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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.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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