Alterations in Surface Structure and Chemical Composition of the Cuticle in Response to the ‘Star Russeting’ Skin Disorder in Persimmon (Diospyros kaki)

Persimmon (Diospyros kaki) fruits accumulate vitamins, carotenoids, flavonoids, and antioxidants in their skin tissues, and therefore, considered as highly nutritional. Yet some persimmon varieties suffer from skin disorders including calyx-end cracking, shallow concentric cracks, and cloudy stains. These unfavorable disorders result in reduced fruit quality and marketability. Recently, a new skin disorder was spotted in commercial persimmon plantations in Israel, appearing at the blossom scar of the lower fruit parts in the shape of a star, and therefore, the disorder was termed ‘star russeting’. Symptoms were spotted mainly in fruits where the wilted remnants of flowers remained attached to the blossom scar, and the russeted skin matched the exact structure of the wilted flower, apparently constituting a flourishing micro-environment for the growth of the necrotrophic fungus Botrytis cinerea. Here, we sought to further determine the outcomes of the star russeting disorder on the fruit skin structure and polymer composition. To this end, we utilized histological studies together with light and electron microscopies, accompanied by profiling of cutin compositions via gas chromatography–mass spectrometry (GC–MS) in intact and russeted skin tissues of immature and mature fruits. Microscopical observations showed that the star-russeting skin disorder in persimmon caused macrocracks in the cuticle and sub-epidermal cell layers, resembling cracking disorders in other fleshy fruits. GC–MS profiling provided an inclusive metabolic repertoire of persimmon fruit skin cuticle for the first time validating major phenolic and aliphatic domains, but also delineated specific cuticle compounds that are associated with appearance of star russeting in persimmon fruit.