Siderophore production by plant growth‐promoting pseudomonas SPP.

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Abstract
Pseudomonas putida strain WCS358, P. fluorescens strain WCS374, and siderophore‐negative mutants of these strains obtained by Tn5 transposon mutagenesis, were used in experiments to assess the role of siderophores in potato growth stimulation by WCS358. The siderophore‐negative mutants used were still able to use the siderophores produced by their respective wild‐types. WCS358 was able to use the siderophore produced by WCS374, but WCS374 could not use the siderophore produced by WCS358. Population densities of siderophore‐negative mutants of WCS358 on potato roots were high in the presence of the wild‐type strains of WCS358 or WCS374, whereas population densities of siderophore‐negative mutants of WCS374 were high only in the presence of wild‐type strain WCS374. It is concluded from these experiments that siderophores of WCS358 and WCS374 are produced in the potato rhizosphere. Root development of potato stem cuttings and potato tuber yields in soils frequently cropped to potato were increased by treatment with the wild‐type strain WCS358, whereas the siderophore‐negative mutant of this strain did not influence root development or tuber yield. Siderophore production seems to be a prerequisite for potato growth stimulation by WCS358.