Table grapes can accumulate significant amount of dust carrying potential inoculum and this can be a
significant problem for late season grapes or in regions with high dust content. Internal decay of table
grapes during storage under SO2 atmosphere is expressed as visually intact berries but extensive internal
decomposition. One hypothesis is that these symptoms are caused by latent infections of Botrytis cinerea
or by another pathogen. Alternatively, SO2 restricts external fungal growth but its initial level is not
sufficient to prevent penetration of external natural inoculum into the berry. To test these hypotheses
clusters of ‘Scarlotta Seedless’ grapes were externally disinfected by dipping in ethanol after harvest and
cold-stored in the presence of one or two SO2 sheets for 6, 10, or 14 weeks followed by 3 days at shelf
life. After 6 weeks of storage the untreated control grapes contained 60% decay – mainly typical gray
mold symptoms – whereas SO2-treated berries displayed internal decay without external symptoms.
Ethanol reduced decay to 4.1% and the combination of ethanol treatment and SO2 sheets eliminated the
symptoms completely. The effect of the combined treatment was sustained after 10 and 14 weeks of
cold storage. Only B. cinerea was recovered from berries that showed internal decay, ruling out potential
involvement other pathogens. While the untreated clusters appeared dusty with dull red color, after
external disinfection the original red color of the berries was apparent. It can be concluded that external
disinfection of grapes after harvest can prevent internal decay under conditions which restrict external
fungal growth.
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