Fungal diseases that may occur before or after harvest are the main challenges of the postharvest citrus industry. Some fungal diseases are slight and only drastically reduce the marketability of the product, while some postharvest fungal diseases of citrus grow rapidly and also infect their adjacent fruits. Infected fruits can neither be stored for a long time nor be exported. For this reason, early detection of fungal infections is very essential. In this paper, all optical methods used to identify citrus fungal diseases, including imaging-based methods and spectroscopic-based methods, are investigated. The application of these methods in detecting citrus fungal diseases is also reviewed.
