Le sucre rare tagatose: un fongicide écologique contre les espèces de phytophtora

Phytophthora species are among the most aggressive and widespread plant pathogens and they are causing enormous economic losses worldwide and whose control is mainly based on the use of chemicals. The overuse of chemical pesticides against these plant pathogens showed many threats to human health and the environment. An extremely scarce number of efficient eco-friendly products are available to control Phytophthora spp. and alternative molecules are therefore needed for sustainable agriculture. The aim of this thesis is to investigate the efficacy and the mechanism of action of the rare sugar tagatose against Phytophthora spp., in order to further develop eco-friendly fungicides based on this active ingredient. Tagatose inhibited mycelial growth and negatively affected mitochondrial processes in P. infestans, but not in P. cinnamomi indicating species-specific responses to this rare sugar. The growth inhibition of P. infestans can be ascribed to structural similarities of tagatose with fructose and to competitive inhibition of key enzymes of the sugar metabolism. On the other hand, P. cinnamomi was able to activate multiple adaptation pathways to modulate the cellular metabolism by the upregulation of genes involved in glucose transport, pentose metabolism, tricarboxylic acid cycle, reactive oxygen species detoxification, mitochondrial respiration and alternative respiration. In addition tagatose affected the composition of the phyllosphere bacteria and increased the number of beneficial plant-associated bacteria. This research showed that tagatose is a promising molecule that could be used in the development of an innovative biopesticide for the sustainable control of crop diseases.