Effect of 2,4-diacetylphloroglucinol producing, overproducing, and nonproducing Pseudomonas fluorescens F113 in the rhizosphere of pea

Pseudomonas fluorescens F113lacZY and modified strains carrying different f unction modifications were assessed for their impact in the rhizosphere of pea. Strain F113lacZY naturally produces the anti-fungal metabolite 2,4-dia cetylphloroglucinol (Phl) useful in plant disease control. The first modifi ed strain of F113 was repressed in production of Phl, creating the Phl nega tive strain F113G22. The second was a plasmid based overproducer of Phl (F1 13Rif (pCUGP)). Both the F113lacZY and the F113Rif (pCUGP) strains increase d the rhizoplane fungal populations, whereas the same strains reduced the r hizosphere soil fungal populations with respect to the control. Similar res ults were found with the rhizoplane and rhizosphere soil bacterial populati ons. The F113G22 treatment resulted in a significantly greater indigenous f luorescent Pseudomonas population than the F113lacZY and F113Rif (pCUGP) tr eatments and a greater total Pseudomonas population than the control, F113l acZY, and F113Rif (pCUGP) treatments. Overproduction of Phl did not affect the establishment of the introduced Pseudomonas population. None of the ino cula displaced the indigenous populations, but the F113G22 inocula had an a dditive effect on the total Pseudomonas population. P (phosphatase), S (sul phatase), and N (urease) cycle enzyme activities were increased while C (gl ucosidase, NAGase) cycle activities were decreased by the F113lacZY and F11 3Rif (pCUGP) treatments, suggesting C leakage from the roots. Overall, most effects of inoculation compared to the wild type were found with the non-P hl-producing strain. Overproduction of Phl had little environmental effect in relation to wild-type inocula.