Powdery mildew is a disease that affects various herbaceous and woody ornamentals in Tennessee, including crepe myrtle, dogwood, Japanese maple, hydrangea, rose, peony, and crab apple cultivars, and can cause serious damage.

HomePlant DiseaseVol. 106, No. 8First Report of Stagonosporopsis heliopsidis Causing a Leaf Spot on Whorled Sunflower, Helianthus verticillatus, in the United States PreviousNext DISEASE NOTE OPENOpen Access licenseFirst Report of Stagonosporopsis heliopsidis Causing a Leaf Spot on Whorled Sunflower, Helianthus verticillatus, in the United StatesS. L. Boggess, E. C. Bernard, A. S. Windham, and R. N. TrigianoS. L. Boggess†Corresponding author: S. L. Boggess; E-mail Address: sbogges1@utk.eduhttps://orcid.org/0000-0003-1817-9400Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996Search for more papers by this author, E. C. BernardDepartment of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996Search for more papers by this author, A. S. WindhamDepartment of Entomology and Plant Pathology, University of Tennessee, Nashville, TN 37211Search for more papers by this author, and R. N. Trigianohttps://orcid.org/0000-0002-7264-1822Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996Search for more papers by this author AffiliationsAuthors and Affiliations S. L. Boggess1 † E. C. Bernard1 A. S. Windham2 R. N. Trigiano1 1Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996 2Department of Entomology and Plant Pathology, University of Tennessee, Nashville, TN 37211 Published Online:20 Jul 2022https://doi.org/10.1094/PDIS-11-21-2568-PDNAboutSectionsView articlePDFSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat View articleWhorled sunflower, Helianthus verticillatus Small (Asteraceae), is a federally endangered species (U.S. Fish and Wildlife Service 2014) growing in only a few locations in Tennessee, Georgia, Mississippi, and Alabama (Ellis et al. 2008; Matthews et al. 2002) and recently in Virginia (Edward Schilling, personal communication) in the United States. This herbaceous perennial produces yellow, daisy-like inflorescences from September through October and is of interest for use in landscapes because the flowers attract numerous native bees and other insects (Edwards et al. 2020; Strange et al. 2020; Trigiano et al. 2021). In May 2021, black necrotic spots surrounded by chlorotic halos appeared on various locations on the blade of mature leaves on landscape plants in Knoxville, TN. Symptomatic leaves were washed in running water for 10 min, surface-sterilized with 1.25% NaOCl for 8 min, and rinsed with sterile, distilled water. Lesions were excised with some healthy tissue, cultured on potato dextrose agar (PDA) augmented with 10 mg/liter of rifampicin, and incubated at room temperature. White to dark-brown hyphae grew from the lesions and were transferred to fresh medium until pure cultures were obtained. Cream-colored and slightly pinkish spore masses were evident after 10 weeks of culture. Conidia were cylindrical and ellipsoidal to subglobose at one end. The mean dimensions of conidia were 5.4 µm (3.9 to 6.8 µm) in length and 2 µm (1.7 to 2.5 µm) in width (n = 20). Conidia matched the description of Stagonosporopsis heliopsidis (formally Phoma heliopsidis and Phyllosticta heliopsidis) (Chen et al. 2015). The morphology of the conidia from S. heliopsidis differs slightly from the globose conidia of its closely related sister species, S. helianthi (Chen et al. 2015). PCR was performed with ITS1 and ITS4 primers (White et al. 1990) using the Phire Direct Plant PCR kit (ThermoFisher Scientific, Waltham, MA) and sequenced at a commercial sequencing center. The sequences were concatenated into one consensus and identified as S. heliopsidis with a 100% match to GenBank number GU237924.1. A sequence was deposited in GenBank with accession number OK315471. Koch’s postulates were completed using detached leaf assays because H. verticillatus is an endangered species and only a few plants were available. Five surface-sterilized, symptomless, sign-free leaves were dissected bilaterally, and halves were placed individually on 1.5% water agar supplemented with 10 mg of rifampicin/liter. Mycelial plugs grown on PDA were positioned in contact with one half-leaf, and the remaining half-leaf was treated with a sterile PDA plug as a control. Cultures were incubated for 7 days at room temperature in ambient light. All control halves of the leaves remained green and healthy, whereas the inoculated leaves developed lesions with the same appearance as lesions on the whole plant. The pathogen was reisolated using the protocol described previously and sequenced (OK315470). This fungus causes very limited aesthetic damage to leaves but does not affect the growth and flowering of ornamental plantings of H. verticillatus. To our knowledge, this is the first report of S. heliopsidis on H. verticillatus in the United States.The author(s) declare no conflict of interest.References:Chen, Q., et al. 2015. Stud. Mycol. 82:137. https://doi.org/10.1016/j.simyco.2015.10.003 Crossref, ISI, Google ScholarEdwards, T., et al. 2020. Front. Genet. 11:410. https://doi.org/10.3389/fgene.2020.00410 Crossref, Google ScholarEllis, J. R., et al. 2008. Heredity 100:574. https://doi.org/10.1038/hdy.2008.11 Crossref, ISI, Google ScholarMatthews, J. F., et al. 2002. Castanea 67:13. Google ScholarStrange, C., et al. 2020. HortSci. 55:1980. https://doi.org/10.21273/HORTSCI15394-20 Crossref, ISI, Google ScholarTrigiano, R. N., et al. 2021. Plants 10:1565. https://doi.org/10.3390/plants10081565 Crossref, Google ScholarU.S. Fish and Wildlife Service. 2019. Fed. Regist. 79:50990. https://www.fws.gov/policy/library/2014/2014-19558.html Google ScholarWhite, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Google ScholarFunding: Funding was provided by USDA-MOA-NACA (586062-006).The author(s) declare no conflict of interest.DetailsFiguresLiterature CitedRelated Vol. 106, No. 8 August 2022SubscribeISSN:0191-2917e-ISSN:1943-7692 Download Metrics Article History Issue Date: 29 Jul 2022Published: 20 Jul 2022First Look: 24 Jan 2022Accepted: 13 Jan 2022 Page: 2266 Information© 2022 The American Phytopathological SocietyFundingUSDA-MOA-NACAGrant/Award Number: 586062-006Keywordscultivar/resistancedisease managementfungiherbaceous/flowering plantsornamentalspathogen detectionThe author(s) declare no conflict of interest.PDF download

