Sporulation, pathogenicity and chemical control of Alternaria protenta, a new seedborne pathogen on sunflower

Alternaria protenta was detected from seeds of sunflower (Helianthus annuus) cv. Taiyo. This fungus sporulated abundantly on glucose-peptone agar (GPA) or Leonian agar (LA). The pathogenicity of A. protenta harvested from GPA or LA was significantly (P < 0.05) greater on seeds of sunflower cvv. Big Smile, Sun Bright and Pachino than the pathogenicity of conidia from dextrose-nitrate agar. The amount of inoculum affected the germination rate of cv. Taiyo but not for cvv. Big Smile and Sun Bright. Disease severity on seedlings of cvv. Big Smile, Sun Bright and Taiyo increased with the increasing concentration of spore suspension from 102 to 105 conidia/mL. Seeds of sunflower cv. Taiyo treated with 100 ppm difenconazole, prochloraz, pyrifenox or triadimenol produced significantly (P < 0.05) less diseased seedlings than untreated seeds. Additional keywords: oil crop, seed disease, seed treatment.