Fluorescent pseudomonads in the rhizosphere of plants and their relation to root exudates

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Abstract
Fluorescent pseudomonads were present in chernozem soil not influenced by plant roots (103–104 per g dry soil), in the rhizosphere soil of various plants (104–105 per g soil) and on roots (103 to 107 per g fresh roots), depending on the species and age of the plant. Relative species representation of fluorescent pseudomonads changed on the roots and in the plant rhizosphere as compared with free soil.Pseudomonas fluorescens, representing 60–93 % of the population of fluorescent pseudomonads predominated on the roots of all plants investigated. Somewhat different results were obtained in rhizosphere soil. Relatively higher numbers ofP. fluorescens were detected in the rhizosphere soil of cucumber and maize, numbers in the rhizosphere soil of wheat were practically the same as in free soil and higher numbers ofP. putida were found in the rhizosphere soil of barley. Almost all components contained in the root exudates of the plants studied, including β-pyrazolylalanine from the root exudates of cucumbers were utilized as carbon and energy sources. Root sxudates of wheat and maize were utilized by the strainP. putida K2 with an efficiency of 73–91%, depending on species and age of the plant.