Differences pathogenicity of the fungus Cercospora beticola Sacc. caused cercospora leaf spot disease in sugarbeets and evaluation of sugarbeet cultivars resistance to the disease

Cercospora leaf spot disease caused by Cercospora beticola Sacc. is considered to be the most destructive foliar pathogen of sugarbeet which result in highest loss of yield and quality of sugarbeet in warm and humid environments. Control of these fungi often has been unsuccessful by the use of pesticides application; hence, the best method for disease control is the production and implementation of resistant likely cultivars. For this purpose, fungal isolates collected from south and north areas of Iran, Purification and Pathogenicity of isolate the genotype (191), susceptible to disease with spore suspension was implemented on leaves in greenhouse Then for characterizing isolates virulence, like pathogenicity method was performed inoculation of the fungus C. beticola on susceptible (191). The disease severity index after the appearance of disease symptoms, 35 days after sporulating was done by KSW method. Cultivars response assessment, 30 cultivars of sugarbeet to leaf spots in Gharakheyl research station under field conditions was conducted on completely random block design with three replications. Statistics from the infection severity were taken in June and July with an interval of one month. Also for evaluation of genotypes resistance of detached leaf disks in laboratory conditions in sterile environment, 1.8 cm diameter discs were prepared from the leaves of mentioned genotypes and laid on water agar rectangular plates and with spore suspension were sporulated . A total of sampling were obtained 18 isolates of pure C. beticola from different areas that all of them were high virulence, Although in terms of the disease severity were different, but the differences placed in the quantity range between 77.7-98.9 percent. In response Study of 30 genotypes of sugarbeet to causal agent in field conditions, the best time recording of disease severity is done from Gharakhey Ghaemshahr in favorable climatic mid June to late July. In this study, only 5 genotype: 32333, 32335, 32295, 32304 and 32319 showed response moderately susceptible "MS" and the rest of the group were susceptible "S" or very susceptible "VS". It was also determined a high correlation (91%) between assessment of detached leaf disks resistance in laboratory and field conditions as well as these two methods can replace each other