Investigating the in vitro and in vivo nematicidal performance of structurally related macrolides against the root-knot nematode, Meloidogyne incognita

Avermectins and spinosyns are structurally related natural products of microbial origin and belong to a new family of macrolides which are active against a vast array of invertebrate pests. In the present study, the effects of four members of macrolides; abamectin (ABM), emamectin benzoate (EMB), spinosad (SPI) and spinetoram (SPIT), on Meloidogyne incognita were investigated under in vitro and in vivo conditions. All compounds reduced egg hatching and led to high mortality of the nematode second-stage juveniles (J₂). ABM showed the maximum rate of egg hatching inhibition and J₂ mortality while SPIT recorded the minimum. All treatments reduced the number of galls, egg masses, eggs/egg mass in roots and J₂ in the soil when compared to the control. Based on the 10 folds of the 24 h-LC₅₀ values of J₂ mortality in vitro, EMB and ABM exhibited higher percent reduction in galls (79.68 and 71.45%), egg masses (75.19 and 70.54%), eggs/egg mass (60.49 and 40.91%) and J₂ in the soil (90.31 and 86.54%), respectively, compared to SPI and SPIT. Significant increase in tomato shoot height occurred in all biopesticides (10 folds) and SPIT (20 folds). SPI at 10 folds of the 24 h-LC₅₀ values of J₂ mortality in vitro, significantly increased root length while ABM at 50 folds and SPIT at 20 folds decreased root length by 5.15% and 5.88%, respectively, compared to the untreated inoculated plants. In all treatments, the dry shoot and root weights increased, compared to the untreated control. Our findings suggest that these macrolides have the ability to regulate nematode population densities and may be an alternative to classical nematicides.