Effects of combining hot water, sodium bicarbonate and biocontrol on postharvest decay of citrus fruit

Chemical fungicides currently provide the primary means for controlling postharvest decay in citrus fruit. However, consumer demands for pesticide-free food and the development of pathogenic strains that are resistant to currently used fungicides necessitates the development of alternative methods for decay control. In the present study, we show that the integrated application of various "safe" postharvest treatments, including hot-water rinsing and brushing (HWB), sodium bicarbonate (SBC) (baking soda) and biocontrol by yeast antagonists, can reduce decay development almost as well as imazalil. Application of HWB (62degreesC for 20 s), SBC (2%, W/V) or Candida oleophila yeast cells (108 cells ml(-1)) 24 h after artificial inoculation of grapefruit with Pencillium digitatum (Pers.: Fr.) Sacc. reduced decay development in the infected wounds by 68, 61 or 23%, respectively. The combination of any two of these treatments or all three of them together reduced decay by 87 to 89% from the level in untreated control fruit. Similarly, HWB, SBC or yeast antagonists reduced decay development following natural infection of wounded fruit by 42, 72 and 69%, respectively. The combination of any two of these treatments or all three together reduced decay by 87 to 90% from that in control fruit. HWB and SBC had sanitizing effects and could disinfect inoculated wounds, while C. oleophila and SBC gave residual protection against later infection in the treated wounds. Postharvest storage experiments with 'Shamouti' orange and 'Star Ruby' grapefruit showed that combined treatments of HWB and yeasts, HWB and SBC, and SBC and yeasts reduced decay development by an average of 80-85% as compared with a 95% reduction observed for imazalil. Thus, the combination of different fungicide-free safe postharvest treatments may be almost as effective as commercial treatment with imazalil.