difference in disease incidence was observed between the control
and hot water-treated fruits after 5 d of incubation at 20 C. However,
HWT significantly (P < 0.05) enhanced the biocontrol efficacy
of P. membranaefaciens. The disease incidence of green and blue
mold decay in the combined-treated fruits was effectively reduced
(P < 0.05) during the whole storage period. The lesion diameters of
blue and green molds in the combined-treated fruits were 16.93%
and 25.76% lower than those in yeast-treated fruits after 9 d of incubation
at 20 C, respectively. These results indicated that HWT
could enhance the biocontrol activity of P. membranaefaciens against
P. italicum and P. digitatum in citrus fruits under the conditions of
pathogen inoculation time after treatments.
3.3. Effects of P. membranaefaciens and HWT on natural infection of
intact fruits
Fig. 3 demonstrates that the application of individual
P. membranaefaciens and HWT resulted in the low average decay
incidence of natural infection on fruit compared with the control.
The control efficacy of yeast or HWT was equivalent to that of
fungicide at half dosage. However, better control efficacy was achieved
when P. membranaefaciens was used with HWT. The percentage
of decayed fruit in the combined-treated fruits was 18.67%,
and that in yeast- and hot water-treated fruits was 38.47% and
43.66%, respectively, after 35 d of treatment at 20 C. No significant
(P > 0.05) difference was observed between the inhibitory effect of
the combined treatment and that of fungicide at full dosage during
the whole storage period. These results indicated that HWT could
enhance the biocontrol activity of P. membranaefaciens against
natural infection of intact fruits.
3.4. Effects of HWT on the population dynamics of
P. membranaefaciens in fruit wounds
No significant differences were noted between the population
dynamics of P. membranaefaciens in wounds of the control and hot
water-treated fruits at 20 C or 4 C (P > 0.05). The yeast population
rapidly increased by over two logs during a 2 d period at 20 C and
then gradually increased within 6 d at 20 C. When fruits were kept
at 4 C, the yeast population increased over 60 times after 5 d of
inoculation, decreased, and then remained relatively steady at the
end of the storage time (Fig. 4). These results indicated that HWT
did not inhibit the growth of P. membranaefaciens in fruit wounds at
room or cold temperature.
3.5. Effects of P. membranaefaciens combined with HWT on
defense-related enzyme activities and total phenolic content
Compared with P. membranaefaciens, which served as the control,
P. membranaefaciens combined with HWT significantly