Among melons, cantaloupes are most frequently implicated in outbreaks and surveillance-based recalls due
to Salmonella enterica. There is limited but compelling evidence that associates irrigation water quality as a
significant risk of preharvest contamination of melons. However, the potential for root uptake from water
and soil and subsequent systemic transport of Salmonella into melon fruit is uncharacterized. The aim of
this work was to determine whether root uptake of S. enterica results in systemic transport to fruit at high
doses of applied inoculum through sub-surface drip and furrow irrigation during field production of melons.
Cantaloupe and honeydew were grown under field conditions, in a silt clay loam soil using standard agronomic
practices for California. An attenuated S. enterica sv. Typhimurium strain was applied during furrow
irrigation and, in separate plots, buried drip-emitter lines delivered the inoculum directly into the established
root zone. Contamination of the water resulted in soil contamination within furrows however Salmonella was
not detected on top of the beds or around melon roots of furrow-irrigated rows demonstrating absence of
detectable lateral transfer across the soil profile. In contrast, positive detection of the applied isolate occurred
in soil and the rhizosphere in drip injected plots; survival of Salmonella was at least 41 days. Despite high
populations of the applied bacteria in the rhizosphere, after surface disinfection, internalized Salmonella
was not detected in mature melon fruit (n=485). Contamination of the applied Salmonella was detected
on the rind surface of melons if fruit developed in contact with soil on the sides of the inoculated furrows.
Following an unusual and heavy rain event during fruit maturation, melons collected from the central area
of the beds, were shown to harbor the furrow-applied Salmonella. Delivery of Salmonella directly into the
peduncle, after minor puncture wounding, resulted in detection of applied Salmonella in the sub-rind tissue
below the fruit abscission zone. Results indicate that Salmonella internalization from soil and vascular
systemic transport to fruit is unlikely to occur fromirrigationwater in CA production regions, even if substantially
above normal presumptive levels of contamination. Although contaminated irrigation water and subsequently
soil in contact with fruit remains a concern for contamination of the external rind, results suggest an acceptable
microbial indicator threshold and critical limit for the presence of Salmonella in applied water may be possible
by defining appropriate microbiological standards for melon irrigation in California and regions with similar
climate, soil texture, and crop management practices.