Abstract:

In this study, we investigated the relationship between activities of various plant defensive proteins and pest-resistance to the Lepidosaphes salicina by testing defensive activities of seven proteins (POD, SOD, CAT,PPO, PAL,TI and CI) from leaves of 13 Syringa species (seven species with high pest-resistance, three species with intermediate resistance, two species with susceptibility and one with very susceptibility) in different pest periods. The results showed that there was highly significant difference in defensive proteins activities among different Syringa species (P<0.01) in the pest period. POD activity of the species with high and intermediate pest-resistance was significantly increased (P<0.05) in the peak-infesting period (by the end of June). However, POD activity of the species with susceptibility and very susceptibility was increased in the weak-infesting period (by the end of July) and the late-infesting period (the end of August), respectively. CAT activity in susceptible and very susceptible species was significantly increased in the peak-infesting period, and the enzyme might play a primary role in protection of the species from pest damage. SOD activity in the high resistant species had no change, while it in other species was significantly decreased in the peak-infesting period.The PPO activity in the pre-infesting period (by the end of May) was positively correlated with the resistance and its activity in the peak-infesting period also had correlation with pest resistance. There were no differences in PAL activity between different resistance species. Similarly no significant correlation was found between the activities of TI and CI in the pre-infesting period and the pest resistance. In summary, the level of PPO activity in the pre-infesting period is recommended as an index for screening the resistant species. Increases in POD, PPO, TI and CI activities in the peak-infesting period were positively correlated with pest-resistance level of Syringa spp.

Key words: Lepidosaphes salicina, Syringa spp., protective enzyme, defensive enzyme, poteinase inhibitor