Mi-1-virulent Meloidogyne incognita Isolates from Resistant Tomato Rootstocks Fail to Reproduce on Susceptible and Resistant Peppers

Root-knot nematodes pose a substantial threat to tomato production in high tunnels. The Mi-1 resistance gene, routinely used to manage the pest, is increasingly challenged by the emergence of virulent populations. In this study, three Meloidogyne incognita isolates collected from grafted tomato rootstocks carrying Mi-1 resistance in high tunnels in Indiana were evaluated for virulence on susceptible pepper cultivars lacking the N resistance gene (‘Baron’, ‘Aristotle’, and ‘California Wonder’), and the resistant cultivar ‘Charleston Belle’ (with N gene). The Mi-1-virulent isolates caused severe galling and reproduced on the Mi-1 tomato cultivar ‘Better Boy’ but failed to reproduce on any of the pepper cultivars tested. In contrast, the two Mi-1-avirulent isolates were virulent on the susceptible pepper cultivars but did not reproduce on the resistant ‘Charleston Belle’. The second-stage juveniles (J2s) root penetration assay showed that J2s from all M. incognita isolates penetrated ‘Baron’ and ‘Charleston Belle’ pepper roots at similar rates, suggesting resistance acts post-penetration. Furthermore, microscopic observation showed hypersensitive response-like tissue damage in ‘Baron’ pepper roots inoculated with Mi-1-virulent isolate. This reciprocal virulence pattern indicates a fitness cost, whereby adaptation to overcome Mi-1 resistance in tomato rootstocks reduced the nematodes’ ability to reproduce on pepper. Our findings suggest that incorporating peppers, even cultivars normally considered susceptible, into rotations could provide an effective and economical strategy to suppress Mi-1-virulent M. incognita populations in high tunnel tomato production, thereby prolonging the durability of Mi-1-mediated resistance.