Induction of resistance to root-knot nematodes by SAR elicitors in tomato

Different concentrations of the systemic acquired resistance (SAR) elicitors, salicylic acid (SA), methyl-salicylic acid (MetSA), acibenzolar-S-methyl (ASM) and 2,6-dicholoroisonicotinic acid (INA), were provided to tomato seedlings as root-dip or soil-drench one day before inoculation with the root-knot nematode, Meloidogyne incognita. Nematode infestation was evaluated by counting egg masses/plant (EM), eggs/plant (Pf), and sedentary forms/plant (SF) in treated and untreated plants seven weeks after inoculation. An index of plant fitness (PF) was also calculated to assess the costs of chemically-induced resistance and the possible phytotoxicity of the treatments. SA and ASM were found to be effective elicitors of resistance when applied at suitable concentrations and method of application. Soil-drench with SA and root-dip in ASM were the most effective treatments as they markedly reduced both nematode reproduction (less than 50% that of untreated plants) and infestation (50–70% EM reduction). MetSA was less effective than SA in eliciting resistance because of its negative effects on plant fitness when it was provided as soil-drench. INA did not reduce nematode infestation at any of the non-phytotoxic rates. The reduction of nematode infestation and reproduction by SA applied as soil-drench was potentiated when the soil was enriched with humic acids. Soil-drenching with SA and MetSA were the only treatments that caused a long-lasting induction of plant defences as they inhibited the infestation by the second generation of the nematode.

Research highlights
► SAR elicitors can induce resistance to root-knot nematodes in susceptible tomato;
► Resistance induced by SAR elicitors to nematodes is dose-dependent;
► Induced resistance depends on soil nature and method of chemical application;
► SA and ASM applications significantly inhibit nematode infestation;
► Chemically-induced resistance can be used in integrated pest management to nematodes.