C. gloeosporioides (ATCC MYA-456; Alternaria tenuissima (ATCC 26513); C. gloeosporioides (ATCC 16330)
Based on phenotypic and molecular characteristics, and 99.93% sequence similarity with Streptomyces spectabilis NBRC 13424 (AB184393), the strain was identified as Streptomyces sp
Summary
Phytopathogenic fungi are most worrying, resulting in significant crop yield losses. Some of the fungi produce toxic compounds (Chaiharn et al, 2009). Fusarium, Penicillium, and Aspergillus species yield mycotoxins that are harmful to human beings (Almaguer et al, 2012). It is necessary that new and effective methods are sought to prevent phytopathogenic fungi, and to produce crops safe for consumption, as well as to increase crop yield (Law et al, 2017). Due to the increasing incidence of resistance and potential environmental contamination from chemical fungicides, researchers are trying hard to search for novel plant protectants It is a good to turn an eye to nature to find antagonistic microorganisms and metabolites (Williams, 2009)
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