Diagnosis, epidemiology and biological control of bacterial spot disease (Xanthomonas euvesicatoria) in pepper production areas of Tokat province

Aims of the present study; a) to determine the prevalence of pepper bacterial spot disease in the region by conducting surveys in the areas where pepper production is intense in Tokat province in 2016 and 2017, and to diagnose the bacterial isolates obtained from infected pepper plant samples by morphological, physiological, biochemical tests and molecular (PCR) analyzes, and to identify the disease in Tokat, b) to determine the epidemiology of the disease, and to determine the first inoculum sources c) to determine the biological control of the disease with the bacteria that promote plant growth and to determine the effect of these bacteria on pepper plant growth. In the field surveys carried out within the scope of the study, a total of 571 isolates were obtained from diseased pepper plants, 346 in 2016 and 225 in 2017. Morphological, physiological, biochemical, pathogenicity tests and molecular (PCR) analyzes were performed with 69 isolates selected to represent each region in Tokat province. All of the isolates obtained as a result of these tests were identified as Xanthomonas euvesicatoria. In the epidemiological studies, the life span of Xanthomonas euvesicatoria in seeds, soil and plant residues was determined. As a result of the study, it was determined that the bacterium survives on the seed for 7 months, so the first inoculum source is the seed. The pathogen bacterium survives In the plant residues upto 60 days in summer and 30 days in winter. Survival time of the pathogen in the soil was 105 days in summer and 14 days in winter. In the study conducted on the biological control of pepper bacterial spot disease, the plant growth promoting bacteria were isolated from the leaf, stem, root pieces and rhizosphere soil of healthy pepper plants from pepper production areas in Tokat province in 2017. Total of 389 candidate isolates were obtained with different isolation methods. As a result of phosphorus reduction and nitrogen fixation tests, 38 isolates were selected as candidates. As a result of the antagonistic effect studies performed with Xanthomonas euvesicatoria, 6 isolates that formed the highest inhibition zone were selected and these isolates were identified as Enterobacter cloacae, Enterobacter aerogenes, Bacillus cereus, Microbacterium testaceum, Pseudomonas putida and Acinetobacter calcoaceticus using MALDI-TOF. Pot and field trials were carried out for the biological control of pepper bacterial spot disease with 6 selected isolates. In studies conducted with single, double and triple combinations of candidate bacterial isolates, it was observed that bacterial spot disease was suppressed by 34.2-49.6% in the pot experiment and by 71.5%-82.7% in the field trial. It was determined that candidate bacterial isolates affected plant growth at different rates in greenhouse and field trials. The results of the study showed that the local plant growth promoting bacteria have the potential in the biological control of pepper bacterial spot disease.