Co-Localization of Resistance and Metabolic Quantitative Trait Loci on Carrot Genome Reveals Fungitoxic Terpenes and Related Candidate Genes Associated with the Resistance to Alternaria dauci

Alternaria leaf blight, caused by the fungus Alternaria dauci, is the most damaging foliar disease of carrot. Some carrot genotypes exhibit partial resistance to this pathogen and resistance Quantitative Trait Loci (rQTL) have been identified. Co-localization of metabolic QTL and rQTL identified camphene, alpha-pinene, alpha-bisabolene, beta-cubebene, caryophyllene, germacrene D and alpha-humulene as terpenes potentially involved in carrot resistance against ALB. By combining genomic and transcriptomic analyses, we identified, under the co-localization regions, terpene-related genes which are differentially expressed between a resistant and a susceptible carrot genotype. These genes include five terpene synthases and twenty transcription factors. In addition, significant mycelial growth inhibition was observed in the presence of alpha-humulene and caryophyllene.

Automated summary

Alternaria leaf blight (ALB) is a destructive foliar disease of carrots caused by Alternaria dauci. Some carrot genotypes show partial resistance to ALB and resistance Quantitative Trait Loci (rQTL) have been identified. Metabolic and rQTL co-localization study revealed the potential involvement of specific terpenes, including camphene, alpha-pinene, alpha-bisabolene, beta-cubebene, caryophyllene, germacrene D, and alpha-humulene, in carrot resistance against ALB. Genomic and transcriptomic analyses identified differentially expressed terpene-related genes, including five terpene synthases and twenty transcription factors, in the co-localization regions between a resistant and a susceptible carrot genotype. Furthermore, alpha-humulene and caryophyllene displayed significant inhibition of mycelial growth.