\u3ci\u3eClavibacter nebraskensis\u3c/i\u3e causing Goss\u27s wilt of maize: Five decades of detaining the enemy in the New World

Goss\u27s 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\u27s 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\u27s 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\u27s 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 27794T; CFBP 2405T; ICMP 3298T; LMG 3700T; NCPPB 2581T. 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

Phenotypic and Molecular-Phylogenetic Analysis Provide Novel Insights into the Diversity of Curtobacterium flaccumfaciens.

A multiphasic approach was used to decipher the phenotypic features, genetic diversity, and phylogenetic position of 46 Curtobacterium spp. strains isolated from dry beans and other annual crops in Iran and Spain. Pathogenicity tests, resistance to arsenic compounds, plasmid profiling and BOX-PCR were performed on the strains. Multilocus sequence analysis (MLSA) was also performed on five housekeeping genes (i.e., atpD, gyrB, ppk, recA, and rpoB) of all the strains, as well as five pathotype strains of the species. Pathogenicity test showed that six out of 42 strains isolated in Iran were nonpathogenic on common bean. Despite no differences found between pathogenic and nonpathogenic strains in their plasmid profiling, the former were resistant to different concentrations of arsenic, while the latter were sensitive to the same concentrations. Strains pathogenic on common bean were polyphyletic with at least two evolutionary lineages (i.e., yellow-pigmented strains versus red/orange-pigmented strains). Nonpathogenic strains isolated from solanaceous vegetables were clustered within either the strains of C. flaccumfaciens pv. flaccumfaciens or different pathovars of the species. The results of MLSA and BOX-PCR analysis were similar to each other and both methods were able to discriminate the yellow-pigmented strains from the red/orange-pigmented strains. A comprehensive study of a worldwide collection representing all five pathovars as well as nonpathogenic strains of C. flaccumfaciens is warranted for a better understanding of the diversity within this phytopathogenic bacterium

Bacterial wilt of dry beans caused by Curtobacterium flaccumfaciens pv. flaccumfaciens: A new threat from an old enemy

Bacterial wilt and tan spot of dry beans (family Fabaceae), caused by Curtobacterium flaccumfaciens pv. flaccumfaciens, is an important emerging disease threatening the edible legume industry around the globe. The management of bacterial wilt has been a major problem since its original description in 1922. This is in part due to the seedborne nature of the pathogen allowing the bacterium to be transmitted long distances via infected seeds, as well as a lack of detailed molecular information concerning the pathogenicity repertoires and virulence determinates of the pathogen. Identification can also be difficult owing to the presence of five different colony colour variants (i.e., yellow, orange, pink, purple, and red) on culture media. In this review, we provide an overview of the aetiology, epidemiology, and management strategies of bacterial wilt disease. First, a comprehensive and comparative symptomology of the disease on different dry bean species is described. Then, the taxonomic history of the causal agent and utility of high-throughput sequencing-based approaches in the precise characterization of the pathogen is explained. Furthermore, we provide an updated outline on the global distribution of the pathogen, highlighting expansion of the causal agent into the areas with no history of the disease until the beginning of the current century. Finally, because there are limited options for use of conventional pesticides against the pathogen, we highlight the use of integrated pest management strategies, for example quarantine inspections, resistant cultivars, and crop sanitation, to combat the risk of bacterial wilt disease in the dry bean industry.Disease symptoms Interveinal chlorosis on leaflets leading to necrotic areas and systemic wilt. Seed discolouration to yellow, orange, pink, or purple is seen in white-seeded cultivars.Host range Causes bacterial wilt and tan spot disease on edible dry beans in the Fabaceae family, including common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), mungbean (Vigna radiata), soybean (Glycine max), as well as a number of weed species.Taxonomic status of the pathogen Bacteria; phylum Actinobacteria; order Actinomycetales; suborder: Micrococcineae; family Microbacteriaceae; genus Curtobacterium; species Curtobacterium flaccumfaciens.Synonyms Corynebacterium flaccumfaciens subsp. flaccumfaciens; Corynebacterium flaccumfaciens pv. flaccumfaciens, Corynebacterium flaccumfaciens, Phytomonas flaccumfaciens, Bacterium flaccumfaciens.Microbiological properties Multicoloured (yellow, orange, pink, purple, and red), gram-positive, aerobic, curved rod, nonspore-forming, polar flagellated, motile cells.Distribution Widespread in America (Brazil, Canada, and the USA), Australia, and Iran. Restricted occurrence in Africa and Europe.Phytosanitary categorization EPPO A2 list no. 48, EU Annex II forward slash B

