Microbial diversity in coastal Casuarina equisetifolia forest and its potential in counteracting bacterial wilt infections

BACKGROUND

Casuarina wilt is a destructive soil-borne disease caused by Ralstonia solanacearum species complex (RSSC). Recent large-scale outbreaks of Casuarina wilt in the coastal regions of Guangdong Province, China, suggest that the originally resistant Casuarina clones become susceptible to RSSC infection. This study aimed to investigate the microbial diversity of environmental microorganisms and its potential in biocontrol of this devastating disease.

RESULTS

The results unveiled the dominant and common microbial species in Casuarina equisetifolia tree tissues, the rhizosphere soils and seawater in the vicinity of Casuarina equisetifolia forest belt. We also found a range of bacterial species with potent antimicrobial activities against Ralstonia pseudosolanacearum. Both the Casuarina endophyte A1-5, identified as Bacillus velezensis, and a combination biocontrol agent named CEP consisting of three mutually compatible soil isolates belonging to Citrobacter farmeri, Enterobacter aerogenes, and Pseudomonas mosselii, respectively, could effectively control the R. pseudosolanacearum infections on Casuarina and tomato. The active substance of strain A1-5 that inhibits the growth of R. pseudosolanacearum was purified and identified as surfactin C.

CONCLUSION

The findings unveiled the microbial diversity and their specific distributions in the Guangdong coastal Casuarina equisetifolia forest areas, and present useful clues and resources for developing new strategies to prevent and control the Casuarina bacterial wilt. © 2025 Society of Chemical Industry.