Vineyard calcium sprays reduce the damage of postharvest grape berries by stimulating enzymatic antioxidant activity and pathogen defense genes, despite inhibiting phenolic synthesis

Calcium supplements have been increasingly used for decay prevention, sanitation and nutritional enrichment of fruits, as more environmentally friendly alternatives to fungicides. However, little is known on the effects of these supplements on grape berry biochemical and molecular properties during storage. In this study, we addressed the hypothesis that the application of calcium chloride (CaCl2) in grapevines throughout the fruiting season reduces damage (and decay) of postharvest grape berries, through several biochemical and transcriptional modifications in sugar transport, secondary metabolism, antioxidant activity, cell wall organization and pathogen defense. Results showed that calcium (Ca) treatments in cv. Vinhão vines increased fruit Ca content and significantly decreased fruit damage by 60%, 10-d after storage at 4 °C. Grape berries from Ca-treated vines displayed lower levels of total phenolics and anthocyanins, compared to control fruits, corroborating the downregulation of PAL1 and STS which resulted in decreased non-enzymatic antioxidant capacity estimated by FRAP assay. In contrast, a strong upregulation of CAT1, ASPX1, ASPX3, GLPX1, CSD3 and CSD6 encoding antioxidant enzymes was observed. Accordingly, catalase enzyme activity was stimulated, significantly reducing hydrogen peroxide (H2O2) levels by 36%. The overexpression of the cell wall and pathogen defense genes PME, PGIP, PIN and PR1 likely contributed to the reduction in fruit rot. This work suggested that preharvest Ca treatment is an efficient agronomical strategy that prolongs the shelf life of grape berries through modifications at molecular and biochemical levels, bringing further insight on the benefits and drawbacks of preharvest Ca applications on postharvest fruit quality attributes.

The authors thank Dr Ana Garcia (CIIMAR, Portugal) for providing access to the experimental fields used in this study. This work was supported by the “Contrato-Programa” UIDB/04050/2020 funded by national funds through the FCT I.P. The work was also supported by FCT, CCDR-N (Norte Portugal Regional Coordination and Development Commission) and European Funds (FEDER/POCI/COMPETE2020) through the project AgriFoodXXI (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). This research was also supported by national funds, through FCT/MCTES, within the scope of UIDB/05748/2020 and UIDP/05748/2020 (GreenUPorto); C. Soares would like to acknowledge FCT for providing a doctoral grant (SFRH/ BD/115643/2016).

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