The density-dependent effect of initial nematode population levels on the efficacy of Trichoderma as a bio-nematicide against Meloidogyne hapla on tomato

Trichoderma strains were tested for their ability to reduce the severity of root-knot nematode (RKN), Meloidogyne hapla galling on tomato roots. In initial glasshouse trials, under low levels of RKN infestation (1.1 eggs mL soil⁻¹), Trichoderma strains applied as a conidial suspension reduced RKN-induced root galling by 42–88 %. When the nematode infestation level was increased (6.2 eggs mL soil⁻¹), these isolates were only able to suppress galling by 21–32 %. At the highest infestation rate trialled (30 eggs mL soil⁻¹), Trichoderma strains were unable to suppress galling. The chemical control oxamyl (Vydate®) (only evaluated at the highest infestation rate) was 98 % effective. The Trichoderma strains were not effective against RKN when treatments of both organisms were applied pre-planting. However, Trichoderma strains were able to reduce symptoms of RKN galling when applied either at seeding prior to nematode inoculation or post seedling emergence together with the RKN inoculation. These results demonstrate that selected Trichoderma strains have biocontrol potential against RKN at low-medium infestation but fail when the infestation level is rated high