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RESEARCH PRODUCT

Biocontrol of Phelipanche ramosa, a parasitic weed of rapeseed in France, using soil-borne fungi

subject

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National audience; Phelipanche ramosa is a major holoparasitic weed, which became a major agronomic problemfor rapeseed crops in France. Weed control in rapeseed does not have a direct impact on thisparasitic weed whose half of the reproductive cycle occurs on the root system of its host. Since1990, broomrape expanded its distribution area starting from the Poitou-Charentes region.Necrosis symptoms on broomrapes from this region should be indicators of potentialpathogenic fungi. Furthermore, these pathogenic fungi should be able to infest differentbroomrape stages. The aim of my thesis is to contribute to the evaluation of an integrated controlsolution for this parasitic weed and focus on the use of pathogenic fungi isolated fromsymptomatic broomrapes as biocontrol solutions. A collection of 99 isolates was constituted.We studied the germination inhibition of broomrape seeds by each fungal isolate to investigatetheir impact on broomrape seeds in petri dishes. The pathogenicity of these fungi was assessedby inoculating them in pots containing soil, rapeseed and broomrape seeds to record the growthinhibition or necrosis induction of young broomrape stages. The 99 isolates showed a variablegermination inhibition of broomrape seeds, from zero to 89% germination. One strain ofFusarium strongly inhibited broomrape germination and was significantly virulent wheninoculated close to broomrape seeds leading to 84% of necrotized broomrapes in averagecompared to 1% necrotized broomrapes with another strain. However, this first strain was notas virulent when inoculated at the surface of the soil. The results highlight the importance ofthe inoculation mode, and the complexity of soil fungi, rapeseed and broomrapes interactions.Further cytological experiments would enlighten the colonization mode of the fungus toimprove its pathogenic virulence against broomrape.