California Agriculture

There are several causes of shriveled fruit in vineyards, including sunburn, dehydration, bunchstem necrosis (BSN), and a recently described sugar accumulation disorder (SAD). Due to the similarities in fruit appearance these disorders are often confused with one another, but they can easily be distinguished by the location and/or composition of the shriveled fruit and by the condition of the rachis. Sunburn is typically exhibited only on berries that are exposed to direct sunlight, and BSN is typified by necrotic rachis tissue, with shriveled berries distal to the necrotic tissue. SAD berries exhibit low sugar content as well as concentration, whereas late season dehydration berries, as well as BSN berries, typically have normal to above normal sugar concentration. SAD berries exhibit lower berry weight, pH, and anthocyanins, as well as differences in many nitrogenous compounds compared to normally-developing fruit. In one location, SAD is expressed at the whole-vine level, but none of the commonly known pathogenic organisms (phytoplasmas, closteroviruses, fanleaf viruses, nepovirusesm, and fleck complex viruses) were found to be associated with SAD.