Is induction ability of seed germination of Phelipanche ramosa phylogenetically structured among hosts? A case study on Fabaceae species.

Phelipanche ramosa is a major root-holoparasitic damaging weed characterized by a broad host range, including numerous Fabaceae species. In France, the agricultural threat posed by P. ramosa has increased over two decades due to the appearance of a genetically differentiated pathovar presenting a clear host specificity for oilseed rape. The new pathovar has led to a massive expansion of P. ramosa in oilseed rape fields. The germination rate of P. ramosa seeds is currently known to vary among P. ramosa pathovars and host species. However, only a few studies have investigated whether phylogenetic relatedness among potential host species is a predictor of the ability of these species to induce the seed germination of parasitic weeds by testing for phylogenetic signal. We focused on a set of 12 Fabaceae species and we assessed the rate of induction of seed germination by these species for two pathovars based on in vitro co-cultivation experiments. All Fabaceae species tested induced the germination of P. ramosa seeds. The germination rate of P. ramosa seeds varied between Fabaceae species and tribes studied, while pathovars appeared non-influential. Considering oilseed rape as a reference species, we also highlighted a significant phylogenetic signal. Phylogenetically related species therefore showed more similar rates of induction of seed germination than species drawn at random from a phylogenetic tree. In in vitro conditions, only Lotus corniculatus induced a significantly higher germination rate than oilseed rape, and could potentially be used as a catch crop after confirmation of these results under field conditions.