| Syringa plants are excellent landscaping trees and many species of them have good medicinal effects. The plants have long been considered less pests and resistant infertility. However, our survey found there were at least11different species of insects damaged Syringa plants and2-3species of them made trees weak growth, even death. Studying the rule of pests damage and insect-resistant mechanism are necessary prerequisite for protecting Syringa plants resources and further develop its using potential. For this purpose, the pest species during the period from clove leaves expansion to deciduous were detailed investigated and the resistance mechanism of Syringa spp. on Lepidosaphes salicina were analyzed from the point of view of the chemical ecology. Furthermore, the effects of cloves tannins, phenolic acids and a variety of defense protein on L. salicina were discussed. Our study will provide basic data for better protection and use of the cloves resources and breeding insect-resistant varieties, and also provide a theoretical basis for the prevention and treatment of L. salicina.Our survey found there were at least11different species of insects damaged Syringa plants in Harbin. Except phassus excrescens and Lepidosaphes salicina, all the other9species are reported for the first time. Thereinto, the trunk borer Phassus excrescens damaged nine variations, including Syringa oblata, Syringa villosa, Syringa emodi, Syringa microphylla, Syringa vulgaris., Syringa velutina, Syringa vulgaris’dahua’, Syringa reticulata var. mandshurica and Syringa dilatata. The hosts of this pest are in large scope, with the highest fatality rate to Syringa plants. The defoliator Psilogramma increta damaged Syringa oblata, Syringa villosa, Syringa emodi, Syringa microphylla, Syringa velutina and Syringa vulgaris ’zihong’. The Phloem-Sucking pests Coccurra ussuriensis was only found in Syringa reticulata var. mandshurica. Pseudococcus comstocki endangers Syringa reticulata var. mandshurica and Syringa microphylla. Lepidosaphes salicina greatly damaged Syringa oblata, Syringa villosa, Syringa emodi, Syringa oblata, Syringa dilatata, Syringa vulgaris and its variations, and occasionally endangered Syringa reticulata var. mandshurica, but not Syringa microphylla, Syringa velutina, Syringax chinensis f. chinensis and Syringa vulgaris’zihong’. Moreover, other insects were also found to damage Syringa spp., for instance, the Dendrothrips ornatus and two Lymantridae larvae that feed on Syringa oblate, and two thrips and one aphid that feed on Syringa reticulata var. mandshurica.On the basis of the population density of L. salicina on Syringa spp.,13species/cultivars of Syringa spp. were categorized into following four groups:highly-resistant group (e.g. Syringa chinensis et al), moderately-resistant group (e.g. S. emodi et al), susceptible group (e.g. S. oblate et al), highly-susceptible group (e.g.5. villosa), by cluster analysis. The contents of various tannins and phenolic acids in leaves of these13species/cultivars of Syringa from four sampling periods:the pre-infesting period (end of May), the peak-infesting period (end of June), the weakly-infesting period (end of July) and the late-infesting period (end of August), were measured with Vanillin-HCl and HPLC methods; and then their relationships with the susceptibility to L. salicina attacks were analyzed. The results showed that in the highly-resistant group, a full range/types of phenolic acids were detected in the uninfected leaves, and the total contents of phenolic acids were significantly higher than those species/varieties in other groups (p<0.05), except S. microphylla. Among the infested Syringa spp. within the highly-resistant group, the contents of tannins in S. dilatata leaves during the pre-infesting period were significantly higher than those in the other infested species within the same group (p<0.05); during the peak-infesting period, except that the increasing range of tannin is not significant in S. dilatata, the contents of tannin and total phenolic acids of the non-infested species were significantly higher (around81.75%to888.43%) than the infected Syringa spp. As for the moderately-resistant group, the increase range of total phenolic acids contents was significantly higher than that in the susceptible group and the highly-susceptible group during the peak-infesting period, and the tannin content was significantly higher than that in the susceptible group. In the susceptible group and highly-susceptible group, the contents of tannin and total phenolic acids were relatively low during the pre-infesting period, and there was a lag of induction in the total contents of tannins and phenolic acids during the peak-infesting period, and the types of phenolic acids were just half of the highly-resistant and moderately resistant groups. In addition, some specific kinds of phenolic acids and the changes of contents were related to the resistance of Syringa spp. eg. From May to August, the cinnamic acid was detected in all highly-resistant group and moderately-resistant group, whereas it wasn’t detected in the susceptible and the highly susceptible groups.We investigated the relationship between activities of various defensive plant proteins and pest-resistance to the L. salicina by testing seven kinds of defensive protein activities (POD, SOD, CAT, PPO, PAL, TI and CI) from the leaves of13Syringa species (seven species with high pest-resistance, three species with general resistance, two species with vulnerable type and one with very susceptible type) in different pest periods. The results showed highly significant difference in defensive proteins activities between different Syringa species (/?<0.01) in the pest period. POD activity of the species with high and general pest-resistance were significantly increased (p<0.05) in the peak-infesting period (end of June). In contrast, POD activity of the species with vulnerable and very susceptible pest-resistance was increased in the weak-infesting period (end of July) and the late-infesting period (end of August). CAT activity was significantly increased in the peak-infesting period; it may play a primary role in protection of the two types of species from pest damage. SOD activity was significantly decreased in all the tested species except the high resistance species in the peak-infesting period. The change of the PPO activity was positively correlated with the resistance in the pre-infesting period (end of May) and its increment also had correlation with pest resistance in the peak-infesting period. There were no differences in PAL activity between different resistance species. Similarly no significant correlation was found between the activities of TI and CI and the pest resistance in the pre-inf esting period. In summary, the level of PPO activity in the pre-infesting period is recommended as an index screening the resistant species.In summary, the resistance of Syringa spp. against L. salicina is related to its constitutive and induced defenses. The species that contain more types of phenolic acids and high contents of total phenolic acids and tannin, or can quickly respond to insect attacks by producing or increasing the contents of tannin or phenolic acids, might have a strong resistance potential against L. salicina, and vice versa. The activity level of the PPO non-harmful period can be used as index for screening cloves insect-resistant varieties. Increment of POD, PPO, TI and CI activities in the peak-infesting period were positively correlated with pest-resistance level of Syringa spp.. Therefore, on the breeding of resistant varieties, the species number of cloves phenolic acid, the total phenolic acid, and tannin contents, PPO activity can be used as breeding index. |
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