Evaluation of Pathogen Characteristics and Management Strategies of Tomato Bacterial Stem Rot under Protected Cultivation in Sri Lanka

Tomato bacterial stem rot, caused by Pectobacterium carotovorum subsp. carotovorum, is a major constraint in protected tomato cultivation in Sri Lanka, particularly under humid polytunnel conditions. This study aimed to characterize the causal pathogen, evaluate resistance among tomato germplasm, and assess the efficacy of selected copper-based compounds for disease management. Five bacterial isolates were obtained from stem rot-infected tomato plants collected from polytunnels in the Kandy and Matale districts and cultured on Potato Dextrose Peptone Agar (PDPA). All isolates were identified as P. carotovorum subsp. carotovorum based on colony morphology, Gram reaction, catalase activity, pathogenicity on tomato plants, hypersensitivity reactions on tobacco leaves, and virulence on carrot slices. Greenhouse screening of 25 tomato germplasm lines revealed disease incidence ranging from 10-65%, with no fully resistant lines identified; however, AVTO 2117 showed the lowest disease incidence (10%) and was classified as moderately resistant. An in vitro poison food assay demonstrated complete inhibition of bacterial growth by copper hydroxide. These findings suggest that moderately resistant germplasm and copper hydroxide have potential as components of integrated management strategies for tomato bacterial stem rot; however, field-based validation is required to confirm their effectiveness under cultivation conditions.