The Pathological And Physiological Research On The Interaction Of Poplar And Physiological Race Of Melampsora Larici-populina Kleb.

Rust caused by Melampsora larici-populina Kleb. occurs on poplars belonging to sections Tacamahaca, Aegiros, Leucoides and their hybrid cultivars. It has impact on the growth of young plant and caused decrease of volume and biomass, and has significant influence on the development of commercial and ecological forest. This rust has a long life cycle and exist pathogenic variation, as a result, host resistance can be overcome by the new physiological race and lead to the prevalence of disease and serious loss in poplar plantation. The main approach to disease control has been breeding for resistance. Therefore, the research on interaction of host and pathogen in order to better understand the host-parasite relationship plays important role in poplar breeding scientifically and successfully.This paper had studied the pathological and physiological changes on the interaction of poplar and physiological race of Melampsora larici-populina Kleb.. After studied on the changes on physiological index, photosynthesis, transpiration of host and cell wall-degrading enzymes of pathogen, the conclusion was made as follow:1. The dynamic changes of physiological metabolism on poplar infected Melampsora larici-populina Kleb. with different compatibilities were studied. The results indicated that the contents of host soluble sugar, protein, reducing sugar, free amino acids, and the activity of CAT, SOD, POD and MDA changed after infected by the rust. All these physiological indexes except the activity of MDA had close relationship with host resistance, and can be served as criteria for assessing the resistance of poplar to Melampsora larici-populina Kleb.2. The dynamic change of carbohydrate content indicated that the poplar rust disease was a kind of high sugar disease, and other physiological indexes also showed that at the early stage of infection, the activity of PAL in incompatible increased quickly during the penetration of rust hypha into the stoma and formation of stomatal vesicle, therefore inhibited the prolongation hypha in the host tissue leading to the low penetration rate in incompatible combination. During the stage of hypha invasion, the content of free amino acids increased in contrast to the content of soluble protein. Meanwhile, the activity of CAT, SOD, POD increased rapidly in order to scavenging reactive oxygen, the compatible combination did not have necrosis because of high activity of CAT, SOD, POD, but the necrosis happened in the incompatible combination because of the low activity of these enzymes.3. The photosynthesis and transpiration of poplar cultivars infected by Melampsora larici-populina Kleb.were monitored dynamically by LI-6400 Portable Photosynthesis System. The photosynthetic rate, intercellular of CO2 concentration, transpiration rate and stomatal conductance of poplar cultivars were examined after inoculated with Melampsora larici-populina Kleb.with different pathogenicity. The photosynthetic rate declined seriously after rust infection especially in susceptible cultivars. The intercellular of CO2 concentration declined after inoculation but was not related to the host resistance. All these indexes indicated that the photosynthesis was inhibited after infection of rust. As to transpiration, the transpiration rate reduced after infected, it increased after the spore breakout. The stomatal conductance increased at the beginning of inoculation, and it had a conspicuous decline between the stages of spore breakout. The change of stomatal conductance had close relationship with the host resistance. As a result, the change of four indexes indicated that the photosynthesis and transpiration of poplar cultivars were influenced by the infection of Melampsora larici-populina Kleb. especially seriously in compatible combinations.4. The activity of cell wall-degrading enzymes produced in poplar cultivars infected Melampsora larici-populina Kleb. was studied. The results showed that PMG, PMTE, CX andβ–glucosidase played roles during infection, the activity of the cell wall-degrading enzymes secreted by rust in poplar was much lower than that secreted by the necrotroph pathogen in the host. After inoculation, the activity of PMG in both susceptible and resistant cultivars had two peak values in 2 dpi and 5 dpi. The activity of PMTE andβ–glucosidase had their peak values in 3dpi, and CX in 2 dpi. Among these cell wall-degrading enzymes, the activity of PMG and PMTE were higher and the activity of CX andβ–glucosidase were relatively lower. Activities of these cell wall-degrading enzymes were significant higher in susceptible cultivars than those in resistant cultivars. The results indicated that the cell wall-degrading enzymes secreted by the rust had expressed sequentially, the rust secreted the enzymes during the stage of penetration and the secretion did not influenced by defensive reaction of host. In addition, the early increase of activity of PMTE, PMG, CX elicited the defensive reaction of poplar and produced some defensive enzymes in order to inhibit the penetration of rust. All these demonstrated that these cell wall-degrading enzymes played certain roles in infection of Melampsora larici-populina Kleb.