Siderophore-mediated competition for iron and induced resistance in the suppression of fusarium wilt of carnation by fluorescent Pseudomonas spp

Abstract

The mechanisms of suppression of fusarium wilt of carnation by two fluorescent Pseudomonas strains were studied.Treatments of carnation roots with Pseudomonas sp. WCS417r significantly reduced fusarium wilt caused by Fusarium oxysporum f. sp. dianthi (Fod). Mutants of WCS417r defective in siderophore biosynthesis (sid) were less effective in disease suppression compared with their wild-type. Treatments of carnation roots with Pseudomonas putida WCS358r tended to reduce fusarium wilt, whereas a sid-mutant of WCS358 did not.Inhibition of conidial germination of Fod in vitro by purified siderophores (pseudobactins) of both Pseudomonas strains was based on competition for iron. The ferrated pseudobactins inhibited germination significantly less than the unferrated pseudobactins. Inhibition of mycelial growth of Fod by both Pseudomonas strains on agar plates was also based on competition for iron: with increasing iron content of the medium, inhibition of Fod by the Pseudomonas strains decreased. The sid-mutant of WCS358 did not inhibit Fod on agar plates, whereas the sid-mutants of WCS417r still did. This suggests that inhibition of Fod by WCS358r in vitro was only based on siderophoremediated competition for iron, whereas also a non-siderophore antifungal factor was involved in the inhibition of Fod by strain WCS417r.The ability of the Pseudomonas strains to induce resistance against Fod in carnation grown in soil was studied by spatially separating the bacteria (on the roots) and the pathogen (in the stem). Both WCS417r and its sid-mutant reduced disease incidence significantly in the moderately resistant carnation cultivar Pallas, WCS358r did not.It is concluded that the effective and consistent suppression of fusarium wilt of carnation by strain WCS417r involves multiple mechanisms: induced resistance, siderophore-mediated competition for iron and possibly antibiosis. The less effective suppression of fusarium wilt by WCS358r only depends on siderophore-mediated competition for iron.

Changes in chemical composition related to fungal infection and induced resistance in carnation and radish investigated by pyrolysis mass spectrometry

“…the virulence of the inoculum and\or the environmental temperature during wilt development. Consequently, expression of induced resistance has been found in only a limited number of experiments [15,51 ]. In the present investigation the stimulus of bacterization appeared to be insufficient to affect the balance between susceptible and resistant interaction in terms of the number of diseased plants.…”

Induced Systemic Resistance as a Mechanism of Disease Suppression by Rhizobacteria

“…Although some rhizobacterial strains appear to be equally effective in inducing systemic resistance in different plant species, others show narrow specificity, indicative of a plant species-specific recognition between bacteria and receptors on the root surface . As shown in Table 1, of the three WCS strains mentioned earlier, WCS358 elicits ISR in Arabidopsis (Van Wees et al, 1997), bean and tomato (Meziane et al, 2005), but not in carnation (Duijff et al, 1993) or radish (Leeman et al, 1995a), WCS374 in radish (Leeman et al, 1995a) but not in Arabidopsis (Van Wees et al, 1997), and WCS417 in all five species Leeman et al, 1995a;Van Wees et al, 1997;Duijff et al, 1998;Bigirimana and Höfte, 2002). Moreover, of ten Arabidopsis accessions tested, eight were responsive to WCS417; accessions RLD and Ws-0 were not (Ton et al, 1999).…”

Inoculation of Sugar Beet Seed with Bacteria P. fluorescens, B. subtilis and B. megaterium – Chemical Fungicides Alternative

“…fluorescens shows distinguished biosurfactant properties (Raaijmakers et al, 2010;Ron & Rosenberg, 2001) and improves general plants condition resulting in arable crops yield and quality. As the results of their research studies some authors stated that P. fluorescens stimulate nutrients uptake (Duijff et al, 1993;Loper & Buyer, 1991), increases photosynthesis intensity (Zhang et al, 2002) as well as solubility of phosphorus inorganic forms. The aforesaid improves plants vigour and increases yield by 15-20% (Whipps, 2001).…”