Effects of the Tomato Pathogen Fusarium oxysporum f. sp. radicis-lycopersici and of the Biocontrol Bacterium Pseudomonas fluorescens WCS365 on the Composition of Organic Acids and Sugars in Tomato Root Exudate

Abstract

The effects of the pathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici and of the bacterial biocontrol strain Pseudomonas fluorescens WCS365, and of both microbes, on the amounts and composition of root exudate components of tomato plants grown in a gnotobiotic stonewool substrate system were studied. Conditions were selected under which introduction of F. oxysporum f. sp. radicis-lycopersici caused severe foot and root rot, whereas inoculation of the seed with P. fluorescens WCS365 decreased the percentage of diseased plants from 96 to 7%. This is a much better disease control level than was observed in potting soil. Analysis of root exudate revealed that the presence of F. oxysporum f. sp. radicis-lycopersici did not alter the total amount of organic acids, but that the amount of citric acid decreased and that of succinic acid increased compared with the nontreated control. In contrast, in the presence of the P. fluorescens biocontrol strain WCS365, the total amount of organic acid increased, mainly due to a strong increase of the amount of citric acid, whereas the amount of succinic acid decreased dramatically. Under biocontrol conditions, when both microbes are present, the content of succinic acid decreased and the level of citric acid was similar to that in the nontreated control. The amount of sugar was approximately half that of the control sample when either one of the microbes was present alone or when both were present. Analysis of the interactions between the two microbes grown together in sterile tomato root exudate showed that WCS365 inhibited multiplication of F. oxysporum f. sp. radicis-lycopersici, whereas the fungus did not affect the number of CFU of the bacterium.

Distribution of organic metabolites after Fusarium wilt incidence in tomato (Solanum lycopersicum L.)

“…The positive and significant correlation between disease incidence and citric acid content supports this notion (Table 3). These results disagree with some earlier reports (Szopinska, 2013;Awadalla, 2008), but support Kamilova et al (2006) who observed that Fusarium oxysporum f. sp. radicis-lycopersicum, the causal agent of foot and root rot in tomato, did not change the total amount of organic acid but instead decreased citric acid content.…”

Impact of root exudates and plant defense signaling on bacterial communities in the rhizosphere. A review

“…Root exudate composition is also influenced by the rhizosphere microflora itself. Application of the bacterial biocontrol strain Pseudomonas fluorescens WCS365 (WCS365) on tomato roots resulted in increased levels of total organic acids, whereas the amount of succinic acid decreased (Kamilova et al 2006a). Inoculation of the tomato roots with the pathogenic fungus Fusarium oxysporum f. sp.…”

Monosaccharide Absorption Activity of Arabidopsis Roots Depends on Expression Profiles of Transporter Genes under High Salinity Conditions

“…The identification of glucose and fructose as major components of root exudates (6,28,29) prompted us to test the uptake of these sugars in wild type and mutant plants under high salinity conditions (Fig. 6, A and B).…”