Assessment of potato cultivars and breeding clones for susceptibility to Rizoctonia solani and Streptomyces scabies

Background. Black scurf (agent Rizoctonia solani J.G. Kuhn) is common in almost all areas of potato cultivation and causes crop yield damage. At present, many cultivars are susceptible to this disease. Common scab is caused by Streptomyces scabies (Thaxter) Waksman et Henrici. This pathogen does not reduce harvest with the same force as black scurf, but produces a considerable negative effect on the commercial quality of tubers. The modern market has a high demand for high commercial tuber quality due to the appearance of new types of potato-based products, including washed and packaged potatoes sold raw. In some years, processing industry suffers losses due to the destruction of industrially grown potatoes by scabs, while producers are forced to pay extra for chemicals, so a search for cultivars with low susceptibility to these diseases is very important. Material and Methods. Susceptibility to black scurf was studied in 219 cultivars of domestic and foreign origin from the VIR potato collection and 17 breeding clones from the collection maintained at the Research Institute of Agriculture “Belogorka”; besides, 217 early cultivars from the VIR collection were analyzed for susceptibility to common scab. Field observations were made during harvesting in VIR’s experimental field (Pushkin). Susceptibility to both pathogens was assessed using a 4-grade scale, where grade 0 means no symptoms and grade 4 denominates 90–100% damage of the tuber surface. Results and conclusions. According to the data obtained, susceptibility to both pathogens was variably present in a number of cultivars introduced from countries with advanced potato breeding, such as Germany, the Netherlands, Poland, etc. As a result of the study, cultivars and breeding clones without disease symptoms or their weak manifestation were identified. Severity of the symptoms of both pathogens depended much on a season. Plant material with low susceptibility to the diseases can be of interest for potato breeders.