Abstract
Bacterial spot of pepper and tomato is caused by at least three species of Xanthomonas, among them two pathovars of Xanthomonas euvesicatoria, which are responsible for significant yield losses on all continents. In order to trace back the spread of bacterial spot pathogens within and among countries, we developed the first multilocus variable number of tandem repeat analyses (MLVA) scheme for pepper- and tomato-pathogenic strains of X. euvesicatoria. In this work, we assessed the repeat numbers by DNA sequencing of 16 tandem repeat loci and applied this new tool to analyse a representative set of 88 X. euvesicatoria pepper strains from Bulgaria and North Macedonia. The MLVA-16 scheme resulted in a Hunter–Gaston Discriminatory Index (HGDI) score of 0.944 and allowed to resolve 36 MLVA haplotypes (MTs), thus demonstrating its suitability for high-resolution molecular typing. Strains from the different regions of Bulgaria and North Macedonia were found to be widespread in genetically distant clonal complexes or singletons. Sequence types of the variable number of tandem repeats (VNTR) amplicons revealed cases of size homoplasy and suggested the coexistence of different populations and different introduction events. The large geographical distribution of MTs and the existence of epidemiologically closely related strains in different regions and countries suggest long dispersal of strains on pepper in this area.
Highlights
Bacterial spot, which is caused by at least three Xanthomonas species, is a threatening disease of pepper and tomato plants worldwide [1,2,3]
In order to trace back the spread of bacterial spot pathogens within and among countries, we developed the first multilocus variable number of tandem repeat analyses (MLVA) scheme for pepper- and tomato-pathogenic strains of X. euvesicatoria by directly assessing the repeat number by sequencing Tandem repeat (TR) loci and applied this new tool to analyse a representative set of 88 X. euvesicatoria strains that were isolated from pepper plants in Bulgaria and North Macedonia
We first evaluated the utility of gyrB to differentiate X. euvesicatoria from the Balkan Peninsula
Summary
Bacterial spot, which is caused by at least three Xanthomonas species, is a threatening disease of pepper and tomato plants worldwide [1,2,3]. The pathogens can cause significant yield losses in pepper- and tomato-growing areas. The disease is characterized by small, irregular, water-soaked, greasy-appearing lesions on all above-ground parts of the plants, followed by cell death, tissue necrosis and egress of Xanthomonas to the leaf surface [4]. Defoliation and shedding of fruits and blossoms are commonly observed in pepper production areas. This leads to a reduction in fruit quality and fruit loss due to the presence of lesions and the proliferation of secondary postharvest pathogens [5]
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