Association of the Pathogen <i>Spiroplasma kunkelii</i> with Corn Stunt Symptoms in Oklahoma, Kansas, Missouri, Arkansas, Nebraska, South Dakota, New York, Wisconsin, Minnesota, Indiana, and Alabama During the 2024 Growing Season

Plant Health Progress · 2025-01-01 · 3 citations

Corn stunt is one of the most significant corn diseases in the Neotropics, leading to severe plant stunting and substantial yield losses. Although four pathogens have been found either singly or in combination in infected plants in the Americas, corn stunt spiroplasma ( Spiroplasma kunkelii) has been the most predominant pathogen associated with the disease in the United States, due to its widespread distribution in the Rio Grande Valley region and persistent occurrence in California and Florida. During the 2024 growing season, reports of chlorosis, leaf reddening, and stunting in corn fields in Southern, Great Plains, Central Corn Belt, and Northeastern states raised concern regarding the possibility of a more widespread distribution of corn stunt spiroplasma in the United States. Symptomatic corn leaf samples were collected in commercial and experimental field sites across the United States. Detection and identification of S. kunkelii were performed using a polymerase chain reaction assay targeting a section of the spiralin gene, followed by amplicon sequencing. This study provides the first report of the pathogen S. kunkelii associated with corn stunt symptoms distributed across 6 counties in Oklahoma, 14 counties in Kansas, 2 counties in Missouri and Arkansas, 4 counties in New York, and 1 county in each of Nebraska, South Dakota, Wisconsin, Minnesota, Indiana, and Alabama. All states with submitted samples had at least one confirmed case of S. kunkelii.

Tracking the Distribution and Risk of Tar Spot of Corn in Indiana from 2015 to 2022

Plant Health Progress · 2025-01-01 · 1 citations

Tar spot of corn ( Zea mays L.), caused by Phyllachora maydis, was first confirmed in the United States in 2015 in Illinois and Indiana but has since spread to a total of 20 states and Ontario and Quebec, Canada. Severe tar spot epidemics have caused unexpected and significant yield losses in corn in the Midwest. It is critical to document the movement and risk factors of this disease to develop effective management strategies. Tar spot distribution and disease intensity data were collected in Indiana from 2015 to 2022. Tar spot severity data were assessed from images of leaves submitted to the Purdue Pest and Diagnostic Laboratory from 2015 to 2018, and a statewide survey was conducted annually from 2019 to 2022. In each county, two or more corn fields were scouted for tar spot, percent field incidence and average leaf severity were documented, and county-level weather data were collected. In Indiana, tar spot severity was negatively correlated with temperature and positively correlated with precipitation during June and August but negatively correlated with July precipitation. High relative humidity (&gt;90%) was also positively correlated with tar spot severity during June, July, and August. Fields in northern Indiana had the highest severity throughout the survey and have the highest risk for the disease in the future. Pockets of tar spot outbreaks indicate that once it is found locally, favorable environmental conditions of moderate temperatures and fluctuating periods of seasonal moisture may increase the risk of a severe epidemic in a field in future years.

Watermelon Crinkle Leaf-Associated Virus 1 and Watermelon Mosaic Virus Mixed Infecting Watermelon ( <i>Citrullus lanatus</i> ) in Indiana

