Annual/Termination Reports:

[08/29/2022] [09/01/2023]

Report Information

Participants

Creamer, Rebecca (creamer@nmsu.edu) - New Mexico State University, Entomology,
Plant Pathology and Weed Science
Carl Strausbaugh (carl.strausbaugh@ars.usda.gov) - USDA-ARS, Kimberly, ID
Tiffany McKay-Williams (tmckay@betaseed.com) - Betaseed Inc, Boise, ID
Erik Wenninger (erikw@uidaho.edu) University of Idaho, Entomology, Plant Pathology, and
Nematology
Punya Nachappa (punya.nachappa@colostate.edu) Colorado State University, Agricultural
Biology
Thomas Koeps (Thomas.koeps@kws.com) KWS Seed, LLC, Twin Falls, ID
Silvia Rondon (silvia.rondon@oregonstate.edu) Oregon State University
Zach Bagley (zach@tomatonet.org) California Tomato Research Institute
Kylie Swisher (kylie.swisher@ars.usda.gov) USDA-ARS, Wapato, WA
Eric Vincill (eric.vincill@usda.gov) - USDA-ARS, Kimberly, ID
Gina Angelella (gina.angelella@usda.gov) USDA-ARS, Wapato, WA
Mary Burrows (mburrows@montana.edu) Montana State University
Raj Majumdar (raj.majumdar@usda.gov) USDA-ARS Kimberly, ID
Tziana Oppedisiano (oppedist@oregonstate.edu) Oregon State University
Batool Alkhatib (batool@nmsu.edu) New Mexico State University
Nicholas Metz (Nicholas.metz@colostate.edu) Colorado State University
Nina Dropcho (ndropcho@nmsu.edu) New Mexico State University
Amy Nelson (amelia.nelson@colostate.edu) Colorado State University
Dennis Lozada (dlozada@nmsu.edu) New Mexico State University
Lauren Murphy (Lauren.murphy@cdfa.ca.gov) California Curly Top Control
Avneesh Kumar (avneesh.kumar@colostate.edu) Colorado State University
Jordan Withycombe (Jordon.withycombe@colostate.edu) Colorado State University
Max Schmidtbauer (max.schmidtbauer@colostate.edu) Colorado State University
Paul Galewski (paul.galewski@usda.gov) USDA-ARS Kimberly, ID
Kevin Dorn (kevin.dorn@usda.gov) USDA-ARS, Fort Collins, CO
Jacob MacWilliams (Jacob.macwilliams@colostate.edu), Fort Collins, CO
Laine Hackenberg (laine.hackenberg@colostate.edu), Fort Collins, CO
Jacob Pitt (William.pitt@colostate.edu), Fort Collins, CO

Brief Summary of Minutes

Summary of Meeting Minutes:

 

      Punya Nachappa, host for the meeting welcomed the group to Colorado State University. Rebecca Creamer, WERA1007 Secretary, explained a bit about the group and its purpose. Introductions were made, and the agenda was discussed. 

      The Administrative Advisor for the group, Mary Burrows, Montana State University spoke by zoom to the group.

      Punya Nachappa presented a brief background on curly top virus and the beet leafhopper as it exists in Colorado.

      Rebecca Creamer presented current disease status in New Mexico in chile and hemp. She discussed the virus strains in chile and hemp and host specificity of certain strains. She discussed how the strains change over time. The most prevalent strain in 2022 is Pepper Yellow Dwarf BCTV-PeYD. She discussed how the warm winter in 2021-2022 influenced the early spring flight of leafhoppers and how that was inconsistent with the current predictive model.

Avneesh Kumar presented his work with Kevin Dorn, USDA-ARS Sugar Beet Genetics Lab, Fort Collins, CO entitled “Mapping BCTV resistance gene in sugar beet crop wild relative Beta corolliflora.”  Sugar beet (Beta vulgaris ssp. vulgaris) is a biennial dicotyledonous plant and a member of the family Amaranthaceae. Sugar beet is one of the only two sugar producing crop. Beet curly top (BCTV) causes one of the major diseases in sugar beet. The virus also infects other important crops such as tomatoes, spinach, pepper, beans and hemp. A low to intermediate resistance is available in the commercial varieties and is difficult to maintain due to its quantitative nature. However, strong resistance was reported in the sugar beet crop wild relative Beta corolliflora. Our aim is to study the genetics of the BCTV resistance in B. corolliflora. We will use monosomic addition lines of B. corolliflora in sugar beet genetic background. We will phenotype MALs of all B. corolliflora chromosomes to determine the chromosomal source of resistance. Furthermore, we will perform random mutagenesis on resistant MALs and will determine the locus conferring resistance to BCTV in B. corolliflora.

