Evaluation of resistance of sunflower genotypes to downy mildew caused by Plasmopara halstedii.
2010
Rahman Pur, Siyamak | Nabi Pur, Ali Reza | Ali Zadeh, Bahram
Sunflower downy mildew caused by Plasmopara halstedii, is one of the most important diseases in most areas of the crop production areas. The use of resistant varieties and hybrids is an effective method to avoid its damage. Based on existence of a dominant race (race 100) of the pathogen in sunflower planting areas, 215 new Iranian sunflower genotypes including hybrids, restorer lines, CMS lines and individuals were evaluated to the disease under controlled conditions. Employing whole seedling immersion method with some modifications, three-day-old seedlings were immersed in zoosporangium suspension to be inoculated and then incubated at greenhouse for two weeks. Six qualitative disease characteristics including damping-off, sporulation on cotyledons, sporulation on leaves and cotyledons, stunt, leaf mosaic or chlorosis and deformation were recorded and converted to quantitative means based on their importance in disease development. Finally the average of the means as disease severity index (DSI) was used for evaluations. The all tested hybrids showed significantly resistance against the downy mildew. Furthermore, their related restorer lines have been tested and demonstrated resistance reaction in the experiments. Totally, 70 genotypes were categorized as resistant, 6 as semi-resistant, 4 as semi-susceptible, 36 as susceptible, and 75 as highly susceptible.
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