Isolation of the Endophytic Fungus Aspergillus terreus from a Halophyte (Tetraena qatarensis) and Assessment of Its Potential in Tomato Seedling Protection

Living in diverse environmentally harsh conditions, the plant exhibits a unique survival mechanism. As a result, the endophytes residing within the plant produce specific compounds that promote the plant's growth and defend it against pathogens. Plants and algae symbiotically harbor endophytes, i.e., microbes and microorganisms living within them. The objective of this study is to isolate endophytic fungi, specifically strains of <i>Aspergillus terreus,</i> from the leaves of the salt-tolerant plant <i>Tetraena qatarensis</i> and to explore the salt tolerance, antagonistic activity, and growth promotion properties. Strain C <i>A. terreus</i> (ON117337.1) was screened for salt tolerance and antagonistic effects. Regarding salt tolerance, the isolate demonstrated the ability to thrive in a concentration of up to 10% NaCl. <i>A. terreus</i> showed inhibitory activity against four fungal phytopathogens, namely <i>Fusarium oxysporum, Alternaria alternata</i>, <i>Colletotrichum gloeosporioides,</i> and <i>Botrytis cinerea.</i> The GC-MS investigation of the fungal (strain C <i>Aspergillus terreus</i>) extract showed the presence of about 66 compounds (secondary metabolites). Secondary metabolites (SMs) are produced, like Hexadecanoic acid, which aids in controlling phytopathogens. Also produced is lovastatin, which is used to treat hypercholesterolemia. Strain C, which showed salinity tolerance and the highest inhibitory activity, was further analyzed for its effect on tomato seed germination under pathogen stress from <i>Fusarium oxysporum</i>. The greenhouse experiment indicated that the fungi increased the length of tomato seedlings and the plant biomass. Therefore, the selected endophytes derived from <i>Tetraena qatarensis</i> were scrutinized for their potential as biocontrol agents, aiming to thwart fungal pathogens and stimulate plant growth. The in vitro and in vivo assessments of strain C (<i>Aspergillus terreus</i>) against <i>Fusarium oxysporum</i> in this investigation indicate the promising role of endophytes as effective biological control agents. Investigating novel bio-products offers a sustainable approach to agriculture, gradually reducing dependence on chemical fungicides.