reaction of sugar beet cultivars to cercospora beticola isolates

twenty four isolates of cercospora beticola were collected from khuzestan, ardebil, golestan and mazandaran provinces and purified, and one isolate was used to represent each province. after optimization of spore production on different media, pathogenic variability of selected isolates on five sugar beet varieties with different levels of resistance was studied under green house condition. four month-old plants were inoculated by the pathogen on each plant, four mature leaves were tagged and each leaf was inoculated with one isolate. spore concentration was adjusted to 3 ×10 4 conidia/ml. the experiment was carried out on the basis of factorial random design with four replications (eight plants per replication). disease severity and incubation period were measured as investigated characters. the results showed that there was a significant difference among cultivars for both characteristics. puma and 191 were the most resistant and susceptible cultivars respectively. cercospora isolates had significant differences for disease severity and were categorized in two groups, while there was no difference for incubation period among the isolates. isolate×cultivar interaction led to no significant differences for both characters. it seems that reaction of cultivars to isolates is not different and in spite of variability among isolates of c. beticola, resistance in sugar beet to the fungus was effective against all iranian isolates.