Introduction. Concerns about the potentially
harmful effects of fungicides on human health and the environment
encourage the search for alternative treatments for perishable fruit
postharvest 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
micrographic 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 Sportak®,
a synthetic fungicide. Activities of defense-related
enzymes such as phenylalanine ammonia-lyase (PAL), β-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 banana fruit were enhanced.
To control anthracnose in harvested bananas, treatment with oligochitosan
above 20 g·L–1 may substitute the use of synthetic fungicide.