Background: Bacterial ring rot of potato ( Solanum tuberosum ) caused by the gram‐positive coryneform bacterium Clavibacter sepedonicus is an important quarantine disease threatening the potato industry around the globe. Since its original description in 1906 in Germany, management of ring rot has been a major problem due to the seedborne nature (via seed tubers not true seeds) of the pathogen allowing the bacterium to be transmitted long distances via infected tubers. Disease symptoms: On growing potato plants: interveinal chlorosis on leaflets leading to necrotic areas and systemic wilt. On infected tubers: vascular tissues become yellowish brown with a cheesy texture due to bacterial colonization and decay. Host range: Potato is the main host of the pathogen, but natural infection also occurs on eggplant, tomato, and sugar beet. Taxonomic status of the pathogen: Class: Actinobacteria ; Order: Actinomycetales ; Family: Microbacteriaceae ; Genus: Clavibacter ; Species: Clavibacter sepedonicus (Spieckermann and Kotthoff 1914) Li et al. 2018. Synonyms (nonpreferred scientific names): Aplanobacter sepedonicus ; Bacterium sepedonicum ; Corynebacterium sepedonicum ; Corynebacterium michiganense pv. sepedonicum ; Clavibacter michiganensis subsp. sepedonicus . Microbiological properties: Gram‐positive, club‐shaped cells with creamy to yellowish‐cream colonies for which the optimal growth temperature is 20–23°C. Distribution: Asia (China, Japan, Kazakhstan, Nepal, North Korea, Pakistan, South Korea, Uzbekistan, the Asian part of Russia), Europe (Belarus, Bulgaria, Czech Republic, Estonia, Finland, Georgia, Germany, Greece, Hungary, Latvia, Lithuania, Norway, Poland, Romania, European part of Russia, Slovakia, Spain, Sweden, Turkey, Ukraine), and North America (Canada, Mexico, USA). Phytosanitary categorization: CORBSE: EPPO A2 list no. 51. EU; Annex designation I/A2.

Goss's bacterial wilt and leaf blight of maize ( Zea mays ) caused by the gram‐positive coryneform bacterium Clavibacter nebraskensis is an economically important disease in North America. C. nebraskensis is included within the high‐risk list of quarantine pathogens by several plant protection organizations (EPPO code: CORBMI), hence it is under strict quarantine control around the world. The causal agent was reported for the first time on maize in Nebraska (USA) in 1969. After an outbreak during the 1970s, prevalence of the disease decreased in the 1980s to the early 2000s, before the disease resurged causing a serious threat to maize production in North America. The re‐emergence of Goss's wilt in the corn belt of the United States led to several novel achievements in understanding the pathogen biology and disease control. In this review, we provide an updated overview of the pathogen taxonomy, biology, and epidemiology as well as management strategies of Goss's wilt disease. First, a taxonomic history of the pathogen is provided followed by symptomology and host range, genetic diversity, and pathogenicity mechanisms of the bacterium. Then, utility of high‐throughput molecular approaches in the precise detection and identification of the pathogen and the management strategies of the disease are explained. Finally, we highlight the role of integrated pest management strategies to combat the risk of Goss's wilt in the 21st century maize industry. Disease symptoms: Large (2–15 cm) tan to grey elongated oval lesions with wavy, irregular water‐soaked margins on the leaves. The lesions often start at the leaf tip or are associated with wounding caused by hail or wind damage. Small (1 mm in diameter), dark, discontinuous water‐soaked spots, known as “freckles”, can be observed in the periphery of lesions. When backlit, the freckles appear translucent. Early infection (prior to growth stage V6) may become systemic and cause seedlings to wilt, wither, and die. Coalescence of lesions results in leaf blighting. Host range: Maize ( Zea mays ) is the only economic host of the pathogen. A number of Poaceae species are reported to act as secondary hosts for C. nebraskensis . Taxonomic status of the pathogen: Class: Actinobacteria ; Order: Micrococcales ; Family: Microbacteriaceae ; Genus: Clavibacter; Species: Clavibacter nebraskensis. Synonyms: Corynebacterium nebraskense (Schuster, 1970) Vidaver & Mandel 1974; Corynebacterium michiganense pv. nebraskense (Vidaver & Mandel 1974) Dye & Kemp 1977; Corynebacterium michiganense subsp. nebraskense (Vidaver & Mandel 1974) Carlson & Vidaver 1982; Clavibacter michiganense subsp. nebraskense (Vidaver & Mandel 1974) Davis et al. 1984; Clavibacter michiganensis subsp . nebraskensis (Vidaver & Mandel 1974) Davis et al. 1984. Type materials: ATCC 27794 ^T ; CFBP 2405 ^T ; ICMP 3298 ^T ; LMG 3700 ^T ; NCPPB 2581 ^T . Microbiological properties: Cells are gram‐positive, orange‐pigmented, pleomorphic club‐ or rod‐shaped, nonspore‐forming, nonmotile, and without flagella, approximately 0.5 × 1–2.0 μm. Distribution: The pathogen is restricted to Canada and the United States. Phytosanitary categorization: EPPO code CORBNE.

