In vitro experiments
2.3.1. Confrontation tests
2.3.1.1. Dual culture of BCA and F. solani mycelia. The antagonistic
activity of Trichoderma spp. (BCA) was evaluated on PDA medium,
using the direct confrontation method as described by Comporta
(1985). Briefly, two discs (5 mm) obtained from one week old culture on PDA of Trichoderma sp. and F. solani respectively were
placed at opposite points on the same diagonal line at 1 cm distance from the edge. Three plates were considered for each
fungus-fungus interaction and the biological control potential of
each endophyte isolate against F. solani was studied. One disc each
of pathogenic agent (F. solani) and BCA (endophyte) alone was prepared as control. Both the dual and individual cultures were incubated at 25 ± 2 C and the linear growth of the fungi was measured
daily for 10 consecutive days. The growth inhibition percentage (%
I) was calculated at the last day following incubation using the formula (1) given below (Mokhtar and Aid, 2013):
ð%IÞ ¼ ð1 T=CÞ 100 ð1Þ
where %I = Percent Inhibition of pathogen growth by antagonists;
C = Radial growth in control (cm); T = Radial growth in the test culture (cm).
Additional biocontrol parameters were determined as described
by Pakdaman et al. (2013) including (i) days required for the two
colonies to come into contact (C); (ii) days required for the BCA
to fully grow over the pathogen colony (Z); (iii) days required for
the BCA to fully grow over the plate (M); (iv) the radial growth distance (in cm) of pathogen colony between the point of inoculation
and the marginal point of contact with the BCA growth zone (P);
(v) the pathogen resistance index (R) to the BCA was defined as a
ratio of Z/M based on the periods required for the full growth of
a fungal BCA in the presence (Z) and absence (M) of pathogen
(Pakdaman et al., 2013).
In addition, the Pakdaman’s biological control index (PBCI)
(Pakdaman et al., 2013) combining temporal parameters and
pathogen growth parameter was calculated following the formula
(2) below.
PBCI ðin cm1Þ ¼ M ðin daysÞ=Z ðin daysÞ P ðin cmÞ ð2Þ