Lauren Murphy, CDFA Beet Curly top Control Program, presented their yearly update. The Beet Curly Top Virus Control Program conducts intensive yearround surveys in California to determine where beet leafhopper (BLH) populations are developing. In 2022, the Program's surveys of traditional areas known for high curly top virus (CTV) incidence showed overall relatively low BLH levels, and therefore low CTV damage in susceptible commodity crops. However, the Program confirmed very high CTV damage in several tomato crops in non-traditional areas that do not normally experience CTV damage. The Program will be looking into whether the changing landscape in California may be having an effect on BLH migratory habits and population dynamics.

Carl Strausbaugh, USDA-ARS Kimberly, ID, in cooperation with Eric Wenninger, University of Idaho, presented their research by zoom on “Beet curly top virus strains in sugar beets, dry beans, and beet leafhoppers along with vector population dynamics in southern Idaho.”  At the request of a sugar beet industry stakeholder, beet leafhopper (BLH) populations in southern Idaho were tracked in four counties during the 2020 and 2021 growing seasons in desert areas and sugar beet and dry bean fields in southern Idaho.  Samples were collected on a weekly basis from mid-April through mid-September to assess all leafhoppers for population levels and the presence of Beet curly top virus (BCTV) strains.  Crop plants from monitored fields were also assessed for the presence of BCTV strains.  Once BLH populations in Elmore Co. began increasing in May, they were present in at least double-digit numbers through most of the summer at all sites both years.  However, the BLH numbers at desert sites in other areas were at or near zero.  In areas with low BLH desert populations, local weed populations appeared to be the primary source of BLH in crop fields.  Preliminary data suggest two haplotypes (based on cytochrome oxidase gene) dominate the BLH population.  Over the 22-week collection period, the horizontal card averaged 75% and 51% fewer BLH than the vertical card in 2020 and 2021, respectively.  In 2020, 42% of the BLH samples were positive for the BCTV coat protein and Worland was the dominant strain of BCTV.  The phytoplasma, morphotyping, and 2021 BCTV strain identifications are currently a work in progress.  Once all data are collected, the project will establish the BCTV strains for which host plant resistance is needed and the best time for when control of BLH is necessary.  

Rajtilak Majumdar, in cooperation with Paul J. Galewski, Imad Eujayl, Eric Vincill, Carl A. Strausbaugh, USDA-ARS, Kimberly, ID, presented their work on “Transcriptional regulation and cross-kingdom RNAi in sugar beet resistance against Beet curly top virus.”

Sugar beet is highly susceptible to Beet curly top virus (BCTV) which significantly reduces yield and sugar content in the semi-arid growing regions. Genetic resistance to BCTV is limited and primarily dependent upon seed treatment with neonicotinoids, the use of which are gradually being restricted. It is not fully understood how sugar beet plants confer resistance against BCTV. Through double haploid production and genetic selection, we have developed BCTV resistant breeding lines in Kimberly, ID. Using BCTV resistant (KDH13, KDH4-9) and susceptible (KDH19-17) lines, beet leafhopper meditated natural infection, mRNA/sRNA sequencing, and targeted metabolite analyses we demonstrate potential mechanisms of resistance against the virus. At early infection stages (within 6 days post inoculation), the differentially expressed micro RNAs (miRNAs) altered expression of their corresponding target genes such as pyruvate dehydrogenase (EL10Ac1g02046), serine/threonine protein phosphatase (EL10Ac1g01374), and leucine-rich repeats (LRR) receptor-like (EL10Ac7g17778), that were highly expressed in the leaves of resistant lines (vs. susceptible). Pathway enrichment analysis showed miRNAs predominantly targeted carbohydrate metabolism related genes. This corroborated well with altered levels of carbohydrates that were generally higher in the resistant lines both under green house and field conditions. We also identified BCTV derived small non-coding RNAs (sncRNAs) targeting critical sugar beet genes such as LRR (EL10Ac1g01206), and transmembrane emp24 domain containing (EL10Ac6g14074) and altered their expression. Sugar beet derived miRNAs targeted BCTV capsid protein genes and downregulated their expression which was more pronounced in the resistant lines. Higher C/N ratio in the leaves of resistant lines also indicate a metabolic shift towards C based primary metabolism as evident from the increased levels of related carbohydrates. The data presented here demonstrate the role of cross-kingdom RNAi in sugar beet resistance against BCTV at early stages of infection and identify potential candidate genes for future genetic manipulation to improve host plant resistance.

