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<i>Verticillium dahliae</i> is a soil-borne plant pathogenic fungus that causes Verticillium wilt on hundreds of dicotyledonous plant species. <i>V. dahliae</i> is considered an asexually (clonal) reproducing fungus, although both mating type idiomorphs (<i>MAT1-1</i> and <i>MAT1-2</i>) are present, and is heterothallic. Most of the available information on <i>V. dahliae</i> strains, including their biology, pathology, and genomics comes from studies on isolates with the <i>MAT1-2</i> idiomorph, and thus little information is available on the <i>MAT1-1 V. dahliae</i> strains in the literature. We therefore evaluated the growth responses of <i>MAT1-1</i> and <i>MAT1-2</i> <i>V. dahliae</i> strains to various stimuli. Growth rates and melanin production in response to increased temperature, alkaline pH, light, and H₂O₂ stress were higher in the <i>MAT1-2</i> strains than in the <i>MAT1-1</i> strains. In addition, the <i>MAT1-2</i> strains showed an enhanced ability to degrade complex polysaccharides, especially starch, pectin, and cellulose. Furthermore, several <i>MAT1-2</i> strains from both potato and sunflower showed increased virulence on their original hosts, relative to their <i>MAT1-1</i> counterparts. Thus, compared to <i>MAT1-1</i> strains, <i>MAT1-2</i> strains derive their potentially greater fitness from an increased capacity to adapt to their environment and exhibit higher virulence. These competitive advantages might explain the current abundance of <i>MAT1-2</i> strains relative to <i>MAT1-1</i> strains in the agricultural and sylvicultural ecosystems, and this study provides the baseline information on the two mating idiomorphs to study sexual reproduction in <i>V. dahliae</i> under natural and laboratory conditions.