Evaluation of sunflower cultivars and hybrids for their resistance to Plasmopara halstedii in west-Azarbaijan, Iran

Sunflower downy mildew is one of the most important and destructive diseases of this crop in West-Azarbaijan. The disease causes epidemic damages and yield losses at favorite environmental conditions for the pathogen activity. Application of disease resistant cultivars is considered as one of the effective control methods. During the growing season of 2009 in West-Azarbaijan, infected sunflower plants were collected and used as a source of Plasmopara halstedii for inoculation of standard differential lines to identify the variation of pathogenicity. The resistance of seven open-pollinating cultivars and two hybrids of sunflower to the dominant race (race 100) of P. halstedii, was evaluated employing the whole seedling immersion (WSI) method in the greenhouse. In this investigation, nine macroscopic disease symptoms including damping-off, sporulation on cotyledons and leaves, sporulation on leaves, stunting, sporulation on cotyledons, mosaic on leaves, deformation of leaves, lesion on hypocotyls and root reduction on the inoculated plants were considered for disease rating and calculating the disease severity index (D.S.I). The experiment was conducted in three replications for each cultivar. The analysis of variance (ANOVA) was performed and the means were compared using Duncan multiple range test (P = 0.05) in SAS ver. 9.1 (SAS institute Inc., Cary, NC.). According to the analysis of variance (ANOVA) for disease severity index, cultivars and hybrids were classified into five significantly different groups (P< 0.05): resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible. Cultivars Lakumka and Master were in the same group as resistant cultivars, whereas Record was highly susceptible.