Plant Disease · 2025-12-18

Watermelon (Citrullus lanatus) production in the USA was valued at $787 million in 2023, with most of the production concentrated in Florida, California, and Georgia. In the Midwest, Indiana leads watermelon production with a value of $49 million (USDA-NASS, 2024). In August 2024, watermelon plants (cv. Guardsman) showing virus-like symptoms, including mosaic, yellowing, leaf deformation, and wrinkling, were observed in southern Indiana (Knox County). No insect vectors were observed in the fields during the site visits. Samples were collected from three plants in each of four separate watermelon fields. A preliminary serological screening using ImmunoStrip® tests (Agdia, Elkhart, IN) for the general potyvirus group and melon severe mosaic virus was performed. Only the ImmunoStrip® tests for the potyvirus group showed positive results. Total RNA was extracted from a symptomatic representative sample from each field using the Spectrum Plant Total RNA kit (Sigma-Aldrich, St. Louis, MO). A pool of total RNA from four individual samples was then submitted for high-throughput sequencing (HTS) using an Illumina NovaSeqX platform as 150 bp paired-end reads (Psomagen, Rockville, MD). The library was prepared using the TruSeq Stranded Total RNA with Plant Ribo-Zero kit. HTS generated 58 million reads. Sequence reads were trimmed with BBDuk software, de novo assembled using SPAdes v3.15, and submitted to the NCBI. Viral contigs were identified using Blastx against the full non-redundant database (as of November 2024). Watermelon crinkle leaf-associated virus 1 (WCLaV-1) was assembled into three contigs: 6.6 Kb viral polymerase (RNA1, 47,009 reads; coverage 1,122X; acc. PQ621806), 1.4 Kb movement protein (RNA2, 6,932 reads; coverage 1,193X; acc. PQ621807), and 1.3 Kb nucleocapsid (RNA2, 5,300 reads; coverage 1,006X; acc. PQ621808). The highest level of nucleotide identity detected ranged from 98.0-99.9% compared with WCLaV-1 isolate Pi-01 from Brazil (LC636068-9). Additionally, a nearly full-length watermelon mosaic virus (WMV) genome (~10 Kb) with >99% identity compared with WMV isolate C05-270 from France (EU660585) was assembled (17,871,776 reads; coverage 24,638X; acc. PQ855772). Putative mycovirus sequences were also detected through HTS; however, further analysis was not conducted due to the incompleteness of the sequences and the limited number of hits. The occurrence of each virus in the individual samples was further validated by RT-PCR using sequence-specific primers designed in this study. WCLaV-1 was detected in 2/4 watermelon samples, while WMV was detected in 2/4 samples, with one sample being infected by both viruses. Three amplicons were sequenced using Nanopore Technology (Plasmidsaurus, Eugene, OR), compared to homologous sequences in GenBank, and uploaded to the NCBI under accessions PV030975-PV030977. Interestingly, HTS did not detect WCLaV-2, commonly detected in mixed infections with WCLaV-1. Although WCLaV-1 and WCLaV-2 were previously associated with symptoms (Xin et al. 2017), the effect on growth and yield is still unknown (Hendricks and Roberts 2023). To the best of our knowledge, this is the first report of WCLaV-1 and WMV infecting watermelons in Indiana, highlighting the need for additional research on the impact of single and mixed infections of these viruses on cucurbit crops.

Diversification of an emerging bacterial plant pathogen; insights into the global spread of Xanthomonas euvesicatoria pv. perforans

PLoS Pathogens · 2025-04-09 · 6 citations

Emerging and re-emerging plant diseases continue to present multifarious threats to global food security. Considerable recent efforts are therefore being channeled towards understanding the nature of pathogen emergence, their spread and evolution. Xanthomonas euvesicatoria pv. perforans (Xep), one of the causal agents of bacterial spot of tomato, rapidly emerged and displaced other bacterial spot xanthomonads in many tomato production regions around the world. In less than three decades, it has become a dominant xanthomonad pathogen in tomato production systems across the world and presents a compelling example for understanding diversification of recently emerged bacterial plant pathogens. Although Xep has been continuously monitored in Florida since its discovery, the global population structure and evolution at the genome-scale is yet to be fully explored. The objectives of this work were to determine genetic diversity globally to ascertain if different tomato production regions contain genetically distinct Xep populations, to examine genetic relatedness of strains collected in tomato seed production areas in East Asia and other production regions, and to evaluate variation in type III secretion effectors, which are critical pathogenicity and virulence factors, in relationship to population structure. We used genome data from 270 strains from 13 countries for phylogenetic analysis and characterization of type III effector gene diversity among strains. Our results showed notable genetic diversity in the pathogen. We found genetically similar strains in distant tomato production regions, including seed production regions, and diversification over the past 100 years, which is consistent with intercontinental dissemination of the pathogen in hybrid tomato production chains. Evolution of the Xep pangenome, including the acquisition and loss of type III secreted effectors, is apparent within and among phylogenetic lineages. The apparent long-distance movement of the pathogen, together with variants that may not yet be widely distributed, poses risks of emergence of new variants in tomato production.

