Assessing preharvest field temperature and at-harvest fruit quality for prediction of soft scald risk of 'Honeycrisp' apple fruit during cold storage

Authors: LEISSO, RACHEL - MONTANA STATE UNIVERSITY; HANRAHAN, INES - WASHINGTON TREE FRUIT RESEARCH COMMISSION; MATTHEIS, JAMES

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2019
Publication Date: 5/1/2019
Citation: Leisso, R., Hanrahan, I., Mattheis, J.P. 2019. Assessing preharvest field temperature and at-harvest fruit quality for prediction of soft scald risk of 'Honeycrisp' apple fruit during cold storage. HortScience. 54(5):910–915. https://doi.org/10.21273/HORTSCI13558-18.
DOI: https://doi.org/10.21273/HORTSCI13558-18

Interpretive Summary: Current commercial technologies enable the long-term storage of apples allowing fruit to be available for months after harvest. Fruit marketability depends on acceptable appearance and edibility, both of which can be impacted by development of fruit disorders. Disorders can be external in the peel or internal in the flesh and are usually characterized by tissue browning that reduces appearance as well as edible quality. While fruit storage protocols usually exist to minimize disorder development, practices that reduce disorder risk sometimes come at the expense of accelerated fruit ripening and a shortened marketability period. Disorder susceptibility for most apple varieties varies due to several factors including weather during the production season and the maturity at which fruit are harvested. Knowing the disorder risk for fruit on an orchard by orchard basis can provide fruit storage managers with information to tailor storage protocols to minimize risk while maximizing for storage duration. Scientists from ARS, Montana State University, and the Washington Tree Fruit Research Commission collaborated on a three-year project to examine the utility of orchard temperatures prior to harvest and fruit maturity assessment at harvest as predictors of disorder risk for the popular apple variety ‘Honeycrisp’. Some components of harvest maturity as well as orchard temperature history were found to have relationships with subsequent disorder development. This information could contribute a portion of a system to estimate risk for individual orchard lots.

Technical Abstract: ‘Honeycrisp’ is a popular dessert apple cultivar in the US. It is susceptible to a postharvest chilling disorder called soft scald that causes necrotic peel lesions on the fruit, rendering the fruit unmarketable. Reducing or preventing this disorder is an important component of postharvest management. Apple fruit storage and packing facilities commonly assess apple fruit maturity and quality by measuring ground color, fruit firmness, soluble solids concentration (SSC), starch index (SI), and titratable acidity (TA). In commercial settings, advanced fruit maturity and orchard history contribute to an estimation of soft scald susceptibility, but if other at-harvest measurements could be used to assess soft scald risk, this would enable better management decisions. In this study, we obtained fruit from commercial orchards for 3 successive years, and assessed field growing degree days (GDD), field chilling hours (CH), and fruit quality metrics at harvest, followed by soft scald incidence assessment at 12 weeks of cold storage. The results of soft scald incidence were then used to categorize the at-harvest orchard field temperature and quality data into "low risk" (less than 5% incidence) or "high-risk" categories (greater than 5% incidence). Statistical tests traditionally used to assess binary biomarkers (positive/ negative for outcome prediction) were then applied to the data to assess these at-harvest metrics strictly as predictors of soft scald disorder susceptibility. The analyses indicated that, in this study, measurements of SI, SSC, internal ethylene, TA, ground color, firmness, GDD or CH do not reliably indicate fruit susceptibility to soft scald. However, SSC and TA were sometimes elevated in fruit that later developed soft scald, and a higher number of GDD also sometimes preceded soft scald, which is consistent with advanced fruit maturity that can enhance soft scald risk. Overall, results suggest that other tools (e.g. molecular biomarkers) may be required to accurately predict postharvest soft scald on a quality control laboratory scale, and that the statistical analyses applied to the present study would have utility in these determinations.