Antagonistic activity of bacterial isolates belonging to Bacillus against boxwood blight disease under greenhouse conditions

The outbreak of boxwood blight disease caused by Calonectria pseudonaviculata in the Hyrcanian forests has led to efforts to find effective methods to control the disease. Biological control of the disease by beneficial microorganisms is one of these measures. In this regard, the present study was carried out in a completely randomized design with four replications at both laboratory and greenhouse levels. First, the antagonistic activity of 15 Bacillus isolates against the fungal pathogen was investigated using the dual–culture test, and the superior isolates (FRBP2, FRBS9, FRBS10, and FRBS15) were identified using standard biochemical tests at the species level. Tebuconazole and Serenade® were used as chemical and biological controls, respectively, according to their relevant instructions. The effect of the superior isolates’ suspension (108 CFU/ml) on the severity percentage of boxwood blight disease was evaluated under greenhouse conditions. Among the isolates, the highest (76.4%) and the lowest (26.5%) inhibition of the fungal colony growth was related to B. subtilis FRBS9 and B. pumilus FRBP2, respectively. In greenhouse conditions, B. subtilis FRBS9 and B. subtilis FRBS10 caused the lowest disease severity and showed no statistically significant difference with Serenade® (P<0.05). Thus, isolates belonging to the same or different species of Bacillus showed different levels of antagonistic activity against the target fungal pathogen. These isolates were able to control the fungal agent of boxwood blight through antibiosis and the production of a range of antibiotics. But more studies are needed to find their other antagonistic mechanisms and prepare their appropriate formulations.