Figure 1.
Inoculating newly formed natural cracks on cantaloupe fruit.
Fruit rind (2×2 cm areas marked) was inoculated with pathogen suspensions or 0.1% peptone (20 µl as 10–15 droplets) and the droplets were then spread out in the marked area with a sterile bristled brush. Arrow head indicates cracks older than those in the area being inoculated.
Figure 2.
Reddish-orange exudate (arrow) observed on the natural cracks of 10–12 day-old cantaloupe fruit rind.
These cracks were naturally healed by deposition of corky material, forming the characteristic netting on cantaloupes at fruit maturity.
Figure 3.
Watersoaked lesion observed under natural light (A) and UV light (B).
Cantaloupe rinds were inoculated with E. tracheiphila (Et- green fluorescing with GFPuv), alone or together with S. enterica (SP- red fluorescing with DsRedExpress), and sampled at 0, 9 or 24 DPI. This rind, sampled at 9 DPI, showed watersoaked lesions observed under natural light (A) and under UV light (B). Arrows: Green-fluorescing E. tracheiphila on the cracks and beneath the cuticle in a watersoaked area. Scale bars represent 2 cm.
Figure 4.
Disease incidence on cantaloupe fruits following inoculation with pathogens.
Fruit rinds were inoculated with E. tracheiphila or a mixture of E. tracheiphila and S. enterica and sampled at 9 and 24 DPI. Bars indicate percentages of cantaloupe fruit showing watersoaking; there were no significant differences between day 9 and 24 for either treatment (Et or SP+Et) (Fisher's exact one-tailed test, P = 0.64 and P = 0.53, respectively).
Table 1.
Recovery of S. enterica Poona and E. tracheiphila from cantaloupe rinds.
Figure 5.
Confocal laser scanning microscope images of cantaloupe rind surfaces.
(A) Fruit rind surface inoculated with S. enterica Poona (labeled with DsRedExpress) and sampled at 0 DPI, (B) Fruit rind surface inoculated with a mixture of S. enterica Poona + E. tracheiphila (labeled with GFPuv) and sampled at 0 DPI (C) Fruit rind surface inoculated with E. tracheiphila and sampled at 0 DPI and (D) Longitudinal section of rind containing watersoaked lesion and sampled at 24 DPI; E. tracheiphila in the intercellular spaces (arrow) (inoculated with mixture of S. enterica plus E. tracheiphila). The scale bars represent 5 µm.
Table 2.
Association, based on PCR detection, of E. tracheiphila-incited watersoaked lesions with the presence of S. enterica on cantaloupe fruits sampled over time*.
Figure 6.
Scanning electron micrographs of cantaloupe rind surface at fruit maturity.
(A) Rind inoculated with 0.1% peptone water; (B) Crack on rind inoculated with 0.1% peptone water; (C) Rind inoculated with E. tracheiphila and had a watersoaked lesion with masses of bacteria seen near a trichome scar; and (D) Crack on rind inoculated with mixed S. enterica + E. tracheiphila that had a waterloaked lesion. All observations were made at 5,000×; scale bar shows 20 µm.
Figure 7.
Incidence of S. enterica Poona (SP) on cantaloupe fruits.
Fruit rinds were inoculated with S. enterica Poona alone (SP), or S. enterica + E. tracheiphila (SP+Et), and sampled at 0, 9 or 24 days post inoculation [(DPI), P values for SP vs S.P+Et at 0, 9 and 24 DPI were 1.00, 0.47, and 0.21]. Values of the same treatment do not significantly differ at p<0.05) according Fischer's Exact test- one tailed. Overall p-value for comparison of proportions among levels of DPI given treatments are <0.001 and 0.0039 for SP and SP+Et, respectively.