EFFECT OF THE BIOCONTROL AGENT PSEUDOMONAS-FLUORESCENS F113 RELEASED AS SUGAR-BEET INOCULANT ON THE NUTRIENT CONTENTS OF SOIL AND FOLIAGE OF A RED-CLOVER ROTATION CROP

The biocontrol agent Pseudomonas fluorescens F113, which produces the antimicrobial compound 2,4-diacetylphloroglucinol and inhibits soil-bo rne phytopathogenic fungi, might also affect non-target resident micro organisms involved in the cycling of soil nutrients. Analyses of soil nutrients and crop foliage were used to assess possible residual effec ts of the pseudomonad on soil fertility. The Bandon field site was sow n in 1994 with sugarbeet seeds that were either untreated, inoculated with the spontaneous rifampicin-resistant mutant F113Rif, or treated w ith chemical fungicides. The field was cropped with uninoculated red c lover in 1995, The inoculant was recovered at only 2.0 log CFU/root sy stem at the first harvest of clovers, and the F113Rif treatment influe nced 5 of 17 levels of readily available nutrients determined by elect ro-ultrafiltration (EUF) analysis of soil. However. this effect was es sentially negligible since it was (1) small in magnitude and of little agronomic significance when compared with reference EUF levels, (2) s imilar in part to those of the commercial seed treatment and other far ming practices followed at Bandon, and (3) not statistically significa nt when data were analysed at the plot level rather than using results from individual soil samples within plots. Clover leaf composition wa s investigated at two harvests. The F113Rif treatment had no effect on the 20 foliage parameters studied except a small (15%) transient decr ease in foliage chlorine at the first harvest. EUF soil analysis and f oliage analysis will be useful in future risk assessment studies of ge netically modified derivatives of F113.