339 AGRICULTURAL SCIENCE AND TECHNOLOGY, VOL. 13, No 4, pp 339-343, 2021 Published by Faculty of Agriculture, Trakia University, Bulgaria ISSN 1313-8820 (print) ISSN 1314-412X (online) http://www.agriscitech.eu DOI: 10.15547/ast.2021.04.055 *e-mail: kkvasileva@abv.bg Introduction Bacterial spot of pepper was a serious disease worldwide where climatic conditions favourable, the pathogens provoked signifcant yield losses (OEPP, 2013; Schwartz et al., 2015; Potnis et al., 2015; Dhakal et al., 2019). In Bulgaria, bacterial spot caused by X. euvesicatoria and X. vesicatoria was a threatening disease and a major limiting factor in the pepper production areas. X. еuvesicatoria was currently the dominant pathogen of pepper, while X. vesicatoria was widespread in tomato. The Bulgarian population of X. euvesicatoria was characterized with genetic diversity and private allelic richness (Bogatzevska et al., 2007, 2021; Kizheva et al., 2011; Stoyanova et al., 2014; Vancheva, 2015; Vasileva and Bogatzevska, 2019; Vancheva et al., 2018, 2021). X. vesicatoria and X. euvesicatoria were of historical importance and prevalent worldwide. According to the gene- for-gene hypothesis, eleventh pepper races had been identifed among Xanthomonas strains worldwide and fve non-allelic dominant genes (Bs1, Bs2, Bs3, Bs4, and Bs7) were reported to control hypersensitive reaction (HR). Currently available commercial bacterial spot-resistant cultivars contain various combinations of resistance genes. Because of the pathogens’ ability to rapidly overcome major genes, breeding for bacterial spot resistance may ultimately dictate incorporation of quantitative resistance and major resistance gene pyramids in commercial cultivars. The predominance of races on the cultivars was to an extent related to the resistance genes present in them (Stall et al., 2009; Potnis et al., 2015). The use of resistant cultivars was the most appropriate for the development of these plants, it was necessary to know the genetic base that controls the resistance, allowing the selection of the most appropriate breeding method. The breeding of varieties with durable and complex resistance was a long and composite process that required extensive, diverse immunity researches, predecessing the selection process. This necessitates to study the species composition of the causes of bacterial spot pepper in Bulgaria, pathotype, race, virulence, aggressiveness, competitiveness of natural populations; the appearance of new races, able to overcome the resistance of established breeding lines and introduce into hybrids and varieties. The cyclical development and spread of the pathogens, the appearing of new species and races in the country requires extensive research on the specifc resistance mechanism, genetic research to establish the resistance genes Bs of pepper, differentially interacts with races of bacterial pathogens, and corresponding avrBs genes in their natural populations. The breeding of resistant lines, hybrids and varieties was associated with the correct choice of resistance components: bacterial pathogens – species; races; host phenophase; infection method; disease ratings on leaves and scale ranging from 0 to 4, classifcation into groups with proven limit values on the basis of mean score (ms) of infestation (Pesti et al., 1990). The aim of this paper was to make statistical analysis of data on resistance variability of pepper accessions to Xanthomonas euvesicatoria and Xanthomonas vesicatoria (2005-2016) and Statistical analysis of resistance variability of pepper accessions to Xanthomonas euvesicatoria and Xanthomonas vesicatoria K. Vasileva 1 *, N. Bogatzevska 2 1 Maritsa Vegetable Crops Research Institute, 32 Brezovsko Shosse Str., 4003 Plovdiv, Bulgaria 2 Institute of Soil Science, Agrotechnologies and Plant Protection “N. Pushkarov”, 7 Shosse Bankya Str., 1331 Sofa, Bulgaria (Manuscript received 16 March 2021; accepted for publication 28 September 2021) Abstract. The limit values of resistance groups were established to Xanthomonas euvesicatoria and Xanthomonas vesicatoria by mean score - ms based on conducted statistical analysis of 155 selection lines of Bulgarian, introduced hybrids and pepper varieties: I- immune; R- resistant; MS- medium sensitive; S- sensitive; SS- strongly sensitive. The genetic diversity between the two bacteria suggest the use of separate resistant groups to determine the resistance. Data on the mean score of infestation on 116 pepper accessions to X. euvesicatoria and 155 (the previous 116 included) to X. vesicatoria were processed and the resistance groups were defned. Breeding pepper accessions with complex resistance requires the application of the established resistance groups to both pathogens. The limit values of the groups by ms based on the statistical analysis of the data on the resistance of pepper accessions to X. euvesicatoria and X. vesicatoria were specifed. Keywords: limit value, pepper accession, Xanthomonas euvesicatoria, Xanthomonas vesicatoria, statistical analysis