Foliar Chitosan, Paraburkholderia tropica and Bacillus infantis Alter Chitinase and β-1,3-Glucanase Activity Independently of Meloidogyne spp. Infection and Reduce Nematode Reproduction in Tomato

Root-knot nematodes (Meloidogyne spp.) are the most economically important group of plant-parasitic nematodes worldwide. We tested whether foliar elicitors induce defense enzymes in leaves and reduce nematode reproduction in the roots of the same plants. Tomato cv. Santa Clara, which lacks Mi-1 resistance, received 50 mL per plant of one of six treatments: chitosan at 2.0 or 2.5 mg mL−1, Paraburkholderia tropica GIBI_0183 or Bacillus infantis GIBI_0177 at 2.5 × 107 cells per plant, or a commercial chitosan or Bacillus subtilis product. Each treatment was applied with and without 1000 s-stage juveniles in the soil. β-1,3-Glucanase and chitinase activities were measured in leaves 1, 2, 6 and 8 days after application (n = 10), and eggs in whole root systems at 60 days (n = 6). Leaves sampled on days 1 and 2 were sprayed; those sampled on days 6 and 8 expanded afterward. Both enzymes showed a treatment × day interaction (permutation p = 0.0001). Every treatment reduced the egg count by 63–75% (p ≤ 0.0003), with no differences detected among treatments at the sample size used. All six raised chitinase in plants without nematodes, whereas β-1,3-glucanase fell below the control under both laboratory chitosans, which reduced the egg count as much as the treatments that raised it. Enzyme induction and nematode suppression are separate outcomes.