Abstract: Mineral amendments influence the performance of antagonistic microorganism to suppress soil-borne fungal and nematode diseases. Experiments were conducted to evaluate the influence of zinc on the production of nematicidal compound(s) in vitro and root-knot infection by Meloidogyne javanica in tomato. Nutrient rich medium amended with various concentrations (0.25-2.0 mM) markedly improved the nematicidal activity of rhizobia in vitro. Species and even strain-specific differences were observed among bacteria with respect to their response to different zinc concentrations. Efficacy of the 10 different isolates (66.6% of the total isolates) was maximum when growth medium was amended with zinc at 1.5 mM while 4 isolates (26.6% of the total isolates) exhibited optimal performance when exposed to 2.0 mM zinc. In vitro nematicidal activity of only one strain was optimal at 1.0 mM zinc. Soil amendment with zinc in the form of ZnSO4 at 0.9 mg/kg of soil alone or in conjunction with rhizobia caused significant inhibition of root-knot development and enhanced the growth of tomato plants under glasshouse conditions.