White rust is one of the most important diseases of horseradish caused by the fungus Albugo candida. The presence of the fungus without chemical control causes serious damage to the plantations of Hajdú-Bihar country. Chemical control can be more efficient or even omitted by planting resistant varieties. In the autumn of 2014, we studied the susceptibility of 20 horseradish varieties and breeds for Albugo candida. The experimental material was selected to represent the four morphological complexes, i.e. “magyar” (Hungarian), “dán” (Danish), “brassói” (Brasov) and “spreewaldi” (Spreewald). This way we could compare not only the varieties but also the different morphological complexes. Foliar infection was assessed on 10 randomly selected leaves in each variety. A 10×10 cm frame was placed on the leaf, then we counted and recorded the number of infection stains and their size. The primary objective was to assess the infection, but we tried to find a relationship between the size and amount of contamination spots. Preparations were made for the purpose of identification of the pathogen. The tolerance of horseradish breeds and varieties to Albugo candida was examined by measuring the size of 50–50 sporangia stems from infected plants. The pathogenicity of the fungus was confirmed by humid box tests. The field observation was carried out in the study farm of the College of Nyíregyháza, while the laboratory tests were carried out at the Department of Agricultural Sciences and Environmental Management.

We have observed that Albugo candida causes white, foam-like, slightly raised spots of various size and irregular shapes on the leaves. The infection can have different levels in different varieties and the differences were shown in the morphological complexes, too. The leaves of Danvit, Norda, Eperjesi-1 and Westsik-telep 5 varieties were not infected with Albugo candida. Szakácsi was infected moderately, Pózna and Pellérdi were strongly infected. The fungus infection of the other varieties and strains was weak.

The varieties of “dán” morhological complex got infected least of all, while the varieties of” spreewaldi” became infected the most. The size of spot symptoms ranges from pinprick to 20 mm diameter. The former is typical in the “spreewaldi”, the latter in the “dán” morphological complex, but we found no clear correlation between the number and size of patches of infection. Varieties vary in the size of conidia, but it is not related to either the different morphological complexes, nor the rate of infection.

Keywords: horseradish (Armoracia lapathifolia), Albugo candida, cultivar, morphological complexes, tolerance