Sour rot in the vineyard is an indicator of Botrytis rot in grapes after storage

At harvest, table grape clusters may seem intact but can suffer from unacceptable levels of decay by Botrytis cinerea after storage. Sour rot is a disease complex that initiates from cracked or injured berries in which yeast and acetic acid bacteria develop, and the disease is propagated by Drosophila flies. Initial results from storage of grapes with and without microcracks showed that the latter had a low level of postharvest decay. Evaluation of the incidence of sour rot in nine Vitis vinifera cv. Scarlotta vineyards showed a range of 2–41% after veraison and 27–83% on day of harvest. Clusters from those vineyards that were free of sour rot symptoms were stored for 9 weeks with SO2 sheets followed by 3 d of shelf life. Decay levels after storage ranged from 3% to 15%, with the highest incidence of decay encountered in grapes from vineyards with the highest level of sour rot at harvest. The correlation coefficient between the sour rot index and Botrytis decay after storage was 0.32 and 0.25 for the evaluations at veraison and harvest, respectively, with significant P values. Further strengthening of these results was obtained by sampling of two vineyards with low and high incidence of sour rot that displayed a 10-fold reduction in Botrytis decay after storage. These results suggest that sour rot in the vineyard can be an important indicator for decay development during storage.