Metabolomics deciphers quantitative resistance mechanisms in diploid potato clones against late blight

Resistance to late blight in potato is either qualitative or quantitative in nature. The quantitative resistance is durable, but the molecular and biochemical mechanisms underlying quantitative resistance are poorly understood, and are not efficiently utilised in potato breeding. A non-targeted metabolomics, using high resolution hybrid mass spectrometry, was applied to decipher the mechanisms of resistance in the advanced breeding diploid potato genotypes (Solanum tuberosum L. Group Phureja), with valuable sources of genetic diversity. The metabolomics profiles of resistant genotypes (AC04 and AC09) were compared with a susceptible commercial genotype (Criolla Colombia), following Phytophthora infestans or mock-inoculation, to identify the resistance related (RR) metabolites. Metabolites belonging to phenylpropanoids, flavonoid and alkaloid chemical groups were highly induced in resistant genotypes relative to susceptible. Concurrently, the biosynthetic genes, tyrosine decarboxylase (TyDC) and tyramine hydroxycinnamoyl transferase (THT), involved in the biosynthesis of hydroxycinnamic acid amides (HCAAs), and chalcone synthase (CHS) and flavonol synthase (FLS), involved in flavonoid biosynthesis, were also upregulated, as confirmed by quantitative real-time PCR. Probable genes coding for these enzymes were sequenced and nonsynonymous single-nucleotide polymorphisms (nsSNPs) were identified. The resistance to late blight observed in this study was mainly associated with cell wall thickening due to deposition of HCAAs, flavonoids and alkaloids.