Modelling cropping system effects on branched broomrape dynamics in interaction with weeds

SPE EA GESTAD Agrosup INRASPEEAGESTADAgrosupINRAInternational audienceBranched broomrape, Phelipanche ramosa (L.) Pomel, is a parasitic weed that infects many crop and weed species. As a holoparasite, it entirely relies on host-plant resources to survive and reproduce. It is a major pest of winter oilseed rape in France. In order to design efficient pest management strategies, we modelled the effects of cropping systems on P. ramosa dynamics in interaction with weeds and crops in a model called PHERASYS. PHERASYS functions and parameters were based on literature and on our own experiments. It simulates processes that determine the multi-annual parasite dynamics, i.e. in situ seed mortality, dormancy and germination, and subsequent parasite fixation and survival on the host plant until seed production and release. In situ seed mortality is very low (6-8% per year) and seeds display seasonal dormancy from mid-November to March (during French winter). We characterized interactions between P. ramosa and crops and weeds by listing host, non-host and false-host species reported in literature, and their ability to stimulate P. ramosa germination. We also showed that parasite survival until reproduction depends on host-plant biomass. The model will be evaluated and improved by adding functions quantifying the effects of parasitism on hosts. PHERASYS is an innovative approach as it models the complete life-cycle of P. ramosa within a cropping system for the first time. Once the software programming is finished, it will be used to test impacts of current and prospective cropping systems on parasitic weed dynamics. It already points to a few potential management improvements. For instance, burying seeds by tillage is not efficient to deplete the parasite seed bank, because the in situ seed mortality is low, but delaying crop sowing would be a promising means to reduce crop infestation due to the parasite seed dormancy characteristics