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COPYRIGHT 2005 Kansas Academy of Science
'Jonathan' apple (Malus x domestica Borkh.) trees at three commercial orchards were sprayed one to eight times with calcium chloride (Ca[Cl.sub.2]) solution containing 3.2 g/L, starting when apple sizes were between 0.9 and 1.6 cm average diameters. Apples were stored for two and four months in regular atmosphere storage at 2[degrees]C (36[degrees]F). Fruit firmness, ratio of soluble solid concentrations to titratable acidity (SSC/TA), and fruit red skin color during the two storage periods and fruit weight after four-month storage were determined. Apples stored for two months had better quality than those stored for four months. Depending on the location, five to eight Ca[Cl.sub.2] applications and two to seven applications were necessary to retain an average of 26% of fruit firmness and an average of 35% of the SSC/TA, respectively, in the two-month storage. At least seven applications were required to retain an average of 29% of fruit firmness of apples stored for four months. Six to seven applications of Ca[Cl.sub.2] retained fruit weight by 22 to 33% more than the non-treated control apple. Fewer Ca[Cl.sub.2] applications were required to sustain fruit skin color during storage than to maintain fruit firmness or fruit weight after two months of storage. Two-month stored apples from Topeka, Conway Springs, and Emporia that were treated with two applications of Ca[Cl.sub.2] were 33, 27, and 17% redder than the control, respectively. In general, Ca[Cl.sub.2] was beneficial for storage quality of 'Jonathan' apples in Kansas. Between six to seven preharvest applications of CaC12 were necessary to retain quality of 'Jonathan' for a short-term regular storage, whereas, more than eight applications should be considered for long-term storage.
Keywords: Jonathan apple, calcium chloride, hue value, regular atmosphere storage, Topeka, Emporia, Conway Springs.
INTRODUCTION
'Jonathan' is an important commercial apple variety, which at one time accounted for about 10% of the U.S. production (Rom 1988). 'Jonathan' is still the major apple variety in Kansas and contributes to more than 70% of the commercial production. This apple is excellent for eating, pie, salsa, and it holds its shape well during cooking. One of 'Jonathan's' serious weaknesses, however, is the apple cannot retain fruit quality under regular storage (Rom 1988). Most of 'Jonathan' apples in Kansas are stored in regular atmosphere storage, which shortens the shelf-life of fruits. Regular atmosphere storage of apples is commonly used for the short-term. The storage consists of an insulated room that is maintained at a temperature of 0[degrees] to 2[degrees]C with proper ventilation to avoid carbon dioxide buildup from the slowly respiring fruit. Harvesting apples early and at a less-mature stage can prevent fruit disorders and fruit softening for a short period at regular storage, but fruit color is often poor. Poor skin color and short shelf-life of the apples reduce the commercial value of 'Jonathan.' Therefore, delaying or slowing down the ripening processes within the fruit is essential for fruit quality retention during storage.
A close correlation has been established between calcium concentrations in fruit tissues, fruit ripening, and physiological disorders in apples (Fallahi, Righetti and Richardson 1985; Ferguson 1984; Poovaiah 1986; Wilkinson and Fidler 1973). Calcium regulates the metabolism of fruit ripening (Glenn, Reddy and Poovaiah 1988; Poovaiah and Leopold 1976) and reduces physiological storage disorders (Faust and Shear 1968). In addition, calcium plays a major role in binding polysaccharides and proteins of the cell wall, which maintains cell-wall integrity (Fallahi, Righetti and Richardson 1985; Rees 1975) and retains firmness (Knee 1974; Solomos and Laties 1973). Marinos (1962) found a relationship between calcium deficiency and the breakup of the nuclear envelope and the plasma and vacuolar membranes in shoot apices of barley. Foliarly applied calcium improved redness of freshly harvested 'Jonathan' (Kadir 2004)...
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