 

Gina Angelella, USDA-ARS Wapato, WA, presented her work on “Characterizing beet leafhopper subpopulations within the Columbia Basin.”  We used molecular markers to examine the role of host-plant association and geographical location in beet leafhopper population structure and sequenced 16s rDNA to characterize the microbiome of beet leafhoppers within the Columbia Basin. Beet leafhoppers were collected during 2020 from 20 locations within the Columbia Basin, WA, and from one location in Elmore Co., ID, from crop and non-crop plants. Crops included sugarbeet, potato, and coriander seed, and non-crop plants included flixweed/pinnate tansymustard, tumble mustard, Russian thistle, and kochia. We submitted DNA for genotyping-by-sequencing services after which sequence data were processed using the Stacks de novo pipeline to call and clean SNPs, generating a dataset contained sequence data from 231 individuals and 2070 loci. We calculated the fixation index (Fst), analyses of molecular variance, and ran a principal components analysis and STRUCTURE analysis. No population structure was evident among specimens grouped by host plant, nor by collection site within the Columbia Basin; however, there was some differentiation between Elmore Co., Idaho, and Columbia Basin specimens potentially indicating limited movement. Nineteen beet leafhoppers were sequenced for microbiome characterization, including specimens on tumble mustard, kochia, Russian thistle, and sugarbeet from Pasco and Moxee, WA, Elmore Co., ID, and a colony at the Wapato facility. We detected Candidatus Sulcia muelleri (obligate endosymbiont) and Wolbachia, as well as Rickettsia and Spiroplasma citri at low frequencies. We screened an additional 448 Columbia Basin specimens for Wolbachia and plant pathogens to test for patterns relative to host plant (carrot, carrot seed, coriander seed, lima bean, potato, sugarbeet seed) or geographical location. Wolbachia infection was not related to host plant or region, and the proportions of beet leafhoppers carrying BCTV did not vary by Wolbachia infection status.

 

Tiziana Oppedisano in cooperation with Silvia Rondon, Oregon State University, presented their work on “Beet leafhopper dynamics in the Lower Columbia Basin of Oregon and transmission efficacy of BCTV in hemp.”  Circulifer tenellus Baker (Hemiptera: Cicadellidae) is the only known vector of the beet leafhopper-transmitted virescence agent (BLTVA), that causes purple top disease in potatoes, and Beet Curly Top Virus (BCTV), an emergent disease in a relatively new crop like hemp in the lower Columbia Basin of Oregon.

Symptoms of BLTVA infection in potatoes include up-rolling of the leaves, swollen nodes, purplish discoloration, aerial tubers, and early plant decline. Severe BLTVA infestations can cause economic losses. Thus, since 2006, the Oregon State University Irrigated Agricultural Entomology Program has conducted a monitoring beet leafhopper program to help producers decide timing management decisions. Each year, from mid-April until September, 30-37 commercial potato fields were sampled in Umatilla and Morrow counties in eastern Oregon. Circulifer tenellus adults were monitored using yellow sticky cards deployed 1.5-3 m outside the field edges next to native weedy vegetation areas. In addition, daily temperatures were obtained from AgriMet weather stations closest to each sampled field. Using the multi-year dataset generated from the pest monitoring and the temperature data, we developed a phenology model based on the accumulated degree-days (DD). Total emergence percentage was modeled as a function of temperature to C. tenellus population growth in the field. According to our model, for our region, C. tenellus population emergence occurred gradually at 582, 1,440, and 2,823 DD, corresponding to 10, 50, and 90% total emergence, respectively. We hypothesized that besides temperature, other factors such as the availability of a preferred host such as sugar beet are likely to trigger C. tenellus to become active early in the season.

BCTV has previously been reported as one of the main constraints affecting hemp production in several US states, including Oregon. In hemp, symptoms of BCTV infections appear in yellowing and stunting, up-curled leaf, twisting, and flat stems. Thus far, little is known about hemp varieties’ susceptibility to the BCTV. In 2021, in a greenhouse experiment, we evaluated ‘Cherry Blossom’ and ‘Cherry Wine’ responses to BCTV transmitted by C. tenellus. BCTV-infected C. tenellus nymphs and adults were exposed to healthy hemp plants for a week. Preliminary data showed a higher transmission percentage using nymphs in ‘Cherry Blossom’, while the transmission rate was similar with both stages of C. tenellus in ‘Cherry Wine’. Currently, our program is testing different BCTV strains in transmission studies.

 

Jordan Withycombe in cooperation with Avneesh Kumar, Kevin Dorn, Punya Nachappa and Vamsi Nalam, Colorado State University, presented her talk on “Enhancing sugar beet breeding efforts through identifying the mechanisms and genes conferring curly top resistance.”  Curly top disease is caused by the beet curly top virus (BCTV) which is exclusively vectored by Circulifer tenellus, the beet leafhopper. Current management strategies for BCTV include the use of BCTV-resistant or tolerant varieties, but the underlying genetic mechanism is not known. It is critical to determine the mechanism of resistance and identify resistant gene(s) that can be implemented in breeding programs. The objectives of my project were: 1) classify the nature of curly top disease resistance in resistant (EL10) and susceptible (FC-709-2) sugar beet varieties using insect preference and performance assays and 2) characterize the transcriptional response to BCTV infection and BLH feeding in both varieties using RNA-Seqencing. There was no significant difference in adult survival and reproduction on resistant and susceptible varieties suggesting that plant resistance mechanism was not antibiosis. In preference assays, BCTV-infected leafhoppers showed preference to susceptible variety compared to resistant variety at all timepoints; however, non-infected leafhoppers did not show a feeding preference. Studies are underway to perform RNASeq experiments with a factorial experiment design: 2 varieties × 3 treatments (non-infected leafhoppers, BCTV-infected leafhoppers, control) × 3 timepoints (1, 7, 14 dpi) ×3 biological replicates). Total RNA will be subjected to stand specific RNA-Seq. The bioinformatic analysis will focus on identifying differences in overall gene expression between EL-10 and FC-709-2 and looking for unique plant response genes expressed by either variety. Overall, outcomes of this study help to identify more durable and broad-spectrum viral resistance in sugar beets.

