Potato is a plant that can be influenced by early blight disease. Early blight is one of the most destructive plant diseases, especially in the members of solanaceae family. This disease can reduce yield. Experiment design was a factorial randomized complete design to evaluate the isolate pathogenic Alternaria solani in National Plant Gene Bank of Iran, during 2008Iran, during -2009. This experiment was conducted with three replications, and the factors include test methods and three lines 9506, 10908-05 and 10908-18 with genotypes of Agria, Casmos and Desiree (susceptible) and Delta (resistant control). Analysis of variance table was based on the area under the disease progress curve, indicating the effects of the experimental methods; genotype and their interactions are significant at the 1% level. In greenhouse evaluation, the symptoms appeared on, the first day. In this method the area under the curve progression was noted in 10 times, but in vitro method, the symptoms of this evaluation appeared on the first or second day. The Evaluation was carried out after inoculation, and was noted 6 times. The results indicate that genotypes and lines are located in four different groups. In this case, line 9506 and Cosmos were quite sensitive to the surface, and Desiree, is located in a sensitive area. Line 10908-18 and Agria, located approximately at the level of resistance, and line 10908-05 and Delta, have been resistant surface.