evaluation of resistance six potato genotypes to early blight disease caused by the pathogenic fungus alternaria tenuissima and alternaria allternata under in vitro and greenhouse conditions

in order to determine the resistance levels and the most suitable potato genotypes to the early blight, an experiment was conducted in a completely randomized factorial design with three replications, in national plant gene bank of iran during 2007-2008. factors included pathogenic fungus, a. tenuissima and a. alternata and six potato genotypes, picasso, marfona, delta, agria, cosmos and armida. analysis of variance, in vitro and greenhouse evaluation showed that there were significant between pathogen, genotype and their interactions. in vitro evaluation, symptoms appeared after the second day and continued until the sixth day. based on area under the disease progress curve for pathogenic a. alternata, cosmos genotype had a lower level of agria (susceptible control), while picasso and marfona with delta (resistant control) were resistant patients.with the pathogenic a. tenuissima, cosmos was sensitive, and only picasso was resistant patient.the method greenhouse, symptoms began on the third day and it lasted until the twentieth day. in this evaluation, using both fungal isolates, cosmos was sensitive level and picasso was resistant level. in vitro and greenhouse assessment, armida not show any signs of disease, it may be referred to as a genotype-immune disease, after field testing. since, the results of the assessment of resistance was generally similar in both in vitro and greenhouse conditions, it can be argued that this study is validated by classifying genotypes to resistant and susceptible.