Abstract
BackgroundPrevious studies showed the ability of Pseudomonas putida strain BTP1 to promote induced systemic resistance (ISR) in different host plants. Since ISR is long-lasting and not conducive for development of resistance of the targeted pathogen, this phenomenon can take part of disease control strategies. However, in spite of the numerous examples of ISR induced by PGPR in plants, only a few biochemical studies have associated the protective effect with specific host metabolic changes.ResultsIn this study, we showed the protective effect of this bacterium in tomato against Botrytis cinerea. Following treatment by P. putida BTP1, analyses of acid-hydrolyzed leaf extracts showed an accumulation of antifungal material after pathogen infection. The fungitoxic compounds thus mainly accumulate as conjugates from which active aglycones may be liberated through the activity of hydrolytic enzymes. These results suggest that strain BTP1 can elicit systemic phytoalexin accumulation in tomato as one defence mechanism. On another hand, we have shown that key enzymes of the lipoxygenase pathway are stimulated in plants treated with the bacteria as compared with control plants. Interestingly, this stimulation is observed only after pathogen challenge in agreement with the priming concept almost invariably associated with the ISR phenomenon.ConclusionThrough the demonstration of phytoalexin accumulation and LOX pathway stimulation in tomato, this work provides new insights into the diversity of defence mechanisms that are inducible by non-pathogenic bacteria in the context of ISR.
Highlights
Previous studies showed the ability of Pseudomonas putida strain BTP1 to promote induced systemic resistance (ISR) in different host plants
Preliminary assays showed that methanol at this final concentration reduced B. cinerea growth by about 25% compared to water treatment but fungal development was absolutely not impaired and we consider these conditions acceptable since significant increases in optical density were recorded during the 48 h-time period of the test
Systemic resistance induced in tomato by P. putida BTP1 The protective effect of P. putida BTP1 was evaluated on five-week-old tomato plants inoculated at the root level.B. cinerea infection from inoculation droplets containing a spore suspension (105 spores/ml) typically resulted in brownish lesions covering the whole leaf area
Summary
Previous studies showed the ability of Pseudomonas putida strain BTP1 to promote induced systemic resistance (ISR) in different host plants. Some plant growthpromoting rhizobacteria (PGPR) are able to reduce disease through the stimulation of inducible plant defense mechanisms that render the host plant more resistant to further pathogen ingress. Since this induced systemic resistance (ISR) [1] is long-lasting and not conducive for (page number not for citation purposes). The reinforcement of cell wall structures through lignification or callose deposition [16,17], the accumulation of antimicrobial phytoalexins [18,19,20] and the induction of defense-related proteins with antifungal properties [21,22,23] have been reported following interactions with a pathogen. The activation of systemic resistance by nonpathogenic rhizobacteria has been associated with the induction of lipoxygenase (LOX) activity in bean and tomato [24,25,26,27]
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