Selection of Antagonistic Fluorescent Pseudomonas spp. and their Root Colonization and Persistence following Treatment of Seed Potatoes

Abstract

One hundred and twelve fluorescent Pseudomonas isolates from potato periderm were screened for antagonistic activity in vitro against 5 pathogenic and saprophytic fungi, 5 Gram‐positive bacteria including Streptomyces scabies and 4 Gram‐negative bacteria including Erwinia car. var. carotovora and Erwinia car. var. atroseptica. Fifty‐seven percent of the isolates showed wide spectrum inhibitory activity, mostly due to the production of fluorescent siderophores. Only 4 % of the isolates were very strong antagonists. By adding iron (Fe3+) to the test medium, the antagonistic activity drastically diminished but revealed some strong antagonists of which the antagonism was not affected. Apparently growth‐inhibiting substances other than siderophores were involved. Antibiotic‐resistant mutants of the antagonists were used to establish that the bacteria on the seed tubers migrated to the roots under different conditions. Drying of the treated potatoes gradually diminished the number of viable cells, but subsequent planting in moist soil led to substantial increases in the first three days. Initially high numbers of the antibiotic‐resistant antagonists on the roots tended to drop quickly in time, probably due to loss of resistance to the antibiotics in the selective medium.

Colonization of the developing rhizosphere of sugar beet seedlings by potential biocontrol agents applied as seed treatments

“…Studies made by other workers have also observed a population revival when seed bearing apparently declining bacterial numbers are introduced into the soil environment. Geels and Schippers (1983) demonstrated that even after large decreases in viable cell numbers during drying of treated potato seed tubers, bacterial numbers subsequently increased substantially during the first three d after sowing. The general trend in rhizosphere population dynamics with bacteria introduced as seed treatments is typified by a rapid increase in numbers (especially in sterile soil) followed by a period of stabilization and slow decline to non-detectable levels (Geels and Schippers 1983;Kloepper et al 1992;Kluepfel and Tonkyn 1992;Kluepfel 1993).…”

“…Geels and Schippers (1983) demonstrated that even after large decreases in viable cell numbers during drying of treated potato seed tubers, bacterial numbers subsequently increased substantially during the first three d after sowing. The general trend in rhizosphere population dynamics with bacteria introduced as seed treatments is typified by a rapid increase in numbers (especially in sterile soil) followed by a period of stabilization and slow decline to non-detectable levels (Geels and Schippers 1983;Kloepper et al 1992;Kluepfel and Tonkyn 1992;Kluepfel 1993). Kluepfel (1993) reported that for a fluorescent pseudomonad seed treatment, regardless of the initial concentration of inoculum applied (within a range of 10 4 -10 9 cells ml -1 ), an optimum rhizosphere population potential was reached which represented the carrying capacity of the root.…”

A Novel Signaling Pathway Controlling Induced Systemic Resistance in Arabidopsis

“…In duplicate, roots of six plants per treatment were harvested, weighed, and shaken vigorously for 1 min in 5 mL of 10 mM MgSO 4 containing 0.5 g of glass beads (0.17 mm diameter). Appropriate dilutions were plated onto King's medium B agar supplemented with cycloheximide (100 mg/L), ampicillin (50 mg/L), chloramphenicol (13 mg/L), and rifampicin (150 mg/L), which is selective for rifampicin-resistant, fluorescent Pseudomonas spp (Geels and Schippers, 1983). After overnight incubation at 28ЊC, the number of rifampicin-resistant colony-forming units per gram of root fresh weight was determined.…”

Involvement of the outer membrane lipopolysaccharides in the endophytic colonization of tomato roots by biocontrol Pseudomonas fluorescens strain WCS417r

“…Densities on the rhizoplane of the aerobic bacteria, of the total fluorescent pseudomonads and of strains WCS417r or B4, were evaluated by numeration of colonyforming units (c.f.u.) after plating (Spiral System®, Interscience, France) serial dilutions of the rhizoplane suspensions on Bacto peptone agar supplemented with 100 ppm cycloheximide (BP^), on KB"â gar (Geels & Schippers, 1983) and on KB"^ agar supplemented with 150 ppm rifampicin, respectively. Colonization within the root was assessed from 16 replicate plants.…”