Abscission agents, preharvest interval, and postharvest storage time affect mechanical damage associated with destemmed ‘Sheegene-12’ table grapes

Summary Table grapes are mostly marketed as whole clusters, but there is increasing interest in destemmed berries, which are “ready-to-eat” as-is, and which can be incorporated into minimally processed products, such as salads. However, destemming may create unsightly stem-end wounds on grapes that are prone to rot and difficult to sanitize. Preharvest application of jasmonic acid (JA) and 1-aminocyclopropane-1-carboxylic acid (ACC), alone or in combination, activates the fruit-pedicel abscission zone (A) of some grape varieties, thereby reducing fruit detachment force (FDF), and mechanical damage associated with destemming. However, the A develops within a few days after treatment such that picking and destemming 2 days after treatment (DAT) may be too soon, with little benefit afforded by abscission agents, whereas picking a day later may be too late, due to unacceptable yield loss from preharvest abscission. We hypothesized that the A may continue to develop in postharvest storage. If so, then growers could apply abscission agents preharvest, harvest intact clusters of grapes before substantial abscission has occurred, and allow the abscission zones to develop in storage before destemming. To test this hypothesis, a study was conducted with ‘Sheegene-12’ table grapes to determine how abscission agents (JA, ACC, and JA + ACC), preharvest interval (PHI), and postharvest storage time affected berry abscission, FDF, proportion of berries with dry stem scars, berry weight, firmness, soluble solids, and color. No treatments caused preharvest abscission with a 2-day PHI, but effects on FDF, and dry stem scars were reduced compared to a 3-day PHI. Efficacy of JA was improved by co-application with ACC, which hastened abscission induced by JA. Without JA, ACC was ineffective. If fruit were destemmed at harvest, then JA + ACC with a 2-day PHI was the best approach. If the fruit could be destemmed after two or three weeks of postharvest storage, then JA alone was sufficient, harvested with a 2- or 3-day PHI.