Purpose: We hypothesized that natural cracks formed during cantaloupe net initiation facilitate SP internalization. We investigated whether SP survives on the rind and internalizes through these cracks, either alone or with the wilt pathogen Erwinia tracheiphila (Et).
Methods: Drops (20µl; 107 CFU/ml) of an SP-Et mixture, or of each pathogen alone, were brushed onto newly formed fruit cracks. Rind or underlying mesocarp samples were assayed by direct and enrichment plating at 0, 9 and 24 days post-inoculation (DPI).
Results: Fruits inoculated with Et (61%) or SP+Et (56%) developed watersoaked lesions. Et was recovered from 80% and 20% of rinds inoculated with Et or SP+Et, respectively, at 0 DPI, but 100% of rinds having lesions yielded Et at 9 and 24 DPI. 25% of mesocarp samples of the same fruits were Et+. SP recovery from rinds inoculated with SP or SP+Et was 7.6 x 102 and 9.2 x 102 cells/ml, respectively, at 0 DPI, but dropped to 1.7 and 2.9 cells/ml (9 DPI) and 0 and 1.6 cells/ml (24 DPI). SP survived longer on fruits co-inoculated with Et, and on fruits with lesions, than on those of other treatments. None of 67 mesocarp samples from fruits receiving SP or SP+Et were SP+. Neither SP nor Et was found on any non-inoculated fruits.
Significance: SP, introduced onto cracks of young cantaloupe fruits, was later recovered from rind surfaces but never from edible mesocarp. SP survived longer on rinds in the presence of Et, suggesting that community microbes influence fitness. Et also survived on the rind but, unlike SP, Et frequently invaded the mesocarp, causing watersoaked lesions. Interestingly, although Et’s usual plant niche is xylem, neither it nor SP was detected in any non-inoculated fruits, suggesting a lack of systemic movement.