Non-structural Mechanisms Of Resistance And Their Contribution Of The Successful Invasion Of The Exotic Plant Wedelia Trilobata

Currently, as the main content of the current global changes and the important international environmental ecological problem, biological invasions continue to homogenize biota, and have already became another major threat to global biodiversity. It threats both global ecological security and economic development. There are many reports about biological invasion mechanisms, however, there is few reports about systematic disease resistance of invasive species. Non-constitutive disease resistance mechanisms of invasive weed Wedelia trilobata and their contribution to W. trilobata’s invasion were first studied from four different aspects in this thesis: community, secondary metabolites, R-gene, and endophytic bacteria. The details are as following:1. By traditional community survey, this study showed that few W. trilobata suffer from disease in the field and its invasion significantly decreased its invaded community’s flora species diversity. And W. trilobata’s invasion showed an positive correlation withlocal economic output,2. Exploration disease-resistance mechanism of W. trilobata from biochemical level. The secondary metabolites from different issues of W. trilobata can suppress the growth of plant pathogen fungus Fusarium oxysporum f.spcuben (Fo) and Rhizoctonia solani(Rs), whereas, it can promote the motility and biofilm formation of plant pathogen bacteria Pseudomonas syringae pv. tomato DC3000(Pst).3. Further research also being conducted to detect the resistance gene analogs (RGAs) which involved two NBS-LRR of RGAs:tir-NBS-LRR (WTRGA1(Genbank Accession No. JX566690) and WTRGA2(Genbank Accession No. JX566691)) and non-tir-NBS-LRR (WTRGA3(Genbank Accession No. JX566692)). Then these two classes’dN/dS of NBS-LRR R-gene/RGAs were calculated. It was found that average dN/dS of invasive plants is significantly higher than that of non-invasive plants for tir-NBS-LRR R-gene/RGAs. While the invasive plants also showed higher dN/dS than that of non-invasion species for non-tir-NBS-LRR R-gene/RGAs.. The higher evolutionary rate of the RGAs of invasive plants compared to that of non-invasion species indicated the stronger ability to produce genetic variation and to identify and resistance to pathogens. And all these ability of the invasive plants will lead to that they win the competition with native plants under the local pathogens.4.156endophytic bacterias, which were isolated from W. trilobata samples, were collected from five provinces by traditional microbiological separation culture methods and16Sr DNA gene sequence analysis. These156strains belonged to21genu. Similar to previous reports, common endophyte bacterias were indentified and existed in each population of W. trilobata, such as Enterobacter. and Pseudomonas. In addition, one strain from three typical potential resistance group(Bacillus, Pseudomonas, and Variovorax), which were termed as JS、Psp、Vp8accordingly, were selected to test resistance to pathogens. The results showed that W. trilobata endophytic bacteria can secrete some antibacterial substances to suppress the plant pathogen fungus Rs, Fo and plant pathogen bacteria Pst. And under pathogen pressure, the growth of the stem segments of W. trilobata inoculated with endophytic bacteria was better than that of without endophytic bacteria inoculation. Meanwhile, stem segments of W. trilobata collected from those above five provinces were cultivated in the sterile soil, watering with sterile water every three days and harvested after three months. Sterile seedlings of W. trilobata were conducted as control treatment. The results indicated that, the growth of stem segments was better than that of sterile seedlings. Each physiological indicator of stem segments was better than that of sterile seedlings.The above researches indicated that W. trilobata might have three non-structural disease-resistance mechanisms, which then strengthened its disease-resistance ability:1) W. trilobata could synthesize metabolites with disease-resistance activity;2) the NBS-LRR R-gene of W. trilobata has a higher evolutionary rate, which potentially increased the richness of its R-gene;3) W. trilobata possesses endophytic bacterias which can depress the growth of indigenous bacteria. Additionally, W. trilobata may be able to attract pathogen bacteria (e.g. Pst) by secreting some metabolites, whereas W. trilobata could not be susceptible to these pathogen bacteria, it even could resistence to these pathogens, which could be used as weapons to depress local plants then to increase its competition with these local plants. And endophytic bacterias of W. trilobata possess promoting effects. All the above mechanisms, which could prevent the infection from local pathogens and use local pathogens to infect local plants and promote the rapid growth of W. trilobata, contributed great to strengthen W. trilobata’s invasiveness.