Whole fruit mineral element content and respiration rates of harvested ‘delicious’ apples

Abstract

Abstract Whole fruit mineral element analysis is used commercially in Great Britain to predict postharvest apple fruit quality and storage life. Similar commercial programs are under development in Washington State; however, mineral element concentration guidelines are not available for important Washington‐grown cultivars. The current study used fruit respiration rate as a criterion for evaluating optimal whole fruit mineral element concentration. ‘Wellspur Delicious’ apple trees (Malus domestica Borkh.) were treated with four biweekly sprays of D, 4.1 and 13.5 kg CaCl2/ha. Fruit of uniform diameter (7.65 to 8.05 cm) were harvested. Four intact single‐fruit samples per treatment were placed into individual respiration chambers maintained at 20°C. Humidified CO2‐free air was continuously pumped into the chambers. Evolved C02 was trapped in NaOH and analyzed by titration. Evolution of C02 was measured for 38 days after which the fruits were analyzed for whole fruit Ca, N, Mg, P and K concentrations. The C02 evolution data was analyzed by linear regression to generate average respiration rates. The preharvest CaCl2 spray treatments did not influence whole fruit Ca concentrations or respiration rates. The respiration rates were not influenced by mineral element concentration or selected ratios of concentrations. The Ca concentrations in the fruit (> 300 mg/kg dry mass) appear to have been sufficiently high to produce uniform low respiration rates and to mask possible influences of the other elements. The results suggest that whole fruit mineral element analysis may not be a sensitive indicator of average respiration rates of ‘Delicious’ apples during ripening.