Purpose: To investigate the relationship between plant pathogenic Fusarium spp., which cause fruit rot on melon, and Salmonella enterica Newport. The survival and growth of Salmonella Newport on five different melon cultivars following inoculation of Fusarium spp. was evaluated.
Methods: Melon rind disks (A=38.5cm2) of the cultivars Arava, Athena, Dulce, Juane and Sivan were inoculated separately with three Fusarium spp. (100 µl- 4 log spore ml-1) or water and incubated. The treatments were 1) no Fusarium infection (control), and Fusarium infection with 2) Fusarium oxysporum, 3) Fusarium fujikuroi, 4) Fusarium armeanicum. Four days later, Fusarium infection was followed by inoculation with 100 µl (~104 CFU ml-1) Salmonella Newport, adapted for rifampicin resistance, and incubated at 25°C for 24 h. The experiment was repeated three times (n=15/cultivar). Salmonella Newport was recovered in 0.1% buffered peptone water, plated onto tryptic soy agar with rifampicin and cycloheximide (50µg ml-1 each), and incubated at 37°C for 24 h. Counts in log CFU ml-1were analyzed using mixed model (JMP).
Results: Salmonella Newport was not recovered from Fusarium-infected only or water only treatments. Fusarium spp. infection of melons had no significant impact on Salmonella Newport populations. However, less Salmonella Newport (P<0.0001) was recovered from the non-netted cultivars, Dulce (3.9, 4.2, and 4.0 log CFU/ml) and Juane (3.5, 3.7, and 3.1 log CFU/ml) compared to the netted, Arava (5.7, 5.6, and 5.7 log CFU/ml), Athena (5.6, 7.0, and 6.2 log CFU/ml), and Sivan (4.5, 5.6, and 5.9 log CFU/ml) when inoculated with F. oxysporum, F. armeanicum and water control, respectively.
Significance: This study provides evidence that Fusarium fruit infection of a variety of melon cultivars does not affect Salmonella melon surface colonization. Salmonella Newport survival and colonization on melons, however differs among cultivars.