RESISTANCE MECHANISMS TO OROBANCHE CRENATA IN PEA (PISUM SATIVUM L.): BEYOND STRIGOLACTONES

Strigolactones (SLs) are a group of carotenoid-derived compounds occurring in plant root exudates, known to stimulate the germination of parasitic weeds belonging to the large family of Orobanchaceae, such as broomrapes and witchweeds. In several economically important crops, resistance to Orobanchaceae is associated with reduced SL biosynthesis and/or altered blend of individual SL molecules. In pea (Pisum sativum L.), we previously selected the line ROR12, associated with low SL levels and nearly complete field resistance to the parasitic weed Orobanche crenata Forsk. (Oc). Here, we performed field trials to select pea genotypes with contrasting response to Oc, starting from: 1) a population of recombinant inbred lines (RILs) originating from the cross between ROR12 and the susceptible cultivar ‘Sprinter’; 2) a germplasm population. Notably, LC-QTOF-MS analysis of root exudates indicated that, in both populations, genotypes showing lower parasitization rates also display significantly lower (although detectable) levels of the pea SLs orobanchol, orobanchyl acetate and fabacyl acetate, suggesting that SLs play an effective role in field resistance against Oc. Unexpectedly, a third field trial carried out with the pea wild-type cultivar Térèse and its mutants rms5 and rms1, impaired for key SL biosynthetic genes, indicated that complete lack of SLs only confers partial resistance to Oc. Overall, our results indicate that ROR12 resistance might be partially due to mechanisms that are independent from SL biosynthesis. In addition, considering negative pleiotropic effects associated with severe SL deficiency, such as extensive branching and dwarfism exhibited by the rms mutants, we envisage that the exploitation of post-germination and post-attachment defense mechanisms to Oc might be valuable for pea breeding.