Control Of Dry Rot In Potato Tubers With Postharvest Chitosan Treatment And Possible Mechanisms Involved

Potato dry rot caused by Fusarium spp. is one of the most important postharvest diseases. Synthetic fungicides are used for controlling the rot, but there is growing concern over the indiscriminate use of synthetic fungicides on crops because of the possible harmful effects on human health and the emergence of pathogen resistance to fungicides. In the study, potato tuber and slices (cv. Atlantic), as a material, were treated with 0.25%, 0.5% and 1% chitosan by vacuum and coating. The inhibition effect of chitosan and its mechanism were studied on potato tissue inoculated with F. sulphureum. The effect of chitosan on F. sulphureum in vitro was also studied. The results showed as below:1. In vitro chitosan inhibited mycelium growth, dry weight of mycelium and spore germination of F. sulphureum. Morphological change and structural alteration of hyphae were induced, including abnormally distribution cytoplasma, non-membraneous inclusion bodies assembling in cytoplasma, considerable thickening of the hyphal cell walls, very frequent septation with malformed septa.2. Chitosan significantly inhibited lesion diameter of tubers inoculated with F. sulphureum. The treatment at 0.5% and 1% showed more effective, but concentration of 1% caused slight phytotoxicity. Lesion diameter was reduced in tubers and slices treated with chitosan at 0.25% then inoculated with F. sulphureum 72 hour, 48 and 72 hours after treatment respectively.3. Chitosan significantly increased the activities of peroxidase (POD), polyphenoloxidase (PPO) and the contents of flavanoid and lignin in tissue. The increase was also observed in activities ofβ-1, 3-glucanase (GLU), phenylalanine ammonialyase (PAL) and content of total phenolic. The activities of POD, PPO and PAL were enhanced furthermore by inoculated with F. sulphureum in treated tissue, more accumulation was also found in total phenolic, flavanoid and lignin in tissue.4. Chitosan significantly increased the contents of H2O2 and ascorbic acid (AsA), and the production of O2-. The activities of catalase (CAT) and glutathion reductase (GR) were also increased in treated tissues, but the activities of superoxide dismutase (SOD) and ascorbic peroxidase (APX) were reduced. The activities of CAT, APX and GR and the production of H2O2 and O2- were enhanced furthermore by inoculated with F. sulphureum in the treated tissue and the control tissue. But the activity of SOD and the content of AsA were reduced.The study suggested that chitosan could directly inhibit the growth of F. sulphureum by interrupting or haunting its metabolism and lesion expansion by inducing bio-chemical defence responce in tuber.