Genetic diversity, plant growth promotion potential, and antimicrobial activity of culturable endophytic actinobacteria isolated from Aconitum carmichaelii Debeaux

Aim: This study evaluated the phylogenetic diversity, plant growth promotion capacity, antifungal activity, and biocontrol potential of culturable actinobacterial endophytes isolated from the medicinal plant Aconitum carmichaelii Debeaux. Methods and results: Isolation of actinobacteria from healthy A. carmichaelii plants was carried out on six different media. Full-length 16S rRNA gene was amplified by PCR from the genomic DNA of each strain. Indole-3-acetic acid and siderophore production were quantitatively assessed by the Salkowski and Chrome Azurol S methods, respectively. Rice seeds germination and seedling growth were employed to evaluate plant growth promotion capacities of candidate strains. Dual-culture assay and pot experiments were performed to investigate the antifungal and biocontrol potential of isolates. We obtained 129 actinobacterial isolates from A. carmichaelii, and they belonged to 49 species in 7 genera. These strains exhibited diverse plant growth promotion ability, among which one strain significantly enhanced rice seeds germination, while 31 strains significantly facilitated rice seedling growth. SWUST-123 showed strong antifungal activity against four pathogens in vitro and was most compatible with Qingchuan cultivar. SWUST-123 reduced around 40% of southern blight disease occurrence compared to blank control treatment.. Conclusion: Aconitum carmichaelii harbored genetically diverse actinobacterial endophytes exhibiting diverse plant growth promotion and antifungal potential, some of which can be served as good candidates for biofertilizers and biocontrol agents. Significance and impact of the study Actinobacterial endophytes play pivotal roles in maintaining plant growth and health. However, systemic study on the genetic diversity, plant growth promotion, and antifungal potential of actinobacterial endophytes from medicinal plants remain largely elusive. We isolated 129 actinobacterial endophytes from healthy A. carmichaelii plants. These strains were designated into 49 species in 7 genera. We screened good candidate strains for biofertilizers and biocontrol agents that would be helpful for overcoming the continuous cropping obstacles of A. carmichaelii