Mycopathogenic bacteria play a pivotal role in the productivity of edible mushrooms grown under controlled conditions. In this study, we carried out a comprehensive farm survey and sampling (2018 to 2021) on button mushroom ( Agaricus bisporus) farms in 15 provinces in Iran to monitor the status of bacterial pathogens infecting the crop. Mycopathogenic bacterial strains were isolated from pins, stems, and caps, as well as the casing layer on 38 mushroom farms. The bacterial strains incited symptoms on mushroom caps ranging from faint discoloration to dark brown and blotch of the inoculated surfaces. Among the bacterial strains inciting disease symptoms on bottom mushroom, 40 were identified as Ewingella americana based on biochemical assays and phylogeny of 16S rRNA and the gyrB gene. E. americana strains differed in their aggressiveness on mushroom caps and stipes, where the corresponding symptoms ranged from deep yellow to dark brown. In the phylogenetic analyses, all E. americana strains isolated in this study were clustered in a monophyletic clade closely related to the nonpathogenic and environmental strains of the species. BOX-PCR-based fingerprinting revealed intraspecific diversity. Using the cutoff level of 73 to 76% similarity, the strains formed six clusters. A chronological pattern was observed, where the strains isolated in 2018 were differentiated from those isolated in 2020 and 2021. Taken together, due to the multifaceted nature of the pathogen, such a widespread occurrence of E. americana on mushroom farms in Iran could be an emerging threat for the mushroom industry in the country.

In 2021, two gram-negative bacterial strains were isolated from garlic (Allium sativum) bulbs showing decay and soft rot symptoms in Central Iran. The bacterial strains were aggressively pathogenic on cactus, garlic, gladiolus, onion, potato, and saffron plants and induced soft rot symptoms on carrot, cucumber, potato, and radish discs. Furthermore, they were pathogenic on sporophores of cultivated and wild mushrooms. Phylogenetic analyses revealed that the bacterial strains belong to Burkholderia gladioli. Garlic bulb rot caused by B. gladioli has rarely been reported in the literature. Historically, B. gladioli strains had been assigned to four pathovars, namely, B. gladioli pv. alliicola, B. gladioli pv. gladioli, B. gladioli pv. agaricicola, and B. gladioli pv. cocovenenans, infecting onion, Gladiolus sp., and mushrooms and poisoning foods, respectively. Multilocus (i.e., 16S rRNA, atpD, gyrB, and lepA genes) sequence-based phylogenetic investigations including reference strains of B. gladioli pathovars showed that the two garlic strains belong to phylogenomic clade 2 of the species, which includes the pathotype strain of B. gladioli pv. alliicola. Although the garlic strains were phylogenetically closely related to the B. gladioli pv. alliicola reference strains, they possessed pathogenicity characteristics that overlapped with three of the four historical pathovars, including the ability to rot onion (pv. alliicola), gladiolus (pv. gladioli), and mushrooms (pv. agaricicola). Furthermore, the pathotype of each pathovar could infect the hosts of other pathovars, undermining the utility of the pathovar concept in this species. Overall, using phenotypic pathovar-oriented assays to classify B. gladioli strains should be replaced by phylogenetic or phylogenomic analysis.

