Exogenous calcium delays grape berry maturation in the white cv. loureiro while increasing fruit firmness and flavonol content

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 upregulating PAL1 expression, and stimulated the accumulation of caftaric, coutaric, and fertaric acids. An increase in the levels of specific stilbenoids, namely E-piceid and E--viniferin, was observed, which correlated with the upregulation of STS expression. 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.

This work was supported by the “Contrato-Programa” UIDB/04050/2020 funded by Portuguese national funds through the FCT IP. This work was also supported by FCT, CCDR-N (Norte Portugal Regional Coordination and Development Commission), European Funds (FEDER/POCI/COMPETE2020) through the project AgriFood XXI (NORTE-01-0145- FEDER-000041) and the research projects BerryPlastid (PTDC/BIA-FBT/28165/2017 and POCI-01-0145-FEDER 028165), and MitiVineDrought (PTDC/BIA-FBT/30341/2017 and POCI-01-0145-FEDER-030341). AT was supported by a postdoctoral researcher contract/position within the project “BerryPlastid”. The Région-Centre Val de Loire (France) supported this work under the grant agreement to Projects CEPATLAS and VINODRONE to AL. This work also benefited from the networking activities within the European COST Action CA 17111 INTEGRAPE, the CoLAB VINES & WINES, and the CoLAB 4FOOD – Collaborative Laboratory for Innovation in the Food Industry

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