藿香耐盐碱内生细菌的筛选及其对盐胁迫下植株的促生作用

Screening of salt-alkali-tolerant endophytic bacteria from Agastache rugosa and assessing of their plant growth-promoting effects under salt stress

摘要:

东北松嫩平原地区盐碱地分布广泛，是制约粮食产量的主要因素。植物内生菌可以促进植物生长，增强宿主植物的抗逆能力。前期试验发现，藿香(Agastache rugosa)具有强耐盐性。目的 从高盐胁迫下生长的藿香中分离、筛选耐盐碱内生细菌，进一步挖掘植物抗逆促生菌资源。方法 以在200 mmol/L NaCl条件下正常生长的藿香为材料，通过组织切块法分离内生细菌，采用平板法鉴定菌株的盐碱耐受性，并对其促生及抗菌能力进行评价。结果 从藿香幼苗的叶、茎、根中分离到内生细菌95株，其中20株可耐受15% NaCl，14株在pH 10.0条件下仍可生长。筛选出的优良耐盐菌株具有生长素(indole-3-acetic acid, IAA)合成、产铁载体及固氮等促生特性，18株对3种植物病原菌表现出拮抗活性。综合促生、耐盐及抑菌特性，经主成分分析筛选出YL-14、YS-35与YR-18菌株，分子生物学鉴定表明其均属于芽孢杆菌属(Bacillus sp.)。在不同盐胁迫条件下，3种菌株处理均对藿香幼苗生长具有促进作用。在100 mmol/L盐胁迫下，YL-14、YS-35及YR-18菌株处理分别使藿香种子萌发率提高5.5%、8.5%和7.0%，根鲜重增加34.9%、124.0%和127.0%，而YS-35和YR-18分别促进主根伸长40.9%和49.5%。结论 本研究从藿香中分离筛选的内生细菌YL-14、YS-35及YR-18兼具优良的盐碱耐受性和促生特性，具备开发为抗逆促生菌剂的潜力，有望应用到其他作物中，为盐碱地的利用提供新的微生物资源。

Abstract:

Saline-alkali soil is extensively distributed in the Songnen Plain of Northeast China, posing a major constraint on the grain yield. It has been demonstrated that endophytic bacteria of plants could promote plant growth and enhance plant tolerance to environmental stress. Agastache rugosa had been experimentally verified to exhibit strong salt tolerance.Objective To isolate and screen salt-alkali-tolerant endophytic bacteria from A. rugosa grown under high-salinity conditions and explore microbial resources for promoting plant growth under stress.Methods A. rugosa seedlings surviving under 200 mmol/L NaCl were selected to isolate endophytic bacteria by the tissue culture method. Salt-alkali tolerance of the endophytic bacteria was assessed by plate assays, and the plant growth-promoting and antimicrobial properties were also evaluated.Results A total of 95 endophytic bacterial strains were isolated from the leaves, stems, and roots of A. rugosa seedlings, of which 20 strains tolerated 15% NaCl and 14 strains could grow at pH 10.0. The selected elite salt-tolerant strains possessed plant growth-promoting properties such as indole-3-acetic acid (IAA) synthesis, siderophore production, and nitrogen fixation. Additionally, 18 strains showed resistance against three plant pathogens. The principal component analysis on plant growth-promoting properties, salt tolerance, and antimicrobial properties screened out strains YL-14, YS-35, and YR-18, which were molecularly identified as Bacillus sp. Under different salt stress conditions, three bacterial strains demonstrated significant growth-promoting effects on A. rugosa seedlings. Specifically, under 100 mmol/L salt stress, YL-14, YS-35, and YR-18 increased the seed germination rate by 5.5%, 8.5%, and 7.0% and the fresh root weight by 34.9%, 124.0%, and 127.0%, respectively. Strains YS-35 and YR-18 increased the main root length by 40.9% and 49.5%, respectively.Conclusion Endophytic bacterial strains YL-14, YS-35, and YR-18 with strong saline-alkali tolerance and plant growth-promoting properties were isolated from A. rugosa. These strains show great potential for development as bioinoculants and application in other crops to enhance crop stress resistance and growth, serving as new microbial resources for the utilization of saline-alkali soil.