Assessment of Lipopeptide Mixtures Produced by Bacillus subtilis as Biocontrol Products against Apple Scab (Venturia inaequalis)

Abstract

Apple scab is an important disease conventionally controlled by chemical fungicides, which should be replaced by more environmentally friendly alternatives. One of these alternatives could be the use of lipopeptides produced by Bacillus subtilis. The objective of this work is to study the action of the three families of lipopeptides and different mixtures of them in vitro and in vivo against Venturia inaequalis. Firstly, the antifungal activity of mycosubtilin/surfactin and fengycin/surfactin mixtures was determined in vitro by measuring the median inhibitory concentration. Then, the best lipopeptide mixture ratio was produced using Design of Experiment (DoE) to optimize the composition of the culture medium. Finally, the lipopeptides mixtures efficiency against V. inaequalis was assessed in orchards as well as the evaluation of the persistence of lipopeptides on apple. In vitro tests show that the use of fengycin or mycosubtilin alone is as effective as a mixture, with the 50–50% fengycin/surfactin mixture being the most effective. Optimization of culture medium for the production of fengycin/surfactin mixture shows that the best composition is glycerol coupled with glutamic acid. Finally, lipopeptides showed in vivo antifungal efficiency against V. inaequalis regardless of the mixture used with a 70% reduction in the incidence of scab for both mixtures (fengycin/surfactin or mycosubtilin/surfactin). The reproducibility of the results over the two trial campaigns was significantly better with the mycosubtilin/surfactin mixture. The use of B. subtilis lipopeptides to control this disease is very promising.

Additive Effect of the Composition of Endophytic Bacteria Bacillus subtilis on Systemic Resistance of Wheat against Greenbug Aphid Schizaphis graminum Due to Lipopeptides

“…The composition of LPs (surfactin + iturin) was studied, which showed an additive aphicidal effect against S. graminum ( Figure 2 ). There are only two works on the antibiotic activity of artificial compositions of LPs, one of which is devoted to the study of the fungicidal activity of fengycin + surfactin and mycosubtilin + surfactin composition against the pathogen the apple scab Venturia inaequalis [ 46 ], and the second focuses on the aphicidal activity of the triple composition plipastatin + mycosubtilin + surfactin (PMS) against rosy apple aphid Dysaphis plantaginea [ 21 ]. Thus, when studying the fungicidal activity of LPs, a composition of mycosubtilin + surfactin (80:20) showed a synergistic effect and good reproducibility of the results in field experiments against apple scab [ 46 ].…”

“…There are only two works on the antibiotic activity of artificial compositions of LPs, one of which is devoted to the study of the fungicidal activity of fengycin + surfactin and mycosubtilin + surfactin composition against the pathogen the apple scab Venturia inaequalis [ 46 ], and the second focuses on the aphicidal activity of the triple composition plipastatin + mycosubtilin + surfactin (PMS) against rosy apple aphid Dysaphis plantaginea [ 21 ]. Thus, when studying the fungicidal activity of LPs, a composition of mycosubtilin + surfactin (80:20) showed a synergistic effect and good reproducibility of the results in field experiments against apple scab [ 46 ]. In the second study, the highest mortality of the rosy apple aphid was caused by surfactin, affecting the feeding behavior of the insect, while mycosubtilin and a composition of PMS in LP at ratio 33:33:33% caused the lowest mortality, but most of all affected the motoric activity of aphids [ 21 ].…”

“…The treatment of plants with endophytic strains Bs26D and Bs11VM in selected growth-stimulating concentrations increased the endurance (tolerance) of plants, accelerating leaf growth, while the composition Bs26D + Bs11VM showed an additive stimulating effect on plant growth ( Table 4 ). Bacteria can influence plant growth by producing phytohormones, such as indole acetic acid, cytokinins and gibberellins [ 10 , 39 , 46 , 47 ]. Our results showed that the Bs26D strain secreted mainly cytokinins [ 32 ], while the Bs11VM strain secreted IAA into the culture medium ( Table 1 ).…”

The Effect of Cultivation Conditions on Antifungal and Maize Seed Germination Activity of Bacillus-Based Biocontrol Agent

“…Members of the genus Bacillus are significant producers of biologically active molecules with inhibitory activity against phytopathogenic species and additional plant-beneficial properties, including the ability to support plant root colonization and act as immune stimulators [ 7 ]. Some of the biocontrol-related metabolic products include lipopeptides with antimicrobial and biosurfactant traits, antibiotics of other classes, and volatile organic compounds [ 8 , 9 , 10 ]. These extracellular metabolites could be separated or purified to be used as biocontrol agents themselves or could be produced during the interaction of the biocontrol strain with a target phytopathogen at the application site, pointing out the significance of microbial viability preservation during the complete production procedure, distribution, storage, and application of the microbial-based biocontrol products [ 11 , 12 ].…”

“…In addition to the beneficial effect regarding the aforementioned PGP activities, representatives of the Bacillus genus also have a biocontrol effect that contributes to their potential, and possible wider application in agricultural practice. Metabolic activity with an emphasis on the production of lipopeptides was defined as crucial factor in antimicrobial activity against different bacterial and fungal pathogens [ 8 ]. The most important cyclic lipopeptides produced by Bacillus species are members of the surfactin, iturin, and fengycin families.…”