Abstract
Soft rot
Pectobacteriaceae
(SRP) are destructive pathogens of potato crops, posing a global threat to food security. SRP populations exhibit significant genetic heterogeneity, with the prevalence of potato-infecting species shifting over time. In this study, we identified
Pectobacterium aroidearum
as a novel agent causing severe tuber soft rot in winter-planted potatoes in Guangdong Province, where it co-occurred with
P. brasiliense
and
P. carotovorum
. However, the pathogenic potential of
P. aroidearum
has been largely uncharacterized. Here, comparative virulence assays demonstrated that
P. aroidearum
is more aggressive than its counterparts. This heightened virulence was linked to enhanced pathogenic traits, including plant cell wall-degrading enzyme production, swimming motility, exopolysaccharide (EPS) production, and air–liquid (AL) biofilm formation. Genomic analysis revealed that although core virulence genes are conserved, a type 1 fimbriae-encoding
fim
cluster is unique to
P. aroidearum
. Deletion of
fimA
,
fimC
,
fimD
, and
fimH
impaired bacterial adhesion, EPS production, AL biofilm formation, and full virulence, functionally characterizing this distinctive factor. Genes within the bacterial cellulose synthesis operon were significantly downregulated across
fim
mutants. Accordingly, the mutant colonies showed a marked decrease in calcofluor binding compared with the wild-type strain. Genes with significant up-regulation in the mutants were primarily involved in responses to extracellular stimuli. These findings indicate that the
fim
cluster underpins the threat posed by this emerging pathogen, which warrants increased attention in disease management. The considerable genetic diversity and frequent gene flow among
P. aroidearum
isolates from various hosts further highlight its epidemiological risk.