819 Assessment of Susceptibility and Prevention of Cracking of ‘Skeena’ Sweet Cherry F. Hoppe 1,2 , S. Huyskens-Keil 1 , Ch. Ulrichs 1 and I. Hanrahan 2 1 Humboldt-Universität zu Berlin, Division Urban Plant Ecophysiology, Section Quality Dynamics/Postharvest Physiology, Lentzeallee 55/57, 14195 Berlin, Germany 2 Washington Tree Fruit Research Commission, 104 N 1 st St., Suite 204, Yakima, WA, 98901, USA Keywords: cracking index, gibberellic acid, Prunus avium L. ‘Skeena’, pitting Abstract Cracking in cherries can lead to a dramatic economic loss, depending on market conditions at time of harvest. To get a better understanding of this phenomenon, two experiments on the cherry cultivar ‘Skeena’ were set up in Washington State, USA in 2011. In two different locations, cracking susceptibility development of fruit during maturation, as well as influence of gibberellic acid (GA) and a rain-repellent material, RainGard (RG), on maturity and storability were investigated. To determine cracking susceptibility, samples were taken weekly, starting four weeks before harvest. Fruit diameter, weight, and calculated cracking index (CI) showed block-by-block variations. In one site, an exponentially increasing CI was observed with increasing fruit weight, while in the second site fruit weight remained constant and CI decreased seven days before harvest. Different cracking expression between sites was related to precipitation levels, irrigation and fruit growth rates. GA (10 ppm once or twice, 20 ppm once) and RG (7.58 L/ha) were applied separately or in combination starting three weeks before estimated harvest. A significant decrease in postharvest fruit pitting was observed in both sites for GA treated fruit. A general observation was a delay of fruit color development, increase of soluble solids and decrease of acids. Fruit firmness was improved by GA at both sites. Neither RG nor GA reduced cracking susceptibility in our trials. INTRODUCTION Cherry cracking is an important problem in all cherry growing areas. Recent findings revealed water uptake occurs mainly via the pedicel/fruit juncture (Knoche and Peschel, 2002) and initial fruit turgor before rain plays an important role in the fruit’s ability to withstand external water. However, cherry cracking is a complex phenomenon, with a dynamic interplay of factors such as physiology, morphology, and genetic predisposition (Christensen, 1996). A reduction of cherry cracking can be achieved by rain covers, application of osmolytes during rain events, plant growth regulators, and hydrophobic coatings (Christensen, 1996; Pennel and Webster, 1996; Schrader et al., 2005). According to Balasubramaniam and Angew (1996), applications of GA improve fruit size, firmness, weight, and soluble solids content, but delay harvest and have no effect on cherry cracking. According to Cline and Trought (2007), GA has more success to improve fruit size in single applications than in repeated applications. Furthermore, GA improves postharvest quality especially handling, storage performance and reduction of pitting (Balasubramaniam and Angew, 1996). A tool to determine the susceptibility of fruit to crack under rain pressure is the cracking index utilized in a modified version by Hanrahan (pers. commun.) for local cherry cultivars in Washington State, USA since 2008. In general, cracking susceptibility increases with fruit weight. However, block-by-block and year-to-year variations play an important role for determining cherry cracking susceptibility. The object of this study was to develop a deeper understanding of preharvest cherry cracking in ‘Skeena’. Two experiments were performed for I) development of cracking susceptibility during maturation and II) effects of GA and RG on fruit maturity, fruit cracking and storability. Proc. II International Symposium on Horticulture in Europe Eds.: J.-C. Mauget and S. Godet Acta Hortic. 1099, ISHS 2015