Abstract
Potent bacterial strains effective against the whitefly, Bemisia tabaci, nymphs (second instar), were isolated from tomato cultivated fields at Fayoum governorate, Giza, Egypt. Of 72 isolates, 12 with the most morphologically distinct-looking bacterial colonies were selected and named A1, A2, A3, A6, A7, A9, A12, A13, A107, B37, B45 and B100. All isolates were preliminarily identified as members of the genus Bacillus based on morphological, physiological and biochemical characteristics. When tested for their pathogenicity against Bemisia tabaci, the 12 isolates revealed varying efficiencies with isolates A1 and A9 being superior, exhibiting maximum mortality of 92.2 and 90.8% on day 10, respectively. Isolate A7 recorded the lowest percentage at 18.3%. Further genetic characterization of the 12 isolates was performed using inter simple sequence repeat (ISSR), randomly amplified polymorphic DNA (RAPD) and 16S rDNA gene sequencing analysis. RAPD and ISSR results confirmed each other. The combined ISSR and RAPD phylogenetic tree showed two major clusters. With 16S rRNA gene analysis, isolate A1 and A12 sequences recorded 100% identity with Bacillus thuringiensis, while isolates A7 and B100 showed 95.7% and 95.6% identity with Bacillus cereus and Bacillus sphaericus, respectively.