The Pacific Northwest region of the United States is an important growing region for the production of blueberry (V. corymbosum L.), blackberry (Rubus L. subgenus Rubus, Watson), raspberry (R. idaeus L.), and strawberry (Fragaria ×ananassa L.) (USDA National Agricultural Statistics Service, 2015). Production of high-value fruit for the fresh market is increasing in many of these crops. Growers need to produce high-quality fruit that has the maximum possible storage or shelf life to be competitive in the market place. Calcium is often applied to fruit crops before harvest at the recommendation of some crop consultants in an effort to increase postharvest fruit quality. Fruit Ca has been found to be related to fruit firmness by strengthening the cell wall, which, in turn, improves shelf life (Van-Buren, 1979). Blueberry (Strik and Vance, 2015) and blackberry (Harkins et al., 2014) cultivars have been found to differ in fruit Ca concentration.
When soil Ca levels are sufficient, localized Ca deficiency such as in leaves or fruit may still become a problem in fruit crops. Calcium-related disorders include bitter pit in apple fruit (Malus domestica, Borkh.), blossom-end rot in tomato (Solanum lycopersicum L.) fruit, and tipburn in leaves of vegetables (Saure, 2005). These deficiencies in Ca may occur as a result of competition between vigorously growing shoots and fruit. Strik and Vance (2015) speculated that ‘Draper’ blueberry may have particularly low fruit Ca concentration due to the presence of many competing shoot tips during the fruit development period. Since Ca is translocated in the xylem and not the phloem, Ca is relatively immobile in the plant and tends to move predominantly to leaves, which have a high transpiration rate.
Penetration of Ca into fruit likely occurs through the stomata on the fruit surface. Penetration rates, however, have been shown to vary with cultivar, application method, and formulation of Ca used (Saure, 2005). The number of possible interactions that can affect Ca uptake and distribution in the plant is so complex that cultural management practices are not likely to increase fruit Ca, without a direct application of Ca to the developing (Bangerth, 1979) or harvested (Hanson et al., 1993) fruit.
Postharvest dips with CaCl2 increased firmness and shelf life of raspberries and blueberries, but resulted in an unacceptable salty taste (Hanson et al., 1993; Montealegre and Valdes, 1993); washing or dipping fruit also removes the desirable, waxy bloom coating on blueberry fruit and decreases shelf life in blackberry, raspberry, and strawberry.
Foliar Ca applied to strawberries has been shown to delay fruit harvest, reduce incidence of fruit rot and improve fruit firmness (Cheour et al., 1990; Singh et al., 2007; Wójcik and Lewandowski, 2003). In blackberries, preharvest Ca applications did not impact initial fruit firmness following machine harvest, but had a positive effect during storage (Morris et al., 1980). Hanson (1995) applied CaCl2 to blueberry plants with minimal impact on fruit quality.
The objectives of this study were to test several Ca formulations with direct sprays of liquid products applied to developing fruit of strawberry, raspberry, blackberry, and blueberry cultivars and determine the impact on Ca concentrations of fruit and leaves, and fruit quality at harvest and during storage. Two methods of application were compared to assess the impact of spray coverage on these factors.
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