Assessment of the Tephrosia toxicaria essential oil on hatching and mortality of eggs and second-stage juvenile (J2) root-knot nematode (Meloidogyne enterolobii and M. javanica)

Abstract

The search for alternative biocontrol methods is necessary. Several molecules with nematicidal effect have already been identified from plant tissues. They can be considered as important alternative for nematode control. Therefore, the objective of this study was to assess the effect of essential oil of Tephrosia toxicaria on hatching and mortality of second-stage juvenile (J2) root-knot nematode (RKN) and eggs of Meloidogyne enterolobii and M. javanica. For this purpose, 50 eggs/J2 were incubated with the essential oil of T. toxicaria at seven concentrations (0.0, 50, 100, 200, 400, 600 and 800 μl.mL-1) with six replicates in 48-well acrylic plates. The number of eggs and juveniles were counted with the aid of camera under a stereoscopic microscope. The analysis of the J2 hatch was performed using the area below the hatching progress curve (ABHPC), calculated by the equation proposed by Campbell and Madden. The J2 mortality rate was carried out concomitantly with the hatching observations, 48 hours and also 16 days after applying the treatments. In the evaluations, all the motionless J2 were counted after 48 hours. To confirm the occurrence of mortality, the specimens were transferred to water, then examined in slides, under an optical microscope at a 40x magnification. The data were submitted to analysis of variance using the F-test and the averages were compared by the Skott-Knott test (p≤0.01). We confirmed that the essential oil of T. toxicaria has effectiveness to reduce juvenile hatching and cause J2 mortality in all the assessed concentrations, demonstrating the nematicidal potential of the active principles present in T. toxicaria. The results of this study show that the T. toxicaria essential oil and its constituents can serve as an environmentally safe and a promising nematicide agent in the control of Meloidogyne spp.