The influence of ammonium and nitrate nutrition of tomato plants on parasitism by the root-knot nematode

Tomato plants grown in sand-silica culture in 0.75-liter pots and 50-liter containers were fertilized with three ratios of NH₄⁺/N0₃^- percentages: 100/0, 50/50, and 0/100. The seedlings were inoculated with the root-knot nematode, Meloidogyne javanica, and 30 and 60 days after inoculation top and root fresh weights, nematode infection degree and sex ratio of the nematode populations were recorded, and N, P, K analyses of plant tops and roots were conducted. Nematode development was not influenced by the nutrient treatments but a reduced nematode population per mm of root, and a high percentage of males in the population were associated with the 100% ammonium treatment. Increased nitrate level in the medium enhanced fresh top and root weights in the pots and, especially, in the containers. High levels of N and K in the first month, and of N, P, K in the second month, accumulated in the inoculated roots, particularly in the nitrate-fertilized plants. The results support the theory of the existence of a metabolic sink in roots of Meloidogyne-infected plants and suggest an increased tolerance to the root-knot nematode in plants receiving nitrate nutrition.