Abstract
A bioassay is described for studying the mechanisms of growth stimulation by fluorescent pseudomonads using rooted potato stem cuttings. Root development of potato stem cuttings was inhibited in short potato-rotation soil compared to development in long potato-rotation soil. Treatment with Pseudomonas fluorescens isolate WCS374 or Pseudomonas putida isolate WCS358 increased root development in short potato-rotation soil, whereas siderophore-negative Tn5 transposon mutants of isolate WCS358 had no effect. Both siderophore-producing and siderophore-negative Tn5 mutants of isolate WCS358 could be recovered in similar numbers from the root systems. These results were obtained in a bioassay of 8 days duration. It is postulated that failure of siderophore-negative Tn5 transposon mutants of isolate WCS358 to induce growth stimulation demonstrates that siderophore production is a prerequisite for growth stimulation in short potato-rotation soil.
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