Physiological Factors Affecting Nutrient Uptake and Distribution and Fruit Quality in ‘Honeycrisp’ and ‘WA 38’ Apple (Malus ×domestica Borkh.)

Abstract

‘Honeycrisp’ is among the most widely grown apple cultivars in the United States and ‘WA 38’ is a new apple cultivar released in Washington State. ‘Honeycrisp’ is highly susceptible to bitter pit and other physiological disorders; however, ‘WA 38’ is not susceptible to bitter pit but little is known about its susceptibility to other disorders. Bitter pit is a calcium-related disorder that has been associated with localized calcium deficiencies in fruit in addition to the proportions of calcium relative to the presence of other nutrients like potassium and magnesium. The objective of this study was to compare physiological differences and fruit quality between ‘Honeycrisp’ and ‘WA 38’ to determine how these differences might correspond to differences in mineral nutrient composition and bitter pit susceptibility. Here, ‘Honeycrisp’ and ‘WA 38’ elemental composition in leaves, fruit, and xylem sap was measured every 20 days starting 30 days after full bloom and compared with leaf gas exchange and stem water potential. ‘Honeycrisp’ had greater foliar transpiration rates that corresponded with greater calcium in the leaves and lower leaf K+Mg/Ca ratio, when compared with ‘WA 38’. In contrast, fruit calcium concentrations were higher for ‘WA 38’ with lower K+Mg/Ca ratios. Xylem conductance was higher during late summer in ‘WA 38’ compared with ‘Honeycrisp’. ‘WA 38’ fruit was denser than ‘Honeycrisp’ and more research is needed to determine whether differences in fruit structure may affect susceptibility to bitter pit in apple.