Effect of preharvest calcium treatments on

postharvest quality of apples grown in Finland

Editors : Ramdane Dris

Summary

In Finland, there has been an increased interest in the production and storage of apples, but often the quality has not beengood enough for marketing throughout the storage season. The present study was conducted to determine whether the postharvest quality of apples could be improved by foliae or soil applications of calcium salts.

During 1994-1995, field experiments were carried out at the Horticultural Research Institute, and in six commercial apple orchards, located in the southwest of Finland including the Åland Islands. The experimental cultivars were Transparente Blanche, Melba, Samo, Raike, Red Atlas, Åkerö, Aroma and Lobo. For all cultivars the treatments were control and preharvest calcium chloride (CaCl₂) foliar sprays. For cultivars grown in the mainland ('Melba', 'Åkerö', 'Lobo'), the additional treatments were calcium nitrate Ca(NO₃)₂ application to soil and preharvest calcium nitrate foliar sprays ('Lobo'). The calcium concentration in both CaCl₂ and Ca(NO₃)₂ spraying solutions was 2.0 g l^-1. The amount of calcium applied to the soil was 70 kg ha^-1. During growing season, leaves of experimental trees were sampled each year two times separately from branches bearing fruit (BF) and not-bearing fruit (BNF) and analyzed for macronutrients (N, P, K, Ca, Mg). Fruit samples were stored for two to six months at +2-4°C and 85-95% RH. The incidence of physiological disorders of stored apples was scored. Fruit firmness, diameter, total dry matter and juice pH, titrable acidity and soluble solids were determined at harvest and after storage and fruit nutrients at harvest.

Significant linear correlations were found between fruit characteristics at harvest and leaf nutrients of experimental cultivars. With the exception of Ca, fruit nutrients correlated positively with each other and fruit total dry matter. Fruit N correlated positively with leaf Ca and Mg, fruit Mg positively with leaf Mg and fruit N and Mg negatively with leaf K. Leaf N correlated positively with fruit diameter and negatively with fruit P, K, Mg, total dry matter and juice soluble solids. Titratable acidity of juice correlated positively with leaf P, juice pH negatively with leaf Ca and soluble solids/titratable acidity ratio of juice negatively with leaf P and Ca.

The CaCl₂ sprays increased leaf Ca of 'Transparente Blanche', 'Åkerö', 'Aroma' and 'Lobo' and fruit Ca in 'Melba' and decreased fruit K/Ca ratio in 'Aroma' and 'Åkerö'. The CaCl₂ sprays increased leaf Ca more than Ca(NO₃)₂ applied to the soil. The CaCl₂ sprays increased fruit firmness of 'Aroma' and 'Lobo' and titratable acidity of 'Melba', 'Raike', 'Aroma' and 'Åkerö' and decreased fruit total dry matter of 'Åkerö' and 'Melba', soluble solids of 'Melba', 'Raike', 'Red Atlas' and 'Lobo' and the soluble solids/titratable acidity ratio of 'Lobo', 'Aroma', 'Red Atlas' and 'Melba' at harvest and often after cold storage. Under CaCl₂ sprays fruit Ca and titratable acidity increased and soluble solids/titratable acidity decreased also as mean of all cultivars harvested in 1995. In 'Lobo', the percentage of soluble solids in juice decreased by Ca(NO₃)₂ sprays and pH increased by Ca(NO₃)₂ sprays and soil application.

The CaCl₂ sprays reduced the mean incidence of physiological storage disorders in apples harvested during 1994 and in 'Lobo', 'Red Atlas' and 'Åkerö' harvested during 1995. Also, Ca(NO₃)₂ sprays reduced the senescence breakdown and rotting of 'Lobo', but soil application did not have a significant effect. The incidence of storage disorders of apples grown in the mainland and in the Åland Islands after three months was 0-85% and 2-13%, and after six months 20-100% anf 10-95%, respectively. The preharvest CaCl₂ sprays was effective in improving the quality of apple cultivars Red Atlas, Åkerö, Aroma and Lobo, which could be stored for two six months.

Contents

• Introduction
• Background
• Calcium nutrition of apple trees
• Interaction of calcium with other nutrients
• Physiological storage disorders of apples
• Calcium treatments of apples
• Objectives of the study
• Leaf diagnosis of apple cultivars
• Effect of preharvest calcium chloride sprays on the quality characteristics of apple fruits in apple flesh
• Effect of preharvest calcium chloride sprays on the quality characteristics of apple fruits at harvest
• Effect of preharvest calcium chloride sprays on the storage behaviour of apples
• Effect of preharvest calcium chloride sprays and calcium nitrate applied to soil on cultivars Melba, Åkerö and Lobo
• Effect of calcium treatments on the quality of 'Lobo' during cold storage
• Conclusions

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