Carbon fractions in the rhizosphere of pea inoculated with 2,4 diacetylphloroglucinol producing and non-producing Pseudomonas fluorescens F113

The aim of this work was to determine the effect of wild type and functiona lly modified Pseudomonas fluorescens strains on C fractions in the rhizosph ere of pea. The lacZY marked F113 strain produces the antibiotic 2,4 diacet ylphloroglucinol (DAPG) useful in plant disease control. The modified strai n of F113 was represented in production of DAPG, creating the DAPG negative strain F113 G22. The F113 treatment resulted in a significantly lower shoo t/root ratio. The F113 G22 treatment had a significantly greater indigenous and total fluorescent Pseudomonas population than the control and F113 (DA PG+) treatment. Both strains significantly increased the water soluble carb ohydrates and the total water soluble carbon in the pea rhizosphere soil. S train F113 significantly increased the soil protein content relative to the control, but not in relation to the F113 G22 treatment. The F113 treatment had a significantly greater organic acid content than the control and F113 G22 treatments, whilst the F113 G22 treatment was also significantly great er than the control. Both inocula resulted in significantly lower phosphate contents than the control. The F113 inocula significantly increased alkali ne phosphatase, sulphatase and urease activities, and reduced beta glucosid ase activities indicating increased carbon availability. Both inocula incre ased C availability; however, antibiotic production by strain F113 reduced the utilisation of organic acids released from the plant resulting in diffe ring effects of the two strains on nutrient availability, plant growth, soi l enzyme activities and Pseudomonas populations.