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Thèse débutée le 1er novembre 2017 - Defended in November, 26th, 2020.
Financement : Métaprogramme MEM / Région Bretagne
Encadrant : Alain Sarniguet

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Abstract:

Plant microbiota can modulate host fitness. Understanding the ecological processes that drive its assembly is a prerequisite for promoting plant growth and health via the manipulation of its composition. Seed and soil are two main sources of plant microbiota inoculum and are therefore critical for its assembly. In this thesis, we showed that the structure of the seed microbiota of Brassica napus is primarily shaped by the environment and to a lesser extent by host genotype. The output of community coalescence between seed and soil microbiota was assessed with soils of contrasting microbial diversity and with distinct seed samples. Soil diversity but not seed diversity modulates seedling microbiota structure in roots and stems. Overall, seedling favors the emergence of seed- and soil-borne rare taxa. Impact of these different levels of initial diversity on a plant disease were monitored during inoculation with the pathogenic fungus Rhizoctonia solani. The soil of high diversity promotes disease reduction for one particular seed lot, giving rise for a role of the seed microbiota. No link between initial seed microbiota, seedling microbiota and disease could be established. The transmission of bacterial synthetic communities was subsequently monitored. Their inoculation on seed influences seedling microbial diversity and disease. Coalescence knowledge, transmission of rare taxa from seed to seedling and synthetic community using, give new inputs to drive seedling microbiota assembly and disease reduction.

Keywords:

seed microbiota, soil microbiota, coalescence, synthetic communities, culturomics, fungal disease

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