Role of Citrus Phenolic Compounds in the Resistance Mechanism against Pathogenic Fungi

摘要

Fungi of the genera Penicillium and Alternaria are responsible for substantial post and pre-harvest losses in Citrus. To prevent their development and reduce commercial losses, chemical fungicides are used. However, such treatments can result in serious problems, such as residues on the fruit and the development of fungicide resistant strains. For this reason, it was of pressing interest to investigate alternatives to chemicals, such as flavonoids, that are believed to be involved in the defence mechanism of the genus, Citrus. The results obtained show that in the case of infection by Penicillium digitatum, certain citric flavonoids may well be involved in the defence mechanism, and may be considered as a phytoalexin against this fungus and to act as a chemical barrier. Although these secondary compounds exhibited phytotoxic activity against Alternaria alternata pv. citri in in vitro studies, the effect was not sufficient to slow down the development of the fungus. This fungus has developed a mechanism to metabolise these phenolic compounds which actually promotes the development of necrotic areas in the fruit, through which the fungus to spread more easily.