Morphological and Ultrastructural Modifications of Chitosan-Treated Fungal Phytopathogens

A number of studies have confirmed the in vitro fungicidal effect of chitosan on various phytopathogenic fungal families including among others, Mucoraceae, Pleosporaceae, and Glomerellaceae. Investigations of the morphology and ultrastructure of the chitosan-treated fungi in in vitro studies and during the plant-pathogen interaction of various pathosystems have been carried out by using conventional optical/light microscopy and with other advanced instruments including SEM, TEM, and confocal microscopy. The electrostatic interaction between chitosan and the microorganism is noted by dramatic alterations observed from the damaged structure of the cell wall and plasma membrane. The integrity of organelles including vacuoles was seriously affected, leading in some cases to lysis of the fungal cell. During the host-pathogen interaction, formation of structural barriers by the host, mainly through inter- and intracellular synthesis of phenolic-lignin-like material that stops fungal invasion, was also observed. Fungal growth was not beyond the outer cortical area of the infected tissues, while damage on fungi was similar to those observed in in vitro studies. Microscopic examinations have confirmed the fungicidal and eliciting properties of chitosan.