Cinnamaldehyde inhibits the mycelial growth of Geotrichum citri-aurantii and induces defense responses against sour rot in citrus fruit

Abstract

Sour rot is caused by Geotrichum citri-aurantii and is one of the devastating diseases in citrus fruit. This disease is difficult to control because of the lack of effective fungicides. In this study, cinnamaldehyde, a common food preservative, was evaluated to control postharvest sour rot in citrus fruit through in vivo and in vitro experiments. Results showed that cinnamaldehyde with a minimum inhibitory concentration and fungicidal concentration of 0.50mLL−1 dose-dependently inhibited the mycelial growth of G. citri-aurantii. The application of wax with cinnamaldehyde (WCA; 0.50, 1.0, and 2.0mLL−1) significantly reduced the incidence of sour rot on citrus fruit inoculated with G. citri-aurantii during storage. After 8 d of storage, the decay incidences in the fruit treated with WCA (0.50, 1.0, and 2.0mLL−1) were only 80%, 77% and 50%, respectively. By contrast, the decay incidence in the control fruit was 100%. In addition, WCA treatment increased the activities of superoxide dismutase (SOD), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL), but did not affect the activities of catalase (CAT) and peroxidase (POD), and the total phenol content. Our results suggested that WCA might induce defense responses against sour rot in citrus fruit.