Turfgrass Diseases and Their Control

Objective: Passalora sequoiae (family Mycosphaerellaceae) causes a twig blight on Leyland cypress that requires numerous fungicide applications annually to minimize economic losses for ornamental plant nursery and Christmas tree producers. The objective was to generate a high-quality draft assembly of the whole genome of P. sequoiae as a resource for primer development and to investigate genotype diversity. Data description: We report here the genome sequence of P. sequoiae 9LC2 that was isolated from Leyland cypress 'Leighton Green' in 2017 in southern Mississippi, USA. The draft genome was obtained using Pacific Biosciences (PacBio) SMRT and Illumina HiSeq 2500 sequencing. Illumina reads were mapped to PacBio assembled contigs to determine base call consistency. Based on a total of 44 contigs with 722 kilobase (kb) average length (range 9.4 kb to 3.4 Mb), the whole genome size was estimated at 31,768,716 bp. Mapping of Illumina reads to PacBio contigs resulted in a 1000 x coverage and were used to confirm accuracy of the consensus sequences.

The eriophyid mite, Phyllocoptes fructiphilus, vectors the causal agent, Rose rosette virus (RRV), that results in rose rosette disease. Parts of the southeastern United States have remained free of the disease, except for infected plant material introductions that were eradicated. A survey of sampling points through Alabama, Georgia, and Mississippi (n = 204) revealed the southeastern border of RRV. The presence of RRV in symptomatic plant tissue samples (n = 39) was confirmed by TaqMan-quantitative reverse transcription polymerase chain reaction (RT-qPCR). Samples were also collected at every plot for detection of eriophyid mites, specifically for P. fructiphilus. Three different species of eriophyid mites were found to be generally distributed throughout Alabama, Georgia, and Mississippi. Most of these sites (n = 60) contained P. fructiphilus, found further south than previously thought, but in low populations (<10 mites/gram of tissue) south of the RRV line of incidence. Latitude was found to be significantly correlated with the probability of detecting RRV-positive plants, but plant hardiness zones were not. Plot factors such as plant size, wind barriers, and sun exposure were found to have no effect on P. fructiphilus or the presence of RRV. The reason for the absence of RRV and low populations of P. fructiphilus in this southeast region of the United States are unclear.

