Antagonism of Bacillus velezensis Isolate from Anaerobically Digested Dairy Slurry against Fusarium Wilt of Spinach

This study was designed to assess the suppressive effects of various anaerobically digested slurries (ADSs), and the microorganisms inhabiting them, against Fusarium wilt in spinach. We used five different ADSs from a range of source materials (dairy cow manure, sewage sludge, food garbage, pig manure, night soil sludge), combined in different proportions. All five raw ADSs suppressed the growth of Fusarium oxysporum f. sp. spinaciae (Fos) on agar plates using a co-culture test. In contrast, filtrate ADSs did not suppress the growth of Fos. In total, 32 bacterial strains were isolated from five ADSs, and eight isolates showed antagonistic activities against Fos. Based on 16S rDNA sequences, the strain AD-3 isolated from ADS from dairy cow manure belonged to Bacillus velezensis. Genome analysis revealed that AD-3 had two kinds of genes related to the production of the non-ribosomal lipopeptides, fengycin/plipastatin (pps genes), and surfactin (srf genes). In pot assays, inoculation of AD-3 (1.0 x 10(6) CFU.g(-1) dry soil) into Fos-infected soil (1.0 x 10(5) bud-cells.g(-1) dry soil) significantly reduced the severity of Fusarium wilt disease at 28 d after seedling. The percentage reductions in disease severity in two replicates were 64.3% and 44.3%, respectively. Thus, bacterial strain AD-3 could be applied to reduce Fusarium wilt in spinach.