Impact of phenolic compounds on Meloidogyne incognita in vitro and in tomato plants.

Exposing second-stage juveniles (J2) of Meloidogyne incognita in vitro to a phenolic compound sometimes fails to cause J2 mortality, but in tests in vivo the same compound may reduce the infectivity and population of the nematode. This work aimed to study the effect of phenolic compounds on M. incognita through in vitro and in vivo assays. In the in vitro assay 49 phenolic compounds were screened for their toxicity to M. incognita J2. As a result, D-(-)-4-hydroxyphenylglycine, t-butylhydroquinone, L-3-(3,4-dihydroxyphenyl)alanine, sesamol, 2,4-dihydroxyacetophenone, and p-anisaldehyde increased the J2 mortality. These compounds presented, respectively, the following lethal concentrations to 50% of J2 (LC): 365, 352, 251, 218, 210, and 85 μg/mL, while Carbofuran (positive control) had 150 μg/mL. However, none of these compounds were efficient in controlling the nematode in inoculated tomato plants, even when 2.77-fold of their LC were used. Although inactive in the in vitro test at 500 μg/mL, hydroquinone (3.5 mg per plant) reduced M. incognita population and galls by up to 99% to levels similar to the nematicide Carbofuran (1.2 mg per plant). Additionally, hydroquinone increased the root weight when compared to the negative and positive controls, water/NaOH and Carbofuran, respectively. In this study, we showed that some phenolic compounds, hydroquinone in particular, revealed a potential new option for the control of M. incognita.