3.5 │ Activity of phenylalanine ammonia-lyase (PAL)
In each of the six cucumber genotypes, the PAL activities of the control plants indicated no significant changes from day 7 to day 21 (Table 6). In the resistant and moderately resistant genotypes, PAL activities showing significant difference from the control at time point after inoculation. After inoculation, PAL activity in the resistant genotype Soheil increased, reaching its first peak on day 7 then, it decreased on day 14 and increased to 1.86 U mg−1 on day 21 after inoculation (Fig 5. A). The CAT activity in resistant Ramezz increased sharply to 2.17 U mg−1 at 7 DAI and then decreased at 14 and 21 DAI (Table 6). The moderately resistant genotype, Baby, showed behavior similar to that of the Soheil, but it increased sharply and reached its maximum on day 21(5.20 U mg−1). The two highly susceptible genotypes Extrem and Mini 6-23 showed completely different patterns of PAL activity, that in the both genotypes increased on day 7 and 14 and then decreased on day 21 (Fig 5.D and E). Whereas on the other genotype Yalda increased on day 7 and then decreased on day 14 and 21 (Fig 5.F). Therefore, changes in PAL activity showed differences among different genotypes and it was significantly higher in inoculated plants of both moderately resistant and resistant genotypes, as compared to susceptible genotypes. The significant negative correlations between activity of PAL and damping-off susceptibility were only observed at 7 and 14 DAI (Supplemental Table 1, r= -0.94 and r= -0.82, respectively), in the highly susceptible genotypes, the increase of PAL activity was lower than in the resistant genotypes.