Brown spot in table grape Redglobe controlled in study with sulfur dioxide and temperature treatments

Abstract

Brown spot is a postharvest disease of grapes caused byCladosporiumspecies 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 threeCladosporiumspecies:Cladosporium ramotenellum, C. cladosporioidesandC. 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 SO2treatment significantly reduced fungal growth of all three species and at all temperatures tested. Redglobe berries inoculated with theCladosporiumspecies, treated with SO2concentrations 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 SO2for allCladosporiumspecies tested.