Efficacy of integrated postharvest treatments against mixed innoculations of penicillium digitatum and geotrichum citri‐aurantii in ‘leng’ navel oranges (citrus sinensis)

Abstract

Green mould (Penicillium digitatum) and sour rot (Geotrichum citri‐aurantii) in early season, thin‐skinned navel oranges (Citrus sinensis) are of serious concern to the Australian citrus export industry. The pathogen causing the disease sour rot is particularly problematic because the control method for the Australian domestic market is to use fungicides containing guazatine, a chemical that is restricted for important export markets. In this study, we have examined possible alternative treatments to combinations of the two pathogens including the use of non‐restricted fungicides in combination with gibberellic acid (GA3), generally regarded as safe (GRAS) compounds, and/or elevated temperature. When inoculated fruit were dipped in solutions containing the fungicide imazalil alone and in combination with GA3, thiabendazole, or carbendazim, the infection rate was reduced. GRAS compounds, sodium carbonate, and mineral oil, were also effective in reducing infection rates when mixed with imazalil, as was sodium carbonate alone and when mixed with GA3. GA3 was not effective at the rate tested (50 mg litre−1). Elevated temperature in most instances did not reduce disease incidence in fruit, although in experiments with control levels of inoculation below 80%, temperature was a factor in some treatments. Further experiments are necessary to demonstrate the potential of alternative treatments to limit sour rot and mould development on export fruit.