Biocontrol potential of Pseudomonas fluorescens against root rot complex in black gram

Abstract:

A single hectare of black gram in Mediterranean cropping systems can lose up to 40 percent of its stand to root rot complex—a consortium of soil-borne fungi including Macrophomina phaseolina, Rhizoctonia solani, and Fusarium solani—before the crop even reaches flowering. Chemical seed treatments offer partial protection but raise concerns about residue persistence and non-target effects on beneficial soil microorganisms. This research evaluated three native strains of Pseudomonas fluorescens (Pf-BG01, Pf-BG02, Pf-BG03) isolated from healthy black gram rhizospheres in Piedmont, Italy, for their biocontrol potential against the root rot complex. In vitro dual-culture assays showed that Pf-BG03 inhibited mycelial growth of M. phaseolina, R. solani, and F. solani by 82.6, 74.8, and 69.3 percent, respectively. All three strains produced siderophores, hydrogen cyanide, and indole-3-acetic acid. In pot and field trials at Collegio di Agricoltura del Piemonte, Turin, during 2022-23, seed treatment with Pf-BG03 (10⁸ CFU mL⁻¹) reduced root rot incidence by 76.4 percent and increased grain yield by 34.7 percent over the inoculated control. The seedling vigor index under Pf-BG03 reached 1,284, compared with 687 in the pathogen-only control. Combining Pf-BG03 with Trichoderma viride gave marginally better results but the difference was not statistically significant over Pf-BG03 alone. These findings position Pf-BG03 as a promising biocontrol agent for managing root rot complex in black gram under European growing conditions.