Bacillus velezensis BVE7 as a promising agent for biocontrol of soybean root rot caused by Fusarium oxysporum

Abstract

Introduction: Soybean root rot (SRR), caused by Fusarium oxysporum, is a severe soil-borne disease in soybean production worldwide, which adversely impacts the yield and quality of soybean. The most effective method for managing crop soil-borne diseases and decreasing reliance on chemical fungicides, such as Bacillus spp., is via microbial biocontrol agents.

Methods and results: In this study, a soil-isolated strain BVE7 was identified as B. velezensis, exhibiting broad-spectrum activity against various pathogens causing soybean root rot. BVE7 sterile filtrate, at a concentration of 10%, demonstrated significant antifungal activity by inhibiting the conidial germination, production, and mycelial growth of F. oxysporum by 61.11%, 73.44%, and 85.42%, respectively, causing hyphal malformations. The antifungal compound produced by BVE7 demonstrated adaptability to a standard environment. The pot experiment showed that BVE7 suspension could effectively control soybean root rot, with the highest control efficiency of 75.13%. Furthermore, it considerably enhanced the activity of catalase, phenylalanine ammonia lyase, superoxide dismutase, and peroxidase in soybean roots, while also preventing an increase in malondialdehyde activity. By improving the host resistance towards pathogens, the damage caused by fungi and the severity of soybean root rot have been reduced.

Discussion: This study presents the innovative utilization of B. velezensis, isolated from soybean roots in cold conditions, for effectively controlling soybean root rot caused by F. oxysporum. The findings highlight the remarkable regional and adaptive characteristics of this strain, making it an excellent candidate for combating soybean root rot in diverse environments. In conclusion, B. velezensis BVE7 demonstrated potential in effectively reducing SRR incidence and can be considered as a viable option for SRR management.

Keywords: Bacillus velezensis; antifungal activities; biological control; growth-promoting effects; soybean root rot.

Figure 1

Antagonistic effect of biological bacteria BVE7 on the mycelial growth of pathogenic fungi on the fifth day after inoculation. 1. Diaporthe longicolla; 2. Clonostachys rosea; 3. Bipolaris zeicola; 4. Chaetomium globosum; 5. Botrytis cinerea; 6. Fusarium acuminatum; 7. F. Solani; 8. F. tricinctum; 9. F. chlamydosporum; 10. F. verticillioides.

Figure 2

Scanning electron micrograph depicting the cellular morphology of Bacillus velezensis BVE7 cultivated for 24 h at 30°C on nutrient agar medium.

Figure 3

Phylogenetic tree depicting the identification of Bacillus velezensis isolate BVE7 based on 16S rRNA gene sequencing. The bootstrap values on the branching nodes were calculated on 1,000 replications.

Figure 4

Effect of BVE7 filtrate on conidial germination, production and mycelial growth of Fusarium oxysporum. BVE7 filtrate was applied at concentrations of 1, 5, and 10%. Error bars indicate standard errors of the mean of two repeated experiments. Different letters above the bars indicate a significant difference within each group (i.e., conidial germination, conidial production, and mycelial growth) as determined by Duncan’s multiple range test (p < 0.05).

Figure 5

Effect of sterile fermented broth from BVE7 on Fusarium oxysporum mycelial growth on the fifth day after inoculation.

Figure 6

Effect of BVE7 filtrate on the mycelial morphology of Fusarium oxysporum (at a magnification of 400x). (A), Non-treated control; (B–D) denote different concentrations (1, 5 and 10%, respectively) of treatment.

Figure 7

Stability of antifungal compounds in BVE7 under varied temperature regimes (A), pH values (B), and durations of ultraviolet exposure (C). Error bars indicate standard errors of the means of two repeated experiments. CK was not exposed to UV. Different letters above the bars indicate significant difference within each treatment group (i.e., temperature, pH value, and ultraviolet treatment time) according to Duncan’s multiple range test (p < 0.05).

Figure 8

Effect of BVE7 on (A), catalase (CAT), (B), superoxide dismutase (SOD), (C), phenylalanine ammonia-lyase (PAL), (D), peroxidase (POD), (E), malondialdehyde (MDA). Two treatments with 3 replicates were included: i, 3 mL of sterile water as a control; ii, 1.5 mL suspension (1 × 10⁸ CFU/mL) of BVE7/each plant. Error bars indicate standard errors of the means of two repeated experiments. Different letters above the bars indicate significant differences (p < 0.05).