ABSTRACT
Agronomy tries, for economic reasons, to reduce crop rotation. This can lead to a significant increase in disease caused by soilborne plant pathogens. Chemical treatment of plant disease is effective for only a short time or has no effect at all. Few plant varieties are resistant to soilborne pathogens. Genetic studies have indicated that phenazine-l-carboxylic acid is responsible for the suppression of take-all of wheat. Numerous reviews have dealt with the agronomic aspects of antagonistic pseudomonads. The taxonomic classification of fluorescent pseudomonads is an art in itself. The beneficial effects of added pseudomonads have been demonstrated in greenhouse and growth chamber experiments. The pseudomonads produce an array of extracellular metabolites that may be of importance in disease suppression. The siderophore hypothesis states that pseudomonads suppress disease by sequestering iron, which then becomes limiting for growth of pathogens in the rhizosphere.
