Exogenous Calcium Delays Grape Berry Maturation in the White cv. Loureiro While Increasing Fruit Firmness and Flavonol Content

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Abstract
Vineyard calcium (Ca) sprays have been increasingly used by grape growers to improve fruit firmness and thus maintain quality, particularly in periods of heavy rains and hail. The observation that Ca visibly modified berry size, texture, and color in the most prominent white cultivar of the DOC region ‘Vinhos Verdes’, cultivar (cv.) Loureiro, led us to hypothesize that Ca induced metabolic rearrangements that resulted in a substantial delay in fruit maturation. Targeted metabolomics by ultra-performance liquid chromatography coupled to mass spectrometry and directed transcriptomics were thus combined to characterize the metabolic and transcriptional profiles of cv. Loureiro berries that, together with firmness, °Brix, and fruit weight measurements, allowed to obtain an integrated picture of the biochemical and structural effects of Ca in this cultivar. Results showed that exogenous Ca decreased amino acid levels in ripe berries while upregulatingPAL1expression, and stimulated the accumulation of caftaric, coutaric, and fertaric acids. An increase in the levels of specific stilbenoids, namelyE-piceid andE-ω-viniferin, was observed, which correlated with the upregulation ofSTSexpression. Trace amounts of anthocyanins were detected in berries of this white cultivar, but Ca treatment further inhibited their accumulation. The increased berry flavonol content upon Ca treatment confirmed that Ca delays the maturation process, which was further supported by an increase in fruit firmness and decrease in weight and °Brix at harvest. This newly reported effect may be specific to white cultivars, a topic that deserves further investigation.
Funding Information
  • Fundação para a Ciência e a Tecnologia (UIDB/04050/2020, PTDC/BIA-FBT/28165/2017 and POCI-01-0145-FEDER-028165, PTDC/BIA-FBT/30341/2017 and POCI-01-0145-FEDER-030341, CoLAB VINES & WINES, CoLAB 4FOOD - Collaborative Laboratory for Innovation in the Food Industry)
  • European Regional Development Fund (NORTE-01-0145-FEDER-000041)
  • European Cooperation in Science and Technology (CA 17111 INTEGRAPE)
  • Conseil Régional du Centre-Val de Loire (CEPATLAS, VINODRONE)

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