The results of the studies carried out over the last 50 years have not provided a clear answer to questions concerning the interaction between Clavibacter sepedonicus (Cs), potato and the environment. The reason is insufficient knowledge of the biology of the causal agent of ring rot, problems of research methodology and the influence of many environmental and biotic factors on the degree of plant infestation. The research conducted in the years 2013–2016 in the Plant Breeding and Acclimatization Institute – National Research Institute concerned the determination of the influence of weather conditions, involved the influence of temperature and Sielianinov hydrothermal coefficient on the development of Cs bacteria in stems and progeny tubers, as well as the occurrence of disease symptoms on plants and in tubers of eight potato varieties. It was found that genotype had the greatest impact on leaf and tuber infestation, while weather conditions were less significant. The results of correlation analysis indicate that the weight of tubers of plants infected by Cs increased statistically significantly with increases in air and soil temperature. On the other hand, air and soil temperature in the initial vegetation period did not significantly affect the number of potato plant tubers infested by Cs. In a 4-year experiment, it was not shown how air and soil temperature and the Sielianinov hydrothermal coefficient affected the degree of potato leaf and tuber infestation. In most cases, potato infestation by Cs caused a decrease in yield.

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The aim of this study was to determine the response of potato cultivars to Clavibacter sepedonicus (Cs) infection in a field experiment. The research focused on the infection in a latent form as it is a risk for unnoticed spread. A total of 18 cultivars were tested in the years 2013–2016. Symptoms of the disease were observed on the leaves during growth and in tubers after harvest and after storage. The infection incidence was determined by microscopic observation of leaf and tuber samples stained by the IFAS method. A diverse response of potato cultivars to Cs infection was found. The lowest number of asymptomatic infected plants was found in cultivars ‘Vineta’, ‘Bila’ and ‘Irga’. As for cultivar ‘Stasia’, the entire tuber yield was latently infected by Cs. A low or medium concentration of Cs cells in leaves did not change significantly or increased depending on the potato cultivar. A higher incidence of tubers with disease symptoms was found after the storage period. In eight of the cultivars tested, the level of tuber infection by Cs confirmed microscopically after harvest was significantly correlated with the occurrence of disease symptoms in tubers after the storage period.

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Search for genotypes resistant to Cercospora (Cercospora beticola Sacc.) in multigerm breeding materials of sugar beetPoszukiwanie genotypów odpornych na Cercospora beticola Sacc. w wielonasiennych materiałach hodowlanych buraka cukrowego Summary. In sugar beet cultivation, one of the main factors causing a significant drop in size and yield quality is the infection of plant leaves by the fungus Cercospora beticola Sacc. The main aim of the work was to identify inbred lines of sugar beet with genes of resistance to this pathogen. The research and selection works were carried out in multigerm breeding materials type 2xZN with a different degree of homozygosity. For the study, 36 genotypes of the S1 generation and 34 genotypes of the S2 generation were selected as well as 1 standard (Andante) variety with an increased level of fungal resistance. The sensitivity of materials to infection of C. beticola was assessed using a laboratory method (in vitro test). After twice selection a high stabilization of resistance was found within the examined progeny and a clear differentiation between the progeny of the S1 and S2 generation. The average number of spots on 10 leaf discs in the studied 9 progeny of S1 generation was from 10.50 to 31.04, and in 11 progeny of S2 generation from 6.30 to 28.49 using infection under optimal conditions for fungal growth. The wide range of variability that occurred in the tested materials made it possible to select 9 genotypes of the S1 generation and the 11 S2 generation with a high level of resistance to the C. beticola and high cultivation value.