Induction of Resistance in Common Bean by <I>Rhizobium leguminosarum</I> bv. <I>phaseoli</I> and Decrease of Common Bacterial Blight

Rhizobium leguminosarum bv. phaseoli was evaluated for its capacity to trigger resistance to common bacterial blight (CBB) of common bean caused by Xanthomonas axonopodis pv. phaseoli (Xap), under greenhouse and field conditions. A common bean cultivar and three lines including two tolerant lines (Ks51103 and BF13607) and the susceptible cultivar Khomein and line Ks21479, were used. R. leguminosarum bv. phaseoli, was applied as a seed treatment and its effect on disease severity (DS) was compared with untreated (control) plants and with urea fertilizer treated plants in both the greenhouse and the feld. R. leguminosarum bv. phaseoli in common bean roots tended to reduce CBB severity and to improve plant growth, particularly the 100-seed weight, in the field. The greatest decrease in CBB in the greenhouse occurred 15 days after inoculation (DAI) of Xap in the cultivar Khomein and line Ks21479, and 30 DAI in lines Ks51103 and BF13607. In the field, however, the greatest decrease occurred 35 DAI in the cultivar and all lines. Furthermore, in the field the greatest improvement in 100-seed weight occurred in the cultivar Khomein treated with R. leguminosarum bv. phaseoli. The potential of using R. leguminosarum bv. phaseoli in the management of CBB and the possible mechanisms that induce resistance in this symbiotic system are discussed

Draft Genome Sequences of the Type Strains of Three Clavibacter Subspecies and Atypical Peach-Colored Strains Isolated from Tomato

Here, we present the draft genome sequences of 10 Clavibacter sp. strains, including the type strains of different subspecies of Clavibacter michiganensis and a potentially novel species within the genus. Genome lengths of the strains varied between 2,982,864 and 3,288,331 bp, with G+C contents of 72.23 to 73.50%

Pathogenicity and molecular‐phylogenetic analysis revealed a distinct position of the banana finger‐tip rot pathogen among the Burkholderia cenocepacia genomovars

Banana (Musa spp.) is one of the most widely cultivated subtropical fruits around the globe. Banana cultivation has been extensively increased in southeastern Iran over the last two decades. Recently, banana fruits possessing rotten and blackened fingertip symptoms were observed in Sistan‐Baluchestan, Iran. Isolation and characterization of the causal agent showed that the pathogen belongs to the multifaceted bacterial species Burkholderia cenocepacia. Pathogenicity tests and host range assays showed that the strains were pathogenic on banana, as well as carrot, onion and potato. All the strains were resistant to 50 mg L−1 rifampicin and 200 mg L−1 copper sulphate. Phylogenetic analysis of 16S rRNA and recA gene sequences showed that the strains belong to two different genomovars of B. cenocepacia (III‐A and III‐B), which also include environmental and cystic fibrosis associated strains of the species. The results obtained from recA phylogeny were confirmed using multilocus sequence analysis (MLSA), although MLSA showed that the banana strains were clustered as a novel phylogroup among the members of both genomovars. Banana‐pathogenic B. cenocepacia strains isolated in Iran were different from the strains isolated in Taiwan, as the ‘B. cepacia epidemic strain marker’ reported in the Taiwanese strains was absent from Iranian strains. To the authors’ knowledge, this is the first MLSA‐based study on the banana‐pathogenic strains of B. cenocepacia. However, further in‐depth molecular studies are needed to decipher the relationships between the banana fingertip rot pathogen and the clinical strains of B. cenocepacia

