Pathogenic Interactions Between Pectobacterium spp. and Pseudomonas syringae in Potato as Influenced by Co-Inoculation and Temperature

Potato production is challenged by bacterial soft rot and blackleg diseases caused by the Soft Rot Pectobacteriaceae (SRP), particularly Pectobacterium species. While Pseudomonas syringae , a common potato-related bacterium and well-studied plant pathogen, is known, its role in mixed infections with SRP under various environmental conditions remains unclear. This research examined the pathogenic potential of several Pectobacterium strains and P. syringae on potato tubers, explored how different strains interact during co-infection either synergistically or antagonistically, and analyzed how temperature influences disease development. Potato tubers were inoculated with either a single strain or a combination of P. syringae strains and then incubated at 5, 25, 30, and 35°C in controlled-environment chambers. Disease severity was measured by lesion area (mm²), and interaction outcomes were expressed as percentage changes relative to single-strain infections. Significant differences in pathogenicity were observed among SRP strains; Pectobacterium parmentieri and P. brasiliense exhibited high virulence, whereas other strains were weak or nonpathogenic when tested alone. Co-inoculation with P. syringae yielded strain-specific effects: it heightened disease severity in weakly pathogenic strains but decreased lesion formation in highly virulent ones, suggesting antagonism. Temperature markedly affected disease expression, with maximum virulence usually at 30°C. Co-inoculation also extended the temperature range conducive to disease development. These results illustrate that potato soft rot severity depends on bacterial strain type, microbial interactions, and temperature, underscoring the limitations of single-pathogen models and highlighting the importance of considering microbial communities and environmental factors in disease prediction and control.