Claire Prigent‐Combaret

Parasitic weeds such as broomrapes ( Phelipanche ramosa and Orobanche cumana ) cause severe damage to crops and their development must be controlled. Given that phloroglucinol compounds (PGCs) produced by environmental Pseudomonas could be toxic towards certain plants, we assessed the potential herbicidal effect of the bacterial model Pseudomonas ogarae F113, a PGCs‐producing bacterium, on parasitic weed. By combining the use of a mutagenesis approach and of pure PGCs, we evaluated the in vitro effect of PGC‐produced by P. ogarae F113 on broomrape germination and assessed the protective activity of a PGC‐producing bacteria on oilseed rape ( Brassica napus ) against P. ramosa in non‐sterile soils . We showed that the inhibition of the germination depends on the PGCs molecular structure and their concentrations as well as the broomrape species and pathovars. This inhibition caused by the PGCs is irreversible, causing a brown coloration of the broomrape seeds. The inoculation of PGCs‐producing bacteria limited the broomrape infection of P. ramosa , without affecting the host growth. Moreover, elemental profiling analysis of oilseed rape revealed that neither F113 nor applied PGCs affected the nutrition capacity of the oilseed rape host. Our study expands the knowledge on plant‐beneficial Pseudomonas as weed biocontrol agents and opens new avenues for the development of natural bioherbicides to enhance crop yield.