Potato-Infecting Ralstonia solanacearum Strains in Iran Expand Knowledge on the Global Diversity of Brown Rot Ecotype of the Pathogen

Bacterial wilt and brown rot disease caused by Ralstonia solanacearum species complex (RSSC) is one of the major constraints of potato (Solanum tuberosum) production around the globe. During 2017-2018 an extensive field survey was conducted in six potato-growing provinces of Iran to monitor the status of bacterial wilt disease. Pathogenicity and host range assays using 59 bacterial strains isolated in Iran showed that they were pathogenic on eggplant, red nightshade, pepper, potato and tomato, while nonpathogenic on common bean, cowpea, cucumber, sunflower, zinnia and zucchini. PCR-based diagnosis revealed that the strains belong to the phylotype IIB/sequevar 1 (IIB/I) lineage of the RSSC. Furthermore, a five-gene multilocus sequence analysis and typing (i.e. egl, fliC, gyrB, mutS, rplB) confirmed the phylogenetically near-homogeneous nature of the strains within IIB/I lineage. Four sequence types were identified among 58 IIB/1 strains isolated in Iran. Phylogenetically near-homogeneous nature of the strains in Iran raise questions about the mode of inoculum entry of the bacterial wilt pathogen into the country (one-time introduction vs. multiple introductions), while the geographic origin of the Iranian R. solanacearum strains remains undetermined. Furthermore, sequence typing showed that there were shared alleles (haplotypes) and sequence types among the strains isolated in geographically distant areas in Iran, suggesting intra-national transmission of the pathogen in the country. <br/

Xanthomonas bonasiae sp. nov. and Xanthomonas youngii sp. nov., isolated from crown gall tissues

International audienceThe genus Xanthomonas contains a set of diverse bacterial strains, most of which are known for their pathogenicity on annual crops and fruit trees causing economically important plant diseases. Recently, five Xanthomonas strains were isolated from Agrobacterium -induced crown gall tissues of amaranth ( Amaranthus sp.) and weeping fig ( Ficus benjamina ) plants in Iran. Phenotypic characteristics ( i.e . biochemical tests and pathogenicity features) and whole genome sequence-based core-genome phylogeny followed by average nucleotide identity and digital DNA–DNA hybridization calculations suggested that these gall-associated strains belong to two new species within the genus Xanthomonas . In this study, we provide a formal species description for these new species where Xanthomonas bonasiae sp. nov. is proposed for the strains isolated from weeping fig with FX4 T (=CFBP 8703 T =DSM 112530 T ) as type strain. The name Xanthomonas youngii sp. nov. is proposed for the strains isolated from amaranth with AmX2 T (=CFBP 8902 T =DSM 112529 T ) as type strain

Thirteen decades of antimicrobial copper compounds applied in agriculture. A review

Since the initial use of Bordeaux mixture in 1885 for plant disease control, a large number of copper-based antimicrobial compounds (CBACs) have been developed and applied for crop protection. While these compounds have revolutionized crop protection in the twentieth century, their continuous and frequent use has also raised concerns about the long-term sustainability of copper (Cu)-based crop protection system. Here, we review CBACs used in crop protection and highlight their benefits and risks, and potential for their improvement and opportunities for further research to develop alternatives to CBACs. The major findings are (i) the relatively high toxicity to plant pathogens, low cost, low mammalian toxicity of the fixed Cu compounds, and their chemical stability and prolonged residual effects are major benefits of these compounds; (ii) phytotoxicity, development of copper-resistant strains, soil accumulation, and negative effects on soil biota as well as on food quality parameters are key disadvantages of CBACs; (iii) regulatory pressure in agriculture worldwide to limit the use of CBACs has led to several restrictions, including that imposed by the regulation 473/2002 in the European Union; and (iv) mitigation strategies to limit the negative effects of CBACs include their optimized use, soil remediation, and development and application of alternatives to CBACs for a sustainable crop protection. We conclude that recent research and policy efforts have led to the development of a number of alternatives to CBACs, which should be further intensified to ensure that growers have sufficient tools for the implementation of sustainable crop protection strategies.</p