Nematicidal effects of Azadirachta indica A. Juss (Neem) seeds on Meloidogyne species (root-knot nematodes)

Abstract

The presence of bioactive substance in plant extracts with nematicidal activity on Meloidogyne spp can reduce crop damage in nematode control and to minimized the use of chemical nematicide which may be toxic to man and the environment. An in vitro experiment was conducted to investigate the bioactive effects of aqueous and methanolic seed extract of neem on root-knot nematodes. The nematodes were isolated by modified funnel Baerman method and identified by comparative morphology, descriptions and lattice keys. Ten mils of homogenized nematodes suspension (50 juveniles) replicated 5 times and kept at room temperature were exposed to varied concentrations (50, 100, 150, 200, and 300 mg/ml) of the seed extracts of test plants for different time periods; 6, 12, and 24 hours. Distilled water served as a control. Data on dead nematodes was recorded for each period of exposure. The data was analysed using Analysis of Variance (ANOVA). Phytochemical screening of crude seed extracts was carried out using standard methods. The results showed that aqueous seed extract of A. indica caused 100 % nematode juvenile mortality at the highest’s concentration (300mg/ml) within 24 hours of exposure while the methanolic seed extract of A. indica caused 100% mortality within 8 hours of exposure. The results revealed that the higher the concentration of both aqueous and methanolic (50 mg/ml-300 mg/ml) seed extract of A. indica, the higher the mortality of root-knot juveniles. Mortality due to the extracts were significantly higher than those of the control at P < 0.05. The plant bioactive chemical screening of the test seed extract revealed the presence of anthraquinones, alkaloids, carbohydrates, cardiac glycosides, flavonoids, saponins, steroids and terpenes. Both methanolic and aqueous seed extract of Azadirachta indica had nematicidal properties with potential for a biological nematicide.