Low strigolactone root exudation: A novel mechanism of broomrape (Orobanche and Phelipanche spp.) resistance available for faba bean breeding

Faba bean yield is severely constrained in the Mediterranean region and Middle East by the parasitic weeds Orobanche crenata, O. foetida, and Phelipanche aegyptiaca. Seed germination of these weeds is triggered upon recognition of host root exudates. Only recently faba bean accessions have been identified with resistance based in low induction of parasitic seed germination, but the underlying mechanism was not identified. Strigolactones are a group of terpenoid lactones involved in the host recognition by parasitic plants. Our LC-MS/MS analysis of root exudates of the susceptible accession Prothabon detected orobanchol, orobanchyl acetate, and a novel germination stimulant. A time course analysis indicated that their concentration increased with plant age. However, low or undetectable amounts of these germination stimulants were detected in root exudates of the resistant lines Quijote and Navio at all plant ages. A time course analysis of seed germination induced by root exudates of each faba bean accession indicated important differences in the ability to stimulate parasitic germination. Results presented here show that resistance to parasitic weeds based on low strigolactone exudation does exist within faba bean germplasm. Therefore, selection for this trait is feasible in a breeding program. The remarkable fact that low induction of germination is similarly operative against O. crenata, O. foetida, and P. aegyptiaca reinforces the value of this resistance. © 2014 American Chemical Society.This work was supported by the Program for Promotion of Basic and Applied Researches for Innovation in Bio-oriented Industry to K.Y., T.K., and X.X. and to projects FP7-LEGATO and AGL2011-22524, cofinanced by FEDER funds to D.R. M.F.-A. has received the support of the European Union, in the framework of the International Outgoing European Marie Curie Postdoctoral Fellowship Programme (PIOF-GA-2009- 252538), and from the Japan Society for the Promotion of Science Postdoctoral Fellowship ID noP 13390.Peer Reviewe