| Worldwide,bacterial wilt caused by R.solanacearum poses a serious threat to the production of Solanaceae crops(such as tobacco,pepper,etc.)and other crops.Ralstonia solanacearum infects plants,invades through roots,colonizes the vascular bundle system,and leads to xylem tissue obstruction.The aboveground part has typical symptoms of unilateral wilting,and even the death of the whole plant.In the integrated control strategy of the disease,cultivation and disease control and chemical control are common and effective control measures.In addition,it also includes improving crop resistance through genetic resistance improvement.However,due to the complex genetic diversity and wide host range of bacterial wilt,the pathogen is widely distributed in soil and plant parts and has a long survival time,the above strategies can not fundamentally solve and completely control the disease.In recent years,the coordinated prevention and control strategy of biological control has been more and more favored by people.It is the most effective method to protect human health and the environment.Plant growth-promoting rhizosphere bacteria(PGPR)are considered to be promising biological control agents.They play an important role in plant health cultivation and disease prevention and control.In this study,Bacillus amyloliquefaciens Cas02 strain was isolated from healthy tobacco rhizosphere soil,and its effect on promoting plant growth and inhibiting bacterial wilt was evaluated.Strain Cas02 showed a variety of growth promoting related characteristics,including iron carrier production,cellulase activity,protease activity,ammonia production and catalase activity.In addition,strain Cas02 has a significant inhibitory effect on the growth of R.solanacearum.Its active substances were separated and identified as macrolide A and macrolide W by HPLC-DAD-ESI-MS/MS.Both greenhouse and field experiments showed that Cas02 showed good performance in promoting plant growth and inhibiting bacterial wilt.In order to explore the potential genetic mechanism,we sequenced the whole genome and identified gene clusters related to the expression of antimicrobial metabolites.In general,strain Cas02 may be a potential biocontrol agent in bacterial wilt management and a source for further development and utilization of antibacterial compounds.Its potential biocontrol mechanisms include niche exclusion,nutrient acquisition and direct interaction.In order to explore the connection between polysaccharide compositions/molecular weight and properties/bioactivities.Using microwave aided hydrothermal extraction method,sulfated polysaccharides from Ulva prolifera were successfully extracted.It was found that the extraction conditions could influence the characteristics and bioactivities of polysaccharides.At 90°C with 0.01 M HCl,rhamnose,galacturonic acid,and glucose were the most abundant monosaccharides.However,at150°C with 0.1 M HCl,glucose was the most abundant monomer.The sulfur content increased with increasing temperature and acid concentration,while the molecular weight dropped.Polysaccharides extracted from 90°C,0.05 M HCl had the highest water-holding capacity(41.32 g/g)and oil-holding capacity(15.09 g/g),while those extracted from 150°C,0.05 M HCl had the highest foaming capabilities(foaming capacity 143 percent and foaming stability 113 percent,respectively).Plants are often exposed to a variety of pathogens(fungi,bacteria,nematodes and viruses),so a complex defense system is needed.In plants,the activation of defense response and related signals is mainly regulated by hormones such as salicylic acid,jasmonic acid and ethylene,which induce systemic resistance to pathogens.For example,polysaccharides and their derived oligosaccharides can promote plant growth,induce plant resistance to pathogens and activate salicylic acid dependent defense pathways.This study found that the synergistic effect of Bacillus amyloliquefaciens and seaweed polysaccharide can play a good role in the prevention and control of bacterial wilt caused by R.solanacearum.The combined application effect of the two is better than single application,and the specific mechanism still needs to be further discussed.Studies have shown that algal polysaccharides and Bacillus spp.promote growth of tomato and tobacco plants and reduce the incidence rate of bacterial wilt caused by R.solanacearum.Therefore,the combined application of PGPR and seaweed polysaccharide has proved to be a key strategy for the prevention and control of bacterial wilt in an environment-friendly manner.At the same time,we also studied the mechanism of how RSSC responds to the important component(monosaccharide)of root exudates.We used several monosaccharides(the main components of tobacco root exudates)as signals to add to the culture medium,and studied the expression patterns of some virulence factors through transcriptome sequencing.It was found that galactose can significantly change the physiological state of RSSC to simulate the state in plants.Compared with several monosaccharides,the induction of galactose can significantly up regulate the expression of type III effectors.In addition,nitrogen metabolism is actively induced to produce active nitrogen such as nitrous oxide,which will promote pathogenicity. |
PDF Full Text Request