Ultrastructural and cytochemical aspects of the effect of chitosan on decay of bell pepper fruit

Abstract

Effect of chitosan treatment on the infection process of bell pepper fruit by Botrytis cinerea was investigated at the ultrastructural level. In inoculated control tissues, fungal colonization proceeded rapidly, causing extensive degradation of host walls and middle lamellae. Such alterations were also observed over walls distant from invading hyphae. In chitosan-treated tissue, however, fungal cells were mainly restricted to wound cavities and ruptured epidermal cells. Host walls, even when appressed against invading hyphae, appeared well preserved and showed no sign of alteration. While in inoculated control tissues, invading hyphae appeared normal, the fungal cells detected in chitosan-treated tissue displayed various degrees of cellular disorganization from wall loosening to protoplasm degradation. Structural host defence responses such as formation of wall appositions and plugging of intercellular spaces with fibrillar material were frequently observed in chitosan-treated tissues. Such structure reacted intensely with an Aplysia gonad lectingold complex, indicating the presence of pectic residues.