Bacterial leaf streak of small-grain cereals is an economically important disease of wheat and barley crops. The disease occurs in many countries across the globe, with particular importance in regions characterized by high precipitation or areas in which sprinkler irrigation is used. Three genetically distinct lineages of the Gram-negative bacterium Xanthomonas translucens ( X. translucens pv. undulosa, X. translucens pv. translucens, and X. translucens pv. cerealis) are responsible for most of the bacterial leaf streak infections on wheat and barley crops. Considering the seedborne nature of the pathogens, they are included in the A2 (high-risk) list of quarantine organisms for some European countries; hence, they are under strict quarantine control and zero tolerance. Due to the taxonomic complexities within X. translucens, the exact geographic distribution of each pathovar has not yet been determined. In this mini review, we provide an updated overview of the detection and diagnosis of the bacterial leaf streak pathogens. First, a short history of the leaf streak pathogens is provided, followed by the symptomology and host range of the causal agents. Then, the utility of conventional methods and high-throughput molecular approaches in the precise detection and identification of the pathogens is explained. Finally, we highlight the role of quarantine inspections and early detection of the pathogen in combating the risk of bacterial leaf streak in the 21st century's small-grains cereals’ industry.

Objective: Bacterial wilt and canker of tomato caused by the gram‐positive corynebacterial species Clavibacter michiganensis is an economically important disease threatening the tomato industry in both open‐air and greenhouse productions around the world. The disease occurs in many countries, with a particular importance in regions characterised by high temperature and water scarcity. Management of bacterial canker has been a major problem since its original description in 1909. This is due in part to the seedborne nature of the pathogen, allowing the bacterium to be transmitted over long distances via infected seeds, as well as a lack of effective treatment to clean seeds. Detection of the pathogen from seeds is difficult due to high competition on culture media with diverse members of the seed‐associated microbiota. Identification of the pathogen can also be difficult owing to the presence of different colony variants on culture media. In this review, we provide a historical perspective and an updated overview on the aetiology, epidemiology and management strategies of the bacterial canker disease. We also gathered recent molecular findings in the pathogenicity mechanisms and bioecology of C. michiganensis to boost management of the bacterial canker disease in the 21 ^st century tomato industry. Taxonomy: Class: Actinobacteria ; Order: Micrococcales ; Family: Microbacteriaceae ; Genus: Clavibacter ; Species: Clavibacter michiganensis . Disease Symptoms: Interveinal leaf chlorosis leading to necrotic areas. Canker on stems and lateral branches of the plant. Discolouration of vascular and pith tissues to dark yellow or brown. Small and early ripened fruits or discolouration of the placenta from white to yellow in the interior part of the ripening fruits. Host Range: Tomato ( Solanum lycopersicum ) is the main host of the pathogen while natural infection has also been reported on eggplant, pepper and wild nightshade plants. Synonyms (Historical/Non‐Preferred Scientific Names): Aplanobacter michiganensis ; Pseudomonas michiganense; Pseudomonas michiganensis; Bacterium michiganense ; Phytomonas michiganensis; Mycobacterium michiganense; Erwinia michiganensis (= michiganense ); Corynebacterium michiganense ; Corynebacterium michiganense pv. michiganense ; Corynebacterium michiganense subsp. michiganense; Clavibacter michiganensis subsp. michiganensis. Microbiological Properties: The bacterium produces domed, round and shiny mucoid colonies on general culture media. Colonies are usually yellow‐pigmented, while pink‐pigmented strains are occasionally observed. Cells are gram‐positive, aerobic, non‐motile, non‐spore‐producing curved rods (coryneform). Distribution: Present in all continents. Phytosanitary Categorization: EPPO A2 List no. 50, EU 2019/2072 RNQP Annex IV. See EPPO ( https://gd.eppo.int/taxon/CORBMI/categorization ) and CABI ( https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.15338 ) databases for further country‐specific categorisations. EPPO code: CORBMI.