Chitosan coatings reduce fruit fly (Anastrepha obliqua) infestation and development of the fungus Colletotrichum gloeosporioides in Manila mangoes.

Background: Mangoes are tropical fruits appreciated worldwide but are extremely perishable, being susceptible to decay, pest infestation and fungal diseases. Using the flavorful and highly valued 'Manila' cultivar, we examined the effect of second-generation chitosan coatings on shelf-life, phenolic compound variation, phytohormones, pest infestation by fruit flies (Anastrepha obliqua) and anthracnose disease caused by the fungus Colletotrichum gloeosporioides.

Results: We observed almost total elimination of A. obliqua eggs with 10 and 20 g L chitosan in diluted acetic acid and a five- to sixfold reduction in anthracnose damage. Treatment with 20 g L chitosan also extended the shelf-life. External (skin) and internal (pulp) discoloration processes were delayed. Fruit firmness was higher when compared with control and acetic acid treatments, and total soluble solids were lower in chitosan-treated fruit. Targeted and non-targeted metabolomics analyses on chitosan-coated fruit identified some phenolic compounds related to the tannin pathway. In addition, abscisic acid and jasmonic acid in the peel were downregulated in chitosan-coated mango peels. Both phytohormones and phenolic content may explain the reduced susceptibility of mangoes to anthracnose development and A. obliqua egg eclosion or larval development.

Conclusions: We conclude that chitosan coatings represent an effective postharvest treatment that significantly reduces anthracnose disease, inhibits A. obliqua egg eclosion and significantly extends 'Manila' mango shelf-life, a key factor currently inhibiting large-scale commercialization of this valuable fruit. © 2020 Society of Chemical Industry.