Publication Search Results

ID: 155710
Type: article
Authors: Arias, Silvina; Block, Charles; Mayfield, Derrick A.; Santillana, Gem E.; Stulberg, Michael E.; Broders, Kirk; Jackson-Ziems, Tamra; Munkvold, Gary P.
Keywords: STRI
Abstract: This paper reports original evidence regarding the potential role of seed transmission of Xanthomonas vasicola pv. vasculorum (Xvv) in the epidemiology of bacterial leaf streak (BLS) in maize. We evaluated the occurrence of the pathogen on seeds from diseased fields and its subsequent transmission to seedlings. In 2016 and 2017, Xvv was detected by TaqMan PCR from 22 of 41 maize seed lots harvested from naturally-infected fields in Colorado (CO), Nebraska (NE) and Iowa (IA). However, many of the PCR-positive samples did not yield culturable Xvv colonies. The highest levels of seed contamination were detected in dent maize and popcorn from NE and CO. Seed transmission was evaluated in greenhouse grow-outs from eight seed lots, totaling more than 14,000 plants. Putative seed transmission events from naturally contaminated seed lots, estimated from PCR results, occurred at a frequency between 0.1 and 0.5% in 10-seedling pooled samples and at a frequency of 2.7% from individual plant assays. However, no seedling symptoms were observed during these assays and live Xvv colonies were not recovered from PCR-positive seedlings. In contrast, seed transmission was readily demonstrated from artificially contaminated seed lots, including typical symptoms and recovery of live bacteria. Seed transmission consistently occurred from seeds soaked in bacterial suspensions with concentrations of ≥106 CFU per mL, suggesting that a threshold population of the bacterium is necessary for the development of BLS-symptoms and recovery of live bacteria. The low bacterial populations on naturally contaminated seeds apparently were not sufficient to result in diseased seedlings.

ID: 156752
Type: article
Authors: Ortiz-Castro, Mary; Hartman, Terra; Coutinho, Teresa; Lang, Jillian M.; Korus, Kevin; Leach, Jan E.; Jackson-Ziems, Tamra; Broders, Kirk
Keywords: STRI
Abstract: Bacterial leaf streak of corn, caused by Xanthomonas vasicola pv. vasculorum, has been present in South Africa for over 70 years, but is an emerging disease of corn in North and South America. The only scientific information pertaining to this disease on corn came from work done in South Africa, which primarily investigated host range on other African crops, such as sugarcane and banana. As a result, when the disease was first reported in the United States in 2016, there was very limited information on where this pathogen came from, how it infects its host, what plant tissue(s) it is capable of infecting, where initial inoculum comes from at the beginning of each crop season, how the bacterium spreads from plant to plant and long distance, what meteorological variables and agronomic practices favor disease development and spread, how many other plant species X. vasicola pv. vasculorum is capable of infecting or using as alternate hosts, and if the bacterium will be able to persist in all corn growing regions of the United States. There were also no rapid diagnostic assays available which initially hindered prompt identification prior to the development of molecular diagnostic tools. The goal of this synthesis is to review the history of X. vasicola pv. vasculorum and bacterial leaf streak in South Africa and its movement to North and South America, and highlight the recent research that has been done in response to the emergence of this bacterial disease.

ID: 152062
Type: article
Authors: Pérez-Quintero, Alvaro L.; Ortiz-Castro, Mary; Wu, Guangxi; Lang, Jillian M.; Liu, Sanzhen; Chapman, Toni A.; Chang, Christine; Ziegle, Janet; Peng, Zhao; White, Frank F.; Plazas, Maria Cristina; Leach, Jan E.; Broders, Kirk
Keywords: STRI
Abstract: Xanthomonas vasicola pv. vasculorum (Xvv) is an emerging bacterial plant pathogen that causes bacterial leaf streak on corn. First described in South Africa in 1949, reports of this bacteria have greatly increased in the past years in South America and in the U.S., where it is now present in most of the corn producing states. Phenotypic characterization showed that the emerging U.S. and South American Xvv populations may have increased virulence in corn compared to older strains. To understand the genetic mechanisms behind the increased virulence in this group, we used comparative genomics to identify gene acquisitions in Xvv genomes from the U.S. and Argentina. We sequenced 41 genomes of Xvv and the related sorghum-infecting X. vasicola pv. holcicola (Xvh). A comparison of all available X. vasicola genomes showed the phylogenetic relationships in the group and identified clusters of genes associated with the emerging Xvv populations. The newly acquired gene clusters showed evidence of horizontal transfer to Xvv and included candidate virulence factors. One cluster, in particular, corresponded to a prophage transferred from Xvh to all Xvv from Argentina and the U.S. The prophage contains putative secreted proteins, which represent candidates for virulence determinants in these populations and await further molecular characterization.

