S01 - Session O6 - Deciphering the role of three specific flavonoids produced by carrot as potential breeding markers for resistance against Alternaria dauci

Authors: Marie-Louisa Ramaroson *, Jean-Jacques Helesbeux, Latifa Hamama, Laurent Ogé, Dimitri Breard, Sébastien Huet, Anita Suel, Philippe Hugueney, Raymonde Baltenweck, Patricia Claudel, Valérie Le Clerc, Mathilde Briard

Carrot ( Daucus carota ), as a natural source of antioxidants and pro-vitamin A carotenoids, is a high nutritional value crop. However, the world carrot production is constantly threatened by a foliar disease caused by Alternaria dauci and impacting on the yield and harvestability of the crop. As described in recent studies (Le Clerc et al. , 2015; Koutouan et al. , 2018), the resistance to A. dauci is governed by several quantitative trait loci (rQTLs), whose underlying mechanisms remain to be unveiled for future resistance breeding. Therefore, the aim of this study was to characterize one of these mechanisms by highlighting the role played by three differentially accumulated flavonoids in carrot leaves. We showed that: i) two genes underlying rQTLs and differentially expressed between resistant and susceptible lines are good candidates to explain the regulation of their biosynthesis; ii) the correlation between the content in these three candidate flavonoids quantified by UHPLC-ESI/MS n and the carrot disease resistance level is obvious, not only within parental lines used for the candidate identification, but also within other sources of resistance; iii) two of the three flavonoids extracted and purified from Mentha x piperita and Daucus carota leaves, strongly interfered with A. dauci conidial germination in vitro ;and finally, iv) through the kinetics of the flavonoids accumulation in the leaves monitored by UHPLC-ESI/MS n over the carrot developmental stages, the earliest carrot developmental stage where resistance and biosynthetic accumulation of these flavonoids were quantitatively correlated, appeared to be as early as the two-leaf stage. This will offer an interesting early breeding tool for breeders.