3.3 │ Superoxide dismutase (SOD)
Analysis of variance and the activities of SOD in roots of susceptible
and resistant cucumber genotypes subjected to pathogen infection are
presented in Table 2 and 4 and Fig 3. The SOD activity in the control of
each genotype showed little change from day 7 to day 21 (Table 4).
However, the SOD activity in the inoculated cucumbers changed
dramatically. Before inoculation, the SOD concentrations of all
genotypes were relatively low. In resistant and moderately resistant
genotypes, the SOD activity increased after inoculation by P.
melonis at 14 DAI, remained high in Soheil and Baby and decreased in
Ramezz at 24 DAI (Fig 3. A, B and C). The levels of SOD in inoculated
Soheil ranged from 0.42 U mg−1 (7 DAI) to 1.68 U mg−1(21 DAI), in Ramezz, it ranged from 0.21 U mg−1 (7 DAI) to 0.35 U
mg−1 (21 DAI) and in Baby from 2.19 U
mg−1 (7 DAI) to 0.79 U mg−1 (21
DAI). The genotype with the highest activities was the moderately
resistant Baby. The SOD activity in ‘Baby’ was 4.09 times greater
compared to control at 14 DAI. The induction of SOD in all genotypes
found little to no significant differences compared to control plants at
7 DAI, except Baby and Yalda (Table 4). The SOD activity of the
susceptible Mini 6-23 also showed increases of 1.47 U
mg−1 on day 21 after inoculation, but the susceptible
Yalda began to decline on day 21 after inoculation. The maximum amount
of SOD activity between the three susceptible genotypes in inoculated
plants was observed in Mini 6-23 at 21 DAI (Fig 3.E). The increase in
SOD activity caused by inoculation did not correlate with damping-off
susceptibility (Supplemental Table 1, varied between −0.56 and -0.14).