Characterization of Young Citrus Rootstock Seedlings Using Metabolomics

Abstract

Choice of rootstocks for commercial citrus production is influenced strongly by tolerance to diseases and other stresses. In this study we examined whether rootstocks can be characterized based on their metabolic profile at an early seedling stage and whether presence or absence of specific metabolites can provide clues for understanding specific rootstock traits. We used four commercial citrus rootstock cultivars with different genetic backgrounds: Cleopatra mandarin (Citrus reticulata), sour orange (C. aurantium), Ridge pineapple sweet orange (C. sinensis), and Swingle citrumelo (C. paradisi x Poncirus trifoliata). Greenhouse-grown seedlings were analyzed for their metabolite composition in leaves and roots via gas chromatography-time of flight-mass spectrometry (GC-TOF-MS). Partial least squares discriminant analysis (PLS-DA) revealed clear metabolic differences among tissue types and rootstock cultivars. In both leaves and roots, largest metabolic differences were observed between 'Swingle' and 'Cleopatra', whereas differences were less pronounced between sour orange and 'Ridge'. Of the 147 chemically identified metabolites, 17 (leaves) and 29 (roots) varied significantly in concentrations among the four rootstocks. Notably, sour orange roots contained highest concentrations of hexitol and myo-inositol, compounds commonly associated with tolerance to osmotic stress, while 'Swingle' roots had lowest concentrations. These observations correspond well with known good and poor field tolerance to unfavorable soil environments for sour orange and 'Swingle', respectively. The information presented in this study provides a foundation for understanding the biochemical mechanisms of rootstock characteristics associated with stress tolerance.