The antifungal activity of Bacillus spp. strains has already been reported against a different number of phytopathogenic fungi3. Some species belonging to this genus such as Bacillus subtilis, Bacillus pumilus and Bacillus licheniformis are considered GRAS (generally regarding as safe) microorganisms and exhibit potential to enhance plant growth by the production of an ample number of beneficial substances1, portraying these species as an environmentally friendly alternative to chemical fungicides. Macrophomina phaseolina (Tassi) Goid is a wide range soil-borne phytopathogenic fungus causing charcoal rot on several significant plant crops in Argentina (soybean, common bean, peanuts and corn)5,6 and is also capable of affecting more than five hundred plant species worldwide4. Its ability to infect these host plants is commonly correlated with the production of viable sclerotia, non-sporic resistance structures constituted by a mass of densely packed hyphae in the field5. In this work, we report the isolation of a Bacillus sp. strain 11.1 obtained from soil samples from Córdoba Province, Argentina2 exhibiting a strong antagonistic activity against M. phaseolina. In order to analyze the potential antagonistic effect of strain 11.1, both microorganisms were grown on dual culture plates containing potato dextrose agar (PDA) and tryptone soy agar (TSA) (1:1, v/v) and incubated for 48–72h at 28°C (Fig. 1). An important and irreversible inhibition of the fungal growth was shown (Fig. 1A). In addition, the fungal mycelium located at the edge of the inhibited region was analyzed by microscopic examination. The most evident antagonistic effect on the fungus was depicted by the lack of black pigmentation and a decrease of sclerotial size in comparison with the control (Figs. 1B and C).
Antagonistic activity by Bacillus sp. strain 11.1 against fungal pathogen M. phaseolina in dual culture assay on PDA/TSA (A). Normal sclerotia formed by M. phaseolina (400×) (B) and (1000×) (C). Abnormal sclerotia lacking black pigmentation and smaller size (black arrows) in comparison with the control (400×) (D) and (1000×) (E). Images of the antagonistic assay were obtained by microscopy using an inverted Nikon microscope (Eclipse TI-S) with NIS-Elements software.
The authors declare that the procedures followed were in accordance with the regulations of the relevant clinical research ethics committee and with those of the Code of Ethics of the World Medical Association (Declaration of Helsinki).
Confidentiality of dataThe authors declare that no patient data are included in this article.
Right to privacy and informed consentThe authors declare that no patient data are included in this article.
Conflicts of interestThe authors declare that they have no conflicts of interest.
This work was supported with a grant provided by the Universidad Nacional de Villa María and the Instituto de Investigación-UNVM for the project “Aislamiento y caracterización de bacterias con potencial actividad promotora del crecimiento vegetal en la región de Villa María”. Res N° 275/2015. The authors are grateful to Dr. Colin Berry (Cardiff University, UK) for his kind revision of the manuscript.
