Management of Root Knot Nematodes (Meloidogyne spp.) on tomato with Castor Bean (Ricinus communis) Aqueous Extracts

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Apart from high cost, increased concern for environmental and health hazards has called for a reduction in the use of synthetic nematicides for nematode control. Experiments were, therefore, conducted to ascertain the nematicidal potential of castor bean’s crude extract and its seven lower concentrations, water being used as control. In vitro studies in Petri dishes showed that castor bean extract and all the different concentrations had toxic effect on eggs and juveniles of root–knot nematodes. Egg hatch inhibition and juvenile mortality decrease with increased dilution of the extract. With an increase in exposure time, juvenile mortality increased. Plant house pot experiments were conducted to observe the effect of the extracts on root-knot nematodes and some growth parameters of tomato plants. The seedlings were either dipped, side-drenched or a combination of both with different concentrations of castor bean extracts. Results showed that plant height, stem girth, fresh shoot and root weights of extract-treated plants were significantly different (P=0.5) from those of the control plants. Numbers of root-knot juveniles and galls on the roots of the extract-treated plants were significantly different (P=0.5) from those of the control. A field trial gave contrary results from those of the plant house experiments. There was no significant difference (P=0.05) between plant height, mean gall score and mean number of juveniles from the tomato roots of all the treatments. The crude castor bean extract was nematotoxic to root-knot nematodes in vitro and potted tomato plants. Aqueous extract of castor bean can, therefore, be used by farmers to manage root-knot nematodes in the nursery before transplanting.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfillment for the award of the degree, Master of Science,