Effects Of External Application Of Functional Bacteria On Tobacco Resistance To Low Temperature Stress And Growth Promotion

In order to alleviate the adverse effects of low temperature and cold stress on tobacco seedlings,this study used microbial complexes with probiotic functions to prepare a complex functional bacterial agent by optimising their culture conditions.The mechanism of low temperature stress in tobacco seedlings was investigated through hydroponic cultivation.The effect of the functional bacterial complex on the growth and development of tobacco at different fertility stages was further investigated through soil culture trials,and the mechanism of the functional bacterial complex on the growth of tobacco plants was also investigated in combination with soil chemical and microbial characteristics.The main findings of the study are as follows.(1)The fermentation medium and culture conditions of the growth-promoting microbial functional flora were optimized by orthogonal experimental design method.The results showed that the optimal medium for the functional microflora was Na Cl 5g/L,glucose 10g/L,tryptone 5g/L and yeast powder 5g/L.The optimum fermentation conditions were as follows: p H8.0,temperature 35℃,inoculation amount 7%,liquid volume 125 m L(300m L triangle flask).(2)The results showed that under low temperature stress,the agronomic traits of tobacco seedling were deteriorated,the root development was blocked,and the activity of antioxidant enzymes was decreased.Compared with the control treatment,the treatment of low temperature stress had better agronomic traits,biomass and root growth of tobacco seedlings,and the treatment of 20 m L bacterial agent per plant had the best effect.In terms of antioxidant enzyme activity,POD,CAT and SOD activity were higher under low temperature stress than control,POD activity was increased 1-2 times,CAT activity was increased 1-3 times and SOD activity was increased about 2 times.The antioxidant enzyme activity was the highest under 20 m L of microbial application.In the aspect of root microenvironment,the microbial community structure and diversity on the root surface of tobacco seedlings were significantly different under low temperature stress compared with the control treatment.The dominant species Clostridium sensu stricto could colonize on the root surface of tobacco seedlings,and the diversity of the bacterial community on the root surface of tobacco seedlings treated with the microbial agent was higher.(3)The effects of the functional microbial agent on the growth and development of tobacco at different growth stages and its promoting mechanism were studied by soil culture test.The results showed that the agronomic characters and biomass of tobacco plant were in the early and middle growth stages,and the best effect was obtained by using 15 m L functional microbial agent.In the late growth stage of tobacco,the treatment with microbial agent was better than that without microbial agent in agronomic traits.In terms of soil nutrient content,application of functional microbial agent had no significant effect on soil p H,total phosphorus and total potassium contents,but application of 10-20 m L microbial agent could significantly increase soil organic matter,total nitrogen,alkali-hydrolyzable nitrogen,available phosphorus and available potassium contents.The results showed that the application of functional microbial agents had no significant effect on the bacterial community composition of tobacco rhizosphere soil at phylum and genus levels,but had significant effect on the diversity of soil bacterial community at early and middle growth stages of tobacco.FAPROTAX function prediction analysis revealed the potential ecological function of bacterial community in each treatment.Applying 15 m L bacterial agent at the early growth stage of tobacco significantly improved the iron respiration of bacterial community in rhizosphere soil.Redundancy analysis also showed significant correlations between soil inter-root bacterial communities and soil chemical properties such as organic matter,total nitrogen,total potassium,fast-acting potassium,total phosphorus and effective phosphorus,as well as tobacco plant growth and development such as fresh weight of leaf,dry weight of leaf,fresh weight of stem,dry weight of stem,effective leaves,leaf weight,leaf width and dry weight of root.In this study,by optimizing the medium and fermentation conditions of microbial functional bacteria,the best quality and yield of fermentation liquid was prepared,the effect of microbial functional bacteria on tobacco seedling resistance to low temperature stress was clarified,and the growth promoting mechanism of microbial functional bacteria on tobacco plant was revealed.It laid a foundation for the development and application of the functional microbial agent,and also provided a new theoretical basis for the high-quality production of flue-cured tobacco in the future.