Botrytis cinerea is an economically important pathogen. Twenty-seven B. cinerea isolates were characterized for their pathogenicity on strawberry fruits. A cheap and simple method was developed for the identification of Botrytis cinerea isolates, the cause of gray mould, using modified Kerssiesʼ selective medium (mKERS). The other fungal species could not grow on this medium. Moreover, there was no relation between the aggressiveness of each tested isolate of B. cinerea and its radial growth level on mKERS. The results showed that the 27 isolates of B. cinerea grew well and produced a dark brown pigment on mKERS. These results indicate that this simple method could be used for the detection of gray mould. Additionally, genetic diversity was investigated using PCR assay. The Egyptian population structure of B. cinerea was investigated by detecting the existence of two transposable elements (TEs): Flipper and Boty in the genome. Among 12 isolates tested, 10 have only one transposable element, Boty element, whereas 2 have neither of these elements (vacuma type). This result. is useful for identifying and classifying the Egyptian population of B. cinerea, especially for the isolates exhibited high virulence according to their genomic structure.