Assessment of phylogenetic signal in the germination ability of Phelipanche ramosa on Brassicaceae hosts

Phelipanche ramosa is a generalist parasitic weed known to cause yield losses in various crops, especially in winter oilseed rape, its new preferred host in France. This parasitic plant is also able to complete its life cycle on many Brassicaceae weeds, which are thus important alternative hosts. We studied a set of 14 common Brassicaceae weeds and characterised their ability to induce the germination of three genetically distinct pathovars of P. ramosa, based on in vitro experiments. We then investigated whether phylogenetic relatedness among Brassicaceae weeds could inform on their ability to induce germination of P. ramosa by testing for a phylogenetic signal in the germination rate of the parasite. In the presence of some phylogenetic signal, phylogenetic distances among species might be used as a surrogate to predict the ability to induce germination of potential additional Brassicaceae hosts. The three pathovars studied showed different germination patterns. Moreover, we found substantial variation in the germination rate of P. ramosa among the different Brassicaceae species, with a significant effect of the clustering of species into two ancient phylogenetic lineages. However, no significant phylogenetic signal was detected overall, that is we could not exclude that germination rates were randomly distributed over the phylogeny. We suggest that further analyses should be conducted across wider sets of potential hosts to better characterise the existence of a phylogenetic signal of the ability of weeds to induce the germination of P. ramosa.