The bacterial wilt pathogen, first known as Bacillus solanacearum, has undergone numerous taxonomic changes since its first description in 1896. The history and significance of this pathogen is covered in this review with an emphasis on the advances in technology that were used to support each reclassification that finally led to the current separation of Ralstonia solanacearum into three genomic species. Frequent name changes occurred as methodology transitioned from phenotypic, biochemical, and molecular studies, to genomics and functional genomics. The diversity, wide host range, and geographical distribution of the bacterial wilt pathogen resulted in its division into three species as genomic analyses elucidated phylogenetic relationships among strains. Current advances in phylogenetics and functional genomics now open new avenues for research into epidemiology and control of the devastating bacterial wilt disease.

Bacterial leaf spot of tomato and pepper (BLS), an economically important bacterial disease caused by four species of Xanthomonas (X. euvesicatoria (Xe), X. vesicatoria (Xv), X. gardneri (Xg), and X. perforans (Xp)), is a global problem and can cause over 50% crop loss under unfavorable conditions. Among the four species, Xe and Xv are prevalent worldwide. Characterization of the pathogens is crucial for disease management and regulatory purposes. In this study, we performed a multilocus sequence analysis (MLSA) with six genes (hrcN, dnaA gyrB, gapA, pdg, and hmbs) on BLS strains. Other Xanthomonas species were included to determine phylogenetic relationships within and among the tested strains. Four BLS species comprising 76 strains from different serological groups and diverse geographical locations were resolved into three major clades. BLS xanthomonads formed distinct clusters in the phylogenetic analyses. Three other xanthomonads, including X. albilineans, X. sacchari, and X. translucens pv. undolusa revealed less than 85%, 88%, and 89% average nucleotide identity (ANI), respectively, with the other species of Xanthomonas included in this study. Both antibody and MLSA data showed that Xv was clearly separated from Xe and that the latter strains were remarkably clonal, even though they originated from distant geographical locations. The Xe strains formed two separate phylogenetic groups; Xe group A1 consisted only of tomato strains, whereas Xe group A2 included strains from pepper and tomato. In contrast, the Xv group showed greater heterogeneity. Some Xv strains from South America were closely related to strains from California, while others grouped closer to a strain from Indiana and more distantly to a strain from Hawaii. Using this information molecular tests can now be devised to track distribution of clonal populations that may be introduced into new geographic areas through seeds and other infected plant materials.

Aims Dickeya species are high consequence plant pathogenic bacteria; associated with potato disease outbreaks and subsequent economic losses worldwide. Early, accurate and reliable detection of Dickeya spp. is needed to prevent establishment and further dissemination of this pathogen. Therefore, a multiplex TaqMan qPCR was developed for sensitive detection of Dickeya spp. and specifically, Dickeya dianthicola. Methods and Results A signature genomic region for the genus Dickeya (mglA/mglC) and unique genomic region for D. dianthicola (alcohol dehydrogenase) were identified using a whole genome‐based comparative genomics approach. The developed multiplex TaqMan qPCR was validated using extensive inclusivity and exclusivity panels, and naturally/artificially infected samples to confirm broad range detection capability and specificity. Both sensitivity and spiked assays showed a detection limit of 10 fg DNA. Conclusion The developed multiplex assay is sensitive and reliable to detect Dickeya spp. and D. dianthicola with no false positives or false negatives. It was able to detect mixed infection from naturally and artificially infected plant materials. Significance and Impact of the Study The developed assay will serve as a practical tool for screening of propagative material, monitoring the presence and distribution, and quantification of target pathogens in a breeding programme. The assay also has applications in routine diagnostics, biosecurity and microbial forensics.

The Gram-positive genus Clavibacter is currently divided into seven species ( Clavibacter michiganensis , Clavibacter nebraskensis , Clavibacter capsici , Clavibacter sepedonicus , Clavibacter tessellarius , Clavibacter insidiosus and Clavibacter zhangzhiyongii ) and three subspecies ( C. michiganensis subsp. californiensis , C. michiganensis subsp. chilensis and C. michiganensis subsp. phaseoli ). Recent studies have indicated that the taxonomic rank of the subspecies must be re-evaluated. In this research, we assessed the taxonomic position of the three C. michiganensis subspecies and clarified the taxonomic nomenclature of other 75 Clavibacter strains. The complete genomes of the type strains of the three Clavibacter subspecies, the type strain of C. tessellarius and C. nebraskensis A6096 were sequenced using PacBio RSII technology. Application of whole-genome-based computational approaches such as average nucleotide identity (ANI), digital DNA–DNA hybridization, multi-locus sequence analysis of seven housekeeping genes (acnA, atpD, bipA, icdA, mtlD, recA and rpoB), a phylogenomic tree reconstructed from 1 028 core genes, and ANI-based phylogeny provided sufficient justification for raising C. michiganensis subsp. californiensis to the species level. These results led us to propose the establishment of Clavibacter californiensis sp. nov. as a species with its type strain C55^T (=CFBP 8216^T=ATCC BAA-2691^T). Moreover, the orthologous and in silico dot plot analyses, along with the above described bioinformatic strategies, revealed a high degree of similarity between C. michiganensis subsp. chilensis and C. michiganensis subsp. phaseoli . Based on these analyses, we propose that both subspecies be combined into a single taxon and elevated to the species level as Clavibacter phaseoli sp. nov., with LPPA 982^T (= CECT 8144^T= LMG 27667^T) as the type strain.

Kale (Brassica oleracea var. sabellica L.), family Brassicaceae, is an economically important vegetable crop and an excellent source of natural antioxidants, consumed in many countries worldwide (L...