[HDR defence] 02/09/2025 - François Lecompte: "Increasing the resistance of vegetable crops to pathogenic fungi by identifying and controlling phenotypic markers, optimising genotype x environment interactions and developing integrated protection methods".

This HDR dissertation retraces a twenty-five year research career that has focused on three thematic areas relating to the interactions between cultivated plants and their biotic and abiotic environment. A body of work has been carried out on the architecture of root systems and its plasticity, particularly under the effect of soil mechanical constraints and phosphorus availability. The results help to show how plants retain a general organisation of their architectural traits, even on an interspecific scale, while adapting to their environment, sometimes with responses that are specific to the species being cultivated. The second theme concerns projects with a more agronomic focus, carried out on vegetable cropping systems (tomato, lettuce, strawberry), largely in conjunction with industry support organisations and private partners. The study of technical itineraries, combined with experimental trials, sometimes factorial, sometimes using systems approaches, has led to proposals for new strategies to reduce inputs, fertilisers, water and pesticides, thereby limiting environmental impact and controlling pests and diseases.

The third theme concerns the defence of plants against necrotrophic fungal pathogens, in particular Botrytis cinereaanalysed using experimental and modelling approaches. This work, carried out in close partnership with INRAE-PACA's Plant Pathology unit, has helped to demonstrate the importance of plant metabolism in building immunity, and the way in which the abiotic environment conditions the formation of metabolic activity favourable to defence. The role of sugars, in particular fructose, has been highlighted by robust empirical observations, but the underlying mechanisms linking fructose to resistance remain to be clarified. This is one of the main thrusts of the research project outlined here, which focuses on plant ecophysiology and also proposes to take a closer look at the coordination of the host plant's hormonal responses in building up its immunity to necrotrophs. With a more agronomic aim, it is also proposed to continue studies on the tactical management of nitrogen nutrition to promote the defence of market garden plants against pathogenic fungi, in order to better integrate nutrition with the other levers used in integrated crop protection.