Black Shank Pathogen-mediated Alteration Of Rhizospheric Microbiome Assembly In Tobacco

Plant growth promoting bacteria are a type of bacteria that can promote the growth and development of host plants through direct growth promoting effects and indirect disease resistance mechanisms.After plants are infected with pathogens,they specifically induce the synthesis of plant root exudates and recruit a group of beneficial rhizosphere microorganisms to help plants resist diseases.Fully exploring rhizosphere microorganisms with promoting growth and disease resistance is of great significance for improving host growth.Tobacco,as a model plant,can be used as experimental material for crop cultivation improvement using its species information,which can lay the foundation for subsequent research.This study used hongda tobacco as the experimental material to determine the soil microbial diversity after being infected by tobacco black shank pathogen,and selected rhizosphere bacteria specifically based on the results.Evaluate the growth promotion and disease resistance of tobacco seedlings by transplanting rhizosphere bacteria alone or in mixtures into tobacco plants.To verify whether plants will recruit a specific group of microorganisms in the rhizosphere after being attacked by pathogens,to help plants that grow in the same soil resist diseases.This experiment pre treated the soil by planting tobacco infected with the pathogen of tobacco black shank disease and tobacco plants treated with sterile water,and planted a second batch of tobacco plants on different pre treated soil.The tobacco was infected with the pathogen and the spore count of the pathogen at the disease site was measured to observe whether the soil formed a soil heritage.The results are as follows:(1)This experiment found that the diversity of tobacco rhizosphere microorganisms changed over time after the infection of tobacco black shank pathogen.Tobacco will recruit rhizosphere bacteria in the rhizosphere to help plants resist diseases.In this experiment,two high abundance and one low abundance rhizosphere bacteria with disease resistance were selected: Arthrobacter sp.,Pseudomonas sp.and Massilia sp.After isolating bacteria from tobacco rhizosphere soil,29 genera were isolated in this experiment,including these three bacterial strains.Through co cultivation,it was found that these three bacterial strains interact synergistically in the formation of biofilms in vitro.Specifically,under co cultivation of the three bacterial strains,more cell biofilms can be formed than under single bacterial cultivation,and the colonies of the three bacterial strains will attract each other on the culture medium.(2)Research on the growth promoting characteristics of rhizosphere bacteria: The three rhizosphere bacteria mentioned above were grafted back to tobacco plants alone or as a combination.The three rhizosphere bacteria and their combination had varying degrees of promoting effects on tobacco growth.The promoting effects of the three bacteria on tobacco plant height,stem width,leaf width,leaf length,net photosynthetic rate(Pn),and aboveground fresh weight were significantly increased compared to plants without rhizosphere bacteria inoculation.The combination of Pseudomonas sp.and three bacterial strains showed the most significant improvement in the net photosynthetic rate(Pn)of tobacco,while the combination of three rhizosphere bacteria showed the most significant promoting effect on the plant height,stem width,and fresh weight of the aboveground parts of tobacco plants.(3)Research on the disease resistance effect of rhizosphere bacteria: The three rhizosphere bacteria mentioned above were individually or as a combination to be grafted back into tobacco infected by the tobacco black shank pathogen.The degree of infection of the plant was quantified by observing the size of the tobacco disease spot and measuring the spore count of the pathogen in the tobacco black shank disease spot.The experiment showed that the three rhizosphere bacteria and the combination of bacteria can help plants resist the infection of the pathogen,Specifically,compared to plants that were not inoculated with rhizosphere bacteria,plants inoculated with rhizosphere bacteria had smaller disease spots and significantly reduced the number of spores in the affected areas.The mixture of three bacterial strains showed the most significant effect in reducing the size of tobacco black shank disease spots and reducing the number of spores in the disease spots.(4)The generation of soil-mediated legacy: This experiment demonstrated that plants infected by pathogens will recruit a group of rhizosphere microorganisms with disease resistance and growth promoting effects to help subsequent plants growing in the same soil resist diseases by planting tobacco in different pre-treatment soils,Specifically,the soil after the first generation of tobacco plants infected with pathogens can gain stronger resistance to disease when the second generation of tobacco plants are infected with pathogens.This indicates that after tobacco is infected with the tobacco black shank pathogen,the plant population will recruit a specific group of rhizosphere microorganisms in the rhizosphere,allowing the second plant population in the same soil to obtain protective rhizosphere microorganisms against that pathogen.In summary,tobacco infection with the pathogen of black shank disease can alter the diversity of rhizosphere microbial communities,as evidenced by the recruitment of three rhizosphere bacteria in tobacco plants: Arthrobacter sp.,Pseudomonas sp.,and Massilia sp.,forming a consortium to help plants resist diseases while promoting plant growth,It can also form soil heritage to help descendants of plants growing in the same soil resist diseases.