Isolation and identification of Serratia marcescens Ha1 and herbicidal activity of Ha1 'pesta' granular formulation

A total of 479 bacterial strains were isolated from brine (Bohai, Qinhuangdao City, Hebei Province, China). Bioassay results indicated that 4 strains named Ha1, Ha17, Ha38, and Ha384 had herbicidal activity. And strain Ha1 had the highest effective herbicidal activity. As a result, this study aims to identify strain Ha1, characterize its physiological and biological activities, evaluate the herbicidal activity of its metabolites, and develop a ‘pesta’ formulation and assess its effectiveness on Digitaria sanguinalis. Ha1 was identified as Serratia marcescens based on 16S rDNA sequencing. This strain has a flagellum, a diameter of 0.5 to 0.8 μm, and a length of 0.9 to 2.0 μm. The indole test shows positive results, and the catalase enzyme exhibits strong positive reactions. Results further showed that the inhibitory concentration (IC50) of the crude extracts to D. sanguinalis radicula and coleoptile were 3.332 and 2.828 mg mL–1, respectively. Both the suppression of D. sanguinalis and the cell viability of the Ha1 formulation in ‘pesta’ were higher when stored at 4°C than at (25±2)°C. These results indicated that S. marcescens Ha1 can potentially be used as a biocontrol agent against D. sanguinalis.