SOIL ENZYME-ACTIVITIES IN THE RHIZOSPHERE OF FIELD-GROWN SUGAR-BEET INOCULATED WITH THE BIOCONTROL AGENT PSEUDOMONAS-FLUORESCENS F113

Pseudomonas fluorescens F113, which produces the antimicrobial compoun d 2,4-diacetylphloroglucinol, is a prospective biocontrol agent. Soil enzyme activities were used to investigate the ecological impact of st rain F113 in the rhizosphere of field-grown sugar beet. There were dis tinct trends in rhizosphere enzyme activities in relation to soil chem istry [determined by electro-ultrafiltration (EUF)]. The activities of enzymes from the P cycle (acid phosphatase, alkaline phosphatase and phosphodiesterase) and of arylsulphatase were negatively correlated wi th the amount of readily available P, whereas urease activity was posi tively correlated with the latter. Significant correlations between nu trient levels determined by EUF and enzyme activities in the rhizosphe re were obtained, highlighting the usefulness of enzyme assays to docu ment variations in soil nutrient cycling. Contrary to previous microco sm studies, which did not investigate plants grown to maturity, the bi ocontrol inoculant had no effect on enzyme activities or on soil chemi stry in the rhizosphere. The results showed the importance of using ho mogenous soil microcosm systems, also employed in previous work, for r isk assessment studies, whereby the effects of inherent soil variabili ty were minimised, and effects of the pseudomonad on soil enzymology c ould be detected.