Pestic. zyxwvutsrq Sci. zyxwvutsrq 1989, 27, 141-154 zyxwvutsr Dominant Rhizosphere Bacteria as a Source for Antifungal Agents* zyx Katelijn H. Lievens, Ronan Van Rijsbergen, Frederik R. Leyns, Bart J. Lambert, Paul Tenning, Jean Swings zyx & Henk J.-P. Joos: Plant Genetic Systems, B-9000 Ghent, Belgium (Revised manuscript received 18 April 1989; accepted 20 April 1989) zyx ABSTRACT A search for micro-organisms associated in high numbers with roots or leaves of corn, grapevine, chicory, soybean, sunflower, barley and sugarbeet yielded a collection zyxwvu of over 10 000 bacterial strains. Within this collection, antifingal strains have been selected, using direct or indirect in-vitro assays against one target fungus per crop. The target .fungi were selected based on their agronomic relevance as pests. Isolates with antifungal activity were tested jor their spectrum zyx of activity against a set of phytopathogenic fungi. In I5 bacterial strains with broad- spectrum activity, belonging to the species Erwinia herbicola. Serratia plymuthica, Pseudomonas fluorescens, P. aureofaciens, P. cepacia and Bacillus subtilis, the active compounds have been identified. Bacterial strains belonging to the same taxon, but isolated fiom different ecological niches andlor different places in Europe, produce identical compounds. In two bacterial taxa (Erwinia and Serratia) this was reflected in a genetic conservation of the regions coding for antifungal activity. In both cases, the biosynthetic pathways proved to be genetically complex. All of the compounds identified in this study have been described previously in bacterial strains isolated jiom analogous or completely different ecosystems. * Paper presented at the symposium 'Natural Products as a Source ]or New Agricultural Chemicals' organised by the Pesticides Group of the Society of Chemical Industry and held in London on 21-22 February 1989. To whom correspondence should be addressed. 141 Pestic. Sci. 0031-613X/89/$03.60 zyxwvut 0 1989 Society of Chemical Industry. Printed in Great Britain