New races of sunflower downy mildew (Plasmopara halstedii) in Germany.
P. halstedii, causal agent of downy mildew of cultivated sunflower, was reported in Germany for the first time in commercial fields. The pathogen was first observed in the Württemberg area, where races 1 and 4 were identified using a set of differential lines. Later, commercial fields near Baden were found to be infected by race 5, which is thought to be the first occurrence of that race outside North America. With the discovery of race 5, there are now 8 races of P. halstedii which have been found in Europe. The sunflower cultivars most frequently grown in Germany were investigated for resistance to races 1, 4 and 5. All cultivars were resistant to race 1 and none was resistant to either race 4 or 5.