In a previous study, the endophytic Bacillus velezensis NC318 was isolated from the rhizosphere of date palm and showed strong antifungal activity against the soil-borne plant pathogenic fungus, Sclerotium rolfsii Sacc, the causal agent of Southern blight. The potential of the Bacillus genus in the inhibition of plant pathogens is mainly due to the production of certain bioactive compounds. In the present study, secondary metabolites extracted from the cell-free supernatant of strain NC318 showed strong antifungal activity on the mycelial growth and germination of S. rolfsii sclerotia in vitro. With 50 μl of bioactive compounds crude extracts, the mycelial growth inhibition rate was 97% and any germination of sclerotia was reported. Chemical analysis of the secondary metabolite crude extracts performed by high performance liquid chromatography coupled with mass spectrometry (HPLC/MS), revealed that the secreted bioactive compounds belonged to the family of lipopeptides (iturin, fengycin, surfactin), polyketides (bacillaene, macrolactin, difficidin and bacilysin) and siderophores (bacillibactin). These results provide a better understanding of the biocontrol mechanism of the bacteria strain B. velezensis NC318 against the soil fungal pathogens, especially S. rolfsii root rot.

In this study Trichoderma harzianum strain A was isolated from the rhizosphere of an argan tree in southern Morocco. Trichoderma harzianum strain A had previously demonstrated a high antagonistic potential in vitro by direct confrontation and in vivo on wheat plants in pots under greenhouse conditions against Zymoseptoria tritici, the agent of septoria leaf blotch. In this study, the activity of filtrates prepared from the liquid culture of T. harzianum A alone and from the confrontation medium with two Z. tritici strains [G1-1 (durum wheat) and A5-1 (soft wheat)] on the inhibition of Z. tritici pycnidiospore germination was studied by nephelometry. The results of the antibiosis assay revealed that filtrate 0 (A in confrontation with G1-1) and F3 (A against A5-1) showed 95% of G1-1 and A5-1 pycnidiospore inhibition at 9/10 dilution of the undiluted filtrates after 4 days of incubation. To understand and explain the antifungal activity of these filtrates, the extraction and identification of secondary molecules of peptaibiotic nature secreted by T. harzianum A in the three studied filtrates were performed. According to the results of high-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses, 38 peptaibiotic molecules reported in the literature for their antifungal activity were identified in the different extracts at high concentrations (high peak intensities). These molecules are divided into nine groups, namely: Trichocryptin, Trichobrevin, Triochocryptin, Hypocompactin, Hyporodicin, Trichocompactin, Alamethicine, Trichoferin, and Trichokonin. It was also shown that the presence of the pathogen induces the production of peptaibols by the antagonistic strain of Trichoderma.