Antagonistic bacteria contribute to the management of plant diseases by stimulating the natural defenses in the host and/or by ensuring direct biocontrol of the aggressors. The objective of this work was to isolate, identify and evaluate (in vitro) various Bacillus spp. for their potential to control phyopathogenic fungi. Selection of the 40 strains of Bacillus previously isolated from the soil in various areas of western Algeria was carried out by direct confrontation on the mycelial growth of four phytopathogens (Fusariumoxysporumf.splycopersici, Alternaria tenuis , Phytophthorainfestans, Ascochytapisi). This strategy involved using the antagonistic potential of microorganisms found in the plant environment in Algeria. The second part of this work consisted of the characterization and identification of tested strainsThe identification of the selected strains was carried out by biochemical tests. The results obtained showed that at the end of the fifth day, the most promising isolates showed antifungal activity and reached an inhibition rate of the mycelial growth of phytopathogenic fungi, respectively, F. oxysporumf. splycopersici 75%, A. tenuis 80%, P. infestans 83.30%, Ascochytapisi 67%. The potential antagonist of Bacillus tested in vitro by direct confrontation against 04 phytopathogenic fungi showed that all strains of Bacillus decreased fungal mycelial growth. Two strains of Bacillus B30 and B41 were found to have the most efficacy against Fusarium oxysporum f.sp. lycopersici, Alternaria tenius, Phytophtora infestans et Ascochyta pisi, with an inhibition rate of 65.25 and 72.25% respectively These results demonstrate that Bacillus sp. presenteds a potential for biological control. However, it is important to understand the mechanisms implemented by these bacteria to develop effective protection strategies.
Background Over the years, excessive use of chemical pesticides to control plant pathogens has caused environmental problems. Therefore, biological solutions such as the use of microorganisms with antimicrobial capacity become indispensable. To inhibit the growth of plant pathogens, biological control agents use different mechanisms, including the production of hydrolytic enzymes. In this study, the production of amylase, an enzyme important for the prevention and control of plant diseases, by a biological control agent Bacillushalotolerans RFP74 was optimized using response surface methodology. Results Bacillus halotolerans RFP74 inhibited the growth of various phytopathogens including Alternaria and Bipolaris with an inhibition rate of more than 60%. In addition, it also demonstrated an essential production of amylase. Based on previous studies of amylase production in Bacillus, three parameters were considered significant: initial pH of the medium, incubation time, and temperature. Using the central composite design with Design Expert software, the optimized amylase production for B.halotolerans RFP74 is at a temperature of 37 °C, incubation time 51 h and pH 6. Conclusion The biological control agent B.halotolerans RFP74 inhibited the growth of Alternaria and Bipolaris, demonstrating its broad spectrum of activity. Knowledge of the optimal condition required for the production of hydrolytic enzymes such as amylase provides information on the most effective application of this biological control agent.
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