Evaluating species diversity and patterns of population genetic variation is an essential aspect of conservation biology to determine appropriate management strategies and preserve the biodiversity of native plants. Habitat fragmentation and potential habitat loss are often an outcome of a reduction in naturally occurring wildfires and controlled prescribed burning, as seen in Helianthus verticillatus (whorled sunflower). This endangered, wild relative of the common sunflower, Helianthus annuus, is endemic to four locations in Alabama, Georgia, and Tennessee, United States. Despite its endangered status, there is no recovery plan for H. verticillatus, and knowledge related to its basic plant biology and importance in ecosystem services is mostly unknown. In this study, we utilized 14 microsatellite loci to investigate fine-scale population structure and genetic diversity of H. verticillatus individuals found on two sampling sites within the Georgia population. Our results indicated moderate genetic diversity and the presence of two distinct genetic clusters. Analyses of molecular variance indicated that the majority of variance was individually based, thus confirming high genetic differentiation and limited gene flow between H. verticillatus collection sites. The evidence of a population bottleneck in these sites suggests a recent reduction in population size that could be explained by habitat loss and population fragmentation. Also, high levels of linkage disequilibrium were detected, putatively suggesting clonal reproduction among these individuals. Our study provides a better understanding of fine-scale genetic diversity and spatial distribution of H. verticillatus populations in Georgia. Our results can underpin an original recovery plan for H. verticillatus that could be utilized for the conservation of this endangered species and to promote its persistence in the wild.

Abstract Eleven switchgrass cultivars (eight ornamental and three agronomic) were inoculated with 40 switchgrass rust isolates collected from the southeastern U.S. to study host resistance, rust virulence and host/pathogen interactions by measuring urediniospore germination percentage, latent period, and the number of uredia and urediniospores produced per cm2 of leaf surface. In general, ornamental switchgrass cultivars had reduced number of uredia and urediniospores produced per cm2 than did agronomic cultivars. Rust isolates were variable for virulence in culture (on grass blades in petri dishes); however they could not be segregated into groups based on collection locations or years. The results of this study will provide information concerning durable horizontal resistance in switchgrass for the ornamental industry. Index words:, Switchgrass, leaf rust, resistance. Species used in the study: switchgrass (Panicum virgatum L., rust (Puccinia emaculata).

Cornus florida (flowering dogwood) is a popular understory tree endemic to the eastern hardwood forests of the United States. In 1996, dogwood powdery mildew caused by Erysiphe pulchra, an obligate biotrophic fungus of large bracted dogwoods, reached epidemic levels throughout the C. florida growing region. In the late 1990s, both sexual and asexual stages of E. pulchra were regularly observed; thereafter, the sexual stage was found less frequently. We examined the genetic diversity and population structure of 167 E. pulchra samples on C. florida leaves using 15 microsatellite loci. Samples were organized into two separate collection zone data sets, separated as eight zones and two zones, for the subsequent analysis of microsatellite allele length data. Clone correction analysis reduced the sample size to 90 multilocus haplotypes. Our study indicated low genetic diversity, a lack of definitive population structure, low genetic distance among multilocus haplotypes, and significant linkage disequilibrium among zones. Evidence of a population bottleneck was also detected. The results of our study indicated a high probability that E. pulchra reproduces predominately via asexual conidia and lend support to the hypothesis that E. pulchra is an exotic pathogen to North America.[Formula: see text] Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Rose rosette is a serious virus disease of roses. It is spread primarily by a microscopic mite. Successful management of rose rosette disease, or RRD, involves early detection of symptoms.

Guide to help growers know when, where and what to observe when diagnosing the cause of many plant problems. Also, specific environmental conditions that favor development of certain diseases are presented.

