Effects of Late Season Foliar Application of Calcium Chloride on Cold Hardiness in Grapevines (Vitis vinifera ‘Thompson Seedless’)

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As a major growth limitation, low temperature-induced injuries may adversely affect grape production in many areas. Ten-year-old grapevines ‘Thompson Seedless’ were sprayed with calcium chloride (CaCl₂) three times at 10-day intervals from 19th September to 8th October 2015 and again in 2016 in a commercial vineyard. Bud samples were collected in December 2015 and 2016, January 2015 and 2016 and February 2016 and 2017. The buds were exposed to freezing treatments: −12, −16, −20, −24, and −28°C for 3 hours, to assess their low temperature tolerance. Moreover, the relationships among freezing tolerance and changes in antioxidant enzyme activity, soluble carbohydrates, proline and total proteins were investigated. Irrespective of foliar spray treatments, the freezing tolerance of buds increased from December to January and decreased in February. Application of CaCl₂ at a 1% concentration resulted in increased bud freezing tolerance compared to the control plants. Application of 1% CaCl₂ considerably increased the concentrations of soluble carbohydrates and total proteins in buds, but had subtle and inconsistent effects on proline. Activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) were increased in response to foliar application of CaCl₂; however, inconsistent changes were found in the activities of catalase and peroxidase following CaCl₂ application. The results showed that application of 1% CaCl₂ increased freezing tolerance of grapevines predominantly via upregulating soluble carbohydrates and total proteins.