Biocontrol Potential of Acinetobacter lactucae and Pseudarthrobacter polychromogenes in Managing Pepper Bacterial Spot Disease

Bacterial spot disease, caused by Xanthomonas euvesicatoria, poses a significant threat to pepper (Capsicum spp.) production, necessitating sustainable control strategies. This study aimed to isolate and evaluate beneficial bacteria from healthy pepper plants as biocontrol agents and plant growth promoters. A total of 344 epiphytic and 192 endophytic bacterial isolates were collected from pepper fields in Şanlıurfa and Adıyaman, Türkiye, and screened for antagonistic activity against X. euvesicatoria and plant growth-promoting traits. Fourteen isolates were selected for greenhouse trials, applied via seed treatment, foliar spray, or combined methods. Notably, this study is the first to report Acinetobacter lactucae UEP50 and Pseudarthrobacter polychromogenes AEND14 as novel BCAs against X. euvesicatoria in peppers, highlighting their potential as effective microbial agents. Acinetobacter lactucae UEP50 and Pseudarthrobacter polychromogenes AEND14 showed promising biocontrol efficacy, reducing disease severity by up to 85% in controlled greenhouse trials with combined seed and foliar treatments. The combined application method demonstrated superior efficacy compared to single applications, achieving a 30%–40% higher reduction in disease severity than seed or foliar treatments alone, suggesting a synergistic effect that enhances disease suppression and plant growth promotion. Further field studies are needed to confirm these results. These isolates also demonstrated strong antagonistic activity (inhibition zones up to 27 mm) and plant growth-promoting traits, including indole-3-acetic acid production (up to 126.92 μg/mL) and phosphate solubilisation. This study reports A. lactucae and P. polychromogenes as promising biocontrol agents against X. euvesicatoria in peppers, suggesting their potential role in integrated pest management. Further literature review is needed to confirm the novelty of this finding. These findings suggest potential for developing microbial-based strategies to enhance pepper production sustainability. However, further research is necessary to validate field efficacy and optimise application methods.