Preharvest fungicide treatments reduce the effective SO₂ threshold of postharvest fumigation to control pathogens and maintain quality of "red globe" (Vitis vinifera) grapes

Sulfur dioxide (SO2) fumigation has been widely used to control pathogens and maintain the postharvest quality of table grapes. However, the effective dosage of SO2 treatment is close to causing bleaching damage on fruits. Further, the SO2 potential residue is a risk to human health. In this study, the dominant pathogens in "red globe" grapes during cold storage (0 and 10 degrees C) were identified as Botrytis cinerea, Alternaria alternata, and Penicillium expansum, while Aspergillus niger was dominant pathogen when the grapes were stored at room temperature (25 degrees C). The isolated dominant pathogens were effectively suppressed by SO2 ranging from 500 mu l L-1 to 800 mu l L-1, but bleaching spots were observed in grapes when SO2 was applied at 800 mu l L-1. To reduce the SO2 residue, the fungicides dimethomorph and thiophanate-methyl were respectively sprayed to control the epiphytic pathogens during the development of grape berries. In addition, the reduced microbial population contributed by fungicide treatments remitted the original density of postharvest microbial growth. The postharvest automated intermittent SO2 fumigation at 500 mu l L-1 was subsequently integrated to control the microbial activities. In addition, SO2 maintained the soluble solid content and titratable acid content, which were 22% and 75% higher than the control (p < .05) on 120 days of storage. The inhibition percentage against dominant fungal pathogens by preharvest fungicides spray was approximately 30%, while the postharvest intermittent SO2 fumigation contributed about 50%. We investigated the suppression role of preharvest and postharvest combined treatment for the grapes, which was concluded as a promising application to reduce decay and extend the shelf life of "red globe" grapes.