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Effect of Essential Oils from Five Ocimum sp. on the Pathogenicity of Pratylenchus brachyurus (Godfrey) in Tomato

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Abstract:

The effect of the essences from hydrodistillation of five Ocimum sp. on Pratylenchus brachyurus was compared with carbofuran in in vitro and greenhouse trials. Nematotoxic concentrations of oil were linearly proportional, but varied from one plant to another. At 25-100 g mL 1, the oils of O. gratissimum and O. basillicum completely inhibited egg hatching and larval survival of nematodes after 24 h. 60.4% of nematode larvae were ruptured following a 22 h exposure to a binary combination of O. gratissimum and O. basillicum oils at 100 g mL 1. The undiluted broth obtained after the isolation of O. gratissimum oil induced 66.1% larval mortality and inhibited egg hatching by 62.8%. The essential oil of Ocimum forskolei exhibited a weaker toxicity; inactivating most of the nematodes at 100 g mL 1. Essential oils of O. canum and O tenuiflorum had no effect on the nematode even at 100 g mL 1. The nematicidally potent essential oils of O. gratissimum and O. basillicum were not phytotoxic to tomato plants at 6.25-100 g mL 1. A significant (p< 0.05) improvement in growth of potted tomato plants in the greenhouse was associated with the essential oils of O. gratissimum and O. basillicum. Plants receiving these treatments were taller and greener, developed fewer root galls and produced more fruits than plants treated with the essential oil of O. forskolei. Amending soil with a binary combination of O. gratissimum and O. basillicum oils at 100 g mL 1 was significantly more efficacious than either oil at 100 g mL 1 and compared with carbofuran treatment at 100 g mL 1. The observed differences in the nematicidal potential of the control plants are natural in terms of the overall chemical composition of the essential oils.

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