Effect of chitosan on the in vitro control of Colletotrichum sp., and its influence on post-harvest quality in Hass avocado fruits

Avocado fruit cv Hass, is from an economic point of view, one of the most important crops for Mexico, because Mexico is the main producer of avocado in the world. However, the production is often reduced due to large postharvest losses because the fruit is susceptible to attack by Colletotrichum sp., the causal agent of anthracnose. In recent years it has been explored new alternatives to combat postharvest fungi because of the risk that involve the use of harmful chemical fungicides on the environment and consumer health. One alternative is the application of chitosan films, which has an antifungal effect. In this study the in vitro antifungal activity of low and medium molecular weight chitosan on two strains of Colletotrichum sp., isolated from Hass avocado fruits whit anthracnose symptoms was evaluated. Additionally, the chitosan effect on the post-harvest quality of the avocado fruit was also evaluated. Chitosan solutions at 0.1, 0.5, 1.0, 1.5 and 2.0% (w/v) were used to assess inhibition of mycelial growth, sporulation and germination of spores recording measurements every 24 h for 9 days. In vivo trials were performed by inoculating avocado fruits with a suspension of Colletotrichum sp (1x10(6) spores . mL(-1)). The fruits were immersed in low molecular weight chitosan solution (1.5% w/v). The incidence of disease, physiological weight loss, firmness and percent of dry matter of the treated fruits were evaluated after 12 days of storage at 25 degrees C. The in vitro results demonstrated that low and medium molecular weight chitosan solution at 1% inhibited more than 90% of mycelial growth and significantly reduced sporulation and germination of conidia of Colletotrichum sp. The in vivo results showed that the application of chitosan on avocado fruits reduced physiological weight loss, kept the firmness and decreased disease incidence. According to our results, the application of chitosan films on avocado fruits could be a plausible alternative to control of anthracnose and preserve the Hass avocado quality during its storage at room temperature.