Fruit infection and disease cycle of Botrytis cinerea causing cosmetic scarring in persimmon fruit (Diospyros kaki Linn.)

Abstract

Dark brown, corky spots on the skin of persimmon fruit (Diospyros kaki Linn.) are a cosmetic disorder known as scarring. In New Zealand the disorder causes substantial revenue losses to the persimmon industry. Microscopical examinations showed that the scarring is associated with Botrytis cinerea Pers. In spring, the fungus first colonises the senescent corolla adhering to the juvenile fruit and subsequently attempts to infect the underlying exocarp tissue. Histological and immunolabelling microscopy revealed that the fungus produces mycelial cushions composed of finger-like clusters of hyphae on the fruit surface. Attempted infection triggers a defence response in the fruit which prevents the fungus from establishment, and causes death and discolouration of the surrounding epidermal cells (hypersensitive reaction). Affected areas appear as dark specks to the naked eye and develop into corky scars as the fruit develops. Monitoring in two persimmon orchards suggested that conidia produced from infected senescent corollas infect the corolla of new emerging blossoms, leading to repeated cycles of infection during the flowering period. Conidia from over-wintering sclerotia in calyxes, pedicels and fruit mummies represent likely primary inoculum sources for infection of the corolla in spring. New foliage also often becomes infected by B. cinerea, resulting in necrotic lesions producing large quantities of conidia in spring. Such leaves, as well as aborted fruitlets and wounded fruit, are probable secondary sources of inoculum. A proposed disease cycle for B. cinerea causing fruit scarring in persimmon orchards in New Zealand is presented.