Effect of the biocontrol agent Pseudomonas fluorescens F113 released as sugarbeet inoculant on the nutrient contents of soil and foliage of red clover rotation crop

The biocontrol agent Pseudomonas fluorescens F113, which produces the antimicrobial compound 2,4-diacetylphloroglucinol and inhibits soil-borne phytopathogenic fungi, might also affect non-target resident microorganisms involved in the cycling of soil nutrients. Analyses of soil nutrients and crop foliage were used to assess possible residual effects of the pseudomonad on soil fertility. The Bandon field site was sown in 1994 with sugarbeet seeds that were either untreated, inoculated with the spontaneous rifampicin-resistant mutant F113Rif, or treated with chemical fungicides. The field was cropped with uninoculated red clover in 1995. The inoculant was recovered at only 2.0 log CFU/root system at the first harvest of clovers, and the F113Rif treatment influenced 5 of 17 levels of readily available nutrients determined by electro-ultrafiltration (EUF) analysis of soil. However, this effect was essentially negligible since it was (1) small in magnitude and of little agronomic significance when compared with reference EUF levels, (2) similar in part to those of the commercial seed treatment and other farming practices followed at Bandon, and (3) not statistically significant when data were analysed at the plot level rather than using results from individual soil samples within plots. Clover leaf composition was investigated at two harvests. The F113Rif treatment had no effect on the 20 foliage parameters studied except a small (15%) transient decrease in foliage chlorine at the first harvest. EUF soil analysis and foliage analysis will be useful in future risk assessment studies of genetically modified derivatives of F113.