Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Nikolaus H. Fischer

Abstract

Obligate root-parasitic flowering plants of the genus Striga (family Scrophulariaceae) cause considerable yield reductions of various crops in tropical and semi-tropical countries. Mature Striga species (witchweeds) plants produce copious quantities of minute seeds which remain dormant in the soil for many years until exudates from roots of various host plants induce germination. Economically effective means of control of Striga species are not yet available for small-scale farmers in developing countries. In the present study data is presented which indicate that the two most effective Striga control measures are crop rotation and suicidal germination. For the first time we have analyzed the dichloromethane extracts of dry and conditioned Striga species seeds by means of gas chromatography coupled to mass spectrometry. Sixteen compounds were identified on the basis of their mass spectra and their retention indices. All Striga species extracts contained tetradecanoic acid, cis,cis-9,12-octadecadienoic acid, cis-9-octadecenoic acid and sitosterol. Also, 2,6-dimethoxy-p-benzoquinone (2,6-DMBQ) and several long chain aldehydes and n-hydrocarbons were detected in some of the extracts. The nature of the chemical changes induced by seed conditioning are discussed. Dichloromethane and water extracts of various parts of legume cultivars were tested for stimulation of germination of Striga species seeds as described in the experimental sections. Also, several pure compounds isolated were assayed. Dilution methods, which are very sensitive and better suited for quantifying germination stimulant activity, were employed in identification of high and low stimulant producing legume cultivars. New and interesting relationships between stimulatory activity and concentration emerged. Most pure compounds tested induced significant germination of isolates of Striga species seeds across a broad concentration range, from $10\sp{-3}$ to $10\sp{-20}$M. The mechanism of Striga germination proposed may foster synthesis of more effective germ stimulants and/or inhibitors.

ISBN

9780591288858

Pages

226

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