Endophytic Streptomyces Boost Eucalyptus Growth Under Heat, Drought, and Salinity: New Study Reveals Genome-Level Insights

A new study published in Frontiers in Agronomy reports the first application of six endophytic Streptomyces strains—isolated from eucalyptus trees thriving in saline soils—to evaluate their ability to enhance Eucalyptus camaldulensis growth under heat, drought, and salt stress. The research also provides genome-level insights into three of the most promising strains.

The investigation tested strains A1–A6 by soaking eucalyptus seeds in actinobacterial spores and growing them hydroponically for 41 days during natural heat-wave conditions. Among the six strains, strain A2 demonstrated the strongest growth-promoting effect, producing the greatest shoot length, root length, fresh weight, and number of lateral roots compared to untreated controls. Strain A3 excelled in enhancing chlorophyll a, chlorophyll b, plant dry weight, and leaf area, while strain A5 produced the highest seedling length vigor index (SLVI) at 200 mM NaCl, indicating superior salinity tolerance.

The study further evaluated strains A2, A3, and A5 in eucalyptus cuttings subjected to three stress conditions: drought, limited water with heat (below 40°C), and heat stress (40–42°C). Under full drought and high heat, all strains increased stress severity compared to controls; however, strains A3 and A5 improved performance under limited water with moderate heat, exhibiting lower stress severity.

Genome sequencing of strains A2, A3, and A5 revealed biosynthetic gene clusters associated with antimicrobial activity, siderophore production, and ectoine synthesis—traits that may support eucalyptus stress tolerance. The genomes also contained stress-response–related genes, including chaperones and heat shock proteins.

Overall, the study identifies strain A2 and A5 as promising candidates for supporting eucalyptus establishment in saline and hydroponic environments, while strain A3 is less suitable due to negative effects under specific stress conditions. The authors suggest that selected Streptomyces strains may be used as future bioinocula to improve eucalyptus resilience in challenging environments.

Reference

Kaewkla, O., Kiakhunthod, K., Chookhampaeng, S., Chutiman, N., Klankeo, P., Pachanakarn, N., & Franco, C. M. M. Streptomyces spp. as plant growth promotors and regulators of Eucalyptus in heat, drought and saline stress and genome insights into three selected potential strains. Frontiers in Agronomy, 7, 1665930. https://doi.org/10.3389/fagro.2025.1665930