Distinctive symptoms differentiate four common types of berry shrivel disorder in grape

Abstract

Shriveled fruit in vineyards has several origins including sunburn, dehydration, bunchstem necrosis and the recently described sugar accumulation disorder. These disorders are often confused with one another, but they can easily be distinguished by the location or composition of shriveled fruit and the condition of the rachis (the stem structure of a cluster). Sunburn is typically exhibited only on berries that are exposed to direct sunlight, and bunchstem necrosis is typified by necrotic rachis tissue. Berries with sugar accumulation disorder exhibit low sugar concentration, whereas berries with late-season dehydration typically have above-normal sugar concentration. Berries with sugar accumulation disorder and bunchstem necrosis exhibit the sugar content when sugar accumulation ceases or stem necrosis occurs, respectively. In tests, berries with sugar accumulation disorder exhibited lower berry weight, pH and anthocyanins, as well as differences in many nitrogenous compounds compared to normally developing fruit. In one location, sugar accumulation disorder was expressed at the whole-vine level, but none of the commonly known pathogenic organisms were found.