 

Max Schmidtbauer in cooperation with the Punya Nachappa laboratory group, Colorado State University, presented his work “A little help from my friend: virus infection reduces susceptibility of beet leafhoppers to neonicotinoid insecticides.”  Sugar beets are grown across the western United States for their lucrative taproot and are an economically important crop generating 1.16 billion dollars in 2021. However, production is threatened by beet curly top virus (BCTV), a viral pathogen that severely reduces yield. The virus is exclusively transmitted by the beet leafhopper, Circulifer tenellus. Current management options for BCTV rely on neonicotinoid seed treatments and pyrethroid foliar sprays. However, there are reports of neonicotinoid resistance in numerous insect pests and this insecticide group may have harmful effects on non-target insects. Hence, the goal of this research is to examine susceptibility of beet leafhoppers to three different application rates (2x, 1x, 0.1x) of insecticides and determine their ability to lower virus transmission. We hypothesize that applying insecticide at a higher label rate will result in an increased mortality of beet leafhoppers, and therefore reduced virus transmission. At the 1x rate, neonicotinoids were more effective than pyrethroids, yielding 100% mortality of BCTV-infected and non-infected insects. However, at the 0.1x rate BCTV-infected leafhoppers had a higher survival rate than non-infected insects. This result was observed in only the neonicotinoid trials and not the pyrethroid trials. Although experiments are ongoing, confirming this potential insecticide resistance in BCTV-infected insects would be a key piece of information to aid in tracking the epidemiology of BCTV and make predictions about leafhopper populations. With this knowledge, farmers would be able to adjust their management strategies to achieve more sustainable and profitable sugar beet production practices.

 

Various participants presented field perspectives from different states.

Idaho – Carl, Eric, Raj – There was a slow late start to initial leafhopper flights because of the cool, wet spring. Some age-related resistance in sugarbeets is present and beans can grow out of symptoms.

• Thomas, Tiffany – Commercial sugarbeets have some tolerance. There was higher BCTV incidence in Idaho, which might be due to the mild winter, which could have promoted the growth of weed hosts

 

Colorado – Punya – BCTV symptoms have been found in early stage hemp in Southern Colorado (Alamosa area). Neonicotinoids were banned in Boulder County, so the rest of the state may follow. BCTV has been found in tomatoes, peppers, and sugarbeets.

 

New Mexico – Rebecca -  An unusually warm winter allowed the beet leafhopper to overwinter in weeds in pecans, which has not been noted before. Leafhopper were collected by sweep net in late December and early January, which has also never been found before.

 

California – Lauren, Zach – There was historically high BCTV only in southern valleys. They had low virus this year due to the malathion treatments and early dry weeds. In contrast more northern and eastern California, including the Sacramento Valley and northern San Joaquin Valley, had highly unusual high BCTV disease pressure. This might be influenced by cultural practices such as growing more tree crops and more fallow fields because of low water availability. Possibly the beet leafhoppers are living year round in the valleys and not migrating from the foothills.

 

Washington – Gina, Kylie – The trapping network is designed to collect around potatoes, but has included vegetables and seed crops. Last year there were around 40,000 leafhoppers collected. The peak in leafhoppers numbers was delayed until the end of June. For the leafhoppers tested, there was higher amounts of BCTV followed by BLTVA, followed by Spiroplasma citri.

 

Research questions and priorities

 

California would like to follow the migratory habits of the beet leafhopper, perhaps by testing for virus strains on the valley floor.

 

Kevin Dorn would like help with a public sugarbeet database the includes genotype and phenotype data. Wants others to add information.

 

What makes a good host for the beet leafhopper? What is the nature of non-host resistance, especially that found in weeds?

 

Barley is a non-host; does the virus replicate in the plant?

 

There is a Kochia panel at Colorado State University with more than 100 curated specimens. This could be helpful in determining beet leafhopper preferences.

 

The 2023 WERA 1007 meeting will be held in California, with Lauren Murphy hosting. Possible dates are July 10-11 or the first week of August.

