Antimicrobial capacity of Pseudomonas brassicacearum strain EnPb against potato soft rot agent

Microorganisms showing endophytic lifestyles can be an ideal candidate to control plant diseases in agriculture ecosystems. Among bacterial endophytes isolated from potato tubers, five strains showed antibiosis towards Pectobacterium carotovorum subsp. carotovorum (Pcc) (JX029052) in vitro. The probable efficacy of the selected endophytes was tested in potato tuber maceration assay and in vivo disease incidence using preventive and curative applications. Moreover, the biocontrol properties of the selected endophytes as antagonists of potato soft rot agent were evaluated. Strain EnPb of Pseudomonas brassicacearum that was identified using phenotypic traits and 16S rRNA sequencing, reduced soft rot development by 62.2% in vivo and, showed significant suppression of symptoms of Pcc in both preventative (58%) and curative (54.6%) applications under storage conditions. This motile fluorescent species produces siderophore, hydrogen cyanide and lytic enzymes including amylase, protease, cellulose, and harbors antibiotic genes including phlD and prnC corresponding to 2, 4-diacetylphloroglucinol (DAPG) and pyrrolnitrin, respectively. The production of DAPG which exhibited anti-Pcc activity was confirmed through using H NMR, FT-IR and LC-Mass methods. In addition, volatile organic compounds (VOCs) emitted by EnPb, inhibited the growth of Pcc in vitro and were identified as sulfur-containing compounds consisting of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) using headspace gas chromatography-mass spectrometry (HS GC-MS). This study is addressing the first application of an endophytic P. brassicacearum stains as a biocontrol agent in the potato-Pcc patho-system decreasing a post-harvest disease.