What are the traits of Phelipanche ramosa (L.) Pomel that contribute to the success of its biological cycle on its host Brassica napus L.?

In France, the fact that the holoparasitic plant Phelipanche ramosa has adapted to oilseed rape over the past two decades is deeply worrying, as it can cause over 80% yield losses. Its distribution area and the range of its host plants, whether they are cultivated plants or weeds, are expanding dramatically. As no natural regression of the infestation has been recorded so far, we undertook a detailed study of the different steps of the biological cycle of the P. ramosa/oilseed rape pathosystem to determine the adaptive traits that favour the parasite's success. We combined experimental approaches involving controlled conditions with in vitro and in pot co-cultivation on the one hand and a field trial on the other hand. These experiments allowed us to determine a 4-mm zone around host roots within which oilseed rape root exudates stimulate the germination of P. ramosa, the early action of host root exudates and the rapid fixation of the parasite on host roots. We also unveiled that P. ramosa was able to tune its biological cycle to that of oilseed rape. The important trophic relationships between the parasite and its host induced phenotypic (dwarfism, leaf chlorosis, silique abortion) as well as agronomical (90% yield losses) consequences on oilseed rape. Our results can constitute a relevant basis for further experimental studies. The research perspectives they open will focus on key-processes of the host–parasite relationship, and more particularly on the trophic relationships that are set up as far as carbon assimilates and minerals such as nitrogen are concerned.