Accomplishments

<p><strong>Project Objectives:</strong></p><br /> <ol><br /> <li><strong>Assess the current status of curly top and set priorities for integrated research on curly top disease.</strong></li><br /> </ol><br /> <ol start="2"><br /> <li><strong>Characterization of curtovirus strains including virus genetic diversity, new virus strains and virus in new hosts. </strong></li><br /> <li><strong>Organize research on the biology and ecology of the leafhopper, virus transmission, and the role of weed hosts in curly top in the western US.</strong></li><br /> </ol><br /> <ol><br /> <li><strong>Organize research to improve virus and vector management.</strong></li><br /> </ol><br /> <ol start="5"><br /> <li><strong>Provide a national platform for education on curly top disease, virus/insect/plant ecology and management, collaboration among scientists involved in these activities, and extension of research-based information for producers.</strong></li><br /> </ol><br /> <p><strong>&nbsp;</strong></p><br /> <p><strong>Objective 1:&nbsp; </strong>&nbsp;Accomplished through annual meeting presentations and goal setting. See above minutes.</p><br /> <p><strong>Objective 2:</strong>&nbsp; Worked toward this goal in individual research programs. See above minutes.</p><br /> <p><strong>Objective 3:</strong> Made progress toward the goal. See above minutes.</p><br /> <p><strong>Objective 4:</strong> Made progress toward goal. See above minutes.</p><br /> <p><strong>Objective 5:</strong>&nbsp; Collaborative curly top projects for 2021-22 season were carried out between Carl Strausbaugh and Rebecca Creamer and between Carl Strausbaugh and Punya Nachappa. Rebecca Creamer is currently conducting a cooperative project with Punya Nachappa.</p>

Publications

Impact Statements

1. Collections of leafhoppers and infected plants in the Columbia Basin (Washington and Oregon) showed the variety of weed hosts that were infected with curtovirus and other pathogens and the endosymbionts found within the leafhoppers. The work also demonstrated a differential reaction in transmission between two varieties of hemp. This could be important in selection of hemp varieties in locations with high leafhopper/curtovirus pressure.

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Report Information

Participants

Participants at Annual Meeting:
Creamer, Rebecca (creamer@nmsu.edu) - New Mexico State University, Entomology,
Plant Pathology and Weed Science
Carl Strausbaugh (carl.strausbaugh@ars.usda.gov) - USDA-ARS, Kimberly, ID
Tiffany McKay-Williams (tmckay@betaseed.com) - Betaseed Inc, Boise, ID
Oliver Neher (oneher@amalsugar.com) – Amalgamated Sugar, Boise, ID
Greg Dean (gdean@amalsugar.com) – Amalgamated Sugar, Boise, ID
Jake Hennessey (jhennessey@amalsugar.com) – Amalgamated Sugar, Boise, ID
Bill Wintermantel (bill.wintermantel@usda.gov) – USDA-ARS, Salinas, CA
Christian Nansen (chrnansen@ucdavis.edu) – University of California, Davis
Punya Nachappa (punya.nachappa@colostate.edu) Colorado State University, Agricultural
Biology
Thomas Koeps (Thomas.koeps@kws.com) KWS Seed, LLC, Twin Falls, ID
Zach Bagley (zach@tomatonet.org) California Tomato Research Institute
Kylie Swisher (kylie.swisher@ars.usda.gov) USDA-ARS, Wapato, WA
Gina Angelella (gina.angelella@usda.gov) USDA-ARS, Wapato, WA
Raj Majumdar (raj.majumdar@usda.gov) USDA-ARS Kimberly, ID
Batool Alkhatib (batool@nmsu.edu) New Mexico State University
Nina Dropcho (ndropcho@nmsu.edu) New Mexico State University
Kendra Tapia (kendra.tapia@cdfa.ca.gov) California Curly Top Control, CDFA, Fresno, CA
Heather Scheck (heather.scheck@cdfa.ca.gov) – California Department of Food and Agriculture, Sacramento, CA
Jordan Withycombe (Jordon.withycombe@colostate.edu) Colorado State University
Max Schmidtbauer (max.schmidtbauer@colostate.edu) Colorado State University

Brief Summary of Minutes

Summary of Meeting Minutes:

 

      Rebecca Creamer, WERA1007 Secretary, explained a bit about the group and its purpose. Introductions were made, and the agenda was discussed. 

      Kendra Tapia – BCTVCP-CDFA- meeting host presented a welcome and BCTV Control Program 2023 Update.

CDFA BCTVCP WERA Presentation Summary

• 2022 winter showed sporadic nymph activity and extensive die-off of summer host plant vegetation in November. Heavy rainfall in December facilitated germination of new vegetation growth on the western hillsides


• Early spring activity was limited due to rain and storm events. BLH averages were 0-1 per sweep set. Annual grasses took over most of the host plant vegetation, limiting the ideal conditions for BLH populations.


• By late spring, some Nymph activity started to appear, but overall BLH averages were in the 0-2 per sweep range. BCTV expanded their staff and started surveying more in the Sacramento Valley. Host plant vegetation observed was Filaree, Plantago, Peppergrass, and Mallow.


• The Program performed control operations on the last of May and First of June. 407 acres were controlled in Fresno and Kings Counties.


