Effect of synthetic cytokinin and vapour pressure deficit on potassium and calcium content in table grape berry

The forchlorfenuron (CPPU) application is recommended in table-grape after fruit-set to boost berry sizing, albeit CPPU application during pre-flowering is gaining attention due to its effect in influencing berry Ca content. This study evaluated the effects of pre-flowering applications of the synthetic cytokinin CPPU and vapor pressure deficit (VPD) manipulation on potassium (K) and calcium (Ca) content in table grape berries (Vitis vinifera L.). The experiment was conducted in southern Italy (Bernalda, Basilicata) in a plastic covered vineyard of the cv ‘Sugrathirteen’N. (Midnight Beauty ®). Forchlorfenuron treatments included single (S_CPPU; 100 inflorescences) and double (D_CPPU; 75 inflorescences) applications, while low VPD was obtained by enclosing, after fruit-set, 50 bunches in transparent PVC bags (VPDLOW). Potassium accumulation in berries was unaffected by VPD and resulted to be synchronized with sugar accumulation, reflecting its predominant phloem-based transport. In contrast, Ca accumulation was significantly influenced by VPD reduction, indeed VPDLOW bunches showed a reduction in both Ca content and berry fresh mass. CPPU treatments per se increased K concentration in the rachis but did not significantly affect Ca accumulation in berries. These findings suggest that VPD conditions around bunches rather then pre-flowering CPPU applications could be pivotal in determining berry fresh mass, Ca content and sugar accumulation.