الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
This study aimed to :
• The use of microbes for disease control is a fast expanding area of plant protection with great potential to replace the chemical control measures now prevalent. Bacillus thuringiensis (Bt) has been widely used as a biological pesticide. The Egyptian isolate of Bt (BtaC18) is an industrial strain used for commercial production of the first Egyptian biopesticide, it suffers from phage infection and huge economic loss. Generally, bacteriophage infection constitutes a major problem for large-scale commercial production of Bt-based biopesticides worldwide. This leads to large economic losses in terms of high production cost and prices for consumers. Therefore, assessment of the genetic diversity among the phage isolates, represent a step forward in controlling the economic damage to the biopesticide industry. Examination of the transmission electron micrographs shows the five phages fell into three morphological types. TPaC18-01 was fairly small phage with hexagonal head of 103.33 nm diameters. TPaC18-02 showed that isometric head of 111.11 nm with a long non-contractile, flexible tail of 388.88 nm length and 17.7 nm wide. TPaC18-03 appear to be similar TPaC18-02 morphologically with dimensions 113.04 nm for head and 188.5 nm X 8.3 nm for tail. These results allowed assignment of TPaC18-01, TPaC18-02 and TPaC18-03 to the Siphoviridae family or Bradley’s group B1, in the order Caudovirales. On the other hand, the rest two phages were differ; where The TPaC18-04 showed a rigid polyhedral protein capsid (93.3 nm) surrounded with tail like tube, while TPaC18-05 was observed as rounded head of 80.0 nm and short non-contractile tail of 53.3 nm X 20.0 nm. This implied that the phages belong to families Tectiviridae (Bradley’s group D4) and Podoviridae or Bradley’s group C1, respectively.The generated tree showed two distinct groups, the first included two viruses (TPaC18-01 and TPaC18-05) while the second group included the other two viruses (TPaC18-04 and TPaC18-03).Alignment of the nucleotide sequences of TPaC18-01 with TPaC18-05, the two phages of group A showing 73.9% Identity (458/620), 73.9% Similarity (458/620) and 10.8% Gaps (67/620).While, alignment of the nucleotide sequences of TPaC18-03 with TPaC18-04, the two phages of group B showing 66.1% Identity (381/576), 66.1% Similarity (381/576) and 2.3 % Gaps (13/576). Keywords: (not more than ten): Bacteriophages, Bacillus thuringiensis, Morphological and genetic diversity ,Nucleotide sequence.