Screening Of Microorganisms For Highly Effective Degradation Of Self-Toxic Substances Secreted By Tobacco Root

With the growth of China's population,land resources are increasingly scarce.At the same time,the degree of intensive crop planting is increasing,and the crop producing areas are more and more concentrated,which making continuous cropping has become a common phenomenon.The continuous cropping obstacle caused by continuous cropping has gradually become the main factor hindering the sustainable development of agriculture in China.The traditional measures such as crop rotation and increasing organic fertilizer are generally adopted to solve the problem,but the effect is not ideal.It is generally believed that phenolic acids represented by benzoic acid and ferulic acid,and fatty acids represented by palmitic acid are the main factors causing allelopathic autotoxins in most crops.Phenolic acids,in particular,have stable chemical structure and are difficult to degrade in the soil,leading to changes in the soil microbial community,increased pathogenic bacteria and reduced probiotics,leading to a high incidence of crop diseases.Tobacco is a forbidden continuous cropping crop,and the economic loss caused by continuous cropping of tobacco is up to 4 billion yuan every year.In order to solve the problem that tobacco autotoxic substances such as phenolic acids are difficult to degrade,this study aimed to screen out strains that can effectively degrade tobacco allelopathic autotoxic substances to solve the problem of continuous cropping of tobacco.In order to find strains that can efficiently degrade phenolic acids,a set of special screening model was designed,which consisted of the following steps: 1.The agar medium plates were prepared with benzoic acid,ferulic acid and palmitic acid as the main carbon sources,and the plate screening model was established.The soil suspension from different sources was coated on the plate to obtain single bacterial colonies.2.The liquid medium was prepared with benzoic acid,ferulic acid and palmitic acid,and the single colonies growing on the agar plate were inserted into the test tube with liquid medium.The degradation ability of the strains was confirmed by checking whether the strains were growing and TLC method was used to detect whether the phenolic acid was degraded.3.After the confirmed strains with degrading phenolic acid and palmitic acid were cultured,the medium was removed by centrifugation,and the effects of the strains on the growth of tobacco seedlings and cabbage seedlings were measured with small glass bottles.The strains that had adverse effects on the growth of tobacco seedlings were excluded;4.The pot experiment confirmed the influence of the strain on tobacco growth;5.pot cultivation test in greenhouse test with soil of continuous cropping obstacle.With the above model,two biodegradable strains,No.39 and No.8,were finally obtained from 3288 strains through the above rounds of screening.The biodegradable strains had obvious effects on the degradation of ferulic acid,benzoic acid and palmitic acid in soil,with degradation effects reaching 69.1% and 73.6%,respectively.The pot experiment showed that it had obvious promoting effect on the growth of tobacco(Honghuadaijinyuan)cultivated in continuous cropping soil,which showed that the plant height increased and the leaf chlorophyll content increased.The two strains were identified as Glutamicibacter protophormiae and Bacillus tequilensis,respectively,and could significantly prolong the activity of tobacco root system.The two strains could increase the biodiversity of the microbial community in the continuous cropping barrier soil.Different from the widely reported in the literature,this study found that although allelotoxic substances such as palmitic acid,benzoic acid and ferulic acid showed inhibitory effects on the growth of tobacco,but these compounds did not inhibit the growth of tobacco in continuous cropping soil,and can promoted the growth of tobacco to a certain extent,such as:The plant height and stem circumference of tobacco in palmitic acid treatment group were 46% and 31% more than those in blank group;The plant height and stem circumference of tobacco treated with ferulic acid increased by29% and 19% in blank group.The combination of these compounds has an even stronger effect on tobacco growth.Although strain 39 and strain 8 could significantly degrade allelopathic autotoxic substances in soil,there was no correlation between the degradation rate of allelopathic autotoxic substances and growth effect.Considering that allelopathic autotoxic substances palmitic acid,benzoic acid and ferulic acid are the components formed by plants when they are infected by pathogenic bacteria,they have significant inhibitory effect on pathogenic bacteria.The high content of pathogenic bacteria in continuous cropping soil stimulates the tobacco to secrete these allelopathic autotoxic substances,thus playing a protective role on tobacco itself.Conclusion: This paper established a set of effective screening model for degradation of allelopathic autotoxic substances,and successfully obtained a strain capable of degrading tobacco autotoxic substances in soil.Although self-toxic substances inhibit tobacco growth,these compounds may be a defense mechanism that tobacco protects itself from infection by pathogens and is not the main cause of the continuous disorder.