Antifungal Activity of a Chitosan and Mint Essential Oil Coating on the Development of Colletotrichum Gloeosporioides in Papaya Using Macroscopic and Microscopic Analysis

Chitosan and mint essential oil treatments have been studied as natural alternatives to chemical fungicides to control fruit diseases caused by phytopathogens, such as Colletotrichum gloeosporioides that causes anthracnose in papaya fruit; however, their combination has been scarcely studied and their microscopic effect on the infected papaya surface has not been reported. The aim of this investigation was to evaluate the effect of chitosan (CH), mint essential oil (MEO) or their combination (CH + MEO) on the in vitro growth of Colletotrichum gloeosporioides, the macroscopic and microscopic development of anthracnose and the postharvest quality of papaya. Fruit were treated by immersion in solutions of CH (1%), MEO (0.2%) or CH + MEO (1%, 0.2%) for 5 min and stored for 20 days at 12 °C. Untreated fruit were used as control. In vitro and in vivo antifungal activity and postharvest quality were assessed for all treatments, and anthracnose development was evaluated using scanning electron microscopy only for control and the treatment with the best antifungal activity. In vitro, the applied treatments exhibited an important antifungal activity due to the high inhibition of mycelial growth and conidial germination. In vivo, the lowest incidence and severity of anthracnose was obtained in fruit treated with CH, which was also observed by microscopic analysis. In addition, the treatments maintained the fruit postharvest quality. CH was effective to inhibit anthracnose development in papaya and the addition of MEO did not provide an additional effect. Chitosan coating may be a useful strategy to control anthracnose and maintain the postharvest quality of papaya fruit.