Isolation and characterization of antagonistic endophytes from Dendrobium candidum Wall ex Lindl., and the biofertilizing potential of a novel Pseudomonas saponiphila strain

Abstract

Many endophytic bacterial strains are now successfully used for plant-growth promotion (PGP) and as biocontrol agents (BCA) against plant diseases. This is a promising strategy for the improvement of crop productivity, thereby reducing the use of chemical pesticides and fertilizers. The objectives of this study were to isolate endophytic bacteria from the medicinal plant Dendrobium candidum Wall ex Lindl in China, and evaluate the biological control and PGP characteristics of these bacteria. Antagonistic tests were performed against fungal pathogens. Twenty-two of the 83 bacterial isolates showed antagonistic activities. These antagonistic isolates were screened in vitro for PGP traits, such as the production of indoleacetic acid (IAA), siderophores, proteases, and phosphate solubilization. Based on the tested PGP traits, strain YW was selected for further study. Strain YW was identified as Pseudomonas saponiphila based on its 16S rRNA and gyrB gene sequences. We detected the antifungal metabolite-encoding genes phlD, and hcnBC genes encoding 2,4-diacetylphloroglucinol (2,4-DAPG) and hydrogen cyanide (HCN) from strain YW. We measured the effect of strain YW on the growth of pepper seedlings under greenhouse conditions. Our results showed that its antifungal potential may be attributed to 2,4-DAPG and HCN antibiotics, as well as protease and siderophore production, and growth promotion may be related to the ability of isolate YW to synthesize IAA and solubilize phosphate. The PGP and antifungal activities of strain YW suggest that it may be exploited as a potential bioinoculant agent. This is the first report of a P. saponiphila strain with PGP attributes.