Characterization and potential antifungal activities of three Streptomyces spp. as biocontrol agents against Sclerotinia sclerotiorum (Lib.) de Bary infecting green bean

Abstract

Background White mold disease, caused by Sclerotinia sclerotiorum the devastating pathogen, attacks green beans (Phaseolus vulgaris L.) and several crops worldwide. The present investigation was carried out to introduce some antagonistic microorganisms as novel antifungal substances to be an alternative and secure method to effectively control the disease. Results Three Streptomyces species, i.e., S. griseus (MT210913 “DG5”), S. rochei (MN700192 “DG4”), and S. sampsonii (MN700191 “DG1”) were isolated, biologically, molecularly characterized, and evaluated in vitro and in vivo. Molecularly, polymerase chain reaction (PCR) amplification and nucleotide sequencing were used to characterize the pathogen and bio-agents. PCR amplification of the pathogen and Streptomyces species (bioagents) exhibited amplicons of around 535 bp and 1300 bp, respectively. The nucleotide sequence analysis of the three Streptomyces spp. indicated that S. rochei was closely related to S. griseus, and both had a distance relationship with S. sampsonii. The evaluation of bioagents was carried out against S. sclerotiorum. Reduction percentages in the mycelial growth of the pathogen ranged between 60.17 and 52.30%, indicating that S. rochie gave the highest inhibition percent. Incorporations of Streptomyces spp. culture filtrate components into culture media proved that S. sampsonii was more efficient as a bioagent in reducing mycelial growth pathogen by 84.50%. The effectiveness of the bioagent volatile compounds inhibited the pathogen growth at a rate of 54.50-72.54%, respectively, revealing that S. rochei was the highest inhibitor followed by S. griseus. The parasitic activity of Streptomyces spp. upon S. sclerotiorum showed deformation, contraction, and collapse when observed by light and scanning electron microscopy. Molecular characterization of the 3 Streptomyces spp. revealed that S. griseus was closely related to S. sampsonii (96%), secondly ranked by S. rochei (93.1%). Viability and germination of pathogen sclerotia were reduced when they dipped into the Streptomyces spore suspensions for 10, 20, and 30 days. Application of the 3 Streptomyces spp. in the field proved a great potential to control the disease. Conclusions The results suggested that the 3 Streptomyces strains and their secondary metabolites can be potential biocontrol agents and biofertilizers for controlling S. sclerotiorum, the causative agent of bean white mold disease.

Characterization of Promising Antifungal Bioactive Compounds from Endophytic Actinobacterium, Streptomyces rochei OM182844

“…The study findings using, Strep. rochei strain SM3 that suppressed the growth of S. sclerotiorum and its resulting disease progression was consistent with (Gebily et al, 2021) report. Kanini et al (2013) found that 39 out of 528 Streptomyces isolates appeared their antifungal activity against the growth of F. oxysporum f.sp.…”

Actinomycete Potential as Biocontrol Agent of Phytopathogenic Fungi: Mechanisms, Source, and Applications

“…These organic compounds travel great distances in structurally heterogeneous environments, as well as in solid, liquid, or gaseous compounds [ 31 ]. VOCs produced by actinomycetes inhibit the growth of phytopathogenic fungi, promote plant growth, possess nematocidal activity, and induce systemic resistance in plants [ 11 , 12 ]. They inhibit the mycelia, causing swelling, conidia collapse, and structural alterations in the fungal cell wall [ 53 ].…”

“…The main antagonistic mechanisms of actinomycetes to control phytopathogenic fungi are competence for space and nutrients [ 8 ], antibiotics [ 9 ], siderophores [ 10 ], lytic enzymes [ 11 ], volatile organic compounds (VOCs) [ 12 ], and host resistance induction [ 13 ]. Additionally, actinomycetes promote plant growth and development through the synthesis of phytohormones, atmospheric nitrogen fixation, and mineral solubilization, among others [ 14 ].…”

Unraveling the tripartite interaction of volatile compounds of Streptomyces rochei with grain mold pathogens infecting sorghum

“…Another supporting evidence was that the antagonist S. rochei was able to produce secondary metabolites that could penetrate and destroy the hyphae and cause lysis of S. sclerotiorum and Pythium sp. ( Arora et al, 2021 ; Gebily et al, 2021 ).…”