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Evaluation of natural products as possible alternatives to methyl bromide in soil fumigation


Anastasiah N Anastasiah
Paul K Ndalut

Abstract

Methyl bromide (CH3Br) is a widely used fumigant in crop production and commodity preservation worldwide. It escapes to the stratosphere and releases bromine atom (Br), which contributes to significant destruction of ozone (O3) layer. It is therefore necessary to explore alternatives to CH3Br that are environmentally safe and economically viable. We present the results of the inhibitory activity of crude extracts from some Kenyan medicinal plants against the soil pathogens, Fusarium oxysporum, Alternaria passiflorae, and Aspergillus niger. Crude organic extracts from Warburgia ugandensis Sprague, Azadirachta indica A. Juss and Tagetes minuta were active against the test soil pathogens while those from Urtica massaica were not. Chromatographic purification of the crude extract from W. ugandensis provided two pure compounds, muzigadial and muzigadiolide. The minimum inhibitory concentration (MIC) for muzigadial ranged from 5 to 100 µg/ml for the different soil pathogens. Muzigadiolide was not active at concentrations tested. Greenhouse tests of W. ugandensis extracts against F. oxysporum pathogen showed the most effective inhibitory concentration to be at least 5 mg/ml.

Keywords: methyl bromide, ozone layer, soil fumigation, plant extracts, soil pathogens, and inhibitory concentration

Journal of Agriculture, Science and Technology Vol. 7(1) 2005: 41-52

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eISSN: 1561-7645