Background
Fungi are one of the microorganisms that cause most damage to fruits worldwide, affecting their quality and consumption. Chemical controls with pesticides are used to diminish postharvest losses of fruits. However, biological control with microorganisms or natural compounds is an increasing alternative to protect fruits and vegetables. In this study, the antifungal effect of Streptomyces sp. CACIS-1.5CA on phytopathogenic fungi that cause postharvest tropical fruit rot was investigated.
Main body
Antagonistic activity was evaluated in vitro by the dual confrontation over fungal isolates obtained from grape, mango, tomato, habanero pepper, papaya, sweet orange, and banana. The results showed that antagonistic activity of the isolate CACIS-1.5CA was similar to the commercial strain Streptomyces lydicus WYEC 108 against the pathogenic fungi Colletotrichum sp., Alternaria sp., Aspergillus sp., Botrytis sp., Rhizoctonia sp., and Rhizopus sp. with percentages ranging from 30 to 63%. The bioactive extract obtained from CACIS-1.5 showed a strong inhibition of fungal spore germination, with percentages ranging from 92 to 100%. Morphological effects as irregular membrane border, deformation, shrinkage, and collapsed conidia were observed on the conidia. Molecularly, the biosynthetic clusters of genes for the polyketide synthase (PKS) type I, PKS type II, and NRPS were detected in the genome of Streptomyces sp. CACIS-1.5CA.
Conclusions
This study presented a novel Streptomyces strain as a natural alternative to the use of synthetic fungicides or other commercial products having antagonistic microorganisms that were used in the postharvest control of phytopathogenic fungi affecting fruits.
Due to contamination of barley grains by Fusarium langsethiae, T-2 toxin can be present in the brewing process. It has been observed that the presence of the yeast Geotrichum candidum during malting can reduce the fi nal concentration of this mycotoxin in beer. In this work, a co-culture method was carried out for both microorganisms in order to evaluate the effect on T-2 mycotoxin concentration in comparison with the pure culture of F. langsethiae in the same conditions. The microbial growth of both microorganisms was assessed using three different methods: dry weight, DOPE-FISH, and DNA quantifi cation. In coculture, both microorganisms globally developed less than in pure cultures but G. candidum showed a better growth than F. langsethiae. The concentration of T-2 was reduced by 93 % compared to the pure culture. Hence, the interaction between G. candidum and F. langsethiae led to a drastic mycotoxin reduction despite the only partial inhibition of fungal growth.
The most common reason for a decrease in the quantity and quality of produced crops is microbial diseases. This study evaluated the antifungal activity of Streptomyces sp. CACIS-16CA against few plant pathogenic fungi. Several fungal pathogens were tested using dual confrontation assays. The anti-fungal activities of CACIS-1.16CA and S. lydicus WYEC108 against Phytophthora capsici, Fusarium oxysporum, and Rhizoctonia solani were evaluated. Additionally, effect of bioactive extract (BE) from CACIS-1.16CA on the germination of conidia from various fungi was evaluated. Results indicated that Streptomyces sp. CACIS-16CA showed a higher percentage of anti-fungal activity (percentage of inhibition (PI), over 43%) than S. lydicus. Moreover, CACIS-1.16CA strain exerted higher percentage of inhibition (PI) against the three damping-off pathogenic fungi (P < 0,05). The BE of CACIS-1.16CA inhibited the conidial germination of Alternaria sp., Botrytis cinerea, and Colletotrichum spp. In conclusion, for the treatment of several plant fungal diseases, Streptomyces sp. CACIS-16CA may be an effective and natural alternative.
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