Older leaves of lettuce (Lactuca spp.) support higher levels of Salmonella enterica ser. Senftenberg attachment and show greater variation between plant accessions than do younger leaves

Salmonella can bind to the leaves of salad crops including lettuce and survive for commercially relevant periods. Previous studies have shown that younger leaves are more susceptible to colonization than older leaves and that colonization levels are dependent on both the bacterial serovar and the lettuce cultivar. In this study, we investigated the ability of two Lactuca sativa cultivars (Saladin and Iceberg) and an accession of wild lettuce (L. serriola) to support attachment of Salmonella enterica serovar Senftenberg, to the first and fifth to sixth true leaves and the associations between cultivar-dependent variation in plant leaf surface characteristics and bacterial attachment. Attachment levels were higher on older leaves than on the younger ones and these differences were associated with leaf vein and stomatal densities, leaf surface hydrophobicity and leaf surface soluble protein concentrations. Vein density and leaf surface hydrophobicity were also associated with cultivar-specific differences in Salmonella attachment, although the latter was only observed in the older leaves and was also associated with level of epicuticular wax.