Biocontrol potential of indigenous pepper seed Bacillus strains against Xanthomonas euvesicatoria

Bacterial spot caused by Xanthomonas spp. is considered an economically important disease affecting pepper. Considering that antibiotics-based treatments in disease control are forbidden in European countries, biological control has emerged as a promising approach.

In this study, we demonstrated high biological efficacy of three indigenous pepper seed-associated Bacillus spp. - Bacillus velezensis (P64), Bacillus safensis (P114), and Bacillus halotolerans (P122) - in the control of Xanthomonas euvesicatoria. Two independent trials based on the pepper growth in pots and in the field resulted in similar performances in terms of disease spread reduction (as calculated by disease incidence and disease severity index) over time compared to the untreated controls. In both trials, treatments included initial preventive or curative applications of these biocontrol bacteria once the secondary apical lateral shoot became visible (BBCH 29), followed by additional application at the beginning of flowering (BBCH 52-55). Ratings conducted at 7-day intervals after the first treatment indicated very high biological efficacy, typically exceeding 80%. All three strains remained active throughout the assessment period, whereby their efficacy started to increase 21 days after the first treatment, reaching 99.59% after 49 days. Although bacterium B. velezensis is already known for its beneficial role in the control of plant bacterial diseases, this is among the first study demonstrating the bactericidal activity of B. safensis and B. halotolerans.

The current research outlines a promising novel approach for X. euvesicatoria control in pepper based on the type of microbial agents as well as the timing of their application. © 2025 Society of Chemical Industry.