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Leptosphaeria maculans (anamorph Phoma lingam) causes stem canker of oilseed rape (Brassica napus) and other crucifers. The disease is present in all regions of the world growing oilseed rape (or canola), except China.

L. maculans has a saprophytic life followed by a lengthy pathogenic life during which it behaves as an hemibiotroph. In Europe, the fungus lives as a saprobe on stem residues for many years, on which sexual reproduction takes place. In Autumn in France, shortly after the sowing of oilseed rape, pseudothecia differentiate and produce ascospores which are the primary and main infectious organs. Ascospores are disseminated by wind and land on cotyledons or leaves on which they germinate. Infectious hyphae penetrate the plant organs via natural apertures (stomata, wounds) and colonize the leaf mesophyl, eventually causing the typical greyish-green primary leaf symptom. This symptom supports production of asexual multiplication spores, of low relevance in the disease cycle, while mycelia undertake a systemic and symptomless colonization of leaf, petiole, stem and eventually crown tissues. Mycelia remain within the tissues as an endophyte for months and the fungus shifts to a necrotrophic behaviour at the end of the growing season in spring/summer. It then causes a stem basis necrosis that may result in lodging of the plant before harvest. Alternating lifestyles suggest the existence of a sophisticated molecular dialogue between the fungus and its host plant, and the ability for the fungus to set up complex and finely tuned biological programs.

Fungicides are uneasy to use efficiently in this system, and control of the disease mainly relies on genetic resistance of oilseed rape. In the agronomical practice, major genes for resistance (Rlm genes) operating at the leaf stage are largely used but they are increasingly combined with high level of general resistance in order to maximise the durability of the Rlm genes.

Objectives of our researches are:

              - Understanding mechanisms underlying biotic interactions within the plant/pathogen ecosystem

              - Understanding adaptation and its spatio-temporal dynamics

              - Identification and evaluation of sustainable disease control methods.

Main results:

The team has established L. maculans as a model for the study of plant-fungal interactions leading to new concepts such as (i) genome plasticity and the rise of the “two-speed” genome paradigm; (ii) consequence of genome structure on waves of effector gene expression during plant colonization and their transcriptional and chromatin-based regulation, and on speed/mechanisms of adaptation to plant resistance, and (iii) occurrence of complex and unusual mechanisms to escape recognition of the fungus by the plant surveillance machinery.