Study On The Mechanism Of Aluminum Ions Affecting The Occurrence Of Tobacco Bacterial Wilt

Tobacco bacterial wilt,a bacterial disease caused by Ralstonia solanacearum,occurs extensively in acidic soil areas of southern China.Due to the difficulty of prevention and treatment of bacterial wilt,it caused serious losses to tobacco production in China.Soil acidification is one of the key environmental factors and soil microorganism is an important ecological factor for the occurrence of bacterial wilt.At soil pH values below 5,Al³⁺ ions will dissolve from the clay minerals and inhibit the root growth and function,which is highly toxic to plant roots and affect the health of plant.So far,researches on the interaction of aluminum ions and plants mostly focused on the toxicity of aluminum ions to plants and the mechanisms of aluminum tolerance and aluminum resistance of plants.However,the relationship of aluminum ions and plant soil borne diseases are rarely reported.In this paper,in order to clarify the relationship between aluminum ions and the occurrence of tobacco bacterial wilt,the effects of aluminum ion on the growth of Ralstonia solanacearum and tobacco,the composition of soil microbial community and the incidence of tobacco bacterial wilt were evaluated.The aim was to provide a theoretical support for the prevention and control of tobacco bacterial wilt by adjusting soil pH balance and microecological balance.1.Distribution of soil pH and exchangeable aluminum ions in tobacco fields in China and the relationship between soil pH and aluminum ionsThe pH and exchangeable aluminum ion of tobacco bacterial wilt soil were determined by electrode method and potassium chloride extraction Aluminum Reagent Colorimetric method respectively.And the effect of adding aluminum ions on the soil pH was tested through laboratory experiments.The results showed that,the soil pH of the tobacco bacterial wilt fields in China were mainly distributed between 4.5 and 5.5,and the exchangeable aluminum ions were mainly between 154.43 mg/kg and 273.28 mg/kg.There was a significant negative linear correlation between pH and exchangeable aluminum ions in the soil of tobacco fields,y=-0.1412x+0.9326,R²=0.7229.The addition of aluminum ions can significantly reduce the soil pH.The results indicated that the relationship between soil pH and exchangeable aluminum ions was interdependent.2.The effects of aluminum ion on the growth of Ralstonia solanacearum and tobaccoThe effects of aluminum ions on the morphology and growth rate of Ralstonia solanacearum were detected on solid TTC medium and liquid medium respectively.The results showed that the low aluminum ion?less than 400 mg/L?could significantly reduce the colony size and affect the colony morphology of Ralstonia solanacearum,so as to delay the growth of Ralstonia solanacearum.The high aluminum ion?greater than 400 mg/L?could significantly inhibit or even completely inhibit the growth of Ralstonia solanacearum.The treatment of 300 mg/L aluminum ions could cause the necrosis of tobacco root tip and 600 mg/L aluminum ion could significantly inhibit the growth of tobacco in nutrient solution.In the soil environment,exchangeable aluminum ion concentration of 347.09 mg/kg could significantly inhibit the growth of tobacco.3.The effects of soil aluminum ions on microbial metabolism activity in tobacco rhizosphere soilBIOLOG ECO microplate method was used to detect the effect of aluminum ions on soil microbial metabolic activity.The results showed that high concentration of aluminum ions significantly reduced the overall metabolic activity of soil microorganisms and the utilization of carbon sources,such as carbohydrates,carboxylic acids and polymer.Moreover,exchangeable aluminum ions and Ralstonia were highly significant positive correlations.And exchangeable aluminum ions had a highly significant negative correlation with the fungus Zygomycota.4.The influences of different concentration of aluminum ion on soil microbial community compositionAfter analyzing the effect of aluminum ions on the metabolic activity of soil microorganism,the effects of aluminum ions on the composition of soil bacteria and fungi were examined by 16 S rRNA and ITS sequencing technology respectively.When the exchangeable aluminum ions concentration in soil was between 142 mg/kg and 269 mg/kg,exchangeable aluminum ions were significantly positive correlated with Chloroflexi and Saccharibacteria,negative correlated with Firmicutes,Nitrospirae,Chlorobi and Zygomycota.However,exchangeable aluminum ions were significantly positive correlated with Ralstonia.5.The effects of adjusting soil aluminum ions to control tobacco bacterial wilt in fieldAfter clarifying the effects of aluminum ions on the growth of Ralstonia solanacearum and tobacco,in order to analyze the control effect of reducing soil aluminum ion on tobacco bacterial wilt,lime and oyster shell powder were used to regulate the concentration of aluminum ions in the soil.The results showed that the treatment of lime and oyster shell powder could significantly reduce the concentration of exchangeable aluminum ions in the soil,but the efficiency of lime was not as good as that of oyster shell powder.The treatment of oyster shell powder could significantly reduce the incidence of tobacco bacterial wilt,and the final control effect against tobacco bacterial wilt reached 35.62%,which was significantly higher than that of 4.75% of lime.6.The influence of soil aluminum ions on the community composition of soil microbes in tobacco rhizosphere soilAfter clarified the control effect of lime and oyster shell powder on the control of aluminum ion to tobacco bacterial wilt,16 S rRNA sequencing was used to analyze the composition of bacterial community in the rhizosphere soil of lime,oyster shell powder and control treatment.The results showed that oyster shell powder treatment significantly increased the bacterial richness and diversity of tobacco rhizosphere soil,but had no significant effect on the relative abundance of Ralstonia solanacearum;Using LEf Se analysis,we found that after oyster shell powder treatment,Bacteroidetes,Gemmatimonadetes and Saccharibacteria became the dominant taxa.And at the level of the genus,the taxa that promoted nutrient absorption became an advantage.It indicated that oyster shell powder could prevent and control bacterial wilt by regulating the health of the soil and enhancing the health of the tobacco plant.In summary,Ralstonia solanacearum is more resistant to aluminum ions than tobacco.Therefore,when the acidification of soil caused the release of exchangeable aluminum ions,the exchangeable aluminum ions in the soil can cause damage to the tobacco root system,but it had no significant effect on the growth of Ralstonia solanacearum,which provided favorable conditions for the infection of the Ralstonia solanacearum.In addition,exchangeable aluminum ions in soil could reduce soil microbial metabolic activity and diversity of community composition,reduce the bacteria that are beneficial to tobacco nutrient uptake,and affect the health of tobacco plants.Based on the above two factors,the release of aluminum ions under soil acidification aggravated the occurrence of tobacco bacterial wilt.