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

Viviana Martins,Hernâni Gerós,António Teixeira,Marianne Unlubayir,Arnaud Lanoue

doi:10.3389/fpls.2021.742887

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 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-ω-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.

Highlights

Calcium (Ca) supplements have been increasingly used in fresh fruits and vegetables toward improved fitness, sanitation, nutritional enrichment, and decay prevention (Martín-Diana et al, 2007)
A multivariate statistical data analysis (MVA) of the samples was performed with SIMCA P+ version 15 (Umetrics AB, Umeå, Sweden), after meancentering all variables and scaling unit-variance
The same effect was observed for CYP15 involved in the cuticle structure, that was downregulated by 82%

Summary

Introduction

Calcium (Ca) supplements have been increasingly used in fresh fruits and vegetables toward improved fitness, sanitation, nutritional enrichment, and decay prevention (Martín-Diana et al, 2007). Increased fruit resistance to infection by Botrytis cinerea during storage was achieved by Ca dips after harvest (Fu et al, 2020), an effect that was reported upon vineyard Ca sprays between fruit set and veraison stages (Amiri et al, 2009; Ciccarese et al, 2013) In line with these observations, Ca sprays during berry development reduce the incidence of microcracks on the fruit surface and the lodging of filamentous fungi in these structures, reducing fruit decay at postharvest (Martins et al, 2020b, 2021a). The inhibition of anthocyanin synthesis was accompanied by a general accumulation of stilbenoids, including E-resveratrol, E-ε-viniferin, E-piceid, and pallidol, demonstrating the powerful ability of Ca in diverting polyphenolic biosynthetic routes (Martins et al, 2020a)

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Discussion

Conclusion