First Report of <i>Xanthomonas dyei</i> Causing Bacterial Blight on Glossy Abelia

Plant Disease · 2024-12-26 · 1 citations

Glossy abelia (Abelia × grandiflora) is an evergreen ornamental shrub used in landscaping globally. From Jun. 2023 to Feb. 2024, bacterial blight symptoms were observed in > 50% of ~20,000 glossy abelia plants (cv. Kaleidoscope, Radiance, and Rose Creek) in an ornamental nursery in North Carolina, USA. Symptoms consisted of small, irregular, water-soaked spots that became brown and coalesced, with defoliation from 20 to 80%. Symptomatic samples were sent to the Purdue University Plant and Pest Diagnostic Laboratory for preliminary identification. A symptomatic leaf was rinsed 3× in sterile deionized (DI) water, cut into 1 mm wide strips, placed in 5 mL of sterile DI water for 5 min, from which a 10 µL loop was streaked onto KB (King's medium B). Individual yellow predominant colonies were transferred to KB after 48 h at 25°C, and the 16s rRNA was sequenced with the 27F/1492R primers (Lane 1991; GenBank accession PP734871). To confirm, three symptomatic plants (cv. Radiance) were sent for isolation to Clemson University in Feb. 2024. One symptomatic leaf per plant was surface sterilized with 70% ethanol. The toothpick method (Noh et al. 2024) was used to extract bacteria into sterile distilled water; suspensions were streaked on nutrient agar plates. Predominant colonies after 48 h incubation at 28°C were convex, mucoid, and yellow. Three isolates (Abs1, Abs2, and Abs3), one per plant, were purified from single colonies; all produced positive results using the Xanthomonas ImmunoStrip® (Agdia) and hypersensitive response 24 h after being infiltrated (~108 CFU/ml) into Nicotiana benthamiana leaves. PCR amplification and sequencing of the gyrB, rpoD, dnaK, and fyuA genes was done for all three isolates using the bacterial suspension as DNA template with the primers and conditions described in Young et al. (2008). The sequences of each gene were 100% identical among isolates and those from Abs1 were deposited in GenBank (accession # PP739553-PP739556). The gene sequences most closely matched Xanthomonas dyei, with 98.60% (848/860 nt), 99.65% (866/869 nt), 99.44% (884/889 nt), and 99.42% (681/685 bp) identity with the gyrB (GQ183098), rpoD (GQ183084), dnaK (GQ183125), and fyuA (GQ183111) sequences, respectively, of the X. dyei type strain ICMP 12167. A neighbor joining tree using the concatenated sequences of these four genes showed Abs1 clustered with X. dyei. To fulfill Koch's postulates, three branches of three healthy ~1-year-old abelia plants were spray inoculated with Abs1 suspension in sterile tap water (~5×108 CFU/ml). An abelia plant sprayed with sterile tap water was the control. The experiment was conducted three times, one cultivar per time (cv. Kaleidoscope, Radiance, and Rose Creek). All plants were maintained in a growth chamber at 21°C with 12 h photoperiod. Leaf chlorosis, significant defoliation, and stem blight symptoms were observed on inoculated branches within 7 days after inoculation with similar disease severity among cultivars. Symptoms were not observed on control plants. Due to excessive defoliation, bacteria were reisolated from blighted stem tissue of inoculated branches and confirmed to be the same isolate via PCR and sequencing as described above. To the best of our knowledge, this is the first report of X. dyei causing disease on Abelia x grandiflora worldwide. Given the severe disease symptoms on this high value crop, more research is needed to determine the inoculum source, disease distribution, and to develop management strategies.

