Susceptibility of Bunch Grape and Muscadine Cultivars to Berry Splitting and Spotted-Wing Drosophila Oviposition

Abstract

Fruit splitting is a physiological disorder that produces surface cracks that promote disease and insect damage. The spotted-wing drosophila (SWD), Drosophila suzukii (Matsumura), is a species of vinegar fly that attacks berry crops worldwide, including grapes, and reduces fruit quality and yield. In this study, we tested the susceptibility of various hybrid bunch grapes and muscadines to berry splitting and SWD attack. Ten grape cultivars were harvested in 2016 and 2017, and Thompson Seedless (Vitis vinifera) was purchased locally. Fruit quality traits examined included Brix (soluble solids), total acidity (TA), pH, fruit firmness, and skin break force. Villard blanc and OK392 were the least susceptible to berry splitting (0%). Although muscadines showed the highest fruit firmness, they were also susceptible to splitting, especially Fry Seedless (88% splitting incidence). There were no significant correlations among soluble solids, firmness, and splitting; however, there was a negative correlation between splitting and TA. Pierce’s disease (PD)-resistant and PD-tolerant grapes also appear to be mostly resistant to or highly tolerant of SWD infestation. SWD females do not appear to be able to oviposit in fruit hosts that have a fruit firmness exceeding 300 g/mm. Wounds or splits in the grape epidermis increased reproductive success of SWD by 400%, suggesting that a well-managed vineyard will not host large SWD populations. Vineyards suffering from severe berry damage might provide SWD with a summer fruit host. Overall, PD-resistant hybrids and muscadines are highly adaptive to subtropical climates and are tolerant of this new invasive vinegar fly.