The name Botrytis cinerea in fact hides a complex of species of which certain members are differentiated on the basis of host specificity and genome structure: certain strains carry several types of transposable elements whereas others are characterized by a total absence of them. The objective is to evaluate the role of transposable elements in the chromosome structure of these two types of strains. Two BAC libraries have been constructed for the K1 strain which lacks transposable elements, and two other libraries have been produced from the T4 strain, in which three families of transposable elements have already been identified. Sequencing of the ends of these BACs should allow the assembly of some of them into "contigs" and then to compare the chromosomal organization of the two strains.