Susceptibility of bunch grape and muscadine cultivars to berry splitting and spotted-wing Drosophila oviposition

Authors: REZAZADEH, AMIR - Mississippi State University; Sampson, Blair; STAFNE, ERIC - Mississippi State University; Shaw, Donna; Stringer, Stephen; Hummer, Kim

Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2018
Publication Date: 4/1/2018
Citation: Rezazadeh, A., Sampson, B.J., Stafne, E., Shaw, D.A., Stringer, S.J., Hummer, K.E. 2018. Susceptibility of bunch grape and muscadine cultivars to berry splitting and spotted-wing Drosophila oviposition. American Journal of Enology and Viticulture. 69(3):258-269.

Interpretive Summary: Two problems with growing grapes in the wet, southern climate is fruit splitting due to excessive rainfall, and fruit infestation by the invasive fruit fly, the spotted-wing Drosophila (SWD). We tested susceptibility of various hybrid grapes and native muscadine grapes to berry splitting and SWD attack. Although muscadine grapes showed the highest firmness, they were similarly susceptible to splitting, particularly ‘Fry Seedless’. Only ‘Thompson Seedless’ grapes were susceptible to egg laying by female SWD. Moreover, grapes resistant to disease showed tolerance to SWD infestations. SWD females are incapable of piercing the fruit skin that has a firmness rating of 300 Newtons or higher. Although, wounds or splits in the grape flesh quadrupled successful egg laying by SWD , suggesting that a well-managed vineyard will harbor few to no SWD flies.

Technical Abstract: One of the main disorders that widely reduces fruit quality and commercial value is fruit splitting. Fruit splitting is a physiological disorder that produces surface cracks that promotes disease and insect damage. Moreover, the spotted wing Drosophila (SWD), Drosophila suzukii (Matsumura), is a species of vinegar fly that attacks various berry crops and reduces fruit quality and yield; this includes grape crops worldwide. In this study, we tested susceptibility of various hybrid bunch grapes and muscadine grapes to berry splitting and SWD attack. Ten grapes cultivars were harvested in 2017 and one vinifera-type, ‘Thompson Seedless’, purchased locally. Fruit quality traits examined included Brix (% sugar content), total acidity (TA), pH, fruit firmness, and skin break force. ‘Thompson Seedless’ was the most susceptible to berry splitting (100%), while ‘Villard Blanc’ and ‘OK-392’ were the least susceptible (0 %). Although muscadine grapes showed the highest firmness, they were similarly susceptible to splitting, especially ‘Fry Seedless’ (88% splitting incidence). No significant correlations existed among sugar content, firmness and splitting; however, we did find a negative correlation between splitting and TA. ‘Thompson Seedless’ was the only truly susceptible host of SWD. Pierce's disease (PD)-resistant and tolerant grapes for the most part appear resistant or highly tolerant of SWD. SWD females do not seem capable of ovipositing in fruit hosts that have a flesh firmness exceeding 300 N. Although, 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 severe damage and disease might provide SWD with a needed summer fruit host. Overall, however, PD-resistant hybrids and muscadine grapes are crops highly adaptive to subtropical climates and tolerant of this new invasive vinegar fly.