Effect of ethephon on sweet cherry pedicel-fruit retention force and quality is cultivar dependent

Ethephon (2-chloroethyl phosphonic acid) is effectively used to promote development of the pedicel-fruit abscission zone in tart cherry (Prunus cerasus) for mechanical harvest. Our research program is investigating the use of ethephon to promote pedicel-fruit retention force (PFRF) reduction on new sweet cherry (P. avium) cultivars to assist mechanized harvest and its affect upon fresh market quality fruit. Ethephon treatments were made at different timings and rates to 'Bing' and 'Chelan' during the 2006 season. Ethephon applications to 'Bing' trees more than 10 days prior to harvest were effective at reducing PFRF and facilitating mechanical harvest, irrespective of rate (1.2, 3.5, 5.8 L ha(-1) [1, 3, 5 pt A(-1)]). Ethephon applied fewer than 10 days prior to harvest did not reduce PFRF sufficiently. In contrast, no rate or timing of ethephon studied induced a reduction in 'Chelan' PFRF sufficient for mechanical harvest. Accompanying PFRF analyses, fruit quality was assessed by measuring firmness (g mm(-1)), soluble solids (A(0)Brix), weight (g) and color (CTIFL, scale 1-7). Ethephon applied 22 days before harvest at a rate of 3.5 L ha(-1) enhanced exocarp color in 'Bing' by 27%, while reducing firmness in both 'Bing' (-19%, 22 days prior to harvest) and 'Chelan' (-15%, 20 days prior to harvest). We observed a significant natural decline in 'Skeena' PFRF to levels acceptable for mechanical harvest. This research documents genotypic-specific pedicel-fruit abscission characteristics and the potential to facilitate mechanical harvest of fresh market quality sweet cherry fruit using ethephon.