Genetic diversity of durum wheat landraces is a powerful tool for the introgression of novel resistance sources to Septoria tritici blotch disease (STB) in commercial breeding programs. STB caused by Zymoseptoria tritici, is one of the most universal and significant disease of wheat in the Mediterranean region where disease incidence could be higher under minimum tillage practices and where crop residue provides higher levels of inoculum.The high level of genotypic diversity in Z. tritici also indicates that sexual spores -ascospores- produced during the course of a season could provide secondary as well as primary inoculum. With the high genetic variability of the pathogen, it seems likely that most resistance genes will not last long so there will be a continual need to identify new strategies for effective disease management. In this study a collection of 1450 accessions from USAID core collection from seven Mediterranean countries were assessed for their respective resistance at seedling and adult growth stages. The collections included accessions from Algeria (202), France (68), Italy (165), Morocco (174); Portugal (352), Spain (160), and Tunisia (329). Six classes were identified, class I includes accessions that show resistance at seedling and adult growth stages whereas class VI has accessions that are susceptible as both growth stages. Other resistance combinations classified as II to V classes will be illustrated. Durum wheat landrace accessions within each class could carry novel seedling and adult plant resistance genes to STB that can be exploited on various breeding strategies.