• Commodity damage has been low in the 0-2% range. The Program has seen a reduction in planted acreage this year due to flooding from the high amount of rainfall we got. Fields that showed above the threshold levels were found to have been near fallow fields or almond orchids that had been recently disked.


• This year has seen low incidences of BLH activity due to the high amount of rainfall we got. Annual grasses essentially seeded out host plant vegetation. Not a typical year, but every year is different.


• The program is expanding further across the state and updating our host plant guide and procedures. The Program continues to evaluate the changes in landscape and environment to see how it will affect BLH migratory patterns.

 

      Rebecca Creamer presented a Curly top overview with New Mexico update on the current disease status in New Mexico in chile and hemp. She discussed the virus strains in chile and hemp and host specificity of certain strains. Pepper curly top BCTV-PCT was found infecting pepper but not hemp. In 2022, both pepper and hemp were found to be infected with Pepper Yellow Dwarf BCTV-PeYD and BCTV-Wor. The warm winter in 2021-2022 influenced the early spring flight of leafhoppers and that was inconsistent with the current predictive model. Beet leafhoppers were shown to prefer CBD hemp and fiber hemp over pepper or grain hemp.

Batool Alkhatib presented Cytopathic effects of curly top virus on infected plants.

Plant virus infection causes significant impacts on crop productivity due to the diseases they cause and to economics and food security. Beet Curly top virus (BCTV) is a highly devastating pathogen affecting a wide range of plant species worldwide and is transmitted only by leafhoppers in the genus Circulifer. During the synthesis of the viral components in the host-infected cell, the cell undergoes characteristic biochemical and morphological changes; such morphological changes in cells caused by viral infection are called cytopathic effects (CPE). This study aimed to investigate the CPE induced by BCTV on various plant hosts, including (Tomato, Pepper, Sugarbeet, and Hemp), In such susceptible hosts, BCTV infection resulted in severe stunting, leaf curling, and yellowing, leading to reduced photosynthetic capacity and yield losses. Transmission electron microscopy images of ultrathin sections of infected leaves from these plants revealed that BCTV infection triggered distinct changes in the ultrastructure of some organelles, such as chloroplast, starch grains, vacuoles, and mitochondria along with uneven thickenings of the cell wall. Furthermore, this study showed variations in BCTV strains and their impact on different plant hosts; certain strains showed higher virulence, causing more severe symptoms and physiological disruptions compared to others, suggesting a complex interaction between viral factors and plant host-specific defenses. This is the first study shed light on the diverse ultrastructural impacts of BCTV infection on different plant species; such studies help in understanding the molecular mechanisms underlying the host-virus interactions, which in turn will aid in the development of effective control strategies to mitigate the detrimental impacts of BCTV on agriculture and safeguard global food security.

 

Christian Nansen and Hyoseok Lee presented Region-wide and real-time mapping of beet leafhopper migration from Coastal Foothills

Beet leafhoppers (Circulifer tenellus) (Hemiptera: Cicadellidae) are the primary vectors of beet curly top virus (BCTV), a major plant-pathogenic virus in tomato and other crops. In California, beet leafhoppers are known to overwinter in coastal foothills and migrate into the Central Valley during spring. We experimentally manipulated drought regimes of individual plants and acquired plant reflectance profiles to generate standardized indices of greenness (enhanced vegetation index, EVI). Plants were experimentally infested with beet leafhoppers, and we found a significantly negative correlation between EVI and flight propensity for two plant species that serve as common hosts. In related field studies, sticky card trapping at three field locations during two tomato growing seasons showed a significant negative correlation between satellite image-derived EVI and spring migration timing of beet leafhoppers. A predictive model was developed and used to examine annual trends in spring migration timing and relationships with incidence of BCTV symptoms surveyed in the Central Valley. Spring migration timing was negatively correlated with regional incidence of BCTV symptoms. The proposed spring migration model accurately predicted major BCTV outbreaks in 2013 and 2021, years that were characterized by unusually early spring migration from coastal foothills. The spring migration model is freely available as a web-based tool: https://hyslee.users.earthengine.app/view/beet-leafhopper-migration-in-ca

Kylie Swisher Grimm, USDA-ARS Wapato, WA, presented her work on “Beet leafhopper testing in the Columbia Basin of Washington.” 

 

In the Columbia Basin of Washington State, beet leafhopper-transmitted pathogens including Beet curly top virus, Beet leafhopper transmitted virescence agent phytoplasma, and Spiroplasma citri cause serious damage to vegetable and seed crops each year. Since 2021, researchers with the USDA Agricultural Research service and Washington State University have sought to obtain near real-time pathogen prevalence data in beet leafhopper specimens captured near potato and other vegetable or seed fields across the region. Through improving extraction and diagnostic protocols, researchers were able to acquire pathogen data on a weekly basis, providing this data to growers through the Washington State University Potato Decision Aid System online tool. This data will allow important seasonal or regional trends to be identified. Ultimately, this data could be incorporated each year into grower IPM programs, improving beet leafhopper management by either decreasing the cost and hazard of unnecessary insecticide sprays or increasing crop yield and quality by preventing disease outbreaks through well-time insecticide applications. 

