Suppression of Fusarium Wilt in Watermelon by Bacillus amyloliquefaciens DHA55 through Extracellular Production of Antifungal Lipopeptides

Abstract

Fusarium wilt caused by Fusarium oxysporum f. sp. niveum is one of the most devastating fungal diseases affecting watermelon (Citrullus lanatus L.). The present study aimed to identify potent antagonistic bacterial strains with substantial antifungal activity against F. oxysporum f. sp. niveum and to explore their potential for biocontrol of Fusarium wilt in watermelon. Out of 77 isolates from watermelon rhizosphere, six bacterial strains—namely, DHA4, DHA6, DHA10, DHA12, DHA41, and DHA55—exhibited significant antifungal activity against F. oxysporum f. sp. niveum, as well as other phytopathogenic fungi, including Didymella bryoniae, Sclerotinia sclerotiorum, Fusarium graminearum, and Rhizoctonia solani. These Gram-positive, rod-shaped, antagonistic bacterial strains were able to produce exo-enzymes (e.g., catalase, protease, and cellulase), siderophore, and indole-3-acetic acid and had the ability to solubilize phosphate. In greenhouse experiments, these antagonistic bacterial strains not only promoted plant growth but also suppressed Fusarium wilt in watermelon. Among these strains, DHA55 was the most effective, achieving the highest disease suppression of 74.9%. Strain DHA55 was identified as Bacillus amyloliquefaciens based on physiological, biochemical, and molecular characterization. B. amyloliquefaciens DHA55 produced various antifungal lipopeptides, including iturin, surfactin, and fengycin, that showed significant antifungal activities against F. oxysporum f. sp. niveum. Microscopic observations revealed that B. amyloliquefaciens DHA55 exhibited an inhibitory effect against F. oxysporum f. sp. niveum on the root surface of watermelon plants. These results demonstrate that B. amyloliquefaciens DHA55 can effectively promote plant growth and suppress the development of watermelon Fusarium wilt, providing a promising agent for the biocontrol of Fusarium wilt in watermelon.

Bacillus amyloliquefaciens: Harnessing Its Potential for Industrial, Medical, and Agricultural Applications—A Comprehensive Review

“…The study identified 2-nonanone and 2-heptanone as the most potent antifungal VOCs, with acetoin and 2,3-butanediol acting as growth promoters in a dose-dependent manner [ 41 ]. Additionally, Al-Mutar et al (2023) reported that B. amyloliquefaciens DHA55 displayed antifungal activity against Fon and other phytopathogenic fungi, mediated by the production of lipopeptides such as iturin, surfactin, and fungycin [ 63 ].…”

Lipopeptide C17 Fengycin B Exhibits a Novel Antifungal Mechanism by Triggering Metacaspase-Dependent Apoptosis in Fusarium oxysporum

“…Therefore, the academic community has now turned to biological control methods, and some members of the Bacillus genus have been developed and found to be effective in controlling Fusarium wilt. Therefore, they have the potential to replace chemical fungicides to avoid their harmful effects . Previous reports have shown that the antifungal activity of Bacillus strains is mainly attributed to the secretion of bioactive lipopeptides, which have attracted great interest in the agricultural community due to their unique properties, including nontoxicity, stability, and broad-spectrum antimicrobial activities …”

“…Therefore, they have the potential to replace chemical fungicides to avoid their harmful effects. 2 Previous reports have shown that the antifungal activity of Bacillus strains is mainly attributed to the secretion of bioactive lipopeptides, which have attracted great interest in the agricultural community due to their unique properties, including nontoxicity, stability, and broad-spectrum antimicrobial activities. 3 Lipopeptides are synthesized by nonribosomal peptide synthetase pathways in Bacillus species and are classified into three main families of iturins, fengycins, and surfactins based on their structural features and sequence variations.…”

Genome and Transcriptome Analysis to Elucidate the Biocontrol Mechanism of Bacillus amyloliquefaciens XJ5 against Alternaria solani

“…These are known to inhibit the growth of fungi and bacteria or induce systemic resistance in host plants [11][12][13][14]. Polyketides and other antibiotics (bacilysin and bacteriocin) exhibit strong bactericidal activity against fungi, bacteria, and algae [15][16][17][18][19].…”