Antagnostic effectof different Bacillus subtillis strains on Alternaria solani isolates in vitro

Abstract

Early blight, caused by Alternaria solani Sorauer (Ellis), is one of the most economically important diseases of potato and tomato in the world. Use of conventional fungicides is unavoidable in controlling the early blight disease, but due to their main downside, fungal resistance, biofungicides are gaining increasing importance in crop production. The goal of this study was to evaluate in vitro sensitivity of five A. solani isolates originating from Serbia to biofungicides (F-stop and Serenade) containing different Bacillus subtilis strains. A. solani isolates were grown on PDA medium at 20-24'C temperature for a period of two to seven days, and their fragments (5 x 5 mm) were then inserted into a liquid potato dextrose (PD) medium and grown for 48 hours on magnetic stirrer. Suspension of selected isolates mixed with 1.2% PDA medium was homogeneously dis-tributed on hardened PDA medium in Petri dishes (90 mm in diameter). Afterwards, a 10 mm wide hole was made in the central part of the Petri dishes, in which 100 pl of the tested suspension of B. subtilis was poured. Suspension of fungicide was used in standard treatment and distilled water in control treatment. Evaluation of antagonistic activity of B. subtilis strains was performed 48 hours after incubation at 25°C temperature by measuring the diameter of inhibitory zone (mm). Bacterial strain ST1/11I (F-stop) exhibited the greatest antagonistic effect. It inhibited mycelial growth of the tested isolates from 1.67 (isolate KR) to 17.8% (isolate BC). QST 713 strain of B. suhtilis (Serenade) managed to inhibit the growth of the isolates from 3.61 (isolate VP) to 10.28% (isolate BC). The greatest percentage of inhibition was achieved with standard fungicide difenoconazole which inhibited mycelial growth from 25.28 (isolate VP) to 88.9%) (isolate ML). Compared to standard fungicide all tested bacterial strains exhibited low percentage of inhibition.