Fifty plants of 60 day-old cole (Zheyou No. 18) or rice (Ezhong
No. 5) were collected from the crop field rotated by rice and cole.
Five gram of the stems and leaves were cut into pieces (1 cm).
The fragments were surface-sterilized by soaking in 75% ethanol
for 1 min, and in 0.1% mercuric chloride (leaves for 2 min, stems
for 4 min). They were washed several times in sterile water,
transferred to an autoclaved mortar, and homogenized with
a mixture of quartz sand and sterile water. An aliquot (100 ml) of
the homogeneous suspension was spread on sterile potato
dextrose agar (PDA), and incubated at 27 C. After incubation for
48 h, single colonies were picked up and tested their inhibiting
activity against fungal pathogens. Among seven endophytic
isolates, only strain CHM1 significantly (p < 0.01) inhibited
growth of six species of fungal pathogens in vitro, as mentioned
in Section 2.1.
The culture solution of CHM1 was prepared by shaking LB liquid
culture at 30 C, 170 rpm for 36 h. It was further centrifuged at
6000 g for 5 min at 4 C and the supernatant collected and
passed through a 0.22-mm filter, yielding CHM1 culture filtrate. The
sterile culture filtrate was obtained by autoclaving the resultant
culture filtrate at 121 C for 30 min.The effects in vitro of CHM1 on mycelial growth inhibition of
plant pathogens were studied according to the method reported
by Leroux et al. (2002). Two ml of CHM1 culture solution, culture
filtrate or sterile culture filtrate were spread on 18 ml of PDA
medium. Three 5.0 mm diameter mycelial plugs, cut randomly
from the margin of a 5 day-old colony, and a plug, containing only
2 ml LB agar as negative control, were placed on a medium on
which one of six fungi was spread. Each experiment was conducted
in triplicate and the experimental design was a CRD.
Eighteen of these Petri dishes were sealed with parafilm and
incubated at 27 C in darkness. The radial growth of mycelia (cm)
was measured in two perpendicular directions on each cultured plate after 48 h of incubation, and the diameter (0.5 cm) of the
inoculation plug was subtracted. The resultant data were averaged.
The antifungal index was determined in comparison with
growth on non-amended medium, and calculated by the
following formula