Organic acids produced by Solanum sisymbriifolium contribute to its resistance against nematodes

Abstract

Much of the current literature on the mechanisms of plant resistance to pathogens has focused on the role of cellular sensors that initiate a “pathogen-associated molecular-pattern triggered immunity” or PTI response. Less attention has been given to the benefits that some common metabolites may provide to plant resistance. In this study, an untargeted metabolomic analysis identified 230 metabolites that were 3-fold higher in the trap crop Solanum sisymbriifolium than in two nematode-susceptible potato varieties. Several of these metabolites had nematicidal activity in vitro against the root-knot nematodes, Meloidogyne chitwoodi, M. incognita, and M. hapla, at concentrations measured in Solanum sisymbriifolium roots. The most effective of the chemicals tested were furoic, aconitic, and quinic acids. Further studies revealed first that the 3 acids were most effective at or below their acid dissociation constant (pKa) implying that the protonated forms were better able than the charged ones to cross cell membranes and/or bind to critical targets. Second, that the effects of these chemicals were due partially to their structures and not to the creation of an acidic environment. Third, that these chemicals acted additively indicating that S. sisymbriifolium resistance may be partially due to a combination of metabolites rather than to any single chemical.