The purpose of this study was to identify and characterize the D. solani genes that are differentially expressed in the early stages of infection of S. tuberosum (model for primary crop host) and S. dulcamara (model plant for alternative non-crop host) by a process of a random mutagenesis of D. solani IPO2222 genome using Tn5 transposon and a promotorless gusA reported gene. This was done as an initial step to better understand the mechanisms used by D. solani to colonize (primary and alternative) plant hosts. The aim of this study was also to associate the identified bacterial genes with phenotypes including ecological fitness and virulence in host plants. The implications of the findings are discussed.