3.3. Effects of chitosan or oligochitosan on postharvest diseases of pear
fruit
The symptom of black spot disease caused by A. kikuchiana
appeared in control and treated pear fruit after 72 h inoculation
(Table 2), while lesion diameter developed slowly (Fig. 3).
Differently, slight disease symptom caused by P. piricola was observed
only in control and oligochitosan-treated fruits at 72 h, thus
disease incidences and lesion diameter were mainly investigated at
96 and 120 h (Table 2, Fig. 3). Treatments with chitosan and oligochitosan
reduced the disease incidence caused by A. kikuchiana
and P. piricola and inhibited the lesion expansion of two fungi in
pear fruit (Table 2, Fig. 3). Moreover, the disease control effects
of chitosan and oligochitosan were concentration-dependent and
weakened over inoculated time. The IC50 of chitosan on disease
incidence caused by A. kikuchiana was 1.32 g/L after inoculation
72 h, 7.94 g/L after inoculation 96 h and 10.7 g/L after inoculation
120 h, meanwhile the IC50 of oligochitosan was 1.75 g/L after inoculation
72 h and 10 g/L after inoculation 96 h (Table 3). The black
spot disease already appeared on all oligochitosan-treated pear
fruit after inoculation 120 h. Relatively, the IC50 of chitosan and
oligochitosan on disease incidence caused by P. piricola was respectively,
1.57 and 7.47 g/L after inoculation 96 h, while 2.05 and
8.79 g/L after inoculation 120 h (Table 3). Therefore, compare to
oligochitosan, chitosan was more effective on disease control,
especially to that caused by P. piricola.