Efficacy of Aqueous Extract of Lemon Grass (Andropogon citratus L.) against Root-Knot Nematode Pests of Okra. (Abelmoschus esculentus (L.) Moench)

Abstract

An experiment to determine the effects of lemon grass, Andropogon citratus L. extract on the rootknot nematodes (Meloidogyne spp.) of okra was conducted. Phytochemical analyses of the bioactive ingredients in lemon grass were carried out to determine the chemical compounds with nematicidal activities present in lemon grass. Okra (var. Clemson 40) was planted in twenty four (24) experimental pots containing 5kg steam-sterilized loamy soil. Each plant stand was inoculated with 30ml of root-knot nematode egg suspension containing approximately150 eggs/ml. A set of 4 pots were left un-inoculated (control). The lemon grass extracts were 0, 25, 50, 75 and 100% concentrations. Two control trials were used: nematode uninoculated and untreated with leaf extract as control 1 and nematode inoculated but not treated as control 2. Each treatment was replicated four times. The experimental design was a completely randomized type. The result of the phytochemical screening showed that lemon grass contained tannins, alkaloids, flavonoids and saponins. The result of the pot trials showed that lemon grass extract significantly (P<0.05) increased growth and yield of nematode-infected okra. At 5-6 weeks after planting, plant height and number of leaves/plant were significantly (P<0.05) higher in the treated plants than the control. At harvest, the shoot weight of plants treated with higher levels of extract (75 and100%) were significantly (P<0.05) higher than the other treatments and the control . Mean fruit weight was significantly (P<0.05) higher in all the treated plants than in the inoculated but untreated control. Root gall index was significantly lower in treated than in the inoculated but untreated control. The higher concentrations of lemon grass extract were significantly more effective than the lower concentrations in controlling the nematodes and consequently improving the growth and yield of treated okra plants.