2017 ASHS Annual Conference

‘Honeycrisp’ apple is gaining in consumer popularity and as such, it has become the most frequently planted apple in the United States. However, inconsistencies in fruit quality, such as color, firmness, flavor and susceptibility to physiological disorders such as bitter pit have limited grower production efficiencies and increased postharvest losses. Here, we sought to sample Honeycrisp from irrigated orchards across a range in growing environments in Washington State to determine the relationship between plant water-status, measured using carbon isotope discrimination (Δ¹³C) and fruit quality at harvest and after four months of storage. Nine commercial orchards were chosen that were planted between 2008 and 2010 with upright architecture and were irrigated with drip or microsprinkler irrigation. Nine trees per orchard were selected that had uniform trunk cross sectional area (TCSA) and bloom. In June, trees were thinned to three crop loads: 3, 5, or 7 fruit cm^-2 TCSA. 16 fruit were tagged for each tree in June and harvested between August 14 and September 6, 2015. 10 leaves per tree were taken at in August for carbon isotope analysis. Color development, firmness, soluble solids content (SSC), titratable acidity (TA), dry matter, and bitter pit incidence was measured for eight fruit per tree at harvest and after 4 months of regular atmosphere storage. Pooled fruit samples were also analyzed for carbon isotope composition. As expected, crop load affected fruit quality metrics where fruit size and bitter pit incidence was greater when crop load was low. However, leaf and fruit Δ¹³C were independent of crop load and ranged from 17.61 to 22.06 in leaves and from 16.06 and 20.01 in fruit. Fruit was more consistently enriched relative to leaves (1.18‰) and the two were significantly correlated (r = 0.695, P<0.001). At the tree level, leaf and fruit Δ¹³C were significantly correlated with dry matter, SSC, firmness and fruit color. Most importantly, Δ¹³C was correlated to fruit size and bitter pit susceptibility. Trees where leaf Δ¹³C was the lowest had fruit that were too small and where leaf Δ¹³C was highest, the fruit were too large and had the highest bitter pit incidence. The linear relationship between Δ¹³C and fruit size suggest that water supply could potentially be used as a tool to control fruit size, increase fruit quality and limit bitter pit incidence in ‘Honeycrisp’ apple.