Blackspot in sunflower sowings in the European part of the Russian Federation

The results on blackspot ( Alternariaster helianthi ) prevalence in sunflower crops in the major regions of this crop cultivation on the European part of the Russian Federation for 2005, 2008-2012 are presented. Prevalence and prevalence rate of the disease were estimated by VNIIMK’s method. The disease was found in all regions, but its prevalence rate was low, not affected economically significant sunflower crops. The new symptoms of the blackspot in newly emerged outbreaks of disease are described. An isolation of a pathogen from sunflower infected tissues followed by obtaining a pure culture was carried out under laboratory conditions on potato-glucose agar (PGA). The pathogen was identified by the Pi-doplichko’s guide (1977). A source of blackspot was registered in the Tambov region in 2015 on the sunflower field over 100 hectares and it caused a massive plant death due to fracture of hollow stems. The disease and following death of sunflower was provoked by non-compliance with agricultural technology, in particular case, the applying of high doses of nitrogen fertilizers during planting. Overdose of nitrogen causes active longitudinal cell growth in sunflower and thinning of the walls, which promotes to easier infection by the pathogens of plant tissues, in this case - a hundred percent infestation by the pathogen of high dangerous disease, fungus Alternariaster helianthi (Hansf.) Pidopl. Earlier blackspot symptoms were detected only in superficial tissues of sunflower plants. In above-mentioned case, the symptoms of the disease and the pathogen were found in the tissues of the sunflower stalk pith. The disease caused structural failure of the mechanical tissues of the stem that furthered stem fracture in combination with other factors.