Abstract
Alternate bearing in citrus trees has been extensively studied as a key feature for citrus growers. Although the genetic and the biochemical process occurring during alternate bearing has been studied extensively, there is a lack of information identifying the presence of metabolic indicators during “on” and “off” years. In citrus plants, leaves play a central role in the metabolic pathway triggering the flowering induction process. To investigate the changes during this transition, a liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis of the leaf profiles of 20 compounds (17 polyphenols, two limonoids, and one furanocoumarin), in bearing and non-bearing branches arising from four different mandarin genotypes, was performed. The same metabolites were found in all the genotypes at both stages: both limonoids and 11 polyphenols. Using these compounds, the chemotaxonomic differentiation between cultivars was assessed. The levels of flavanones and limonoids showed differences in both bearing stages and the transition from vegetative to flowering could be shown by the activation of the polyphenol biosynthetic pathway, from precursors like naringenin to metabolic end-points such as narirutin and polymethoxyflavones. Narirutin levels showed significant differences between both stages, suggesting it as a possible marker of the physiological status of the branch.
Highlights
Citrus is one of the main fruit crops worldwide with more than 143 million tons produced in 2019 [1]
This study allowed the differentiation between leaves from non-bearing and bearing branches
Leaves from both physiological stages accumulated limonin, but nomilin showed an increased leaf concentration in non-bearing branches compared to bearing ones
Summary
Citrus is one of the main fruit crops worldwide with more than 143 million tons produced in 2019 [1]. The mechanism by which the developing crop influences blooming and fruit yield the forthcoming year has not been fully understood yet. One hypothesis holds that return bloom and yield are related to tree carbohydrate status and, lack of carbohydrate in the “on” year directly or indirectly reduces flowering the following year [2]. Other authors claim that developing fruit produces an inhibitor that directly or indirectly reduces flowering in the spring following the “on” crop [2,3]. Extensive research has been conducted to unravel the hormonal and genetic regulation of flowering induction in Citrus [4,5], there is still a lack of information describing metabolites’ changes (in terms of quality and quantity) occurring during “on” and “off” years as putative markers depicting this transition
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