Plants stressed by pathogens activate a variety of defense mechanisms to survive. The osmoprotector amino acids, including proline, are among these defense mechanisms. In this work, the effects of arbuscular mycorrhizal fungi on plants infested by root-knot nematodes were evaluated with regard to the accumulation of the osmoprotectant proline. A 2x3 factorial design was established with 8 treatments -with and without nematodes, with and without mycorrhizae, and with and without fertilizer application - with 4 replicates. Two weeks after inoculation with arbuscular mycorrhizal fungi, the plants were infested with 4 nematode egg masses, and 8 weeks later, the plants were harvested. The inoculation with the arbuscular mycorrhizal fungi significantly reduced the proline content, with the non-inoculated plants exhibiting a higher concentration. Neither the infestation of the nematodes nor the addition of fertilizer significantly affected the proline content. Plant height, stem diameter, leaf area, number of leaves, and fresh weight were significantly improved by the presence of the arbuscular mycorrhizal fungi. The interaction of the fungi and the fertilizer did have a significant effect for height and leaf area. The nematode infestation and the fertilization did not affect mycorrhizal colonization.