LATENT INFESTATION OF POTATO TUBERS WITH SOFT ROT AND RING ROT PATHOGENS UNDER CHANGING WEATHER CONDITIONS IN UKRAINE.

Potato is one of the most important food crops in the world. Cultivation of potatoes is an important segment of the agriculture and economy as a whole in Ukraine. Bacterial diseases such as ring rot caused by Clavibacter sepedonicus, as well as soft rot and blackleg caused by Pectobacterium atrosepticum evoke tremendous losses of the potato crop. Stored seed tubers are the main source of accumulating pathogens in latent form. In addition, potato crop yield and quality are significantly affected by weather conditions. Along with affecting potatoes directly, meteorological factors such as air temperature and humidity can also impact tuber infestation with bacterial pathogens. The aim of the study was to monitor the prevalence of bacterial ring rot pathogen C. sepedonicus and soft rot pathogen P. atrosepticum in potato tubers on the territory of Ukraine in 2020 and 2021 years and assess its association with different weather conditions. Methods. Potato seed lots from newly harvested crops in eight regions of Ukraine (Odesa, Kyiv, Donetsk, Kherson, Cherkasy, Mykolaiv, Dnipropetrovsk, and Zhytomyr regions) without visual symptoms of diseases were used for the experiments. The detection of C. sepedonicus and P. atrosepticum was conducted by the immunochemical method DAS ELISA. Basal meteorological data (the sum of precipitation (mm/month) and average air temperature (°C) were obtained from the local meteorological stations. The amplitude of air temperature and the sum of precipitation during potato planting, growing, and harvesting seasons, as well as Sielianinov's hydrothermal coefficient (K) were additionally calculated. The Spearman correlation coefficient was used for the analysis of the correlation between pathogen prevalence and weather parameters. Results. Both ring rot pathogen C. sepedonicus and soft rot pathogen P. atrosepticum were detected in potato lots from all surveyed regions, but the prevalence of latent infestation varied between 2020 and 2021. In 2020, the highest soft rot pathogen prevalence values were registered for Mykolaiv, Kyiv, and Cherkasy regions (21.7, 10.5, and 10% respectively), where high rainfall levels in May and June were observed. In 2021, potato planting, growing, and harvesting seasons were marked by significantly higher precipitation levels, as compared to 2020, in all regions. Average occurrence values for P. atrosepticum in potato lots were 1.7 times higher than that in 2020. The highest prevalence (40%) was observed in the Donetsk region wiThextremely high air humidity during the potato growing period. Strong positive correlation (r = 0.721) was found between soft rot pathogen prevalence and K coefficients during the potato growing season, as well as between P. atrosepticum prevalence and the sum of precipitation during planting and early growing seasons. Prevalence of ring rot pathogen didn't differ significantly in 2020 and 2021. The highest C. sepedonicus prevalence was observed in 2020 in the Kyiv region (18.9%), and in 2021 -- in the Donetsk region (20%). A moderate positive correlation (r = 0.591) was found between pathogen prevalence and air temperature during planting and early growing season. Conclusions. Weather factors such as air temperature and humidity over the planting and early growing potato season can influence progeny tuber infestation with P. atrosepticum and C. sepedonicus. Knowledge of the effect of the changing weather conditions on the susceptibility of potato varieties with different genetic features to infestation with soft rot and ring rot pathogens warrants future investigation since it is crucially important for developing measures for disease control by potato producers. [ABSTRACT FROM AUTHOR]