Carl Strausbaugh, USDA-ARS Kimberly, ID, in cooperation with Eric Wenninger, University of Idaho, L. Jackson, and E. Vincill presented their research by zoom on “Beet curly top viruses and phytoplasmas in sugar beets, dry beans, and beet leafhoppers along with vector population dynamics in southern Idaho.” 

Beet curly top in sugar beet and common bean is a major yield limiting disease which is caused by Beet curly top virus (BCTV) and is vectored by the beet leafhopper (BLH; Circulifer tenellus).  BLH populations in southern Idaho were tracked during the 2020 and 2021 growing seasons in desert areas and sugar beet and common bean fields with yellow sticky cards to assess BLH population levels and identify the curly top virus species/strains and phytoplasmas present.  Plants from monitored crop fields were also assessed for the same pathogens.  Once BLH populations in Elmore Co. began increasing in May, they were present in double-digit numbers per card through the summer at all sites both years.  However, the BLH numbers at other desert sites were at or near zero; local weed populations and not desert areas appeared to be the primary source of BLH in crop fields.  Based on cytochrome oxidase gene, two haplotypes dominated the BLH population both years.  Both years, BCTV strains Worland (Wor) and Colorado (CO) were the primary strains in BLH and plant samples.  The CA/Logan, Pepper curly top (PeCT), and Severe strains of BCTV were also detected in BLH along with Spinach curly top Arizona virus (SpCTAV).  Phytoplasmas were detected in 1% of BLH samples both years.  Phytoplasmas, SpCTAV, and PeCT were not detected in plant samples.  This project established the curly top species/strains for which host plant resistance is needed as well as the time and areas when crops are at highest risk for infection.

 

Max Schmidtbauer in cooperation with Laine Hackenberg, Colorado State University, presented his work “Occurrence of beet curly top virus in hemp in Colorado and insights into the potential seed transmission. 

 

Beet curly top virus (BCTV) is vectored solely by the beet leafhopper (Circulifer tenellus) and is the most serious disease affecting sugar beet production in the United States. Hemp is characterized as Cannabis sativa L. which expresses THC at or under a federally set limit of 0.3% and has become a crop of interest in many states. While BCTV has been studied in sugar beet for over one hundred years, in 2015, BCTV was first reported to infect hemp in western Colorado. Starting in 2021, Laine Hackenberg conducted a virome survey of hemp in different counties in Colorado. Using next generation sequencing, she hopes to provide understanding around the occurrence and distribution of BCTV and other viruses of interest in hemp in Colorado. Beet curly top virus is also not known to be seed transmitted in sugar beet, tomatoes, and a handful of other crops. With hemp emerging a new host of BCTV, it is important to also determine if seed transmission of this virus is possible in hemp. Through a variety of serological assays, we hope to give answers to our growers who rely on a secure, pathogen free hemp seed stock for their livelihoods.

 

Jordan Withycombe in coordination with Jinlong Han, Punya Nachappa, Vamsi Nalam, presented her talk on “Sweet Surprise: The search for genes conferring curly top resistance in sugar beet.” 

 

Curly top disease is caused by the beet curly top virus (BCTV) which is exclusively vectored by Circulifer tenellus, the beet leafhopper. Current management strategies for BCTV include the use of BCTV-resistant or tolerant varieties, but the underlying genetic mechanism is unknown. The objectives of my project were: 1) classify the nature of curly top disease resistance in resistant (EL10) and susceptible (FC-709-2) sugar beet varieties using insect preference and performance assays and 2) characterize the transcriptional response to BCTV infection and BLH feeding in both varieties using RNA-Sequencing. There was no significant difference in adult survival and reproduction on either variety suggesting that plant resistance mechanism was not antibiosis. In preference assays, BCTV-infected leafhoppers showed preference to feed on the susceptible variety compared to resistant variety; however, non-infected leafhoppers did not show a preference. RNA-seq experiments were conducted using a factorial experiment design: 2 varieties × 3 treatments (non-infected leafhoppers, BCTV-infected leafhoppers, control) × 3 timepoints (1, 7, 14 dpi) ×3 biological replicates). Following sequencing, the bioinformatic analysis was conducted using CLC genomics workbench where differentially expressed transcripts (DETs) were identified for each variety and timepoint. Final analysis is still in progress, but genes associated with plant hormonal pathways (ABA and JA pathways) and protein synthesis and ubiquitination are of interest.

