Flavonoid compounds as a way to identify sources of carrot resistance to Alternaria leaf blight.

Breeding varieties that are highly resistant to Alternaria leaf blight is crucial to enable carrot growers to drastically reduce their use of synthetic fungicides. Some sources of resistance have been identified in recent years, but in limited number and the genetic control as well as the screening for resistance remain complex and tedious. Flavonoid compounds have been reported to be involved in plant resistance to biotic or abiotic stresses. Their level of variation could therefore be a way of assisting screening activities for resistance. The aim of the study is to validate this link throughout the carrot growth cycle, in various environments and across a wide genetic diversity. A kinetic study showed that three flavonoid compounds are differentially accumulated between resistant and susceptible accessions as early as the 2-leaf stage and all along the plant development. Moreover, this differential is maintained throughout the potential infectious process in different environments. The analysis of a large range of accessions representing a very wide diversity of geographical origins, genetic structures, breeders and varietal types validates the link between resistance and the content in flavonoid compounds. These results open up extremely interesting prospects for the development of a marker-assisted early selection tool that would facilitate the screening and introgression of resistances into elite material, a complex task due to the polygenic control of resistance and biennial nature of the crop. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-025-01573-1.