Pectobacterium carotovorum subsp. brasiliense is a newly identified
member of the potato soft rot enterobacteriaceae. The pathogenesis of this
pathogen is still poorly understood. In this study, an mCherry-P. carotovorum
subsp. brasiliense-tagged strain was generated to study P.
carotovorum subsp. brasiliense—potato plant interactions. Prior to use,
the tagged strain was evaluated for in vitro growth, plasmid stability, and
virulence on potato tubers and shown to be similar to the wild type. Four
potato cultivars were evaluated for stem-based resistance against P. carotovorum
subsp. brasiliense. Confocal laser-scanning microscopy and in
vitro viable cell counts showed that P. carotovorum subsp. brasiliense is
able to penetrate roots of a susceptible potato cultivar as early as 12 h
postinoculation and migrate upward into aerial stem parts. Due to the
phenotypic differences observed between tolerant and susceptible cultivars,
a comparison of P. carotovorum subsp. brasiliense colonization
patterns in these cultivars was undertaken. In the susceptible cultivar, P.
carotovorum subsp. brasiliense cells colonized the xylem tissue, forming
“biofilm-like” aggregates that led to occlusion of some of the vessels. In
contrast, in the tolerant cultivar, P. carotovorum subsp. brasiliense appeared
as free-swimming planktonic cells with no specific tissue localization.
This suggests that there are resistance mechanisms in the tolerant
cultivar that limit aggregation of P. carotovorum subsp. brasiliense in
planta and, hence, the lack of symptom development in this cultivar.