First Report of <i>Erwinia pyrifoliae</i> Causing Flower Blight and Fruit Rot on Greenhouse-Grown <i>Fragaria</i> × <i>ananassa</i> in the United States

Plant Disease · 2024-08-23 · 4 citations

Erwinia pyrifoliae causes disease of pear (Pyrus spp.), apple (Malus spp.), and strawberry (Fragaria × ananassa) (Wenneker and Bergsma-Vlami 2015), which are economically important commodities in the US. Disease symptoms on pear and apple are indistinguishable from those caused by the non-quarantine fire blight pathogen, E. amylovora (Kim et al. 1999), which also causes disease on strawberries (Atanasova et al. 2005). Samples of greenhouse-grown strawberry 'Albion' from Ohio were submitted to the Purdue Plant and Pest Diagnostic Lab in December 2023. Fruits were stunted with brown lesions, while sepals and pedicels had brown-black water-soaked lesions. Cut fruit exuded bacterial ooze from the main vascular bundle. Bacterial streaming was observed microscopically from symptomatic tissue which tested positive with the E. amylovora ImmunoStrip® (Agdia Inc., Elkhart, IN); reported by the manufacturer to cross-react with E. pyrifoliae. Isolation from symptomatic tissue produced pure cultures on sucrose peptone agar and Kings medium B after incubation at 27°C for 48 hr, and colonies appeared circular and white/opaque. Crude DNA extractions were prepared by boiling colony suspensions in Tris-EDTA buffer. Two independent real-time PCR tests specific for E. pyrifoliae (Lehman et al. 2008; Yasuhara-Bell et al. 2024) produced positive results. Conventional PCR using an E. pyrifoliae-specific primer set targeting a divergent region between pstS and glmS genes (Wensing et al. 2011) also produced positive results. The amplicon was Sanger-sequenced and deposited into NCBI GenBank (Accession PP757383). BLASTn analysis using the Nucleotide collection and Whole-genome shotgun contigs revealed top matches (100% query coverage; 97.5% identity to type strain DSM 12163) with E. pyrifoliae only; next closest match was E. amylovora (53% query coverage). To confirm Koch's postulates, immature fruit of six healthy strawberry 'Albion' plants were wounded with a sterile pipette tip and then submersed in a bacterial suspension in sterile deionized water (DI H2O) (3.1×107 cells/ml). Fruit of six additional plants were mock inoculated using sterile DI H2O. Plants were placed in plastic bags for 48 hr at room temperature with a 12-hr photoperiod. Symptoms were first observed on inoculated plants 1.5 days post-inoculation (DPI). Brown discoloration was observed within fruit and as spreading lesions on fruit pedicels by 4 DPI; mock-inoculated plants remained asymptomatic. Bacterial streaming from symptomatic tissue allowed successful re-isolation of the bacterium. Molecular testing confirmed isolates to be E. pyrifoliae, thus completing Koch's postulates. Following initial confirmation, additional samples of infected strawberry ('Albion' and 'GB96') from the same greenhouse were confirmed positive for E. pyrifoliae by molecular testing and sequencing. To our knowledge this is the first time Erwinia pyrifoliae was detected in the US. There are many known pathways of introduction from Asia and Europe; however, pstS-glmS sequence comparison with strawberry isolates from the Netherlands (sequences provided by M.J.C. Pel) suggests this US strawberry strain is unique, but most closely related to Japanese strains (98.5% identity). Potential origin of this strain is unknown, but comparative genomics studies to investigate relatedness among strains are planned.

