2017 ASHS Annual Conference

Malus domestica Borkh cv. ‘Honeycrisp’ and ‘Gala’ are two of the most commonly planted apple cultivars in Washington State. ‘Honeycrisp’ is susceptible to bitter pit and hot and dry conditions exacerbate it. Newly available rootstock selections with variability in nutrient uptake capacity may improve this problem but little is known about how nutrient uptake capacity is affected by soil abiotic stress (e.g. heat and drought). The objective of this study was to evaluate the response of potted ‘Gala’ and ‘Honeycrisp’ apple plants grafted to two different rootstocks, Bud-9 and Geneva-890 to decreased water supply and increase soil temperature. At the WSU Tree Fruit Research and Extension Center, 36 trees (9 of each rootstock-scion combination) were grown in a greenhouse for 60 days. After 60 days of growth, the water supply was reduced in one treatment (65% of field capacity), soil temperature was elevated by approximately 5°C using a thermostat controlled heating cables in another treatment, and the remaining trees were left as an untreated control. After 60 days of treatment, all trees were destructively sampled to determine stem length, total leaf area (TLA), stems dry mass (SDM) and roots dry mass (RDM). Samples from roots, stems, and leaves were analyzed separately for calcium (Ca), magnesium (Mg) and potassium (K). RDM decreased by 26% in ‘Gala’ when exposed to abiotic stress. However, there was no significant difference between stress treatments. SDM for ‘Gala’ was 20% and 11% less than the control for drought and heat stress, respectively. For ‘Honeycrisp’, RDM was not significantly different between treatments. Leaf Ca concentration was 8% and 14% lower for ‘Honeycrisp’ on ‘Bud-9’ under drought and heat treatments, respectively. Leaf Mg concentration was 17% and 24% lower in both treatments, respectively. Leaf K concentration was 4% lower in both stress treatments. For ‘Gala’ on Bud-9, Ca concentration decreased by 10% under drought. K and Mg increased by 15% and 23%, respectively, for the heat treatment compared with the control. For ‘Gala’ on ‘G-890’, Mg was 2% and 10% lower for drought and heat, respectively while K increased by 13% in the two treatments compare to control. Combined Ca, Mg and K content was 35% higher for ‘Gala’ on both rootstocks compared to ‘Honeycrisp’. In conclusion, preliminary results show that ‘Gala’ is more sensitive to abiotic stress than ‘Honeycrisp'.