5508
Moustafa Mohamed Abd El Hady Zohair
Biochemical Studies On Bioactive Products From Soil Fungi
Aspergillus pseudocaelatus, Trichoderma gamsii, Mycoparasitism, VOC, Biocontrol, Phytopathogenic Fungi, Antioxidant and Secondary Metabolites
The objectives of this thesis were to isolate, screen and select the most active fungal isolates from the rhizosphere of the medicinal plants Basil, (Ocimum basilicum), Peppermint (Mentha piperita) and (Aloe vera) and evaluate their efficacy to introduce a promising solution in biological control applications. Also using agro-industrial wastes as solid support, carbon source in solid-state fermentation processes for the production of value-added compounds such as antioxidant and antimicrobial agents. Among the collection of 104 fungal isolates, 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. Chemical investigation of extracts of A. pseudocaelatus, T. gamsii strains and mixed culture of them was analyzed using GC/MS analysis of volatile organic compounds (VOCs), preliminary metabolomic profile analysis by LC/MS. Biological investigation on the ethyl acetate extract of A. pseudocaelatus MG772677 and T. gamsii KX685665 strains 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 and T. gamsii, displayed antagonistic activities against the pathogenic fungi and presented appreciable biocontrol efficacy. The profile of produced volatiles from mixed culture was obviously different of independent culture of the strains. A total of 21 volatile compounds were included. Neither microbes produced these compounds when cultured alone, and the amounts of VOCs were greater than those in the independent culture of each isolate. Chemical investigation of the active secondary metabolites led to isolation of compound 1 which was identified as ergosterol. Compared to the fungal monoculture, co-cultivation of both of the A. pseudocaelatus and T. gamsii showed a strong antifungal activity against F. solani, R. solani, S. rolfsii and V. dahliae with inhibition zones 22.5, 11.5, 18.5 and 15.0 mm diameter, respectively. Utilization of different agricultural wastes in SSF resulted in higher inhibitory activity of ethyl acetate extract of A. pseudocaelatus on media containing a sorghum as natural alternative carbon sources against the tested microorganism than using PDA media. Also, the same finding was found in antioxidant activity.
2018
M.Sc
Cairo
Agriculture