الفهرس 
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Abstract
The use of biological control agents for disease control is very important for plant protection against several diseases with great potential to replace of the chemical control agents which have many hazards on health and environment. Trichoderma genus is one of the best bio-agents for biological control, as it is effective against a wide variety of soil and foliar pathogens. However in field Trichoderma spp. suffer from mycovirus infection causing huge economic loss. Therefore, this investigation was designed to isolate, purify and characterize mycovirus (s) infecting Trichoderma spp. and to reveal the sequence analysis of mycoviral genome for determination the open reading frames and conserved motifs, which is a platform and a step forward in controlling the damage to biocontrol agents. Different research activities have been implemented according to standard approaches and integrated to fulfill the objective of the present thesis. In this study, a dsRNA element was found in one isolate of 17 isolates tested. A novel mycovirus was discovered in Trichoderma hamatum which was isolated from New Damietta, according to this report. This Trichoderma associated virus was described as a new unclassified mycovirus based on phylogenetic analysis of the complete amino acid sequence of its RdRp. ThaMV1 caused dramatic changes on its host such as decreasing in growth rate, absence of sporulation and pigmentation and therefore its role as a biocontrol agent.