Mechanisms underlying the protective effect of the biocontrol agent Bacillus subtilis 30B-B6 in Solanaceae
(2021)
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Details
- Authors
- Supervisors
- Legrève, Anne
- Abstract
- Bacillus spp. offer a promising and sustainable alternative in crop protection. Both their direct antagonism towards pathogens as well as their indirect action by either eliciting systemic resistance or stimulating plant growth is mostly explained by the numerous bioactive compounds they produce. Our objective was to evaluate and understand how the B. subtilis 30B B6 can control early and late blight diseases on Solanaceae. Recent work reported the interest of 30B-B6 against potato late blight caused by Phytophthora infestans, an hemibiotrophic pathogen. This research aims to deepen knowledge on the effective biocontrol potential of this strain by performing further field trials and investigating its activity against potato early blight caused by the necrotrophic pathogen, Alternaria solani. Field experiments have proved that 30B-B6 can contribute to reducing the potato late blight pressure. Greenhouse experiments on tomato revealed that 30B-B6 also reduced (up to 76%) the disease pressure caused by A. solani, showing that 30B-B6 exhibits effective antagonistic properties against hemibiotrophic and necrotrophic pathogens. Bioassays performed on tomato plants also revealed the that the application of the bacterium on the root substrate led to reduce the disease severity to the same level as the foliar treatment. B. subtilis 30B-B6 is able to control the pathogen by direct antagonism and by stimulation of the plant defenses. This work gives a first insight into the molecular pathways involved in the induction of systemic resistance by 30B-B6 in tomato. We used RT qPCR and salicylic acid (SA) quantification to understand the action of 30B-B6 on plant defenses. We showed that the genes PR2b and WRKY1, coding for a glucosidase and a transcription factor involved in the expression of SA dependent genes, are overexpressed in plants displaying resistance to the pathogen after a treatment with the bacterium. The higher content of SA in these plants supports the involvement of SA in response to treatment with B. subtilis 30B-B6. In order to test the bioactive compounds produced by 30B-B6, comparative bioassays were performed. We investigated the potential implication of lipopeptides (LPs) and siderophore produced by 30B-B6 in the induction of the systemic resistance. LPs and siderophores partially purified from culture in G-A medium significantly reduced symptoms of early blight (protection around 53%). This thesis shows that the stimulation of tomato systemic defenses by the bacterium against a necrotrophic fungus involved the SA-pathway. While resistance to necrotrophic pathogens is generally described as independent of the SA-pathway. Taken together, this thesis reveals how B. subtilis 30B-B6 acts via direct antagonism and by stimulating the plant host defense mechanisms. The interest of this bacterium as a biocontrol agent is thus confirmed.
- Affiliations
Citations
Colau, G. (2021). Mechanisms underlying the protective effect of the biocontrol agent Bacillus subtilis 30B-B6 in Solanaceae. https://hdl.handle.net/2078.5/114520