2.3.2.3. Inhibitory effect of BCA on F. solani conidia germination.
2.3.2.3.1. Inhibition by Trichoderma spp. culture filtrates. The inhibition of F. solani spore germination was assessed by the M38-A2
broth macrodilution assay described by CLSI (2008) with minor
modifications. Briefly, 250 lL, 500 lL and 625 lL of sterile PDB
were distributed in 1.5 mL glass tubes. Thereafter, 500 lL, 250 lL
and 125 lL of Trichoderma spp. culture filtrates were respectively
distributed in the tubes and finally 250 lL of conidia (4 105 -
spore/mL) prepared in PDB were introduced in each tube to reach
a final volume of 1 mL. Negative control consisted of tubes containing culture medium with F. solani and sterility control contained
only the culture medium. Triplicate test and control tubes were
incubated at 25 ± 2 C for 24 h. Samples (loop full drop) were taken
from each tube after incubation and examined microscopically.
Conidia enumeration was done using a haemocytometer. Activity
was expressed as percentage of inhibition of conidia germination
(%SGI) calculated as follows:
%CGI ¼ ðGc Gt=GcÞ 100 ð4Þ
where Gc: Germination in control tubes; Gt: Germination in treated
tubes.
2.3.2.3.2. Inhibitory effect of BCA ethyl acetate extract on F. solani
conidia germination. The ethyl acetate partition was prepared from
the filtrate of the more promising BCA (T. atroviridae) upon the
above experiments. The spore germination assay was performed
using the M38-A2 method (CLSI, 2008) with minor modifications.
Briefly, 100 lL of PDB (Sigma Ltd) were distributed in triplicate
in the wells of a 96-wells plate followed by addition of 100 lL of
stock ethyl acetate extract of T. atroviridae at 5.32 mg/mL to the
first well. After thorough mixing, a twofold serial dilution was
achieved by successive transfer of 100 lL into subsequent wells.
Then, 100 lL of F. solani conidia (4 105 conidia/mL) were introduced in the wells containing the test substances. Sterility control
consisted of blank wells without F. solani conidia. Upon incubation
of the plate at 25 ± 2 C for 24 h, an aliquot of culture was taken
from each well and examined microscopically. The percentage of
inhibition was determined according to the formula (4) given
above.
The lowest concentration of ethyl acetate extract exhibiting
100% inhibition of the germination of F. solani conidia was considered as the Minimum Inhibitory Concentration (MIC).