The use of 8-hydroxyquinoline for the isolation and prequalification of plant growth-stimulating rhizosphere pseudomonads

Summary The application of 8-hydroxyquinoline (8OHQ) in a low-iron medium is demonstrated to be an important selective agent providing a simple and non-laborious method in the search for plant growth-stimulating and antagonistic fluorescent pseudomonads. Eleven isolates obtained from low-iron plates containing 120 ppm 8OHQ possessed similar or even better antagonistic properties in vitro than the reference strains Pseudomonas fluorescens WCS 374 and pseudobactin-producing strain B10 with plant growth-stimulating properties. One out of four of the best in vitro antagonists showed significant growth stimulation of radish (Raphanus sativus), comparable to that of the plant growth-stimulating reference strains. Iron supply abolished their antagonism in vitro, indicating that siderophores were primarily involved. The selective mode of action of 8OHQ was demonstrated to be iron stress induced by the strong chelation of available iron.