The differences between chitosan (350 kDa) and oligochitosan (6 kDa) in inhibitory effect on phytopathogenic
fungi and on decay control were investigated. Both chitosan and oligochitosan strongly inhibited
spore germination and mycelial growth of Alternaria kikuchiana Tanaka and Physalospora piricola Nose.
Relatively, chitosan and oligochitosan showed more obvious inhibitory effect on mycelial growth than
spore germination. Although oligochitosan had better inhibitory effects on fungal pathogenicity
in vitro, chitosan was more effective on disease control in pear fruit stored at 25 C. When treated with
oligochitosan, pear fruit increased the activities of chitinase (CHI) and b-1,3-glucanase. Differently, chitosan
treatment significantly increased peroxidase (POD) activity of pear fruit. These results suggested that
chitosan and oligochitosan triggered different mechanism for pathogenicity inhibition and disease
control.