Abstract Rose rosette disease, caused by rose rosette virus (RRV), is an epidemic affecting nearly every rose cultivar in the United States. The only hosts for Phyllocoptes fructiphilus, the eriophyid mite that vectors RRV, are Rosa species. Eighteen Rosa species were evaluated for mite resistance by collecting foliage samples from July to November in 2016 and 2017, from which mites were extracted. Mites were isolated through a series of sieves and counted using a stereomicroscope. The response variable was expressed as the number of mites per gram of optimal rose tissue. Mite data were evaluated to determine the peak week for mite populations for each year. The mite populations varied by rose species (α = 0.05) in 2016 but not 2017. Due to high variability in mite counts, the species were not as clearly distinguishable as expected. This high variability is likely due to factors such as differential growth rates of the roses, weather, presence of RRV in the rose, and the quality of the tissue collected throughout the season. Experimental design revisions are proposed for future studies looking at Rosa species resistance to eriophyid mite populations. Index words: rose rosette virus, rose rosette disease, Phyllocoptes fructiphilus Keifer, virus, vector. Species used in this study: Phyllocoptes fructiphilus (Keifer), Prairie Rose [Rosa arkansana (Porter), Forest Farm]; Carolina Rose [Rosa carolina (L.), Forest Farm]; Rosa clinophylla (Thory), Rogue Valley Rose; White Prairie Rose [Rosa foliolosa (Nutt.), Rogue Valley Rose]; White Prairie Rose [Rosa foliolosa (Nutt.) Antique Rose Emporium]; Father Hugo Rose [Rosa hugonis, Rogue Valley Rose]; Musk Rose [Rosa moschata (J. Herrm.), Antique Rose Emporium]; Multiflora Rose [Rosa multiflora (Thunb.)]; Shining Rose [Rosa nitida (Willd.), Rogue Valley Rose]; Shining Rose [Rosa nitida (Willd.), Antique Rose Emporium]; Nootka Rose [Rosa nutkana (C. Presl.), Rogue Valley Rose]; Tea Rose [Rosa odorata (Andrews), Foundation Plant Services, Davis, CA]; Swamp Rose [Rosa palustris (Marshall), Antique Rose Emporium]; Swamp Rose [Rosa palustris (Marshall), Ever Blooming Antique Rose Emporium]; Chestnut Rose [Rosa roxburghii (Tratt.), Antique Rose Emporium]; ‘Plena' Chestnut Rose [Rosa roxburghii (Tratt.), Rogue Valley Rose]; Rugosa Rose [Rosa rugosa (Thunb.), Bailey's Nursery]; ‘Alba' Rugosa Rose [Rosa rugosa (Thunb.), Bailey's Nursery]; Climbing Prairie Rose [Rosa setigera (Michx.), Antique Rose Emporium]; Rosa soulieana (Crép.), Ralph Moore; Virginia Rose [Rosa virginiana (Mill.), Forest Farm]; Porterfolia Memorial Rose [Rosa wichuraiana (Crép.), Antique Rose Emporium]; Mountain Woods' Rose [Rosa woodsii (Lindl.), Rogue Valley Rose].

Current eriophyid mite quantification techniques require transportation of the Rosa spp. cuttings to the laboratory. It is thought that the change in xylem hydraulic conductance within the cut cane could trigger the mites to abandon their host, owing to the changes to the microenvironments that these mites are inhabiting. An experiment was conducted to determine the necessity of floral cuts (reducing stem embolisms by an additional cut underwater) for the retention of eriophyid mites during transit. Four groups of plants (rose rosette virus (RRV)-free Knock Out roses, RRV-infected Knock Out roses, RRV-free multiflora roses, and RRV-infected multiflora roses) were evaluated at different time intervals (0.5, 2, 4, 8, 24, 48, 72, and 96 h postharvest) to assess mite populations on each plant (number of mites per gram of tissue). Cut type (floral or dry cut) and rose species were found not to have a significant effect on the number of mites per gram of tissue found, indicating that floral cuts are not needed for accurately estimating eriophyid mite populations. Rose cuttings infected with RRV were found to have an average of 46 times more mites per gram in comparison with RRV-free cuttings.

In the past few decades, Rose rosette disease (RRD) has spread from its source in western North America through the Mid-West to the East coast. It now threatens to decimate the US rose industry. Garden roses, which form the cornerstone of the multi-billion dollar landscape industry, annually generate wholesale US domestic bare root and container production valued at around $ 400 million. RRD is caused by an emaravirus, Rose rosette virus (RRV), which is transmitted by wind-blown eriophyid mites (Phyllocoptes fructiphilus). Unlike other rose diseases, it can kill a rose within two to three years of infection. In collaboration with scientists from 6 states, private rose breeders, the American Rose Society, AmericanHort, and the rose industry, a project was initiated to develop a multidisciplinary approach to control the disease. In the short term, the project team is working to develop Best Management Practices and educational materials based on host, virus, and vector biology to minimize the effects of RRD. Key to this effort is the development of efficient user-friendly diagnostic tools. In the long term, roses are being assessed for resistance to RRD using both replicated field trials and observational data from collaborators. Marker-trait associations for RRD resistance and consistent flower productivity are being identified to move RRD resistance efficiently into elite rose germplasm. Economic and marketing studies are being done to assess the economic effect of RRD on the rose industry, improve our understanding of consumer preferences, and identify barriers to rose sales.

In 2018-19, boxwood blight was reported in gardens where no new boxwoods were introduced. All commonly used boxwood cultivars are thought to be susceptible to infection. Publications gives symptoms of boxwood blight, causes and best management practices.

Learn how to identify rose diseases and choose best management strategies that will help minimize the impact of plant diseases.

Contains management strategies for diseases such as mildew, mold and leaf spot, among others.