The Application Of PGPR Microbial Inoculum In The Cultivation Of Flue Cured Tobacco

Flue-cured tobacco is an important economic crop in China,and Sichuan province is one of the three major tobacco production bases in China.In recent years,due to unreasonable fertilization regimes and excessive use of fertilizers and pesticides,tobacco cultivation soil becomes compact,the soil nutrients appeared to be unbalanced,and soil quality decreased.Plant growth promoting rhizospheres(PGPR)play an important role in fertilizing soil and realizing soil sustainable development,and are widely applied in agricultural cultivation.To screen PGPR microbial inoculum suitable for flue-cured tobacco production and protect the tobacco planting soil quality.Gulin county of Luzhou city in Sichuan province,a traditional tobacco culitivation area,was established as the experimental platform to study the impact of different PGPR microbial inoculum on the agronomic characters,yield,output value and chemical quality of flue-cured tobacco.Moreover,the effects of PGPR inoculants on the soil physicochemical properties and soil microbial community composition were also determined.The main results are list as following:(1)The agronomic characters of flue-cured tobacco under different fertilization systems were analyzed.The results showed that at the rosette stage,both of the plant height and leaf number were higher in the soil treated with different PGPR inoculum than those in CK soil(control).Compared to the CK,the impact of C8 treatment on the tobacco height and leaf number was the best,in which the plant height and leaf number were improved 27.94 % and10.97%,respectively.In vigorous growing period,the application of PGPR microbial inoculum is superior to other treatments in terms of plant height,leaf number and the diameter of plant stem,which were improved 27.94%,4.57%,and 6.03%,repectively.In terms of controlling the incidence of black stem disease and brown spot disease,the treatments with PGPR inoculum(e.g.C5,C6,C7,and C8)were also more effective than those without PGPR.(2)The yield of flue-cured tobacco under different PGPR inoculum varied sigficantly(P<0.05).The yield showed a variation trend as following C6>C8>C7>C5.Compared to the conventional fertilization(C3),the tobacco yields under different PGPR treatments in were increased 6.13% to12.4%.And the tobacco yield under C6 treatment was the highest,which was 10% higher than the other treatments.For the tobacco output value,the variation trend was as following C6 > C8 > C7 > C4 > C5 > C3 > C2 > C1.C6 had the highest output value while C8 was the lowest.Compared to the treatment of C3,the output value under C6 and C8 treatments were 18.2% and 16.6% higher,respectively.In terms of the average price,the C8 treatment was the highest,which was 21% higher than it in the conventional fertilization treatment.(3)The quality of flue-cured tobacco treated with different PGPR inoculants also showed a significant difference.Generally,the content of total nitrogen in tobacco leaves was1.61%-2.85%,and the optimum content is 2.5%.In our study,the total nitrogen content under the treatments containing PGPR microbial inoculum(e.g.C5,C6,C7,and C8)was ranged from 1.64% to 2.8%.The ratios of total nitrogen to nicotine in high-quality tobacco leaves are alwayes lower than 1.In the present study,the nitrogen and nicotine ratio of the middle and upper leaves were all less than 1particularlly for the C5 and C6 treatments which revealed that the PGPR inoculum can improve the ratio of nitrogen to nicotine of flue-cured tobacco.For the content of potassium,chlorine and nicotine,all the middle and upper leaves were within the suitable range.Compared to the conventional fertilization,the total sugarand nicotine ratio of the upper tobacco in the soil with C8 treatment decreased 3.66%,while those in the middle and lower parts leaves were increased by 3.48% and 6.11%.(4)The soil physicochemical parameters were also significantly affected by different PGPR inoculum treatments.The soil organic matter under the PGPR inoculum treatments(C5,C6,C7,and C8)was higher than those of the conventional fertilization treatment(C3).The soil organic matter under C8 treatment was 29% higher than it in C3,which achieved the best effect.The soil total nitrogen,available nitrogen,available phosphorus and available potassium were all higher in the soils treated with PGPR inoculum(C5,C6,C7 and C8).And the available nitrogen,available phosphorus and available potassium in the C8 treatment was24.28%,107.78%,and 53.51% higher than those in under the conventional fertilization treatment(C3).(5)Denaturing gradient gel electrophoresis(DGGE)was used to analyze the impact of different fertilizer treatments on the soil bacterial community composition.The results showed that there were no significantly difference about the DGGE band number,yet some specific band emerged in the soil treated with PGPR inoculum indicated that the application of PGPR inoculum affect the bacterial community compostion in the tobacco cultivation soil.In addition,the diversity index,richness and evenness of bacterial community compsotion in soils treated with PGPR inoculum were also increased compared with those under conventional fertilization.Based on the phylogenetic analysis of the DGGE band,the predominant bacteria species in tobacco cultivation soil belonged to Proteobacteria,Chloroflexi,Acidobacteria,Bacteroidetes,Firmicutes,Actinobacteria.(6)The relationship between bacterial community composition and edaphic parameters was analyzed by canonical corrrespondce analysis(CCA).The result showed that among the determined soil parameters such as soil p H,available nitrogen,available phosphorus,total phosphorus,organic matter,soil organic matter and available phosphorus are the key factors in shaping thebacterial community composition.In summary,the application of PGPR inoculum could modify the agronomic traits and chemical quality of tobacco leaves,and also improve the capabilty of disease resistance,and increase the yield and output value of flue-cured tobacco.