The presence of genetic determinants homologous
to rulAB genes for ultraviolet (UV) radiation resistance was
determined in a collection of Pseudomonas syringae pv.
syringae strains isolated from mango. The potential role of
these plasmids in UV tolerance and ecological fitness in the
mango phyllosphere was also evaluated. Nearly all of the
62-kb plasmids present in the P. syringae pv. syringae
strains hybridized with a rulAB probe, but these 62-kb
plasmids showed differences in restriction patterns. In vitro
assays of tolerance to UV radiation of P. syringae pv.
syringae strains showed a higher survival of the strains
harboring the 62-kb plasmids compared to strains lacking
plasmids when exposed to UVC or UVA+B fractions.
Similar results were observed when transconjugants harboring
the 62-kb plasmid were tested. Survival assays were
carried out under field conditions, and a higher survival of
P. syringae pv. syringae strains harboring 62-kb plasmids
under direct solar radiation on the adaxial surface of leaves
was also observed. When the assays were carried out in shady areas or on the abaxial surface of leaves, survival
time was comparable for all the assayed strains, whether or
not they contained a 62-kb plasmid hybridizing to rulAB.
Our results indicate that P. syringae pv. syringae strains
harboring 62-kb plasmids show an increase in ecological
fitness when colonizing the mango phyllosphere.
