Screening Of Affinity PGPRs From Tobacco And The Growth-promotion Effects On Tobacco

The aim of this paper is to screen affinity potassium-solubilizing bacteria PGPR?Plant Growth-Promoting Rhizobacteria?strains from tobacco roots,to examine their effects on the growth and potassium content in leaves of tobacco,and to provide test materials and theoretical basis for the research and development of tobacco-specific biofertilizer.The methods of potassium-solubilizing bacteria culture and tobacco lectin were applied,and tobacco affinity potassium-solubilizing strains with a high potential for growth-promotion were selected from healthy tobacco seedlings rhizosphere soil.Strains with excellent potassium-solubilizing ability were selected by potassium-solubilizing abilities and other plant growth promoting traits.The effects of the strains on growth and potassium content in leaves of tobacco were investigated with pot experiment and Semi-solid test.Total 101 Rhizobacteria strains were obtained from potassium-solubilizing bacteria culture plates,and the number of tobacco-affinity bacteria accounted for 84.11%of all isolates.Fifty-seven strains had strong ability to solubilize potassium;The potassium concentrations of the culture broth were higher than 55.86?g/mL,and increased by more than 100%compared with those of the control.Among 57 strains,17 strains had extremely abilties to solubilize potassium;And the potassium concentrations of the culture broths were increased by more than 150%.77 PGPRsproduced IAA?Indole-3-acetic acid?and siderophore.Among them,the IAA concentrations of broth of18 strainswere more than 10?g/ml,siderophoreyield of 52 strains reached the level of3+and above28 PGPRs could inhibit the growth ofplant pathogens in plate confrontation experiments;five strains could inhabit six or seven kinds of plant pathogens;seven strains could inhabit Ternalia alternat and Colletotrichum destructivum.Investigation of growth-promote effects of 63 PGPR strains with strong potassium-solubilizing capability found that growth-promoting effects on tobacco seedlingswere significantlydifferent.44 strains?69.84%?significantlypromoted the dry weight of tobacco straws and roots.According to preliminary test mentioned above,18 outstanding PGPRs were selected to investigate the growth-promoting effects of PGPR with semi-solid and pot experiments.The result showed that pot was more suitable than a semi-solid for the study of growth-promoting effects of PGPRon tobacco.In the pot experiment,seven PGPR strains significantly promoted the growth of root and the accumulation of dry matter of roots and straws of tobacco seedlings.Analysisof root systemshowed that a total of 13 PGPRs significantly promoted tobacco root development.Total 6 parameters of roots development,e.g.total root length,total surface area,mean diameter,total volume,number of tips and branch number,were determined,12 PGPRs?66.67%?had significant promotion effects for more than 3parameters;5 PGPRs obviously promotedthe total number of tertiary roots oftobacco.Thirty-four strains and 11strains were selected to investigated their effects on potassium concentrations in tobacco leaves at high and low potassium level in pots experiment,respectively.The potassium fertilizer level of tobacco treated with all strains and control 1?CK1?was 50%of control 2?CK2?.At low fertilizer level,the K₂O level in tobacco leaves treated with26 strains were higher than that of CK1,respectively;and the K₂O levelof 13strains were even higher than that of CK2,respectively.At high fertilizer level,the K₂O in tobacco leaves treated with11 strains higher than that of CK1,respectively.The results showed that PGPR couldsubstantially increase potassium content in tobacco leaves.At low potassium fertilizer added level,the available potassiumlevel of soil treated with25 strains were significantly lower than that of CK1;the available potassium level of soils treated with 23 strainswere lower than that of CK0?nopotassium fertilizeradded?;The total potassium level in tobacco treated by33 stains were higher than that of CK1;the available potassium level of soils treated with 26 strains were higher than that of CK2.At highpotassium fertilizeraddedlevel,the available potassiumlevel of soil treated with 7 strains were higherthan that of CK1;the total potassiumlevel in tobacco treated with10 strains were higher than that of CK1.The results showed that PGPRs helped tobacco to absorb and utilize the potassium in soil.At lowpotassium fertilizer added level,with potassium added increased the apparent recovery efficiency?RE?ofpotassium fertilizer in potsincreased gradually.The RE of all soils treated with32 strains were higher than that of CK1,and the values of potstreated with 31 strains were higher than that of CK2.At high potassium fertilizer level,along with potassium added increased the RE decreased.The RE of potsin pots treated withten strains were higher than that ofCK1.The experiment showed that PGPRs could enhance the RE of potassium fertilizerin pot.Eighteen efficient PGPRs were identified to belong to 7 genera.Bacillus sp.,Paenibacillus sp.and Pseudomonas sp.were common potassium solving bacterial members;but Microbacterium sp.,Curtobacterium sp.,Streptomyces sp.and Sphingomonas sp.were new members with strong potassium-solving ability for the first time.Being evaluated comprehensively with the parameters of the promotion on growth and potassium content of tobacco leaf and other characteristics,these were considered the efficient affinity tobacco PGPR strains,and have the high potential for further research and applications.The rhizosphere potassium-solving bacteria strainsin this paper shows that this group has a rich diversity of genera.Tobacco lectin can be used as an effective tool for screening high-efficiency tobacco affinity PGPRs,and 18 excellent PGPRs obtained provide a reliable material for the development of the tobacco-specific potassium-solving fertilizer.