One of the most fatal diseases that harm Allium species is purple blotch, which is brought on by Alternaria porri. As the disease's severity rises, crop production may decrease. In this study, 12 isolates of A.porri exhibiting purple blotch symptoms have been isolated from diseased onion plants. Sequencing of the internal transcribed spacer region (ITS) allowed for the identification of the isolate that was the most virulent and caused a disease severity of 85.93%. Under greenhouse and field growing conditions, the efficiency of two bio-agents, Trichoderma asperellum T34 and Saccharomyces cerevisiae AUMC 10203, as well as three doses (50, 25, and 12.5 ppm) of their green-synthesized silver nanoparticles (AgNPs) against purple blotch disease was assessed. For avoiding or treating purple blotch disease in onion plants, it has been demonstrated that the T.asperellum T34 spore suspension was the most effective resulting in a 76% reduction in disease severity. The spore suspension of S. cerevisiae and a 50-ppm dosage of AgNPs were the top contenders for T. asperellum. When compared to the control plants, the plants treated with bio-agents and AgNPs showed a significant decline in disease incidence and disease severity. Additionally, improvements were made to the broadness of inflorescences, the number of flowers and seeds, the weight of seeds per inflorescence, and the seed productivity.Therefore, it is recommended in this study to use T. asperellum T34 spore suspension as a potent bio-agent to manage the symptoms of purple blotch on onions.