Control of postharvest anthracnose in papayas (Carica papaya L.) by hot water and chitosan

Anthracnose in papayas, caused by Colletotrichum fructicola, is responsible for large economic losses during the export of this tropical fruit. Chemical fungicides are commonly used to control postharvest rots in papayas. The continued use of fungicides can result in the evolution of resistant fungal strains and the accumulation of chemical residues in harvested fruit. Combinations of alternative methods have the potential to improve the effectiveness of these treatments compared to when they are applied individually. In this research, a hot water dip (49°C for 20 min) combined with chitosan (1 and 2%) was assessed for its effectiveness against C. fructicola on papayas in cold storage. After 28 d at 10°C, anthracnose reduction on fruit treated with a combination of a hot water dip plus 2% of chitosan (50.7%) was significantly better (p<0.05) than disease reduction on papayas treated with synthetic fungicide (48.6%) and papayas treated with hot water dip plus 1% of chitosan (37.8%). All treatments were compared to untreated fruit. In addition, immersion at 49°C for 20 min plus a spray with 2% chitosan significantly reduced (p<0.05) weight loss, maintained firmness of papayas, and inhibited changes in quality parameters (total soluble solids (TSS), titratable acidity (TA) and pH), after 28 d of cold storage at 10°C. According to results obtained in this study, a combined hot water dip and chitosan treatment may be potentially used for controlling anthracnose on papayas during postharvest storage without a negative influence on its physicochemical quality. It is a residue-free method, and is safe for human health and the environment. However, further experiments will be needed to overcome the lack of knowledge about combinations of alternative treatments for controlling postharvest diseases in tropical fruit.