Promising biocontrol agents isolated from medicinal plants rhizosphere against root-rot fungi

Among of the collection of 104 fungal isolates from the rhizosphere of the medicinal plants basil (Ocimum basilicum), peppermint (Mentha piperita) and (Aloe vera), 59 of them were assessed for in vitro antagonistic activity against phytopathogenic fungi; Fusarium solani, Rhizocotina solani, Sclerotium rolfsii and Verticillium dahliae. The most active antagonistic isolates were identified using molecular tools based on 18S rDNA. The sequence data of Aspergillus pseudocaelatus and Trichoderma gamsii have been submitted to GenBank given the accession no. MG772677 & KX685665, respectively. The antagonistic mechanisms were evaluated using confrontation method and scanning electron microscopy. The volatile organic compounds (VOCs) were analyzed using GC/MS. Biological investigation on the ethyl acetate extract of A. pseudocaelatus MG772677 and T. gamsii KX685665 isolates was evaluated. The greenhouse application with the selected isolates on basil seedlings was performed. In vitro antagonistic results indicated that the highest percentage of inhibition was observed with A. pseudocaelatus, 77.90% and T. gamsii, 77.98%. The average emergence rate in the treatments with T. gamsii and A. pseudocaelatus reached up to 100%, much more than that in the control (average 40%). The results indicated that A. pseudocaelatus MG772677 and T. gamsii KX685665, displayed antagonistic activities against the pathogenic fungi and presented appreciable biocontrol efficacy. Also the two isolates could enhance the plant growth and improve the seedlings' emergence.