Biological Control Agents and Resistance Inducers for Managing Anthracnose, Common Bacterial Blight, and Angular Leaf Spot in Common Bean
Xanthomonas citri pv. fuscans, Colletotrichum lindemuthianum, and Pseudocercospora griseola are among the most important pathogens affecting common bean production, causing significant yield losses worldwide. Despite previous reports on biological control agents, there is limited evidence on the integrated performance of Bacillus amyloliquefaciens and Trichoderma harzianum combined with resistance inducers under field conditions, particularly across different cultivars and growing seasons. This study evaluated the field efficacy of biological control agents and resistance inducers for managing common bacterial blight (CBB), anthracnose, and angular leaf spot in bean cultivars, and their effects on yield components and normalized difference vegetation index (NDVI). We hypothesized that seed treatment combined with foliar application at V3 would provide superior disease suppression and yield improvement compared with seed treatment alone. The treatments included B. amyloliquefaciens, T. harzianum, citric acid, and sulfur, applied either as seed treatment (ST) or as seed treatment combined with foliar application at the V3 growth stage (ST+V3). The bean cultivars IPR Campos Gerais and IPR Tangará were used across two dry-season and one rainy-season trials conducted in 2023 at IDR-Paraná, Londrina, PR, Brazil. Application rates followed the manufacturers’ recommendations for both seed and foliar treatments. Disease severity, spectral reflectance indices, and yield components were evaluated. All treatments significantly reduced disease severity, with particularly pronounced effects on CBB in both cultivars. Across application methods, B. amyloliquefaciens and T. harzianum improved yield components and grain yield and reduced the proportion of shriveled seeds. In IPR Tangará, grain yield was negatively correlated with CBB severity. Furthermore, B. amyloliquefaciens consistently resulted in a lower incidence of CBB, anthracnose, and angular leaf spot compared with untreated controls, regardless of cultivar. These findings demonstrate the potential of biological control agents and resistance inducers as components of integrated disease management strategies to improve disease control and yield performance in common bean systems. These findings demonstrate the potential of biological control agents and resistance inducers as components of integrated disease management in common bean, though multi-location validation is required before large-scale recommendations can be made.