Effect of oligochitosan on development of Colletotrichum musae in vitro and in situ and its role in protection of banana fruits

摘要

Concerns about the potentially harmful effects of fungicides on human health and the environment encourage the search for alternative treatments for perishable fruit pos-tharvest disease control. To this end, the potential use of oligochitosan as a natural antifungal compound to control postharvest anthracnose caused by Colletotrichum musae was investigated in banana fruits from the Cavendish group (genome AAA). Materials and methods. The influence of oligochitosan on the growth of C. musae was determined in vitro by micrographie analysis, while its in situ antifungal activity was monitored in banana fruits that were artificially injury-inoculated with C. musae; the activities of several defense-related enzymes were measured. Results and discussion.Oligochitosan at (4 and 8) g-L~(-1) markedly inhibited radial mycelial growth of C. musae in vitro. The scanning electron micrograph of C. musae treated with oligochitosan at inhibitory concentrations showed distortion and thinning of the hyphal wall and reduction in fungus colony diameter. Dipping banana fruits in oligochitosan solution at (5 to 20) g-L~(-1) significantly reduced the diameter of the anthracnose lesion, and 20 g oligochitosan-L~(-1 almost reached the same inhibitory effect as 0.5 g-L~(-1 of Sportaka, a synthetic fungicide. Activities of defense-related enzymes such as phenylalanine ammonia-lyase (PAL), beta-1, 3-glucanase (GLU) and chitinase (CHT), but not polyphenol oxidase (PPO), increased in banana fruits treated with 0.5 g oligochitosan-L~(-1). Conclusion. The inhibitory effect of oligochitosan on anthracnose development is due to the combination of a direct antifungal effect on the pathogen and an indirect effect, whereby the activities of defense-related enzymes in the bananafruit were enhanced. To control anthracnose in harvested bananas, treatment with oligochitosan above 20 g-L~(-1) may substitute the use of synthetic fungicide.