Untargeted metabolomic LC-MS fingerprinting of apple cultivars for the identification of biomarkers related to resistance to rosy apple aphid

Abstract

Phenolic compounds may play important roles in plant responses to biotic-stress and in resistance mechanisms. In a previous work, we demonstrated the correlation between phenolic composition of apple cultivars and their tolerance to rosy apple aphid (RAA), Dysaphis plantaginea, a key pest of apple. The study was performed on a full-sib family produced at SERIDA, derived from a crossing between the local apple cultivar ?Meana? and the resistant cultivar ?Florina?. It consisted in the determination of the concentrations of individual flavan 3 ols, hydroxycinnamic acids, dihydrochalcones and flavonols by UHPLC-DAD present in the two parents and 154 descendants; and their resistance to RAA was determined after aphid inoculation in greenhouse. A relationship between the concentration of three caffeoylquinic acid isomers (4-CQA, 1-CQA and 3-CQA) and 4-p-coumaroylquinic acid (4-pCoQA) and the resistance to RAA was found by pattern recognition techniques. Cultivar resistance to RAA was concluded to be related with the phenylpropanoid pathway; the isomerisations being the key metabolic reactions for a cultivar to be resistant or susceptible to RAA.In the present work, the phenolic profiles of the same set of samples were analysed by UHPLC-ESI(+)-QTOF/MS to use an untargeted metabolomic approach to identify biomarkers related to resistance to RAA. Apple phenolic fingerprints and their resistance to RAA were submitted to multivariate data analysis by Principal Component Analysis, Hierarchical Clustering Analysis, Partial Least Square-Discriminant Analysis (PLSDA) and Orthogonal-PLSDA (O-PLSDA), which disclosed that the main features related to resistant cultivars were due to 4-CQA, and those related to susceptible cultivars to 5-pCoQA. These results agreed with previous ones since both phenolics are involved in the isomerisation reactions mentioned above.