California Agriculture

Brown spot is a postharvest disease of grapes caused by Cladosporium species in the San Joaquin Valley of California. It spreads during cold storage and transport, resulting in severe economic losses to late table grape cultivars, which are grown mainly for export to countries such as China and Mexico. We examined the effect of temperature and sulfur dioxide (SO2) treatments on fungal growth and infection of Redglobe berries by three Cladosporium species: Cladosporium ramotenellum, C. cladosporioides and C. limoniforme. Redglobe is especially popular for export. Fungal colonies growing on potato dextrose agar in petri plates stored at -2°C grew slower than those stored at 2°C, and an 400 ppm-h SO2 treatment significantly reduced fungal growth of all three species and at all temperatures tested. Redglobe berries inoculated with the Cladosporium species, treated with SO2 concentrations of 100 ppm-h, 200 ppm-h and 400 ppm-h and incubated in high relative humidity chambers for 28 to 32 days at 2°C, showed little incidence of disease. The development of brown spot on berries was entirely prevented with the treatment of 200 ppm-h SO2 for all Cladosporium species tested.