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

Mitigating citrus fruit cracking: the efficacy of chelated calcium or silicon foliar fertilizers in 'Okitsu no. 58' citrus fruit

The 'Okitsu No. 58' citrus variety is highly prone to fruit cracking, which jeopardizes yield and results in economic losses. In this study, we investigated the impacts of spraying 5 distinct concentrations (0.1, 0.2, 0.3, 0.4, and 0.5 g/L) of chelated calcium (Ca) or silicon (Si) fertilizers at the young fruit stage (60-90 days after flowering, DAF) on fruit cracking and quality in the citrus variety 'Okitsu No. 58'. The results showed either Ca or Si fertilizer treatments reduced fruit cracking. We found that all Ca and partial Si treatments (0.4 and 0.5 g/L) significantly promoted the accumulation of Ca content in the peel. Notably, Ca or Si treatments significantly reduced polygalacturonase (PG) activity and inhibited the production of water-soluble pectin (WSP) in the peel. Additionally, Ca or Si treatments elevated the superoxide dismutase (SOD) activity and decreased the malondialdehyde (MDA) content of the peels. Changes in these parameters likely contributed to strengthening the durability of peel cell wall constituents, thus enhancing the fruit's resistance to fruit cracking. Overall, except for the C3 (0.3 g/L of Ca), Ca or Si fertilizers contributed to fruit conventional quality, mainly in terms of higher soluble sugars (SS) and SS/TA (titratable acid). Therefore, our findings will provide a reference for the prevention and control of citrus fruit cracking and the development of new fertilizers.

Cell Wall Integrity Signaling in Fruit Ripening

Plant cell walls are essential structures for plant growth and development as well as plant adaptation to environmental stresses. Thus, plants have evolved signaling mechanisms to monitor the changes in the cell wall structure, triggering compensatory changes to sustain cell wall integrity (CWI). CWI signaling can be initiated in response to environmental and developmental signals. However, while environmental stress-associated CWI signaling has been extensively studied and reviewed, less attention has been paid to CWI signaling in relation to plant growth and development under normal conditions. Fleshy fruit development and ripening is a unique process in which dramatic alternations occur in cell wall architecture. Emerging evidence suggests that CWI signaling plays a pivotal role in fruit ripening. In this review, we summarize and discuss the CWI signaling in relation to fruit ripening, which will include cell wall fragment signaling, calcium signaling, and NO signaling, as well as Receptor-Like Protein Kinase (RLKs) signaling with an emphasis on the signaling of FERONIA and THESEUS, two members of RLKs that may act as potential CWI sensors in the modulation of hormonal signal origination and transduction in fruit development and ripening.

Effect of CaCl2 Sprays in Different Fruit Development Stages on Grape Berry Cracking

Grape cracking is a common phenomenon that can reach more than 50% in some varieties and can cause enormous economic losses. "Li Xiu" grapes in different developmental stages were treated with calcium chloride (5 g/L), and the cracking rate and related biochemical and genetic indices were measured in the fruit ripening stage. The results showed that calcium treatment during the flowering period could significantly reduce grape cracking. Based on the experimental results, there are several reasons as follows: first, calcium spraying during the flowering period was more favorable to calcium absorption in grapes, and the increased calcium content in the peels helped to improve the mechanical properties of the peels, thus increasing crack resistance; second, calcium treatment reduced the expression levels of genes related to glucose metabolism, which in turn reduced PG and cellulase activities, delaying the degradation of pectin and cellulose and resulting in more structural integrity of the peels; third, calcium treatment increased fruit hardness and reduced fruit ventral pressure by decreasing the expression levels of ABA-related genes and synthesis of endogenous abscisic acid (ABA), soluble sugars (SSs), and total soluble solids (TSSs).

Calcium and Potassium Accumulation during the Growing Season in Cabernet Sauvignon and Merlot Grape Varieties

The evolution of calcium (Ca) and potassium (K) accumulation in grape berries during the growing season provided information on the productivity and quality of grape crops, considering that both elements have numerous physiological effects. The aim of the study was to determine and compare Ca and K accumulation in berries from ‘Cabernet Sauvignon’ and ‘Merlot’ grape varieties influenced by the number of days after flowering (DAF) over three consecutive growing seasons (2019–2021) in Recaş vineyards, from Banat Region in Western Romania. Results showed that Ca accumulation in the berries continued at slow rates after veraison when water was available for both varieties; accumulation was observed mainly in the skin, suggesting translocation from the flesh. Regression analysis showed a strong dependence on the interval of 65–75 DAF for Ca accumulation in the skin. K accumulation increased after the onset of veraison until 70 to 90 DAF in both varieties, with higher accumulation in the flesh than in the skin. No significant differences were found among varieties regarding the Ca and K content during the study period. In both varieties, the relationship between sugar accumulation and the Ca/K content was highly significant. Given the importance of both elements, new data may contribute to establishing the optimum grape ripeness in relation to the sugar concentration in the berries.

The restructuring of grape berry waxes by calcium changes the surface microbiota

The observation that exogenous Ca shifted the polyphenolic profile of grape berries and conferred a glossy appearance to mature fruits led us to hypothesize that the composition of grape berry waxes and thus surface microbiota are modified. In two cultivars sharing the same microclimate, the triterpenoid and steroid profile of berry cuticle was characterized by a targeted metabolomic approach, and surface microbial communities were surveyed by ITS and 16S metabarcoding. Results showed that Ca strongly decreased the levels of oleanolic acid, while steroids and neutral triterpenoids were affected in a cultivar-dependent manner. A total of 174 fungi and 192 bacteria OTUs were identified, with Dothideomycetes, Leotiomycetes, Alphaproteobacteria and Gammaproteobacteria comprising the most abundant classes. Ca decreased fungi biodiversity, favoring the growth of Basidiomycetes, and shifting fungi-bacteria relationships. Metabolite-microbiota networks revealed a tight relationship between microbial communities and triterpenoid components of fruit waxes, mainly stigmasterol, tremulone and oleanolic acid.