Genetic variation in phytochemicals in leaves of pepper (Capsicum) in relation to thrips resistance

Phytochemicals not only determine the taste and smell of plants and their products, they also play a crucial role in resistance against pests and pathogens. In previous work, we identified a form of resistance to thrips (Frankliniella occidentalis) expressed in leaves of pepper (Capsicum annuum). In the current study, we characterized leaves of an interspecific C. annuum × C. chinense F₂ population for variation in their global phytochemical composition by an untargeted metabolomics approach. Quantitative trait locus (QTL) mapping resulted in metabolite QTLs (mQTLs) for 304 of the 674 metabolites detected. We compared the QTL mapping results to those obtained earlier on fruits in the same population. Very different QTL hotspots were found, suggesting that the metabolite composition of leaves and fruits is regulated independently. Six leaf mQTLs co-located with the major QTL for resistance to thrips, which we previously identified in the same F₂ population. Four of them were significantly correlated to thrips resistance, including two diterpene glycosides and a flavonoid compound which may indicate a possible role of these metabolites in thrips resistance. If a causal role of some of these metabolites in resistance can be proven this will help in the identification of the causal gene(s) and it may provide leads for the identification of other sources of thrips resistance in Capsicum and in other species.