ASHS 2025 Conference

Although sunlight is crucial for optimal apple production, excessive sun exposure can negatively impact appearance and alter internal quality of the fruit. Sun stress-related disorders are the primary cause of economic losses in major apple-growing regions. Granny Smith, the third most produced variety in Washington State, is notably prone to sunscald, a postharvest disorder manifested by the superficial darkening of the peel, rendering the fruit unmarketable. Lower chlorophyll and higher carotenoid concentration in Granny Smith peel is associated with increased sunlight exposure and a higher likelihood of sunscald development. In this research, the chlorophyll-to-carotenoid ratio measured non-destructively with a hyperspectral imager at harvest was used to categorize apples according to sunscald susceptibility: high, moderate, low, and very low. The quality parameters for apples in each sunscald risk category were evaluated to determine whether pre-storage sorting based on sun exposure could enhance the consistency of cold chain quality and performance. It was hypothesized that relative sun exposure has a significant influence on apple quality parameters and ripening patterns during storage. Apples were harvested from three orchards over three consecutive years and subsequently stored in air for six months before quality analyses. During the final year, additional assessments were conducted at four and five months of storage to monitor the progression of ripening and sunscald incidence. A multi-year analysis including firmness, soluble solids, titratable acidity, greenness (Iad), peel lightness (L*), and the chromatic shift from green to yellow (a/b) resulted in similar classifications among categories. However, changes in internal quality parameters attributable to relative sun exposure were evident when analyzing fruit from a single location and season. Overall, apples classified as having high and moderate sunscald risk exhibited elevated soluble solids and reduced titratable acidity compared to those in lower sunscald risk categories. Additionally, these quality parameters were more variable for fruit with high and moderate sunscald risk. The ripening pattern was similar for fruit in the low and very low categories, with a more homogeneous data distribution. The incidence of sunscald increased over time and with increased sun exposure, resulting in 11% fruit loss after 6 months of storage. Although the primary benefit of the sunscald susceptibility index is to enhance commercial viability by enabling apples in high-risk categories to be sold before sunscald symptoms render them unmarketable, sorting and grouping fruit based on relative sun exposure rendering a more homogenous storage outcome, potentially reducing economic losses for growers and packers.