Water relations in detached sweet cherry fruit and their role in the postharvest disorder 'orange peel' (shrivelling)

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Shrivelling (orange peel) and pedicel browning are disorders that impair the appearance of sweet cherry fruit postharvest. The orange peel disorder is characterized by localized depressions in the fruit skin that cover increasing portions and ultimately the entire surface of mature sweet cherry fruit postharvest. Fruit exhibiting orange peel symptoms are rejected by the market and culled. Since only high quality cherries is subjected to postharvest procedures (grading, hydrocooling, MAP, storage, international world wide shipping), the resulting economic loss is significant. Little is known about the mechanistic basis of the orange peel disorder. Unlike pitting, orange peel is not caused by mechanical impact. Indirect evidence suggests that the orange peel disorder is linked to the fruit s water relations. The objectives of our proposal are to (1) characterize the postharvest orange peel disorder in sweet cherry fruit and identify factors affecting the disorder, (2) quantify flow rates, fluxes, driving forces and permeabilities for water transport through the surface of pedicel and fruit and for the transport between fruit and pedicel and (3) identify and locate any water potential gradients and transport resistances within the fruit, that might account for radial water transport from the fruit skin into cell layers of the underlying parenchyma. The data generated will not only unravel the mechanistic basis of the orange peel disorder, but they will also provide new insights in the complex water relations of fleshy fruit. These fruit are unique in that their high carbohydrate concentrations generate significant osmotic pressures. Because of their soft texture these osmotic pressures apparently are not contained by rigid cell walls that would be required to contain the resulting high turgor pressures. Whether the orange peel disorder and possibly the browning of pedicels is also related to these phenomena, will be identified in the course of the project.