Physiological factors affecting nutrient uptake and distribution in apple

Raquel Gomez

doi:10.7273/000003980

'Honeycrisp' is growing in production across the United States and Washington State and is popular with consumers. However, it commonly has high economic losses due to its susceptibility to bitter pit. Bitter pit is a calcium related disorder caused by localized fruit calcium deficiency. Calcium uptake into aboveground tissues is dependent on transpiration and is immobile in the phloem. Lower fruit and higher leaf transpiration rates lead to imbalances in calcium delivery. Abscisic acid (ABA) is a phytohormone that regulates stomatal aperture and transpiration. Many factors affect fruit calcium delivery like fruit: leaf competition, xylem functionality, and environment. The aim of the study was to understand the physiological factors contributing to the susceptibility of 'Honeycrisp' to BP and explore how reductions in foliar transpiration, via foliar ABA application, affect nutrient uptake and distribution. In 2018 and 2019, two experiments; a field experiment with fruit and a potted experiment were conducted to compare 'Honeycrisp' to cultivars of varying BP susceptibility ('WA 38', 'Granny Smith' and 'Gala'). Another experiment was conducted to determine how alterations to foliar transpiration through foliar ABA application affected nutrient distribution in 'Honeycrisp' apples. Here, we found 'Honeycrisp' accumulated less calcium than 'Gala' and transpiration affected calcium distribution. 'Honeycrisp' had lower leaf transpiration than 'WA 38', a BP non-susceptible cultivar. 'WA 38' fruit accumulated more fruit calcium and had lower fruit K+Mg/Ca ratios. However, xylem sap elemental concentrations were similar in 'WA 38' and 'Honeycrisp'. Therefore, poor calcium distribution is likely contributing to high BP susceptibility in 'Honeycrisp' and is not related to limitations in nutrient uptake. ABA treatments inconsistently reduced foliar transpiration and did not increase fruit calcium in 'Honeycrisp'. We report that 'Honeycrisp' distributes more calcium to leaves and less to fruit when compared to BP resistant cultivars. Lower transpiration rates observed at the leaf level for 'WA 38' may contribute to improved fruit: leaf distribution of calcium and lower bitter pit incidence. Future work should target fruit transpiration and xylem-phloem interactions that can affect the movement and balance of mobile and immobile nutrients.

Physiological factors affecting nutrient uptake and distribution in apple

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