First Report of Anthracnose Caused by <i>Colletotrichum sansevieriae</i> on <i>Dracaena trifasciata</i> (Snake Plant) in Tennessee

Plant Disease · 2024-12-01 · 1 citations

Phylodynamic Insights into Global Emergence and Diversification of the Tomato Pathogen <i>Xanthomonas hortorum</i> pv. <i>gardneri</i>

Molecular Plant-Microbe Interactions · 2024-07-01 · 9 citations

The emergence of plant pathogens is often associated with waves of unique evolutionary and epidemiological events. Xanthomonas hortorum pv. gardneri is one of the major pathogens causing bacterial spot disease of tomatoes. After its first report in the 1950s, there were no formal reports on this pathogen until the 1990s, despite active global research on the pathogens that cause tomato and pepper bacterial spot disease. Given the recently documented global distribution of X. hortorum pv. gardneri, our objective was to examine genomic diversification associated with its emergence. We sequenced the genomes of X. hortorum pv. gardneri strains collected in eight countries to examine global population structure and pathways of emergence using phylodynamic analysis. We found that strains isolated post-1990 group by region of collection and show minimal impact of recombination on genetic variation. A period of rapid geographic expansion in X. hortorum pv. gardneri is associated with acquisition of a large plasmid conferring copper tolerance by horizontal transfer and coincides with the burgeoning hybrid tomato seed industry through the 1980s. The ancestry of X. hortorum pv. gardneri is consistent with introduction to hybrid tomato seed production and dissemination during the rapid increase in trade of hybrid seeds. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Diversification of an emerging bacterial plant pathogen; insights from the global spread of <i>Xanthomonas euvesicatoria</i> pv. <i>perforans</i>

bioRxiv (Cold Spring Harbor Laboratory) · 2024-03-22 · 2 citations

Abstract Emerging and re-emerging plant diseases continue to present multifarious threats to global food security. Considerable recent efforts are therefore being channeled towards understanding the nature of pathogen emergence, their spread and evolution. Xanthomonas euvesicatoria pv. perforans (Xep ), one of the causal agents of bacterial spot of tomato, rapidly emerged and displaced other bacterial spot xanthomonads in tomato production regions around the world. In less than three decades, it has become a dominant xanthomonad pathogen in tomato production systems across the world and presents a model for understanding diversification of recently emerged bacterial plant pathogens. Although Xep has been continuously monitored in Florida since its discovery, the global population structure and evolution at the genome-scale is yet to be fully explored. The objectives of this work were to determine genetic diversity globally to ascertain if different tomato production regions contain genetically distinct Xep populations, to examine genetic relatedness of strains collected in tomato seed production areas in East Asia and other production regions, and to evaluate variation in type III effectors, which are critical pathogenicity and virulence factors, in relationship to population structure. We used genome data from 270 strains from 13 countries for phylogenetic analysis and characterization of Xop effector gene diversity among strains. Our results showed notable genetic diversity in the pathogen. We found genetically similar strains in distant tomato production regions, including seed production regions, and diversification over the past 100 years, which is consistent with intercontinental dissemination of the pathogen in hybrid tomato production chains. Evolution of the Xep pangenome, including the acquisition and loss of type III secreted effectors, is apparent within and among phylogenetic lineages. The apparent long-distance movement of the pathogen, together with variants that may not yet be widely distributed, poses risks of emergence of new variants in tomato production.

Strawberry Cultivar Susceptibility to <i>Neopestalotiopsis</i> Leaf Spot in Indiana

Plant Health Progress · 2023 · 14 citations

• Biology
• Horticulture
• Agronomy

In June 2020, a leaf spot caused by Neopestalotiopsis sp. in Indiana strawberry production was confirmed to be the same disease recently found in Florida strawberry production. Differences in cultivar susceptibility were observed in the field. Greenhouse trials using either bare-root or plug plants were conducted to explore possible differences in host resistance to the foliar phase of the disease caused by Neopestalotiopsis sp. Clear differences in cultivar susceptibility were observed. Florida Brilliance, Florida Sensation, Camino Real, and Florida Radiance were among the most susceptible cultivars evaluated in these trials. Several short-day cultivars, including AC Valley Sunset, Darselect, Earliglow, Flavorfest, Galletta, Honeoye, Jewel, and Sonata, remained asymptomatic in the trials. Because many of the abovementioned asymptomatic short-day cultivars are commonly used in matted row systems typical of Indiana strawberry production, future field trials with the matted row system could demonstrate that the foliar phase of the disease caused by Neopestalotiopsis sp. may be less common in Indiana than in other areas of the United States.