ID: 152064
Type: article
Authors: Stulberg, Michael; Santillana, Gem; Studholme, David J.; Kasiborski, Beth; Ortiz-Castro, Mary; Broders, Kirk; Arias, Silvina; Block, Charles; Munkvold, Gary P.; Rascoe, John
Keywords: STRI
Abstract: Xanthomonas vasicola pv. vasculorum (syn. X. campestris pv. vasculorum) was initially identified as the causal agent of bacterial leaf streak of corn in South Africa. The pathovar vasculorum causes disease on sugarcane and corn, but a subset of these strains was noted for its increased disease severity in corn. This subset was re-classified as Xanthomonas campestris pv. zeae in the early 1990s and was found to have slightly different biochemical and genetic properties than isolates from sugarcane. There has been an emergence of X. campestris pv. zeae-like strains of X. vasicola pv. vasculorum in both the United States and Argentina since 2010. We performed whole genome sequencing on U.S. isolates to confirm their identity. Informed by comparative genomics, we then developed specific TaqMan qPCR and loop-mediated isothermal amplification (LAMP) assays for the detection of this specific subset of X. vasicola pv. vasculorum strains. The qPCR 4909 assay was tested against 27 xanthomonads (diverse representation), 32 DNA extractions from corn leaves confirmed as positive or negative for the bacterium, 41 X. vasicola pv. vasculorum isolates from corn in the United States and Argentina, and 31 additional bacteria associated with corn, sugarcane, or sorghum. In all cases the assay was shown to be specific for the X. vasicola pv. vasculorum isolates that cause more severe disease on corn. We then tested the LAMP 166 assay against the 27 xanthomonads and 32 corn leaf DNA samples, and we found this assay was also specific for this subset of X. vasicola pv. vasculorum isolates. We also developed a live/dead cells distinction protocol using propidium monoazide prior to DNA extraction for analyzing seed washes using these assays. These two detection assays can be useful for both diagnosticians and researchers to specifically identify the X. vasicola pv. vasculorum isolates that cause more severe symptoms on corn.

ID: 152058
Type: article
Authors: Flieger, Miroslav; Stodůlková, Eva; Wyka, Stephen A.; Černý, Jan; Grobárová, Valéria; Píchová, Kamila; Novák, Petr; Man, Petr; Kuzma, Marek; Cvak, Ladislav; Broders, Kirk D.; Kolařík, Miroslav
Keywords: Pre_SI
Abstract: Ergot, fungal genus Claviceps, are worldwide distributed grass pathogens known for their production of toxic ergot alkaloids (EAs) and the great agricultural impact they have on both cereal crop and farm animal production. EAs are traditionally considered as the only factor responsible for ergot toxicity. Using broad sampling covering 13 ergot species infecting wild or agricultural grasses (including cereals) across Europe, USA, New Zealand, and South Africa we showed that the content of ergochrome pigments were comparable to the content of EAs in sclerotia. While secalonic acids A–C (SAs), the main ergot ergochromes (ECs), are well known toxins, our study is the first to address the question about their contribution to overall ergot toxicity. Based on our and published data, the importance of SAs in acute intoxication seems to be negligible, but the effect of chronic exposure needs to be evaluated. Nevertheless, they have biological activities at doses corresponding to quantities found in natural conditions. Our study highlights the need for a re-evaluation of ergot toxicity mechanisms and further studies of SAs’ impact on livestock production and food safety.

ID: 152063
Type: article
Authors: Studholme, David J.; Wicker, Emmanuel; Abrare, Sadik Muzemil; Aspin, Andrew; Bogdanove, Adam; Broders, Kirk; Dubrow, Zoe; Grant, Murray; Jones, Jeffrey B.; Karamura, Georgina; Lang, Jillian; Leach, Jan; Mahuku, George; Nakato, Gloria Valentine; Coutinho, Teresa; Smith, Julian; Bull, Carolee T.
Keywords: STRI
Abstract: Members of the genus Xanthomonas , within the gamma-Proteobacteria, collectively cause disease on more than 400 plant species (Hayward 1993]1]), though some members are apparently non-pathogenic (Vauterin et al. 1996]2]) and some have been isolated from clinical samples such as skin microbiota