Induced resistance in wheat [thesis]

Fares Bellameche
During evolution, plants have developed a variety of chemical and physical defences to protect themselves from stressors. In addition to constitutive defences, plants possess inducible mechanisms that are activated in the presence of the pathogen. Also, plants are capable of enhancing their defensive level once they are properly stimulated with non-pathogenic organisms or chemical stimuli. This phenomenon is called induced resistance (IR) and it was widely reported in studies with
more » ... plants. However, mechanisms governing IR in monocots are still poorly investigated. Hence, the aim of this thesis was to study the efficacy of IR to control wheat diseases such leaf rust and Septoria tritici blotch. In this thesis histological and transcriptomic analysis were conducted in order to better understand mechanisms related to IR in monocots and more specifically in wheat plants. Successful use of beneficial rhizobacteria requires their presence and activity at the appropriate level without any harmful effect to host plant. In a first step, the interaction between Pseudomonas protegens CHA0 (CHA0) and wheat was assessed. Our results demonstrated that CHA0 did not affect wheat seed germination and was able to colonize and persist on wheat roots with a beneficial effect on plant growth. Once we showed the absence of side effects of CHA0 on wheat plants, in the second step, we evaluate efficacy of CHA0 or β-aminobutyric acid (BABA) to induce resistance against leaf rust caused by the biotroph Puccinia triticina in wheat. Our results confirmed the capacity of CHA0 to control leaf rust at the seedling stage. BABA showed dose-dependent reduction of leaf rust infection accompanied with plant growth repression at 20 mM. Balancing between protection and growth repression, a concentration of 15 mM was chosen as suitable dose for leaf rust control. Defence reactions such as callose deposition and H2O2 regeneration involved in the observed resistance were investigated. Both treatments reduced fungal penetration and haustoria formation of P. triticina with differences in timing and amplitude, leading to different levels of resistance to leaf rust. IR in wheat was accompanied with high deposition of callose and the accumulation of H2O2 during fungal infection, showing their importance in mechanisms involved in this resistance. To deeply clarify differences and similarities between CHA0- and BABA-IR at transcriptomic level, in the third step, the expression level of defence-related genes was analysed by RT-qPCR during IR induced by CHA0 and BABA against leaf rust. A correlation between induction of genes and P. triticina infection events was observed. A clear difference between the two induced responses is that BABA target more defence-related genes compared to CHA0 treatment. The last step was to evaluate the two mentioned elicitors (CHA0 and BABA), Pseudomonas chlororaphis PCL1391 and Benzothiadiazole (BTH) for their ability to induce resistance in wheat against the hemibiotrophic fungus Zymoseptoria tritici. Only BABA efficiently enhanced plant resistance to Z. tritici. In conclusion, exploiting IR might be a prominent strategy to control wheat disease. However, its effectiveness depends on the combination inducer/pathogen. Arguably, CHA0 bacteria and BABA induce similar defence reactions leading both to enhanced levels of resistance. However, only BABA enhanced defences against the hemibiotroph Z. tritici, suggesting that resistance of the plants react to the lifestyle of the pathogen and IR enhances does not involve necessarily all of them. More understanding is needed on both on capacity of the inducer to induce and the plant to become induced.
doi:10.35662/unine-thesis-2819 fatcat:y2vjehxjmrboppcvxe2eqwqyim