Culture Media and Rootstock Influence on Lemon Tree Cultivation: Metabolomic Leaves Profile

The development of new methodologies and analysis technologies is allowing to increase in knowledge about the biochemical interactions of plant organisms, as is the case of woody crops. In this sense, metabolomic studies through hydrogen nuclear magnetic resonance (1H-NMR) enable the elaboration and definition of "metabolic fingerprints". These unique metabolic footprints can support both the determination of plant varieties and the identification of plant responses and adaptations to external and/or internal factors. In this study, the primary and secondary foliar metabolites of Citrus limon Burm were identified, because it is one of the most important crops in the southeast of Spain and is frequently consumed worldwide. Thus, the trial evaluated two-year-old lemon leaf samples (variety 'Verna'), cultivated under different conditions (three rootstocks and three culture media) aiming to identify the impacts of these variables on the vegetative development of the plant. In total, 19 metabolites were identified for all the samples, of which 9 were amino acids, 5 organic acids, 3 sugars, and 2 intermediate metabolites. Sucrose and maltose were the major sugars identified, which confirms the maturity degree of the studied leaves since the mature leaves are in charge of photosynthesis and provide sources of energy and carbon (mainly sugars such as glucose) to the other plant parts. The variable importance projection (VIP) study identified quinate, arginine and malate metabolites as significant and differentiated between substrates; and arginine, quinate and sucrose metabolites as significant between rootstocks. The results pointed to a limited influence, both of the substrate and the rootstock of the crop, in the metabolomic differentiation of the lemon tree leaves. The knowledge and foliar metabolomic differentiation can offer important information that supports the application of foliar treatments of crops and also helps in the management of diseases and pests.