花生种子相关促生菌分离鉴定及功能评价

【背景】利用微生物促进植物健康生长是农业可持续发展的重要方向之一，而种子相关的促生菌可在植物生命周期早期与植物相互作用，对植物健康生长具有重要意义。【目的】发掘与利用种子相关促生菌的前提是筛选获得促生菌菌种资源，验证其益生能力，为其进一步应用与机理研究提供依据与支持。【方法】以花生种子为研究对象，从种子表面及种子内部分离纯化多株菌，测定菌株的固氮、解磷、解钾、吲哚乙酸合成和铁载体合成等促生能力，并验证菌株对常见植物病原菌的生长抑制特性；通过16S rRNA基因序列进行系统发育分析，确定分类地位；通过生物膜形成能力及根际定殖能力测定菌株在植物根际的生存能力；最后通过催芽及盆栽试验测定菌株对花生种子发芽及幼苗生长的影响。【结果】从花生种子表面、种子内和胚根内分离筛选到41株菌，均有吲哚乙酸合成能力，其中35株有固氮能力，2株有铁载体分泌能力，14株有植物病原菌生长抑制能力。各选一株为代表的菌株，即PS3、PE5和PR5，经16S rRNA基因序列比对分析鉴定为芽孢杆菌属(Bacillus)。PS3、PE5和PR5均可在MSgg液体培养基表面形成褶皱较强的生物膜，也可在花生根际形成有效定殖。催芽试验结果表明经过促生菌浸种后花生种子萌发率明显提高，在第2天时，PS5将发芽率由14.17%提高至38.33%，PE5发芽率提高至30.83%，PR5发芽率提高至39.17%。三株菌能够明显促进花生幼苗生长，PS5对花生幼苗苗高、根长、鲜重和干重分别提高21.82%、22.20%、37.11%和35.64%，PE5分别提高17.45%、18.93%、26.10%和21.18%，PR5分别提高23.11%、23.92%、38.66%和37.47%。【结论】筛选获得的花生种子相关促生菌，具有促进植物生长的潜力，明显促进种子萌发及幼苗生长，是良好的促生菌生物资源，具有较好的应用潜力。

Isolation, identification, and functional characterization of plant growth-promoting bacteria from peanut seeds

Background] The application of plant growth-promoting bacteria is an important measure for the sustainable development of agriculture. The seed-associated bacteria can interact with plants in the early lifecycle, being of great significance to plant growth. Objective] To screen out the seed-associated bacterial strains with the function of promoting plant growth and inhibiting plant pathogens, to underpin the application of the strains in agricultural production. Methods] The plant growth-promoting bacteria were isolated from the surface and the inside of peanut seeds. The roles of the isolates in promoting plant growth (nitrogen fixation, phosphorus solubilization, and IAA and siderophore production) and inhibiting the growth of plant pathogens were examined. The 16S rRNA gene sequencing was employed to determine the taxonomic status of the isolates. The biofilm formation and rhizosphere colonization tests were carried out to measure the viability of the strains in plant rhizosphere. Finally, pot experiments were conducted to examine the effects of the plant-growth promoting bacteria on the seed germination and seedling growth of peanut. Results] A total of 41 plant-growth promoting bacterial strains were isolated from peanut seeds. All of the strains were capable of producing IAA, and 35, 2, and 14 strains showed the abilities of fixing nitrogen, secreting siderophores, and inhibiting plant pathogens, respectively. The representative strains (the surface/inside of peanut seed and the inside of peanut radicle), PS3, PE5, and PR5, were chosen according to the results of phylogenetic analysis and identified as Bacillus sp. The three strains formed folded biofilms on the surface of MSgg liquid medium and colonized the surface of peanut roots. They increased the seed germination rate and promoted the seedling growth of peanut. Specially, PS3, PE5, and PR5 increased the seed germination rate from 14.17% to 38.33%, 30.83%, and 39.17%, respectively, on day 2. Compared with the control, PS5 increased the seedling height, root length, fresh weight, and dry weight by 21.82%, 22.20%, 37.11%, and 35.64%, respectively; PE5 increased them by 17.45%, 18.93%, 26.10%, and 21.18%, respectively; PR5 increased them by 23.11%, 23.92%, 38.66%, and 37.47%, respectively. Conclusion] The bacterial strains with high efficiency in promoting plant growth were isolated from peanut seeds, and significantly promoted seed germination and seedling growth. The strains provide potential resources for agricultural production, with excellent application potential.