Tomato Fruit and Seed Colonization by Clavibacter michiganensis subsp. michiganensis through External and Internal Routes

Abstract

ABSTRACTThe Gram-positive bacteriumClavibacter michiganensissubsp.michiganensis, causal agent of bacterial wilt and canker of tomato, is an economically devastating pathogen that inflicts considerable damage throughout all major tomato-producing regions. Annual outbreaks continue to occur in New York, whereC. michiganensissubsp.michiganensisspreads via infected transplants, trellising stakes, tools, and/or soil. Globally, new outbreaks can be accompanied by the introduction of contaminated seed stock; however, the route of seed infection, especially the role of fruit lesions, remains undefined. In order to investigate the modes of seed infection, New YorkC. michiganensissubsp.michiganensisfield strains were stably transformed with a gene encoding enhanced green fluorescent protein (eGFP). A constitutively eGFP-expressing virulentC. michiganensissubsp.michiganensisisolate, GCMM-22, was used to demonstrate thatC. michiganensissubsp.michiganensiscould not only access seeds systemically through the xylem but also externally through tomato fruit lesions, which harbored high intra- and intercellular populations. Active movement and expansion of bacteria into the fruit mesocarp and nearby xylem vessels followed, once the fruits began to ripen. These results highlight the ability ofC. michiganensissubsp.michiganensisto invade tomato fruits and seeds through multiple entry routes.