 

 

Rajtilak Majumdar presented his work in cooperation with Paul Galewski, Matthew Lebar, Carl Strausbaugh, Rakesh Minocha, Stephanie Long, Imad Eujayl, Christopher Rogers on “Untargeted metabolome and targeted analyses of C and N metabolites, and degradome reveal distinct mechanisms associated with resistance and susceptibility during sugar beet interactions with Beet curly top virus”

  Sugar beet is highly susceptible to Beet curly top virus (BCTV) which significantly reduces yield and sugar production in the semi-arid growing regions worldwide. Sources of genetic resistance to BCTV is highly limited and primarily dependent upon seed treatment with neonicotinoids, the use of which is gradually being restricted. Through double haploid production and genetic selection, we have developed BCTV resistant sugar beet breeding lines. Using BCTV resistant (R) [KDH13 and KDH4-9] and susceptible (S) [KDH19-17] lines, beet leafhopper meditated natural infection, and combined omics approaches we demonstrate potential mechanisms of resistance against the virus. Untargeted metabolome analysis revealed higher accumulation of specific isoflavonoid O-glycosides, flavonoid 8-C glycosides, triterpenoid, iridoid-O-glycosides in the leaves of the ‘R’ lines (vs. ‘S’). In general, majority of the amino acids were higher in the ‘S’ line except for GABA that was significantly higher in the ‘R’ lines with infection. The ‘S’ line accumulated higher amounts of polyamines (PAs) especially Spm at early [2- and 6- days post inoculation (dpi)] infection stages (vs. ‘R’ lines) with no visible disease symptoms. Higher PA and amino acid (AA) contents in the leaves of ‘S’ line corroborated well with the higher expression of genes involved in the biosynthesis of ornithine (Orn), arginine (Arg), and PAs during early stages of infection. The trend in PAs and AAs stated earlier under greenhouse conditions was similar in plants exhibiting disease symptoms under field conditions, and ‘R’ lines (vs. ‘S’) maintained higher leaf sucrose, glucose + galactose, fructose contents, and C/N ratio. The overall findings suggest a combination of transcriptional regulation and production of putative antiviral metabolites might contribute to BCTV resistance. In addition, genome divergence among BCTV strains differentially affects the production of small non-coding RNAs (sncRNAs) which may potentially affect pathogenicity and disease symptom development.

 

 

Various participants presented field perspectives from different states.

Idaho – There was earlier infection and hoppers were found even during heat waves. There has been a decrease in curly top in Idaho, with only very low levels of disease. Used to be highest in Treasure Valley. Neonicotinoids have nearly eliminated the disease. Now only find single infected plants. Working toward breeding for frost tolerant high sugar varieties.

 

Montana and Wyoming had very low levels of curly top.

 

Colorado – Have found curly top on hemp and on leafhoppers on sticky traps.

 

California -  There were low levels of insect-transmitted pathogens this year due to the high rainfall. Sacramento Valley had curly top in 2021 and 2022 and the presence of spinach curly top. Those years were warm and dry with increased fallowing of fields due to water conservation.

 

Washington – The trapping network is designed to collect around potatoes, but has resulted in very good prediction for curly top.

 

Research questions and priorities

 

California would like to follow the migratory habits of the beet leafhopper, perhaps by testing for virus strains on the valley floor.

 

How long after neonicotinoids are banned before the leafhoppers and curly top take explode?

 

Can we bridge the gap between planting and when disease kicks in with other insecticides?

 

How beneficial is a leafhopper trapping system program for control of curly top?

 

What are alternative pesticides that could help with curly top?

 Can new technologies such as CRISPR or RNAi help with BCTV?

 

The 2024 WERA 1007 meeting will be held in Salinas, CA, with Bill Wintermantel hosting. Possible dates are July 22-23 or August. 6-7.

 

Project Objectives:

1. Assess the current status of curly top and set priorities for integrated research on curly top disease.

2. Characterization of curtovirus strains including virus genetic diversity, new virus strains and virus in new hosts.


3. Organize research on the biology and ecology of the leafhopper, virus transmission, and the role of weed hosts in curly top in the western US.

1. Organize research to improve virus and vector management.

5. Provide a national platform for education on curly top disease, virus/insect/plant ecology and management, collaboration among scientists involved in these activities, and extension of research-based information for producers.

 

Objective 1:   Accomplished through annual meeting presentations and goal setting. See above minutes.

Objective 2:  Worked toward this goal in individual research programs. See above minutes.

Objective 3: Made progress toward the goal. See above minutes.

Objective 4: Made progress toward goal. See above minutes.

Objective 5:  Collaborative curly top projects for 2021-22 season were carried out between Carl Strausbaugh and Kylie Swisher Grimm and between Rebecca Creamer and Punya Nachappa. 

 

 

 

Impact Statement

 

Curly top is an economically important disease in many states in the western U.S. Members of the WERA1007 group increased the knowledge of the virus biology, its transmission, and the management of the disease.  The range of virus strains was expanded in California, Colorado, Washington, and New Mexico. The resistance to curly top in sugarbeets was assessed, aspects of the curly top virus transmission were characterized, and the use of foliar insecticides for vector control was tested. These findings should help improve the management of curly top in sugar beet and other affected crops in the western U.S.

Accomplishments

Publications

<p><strong>Publications</strong></p><br /> <p>The group did not publish a report together.&nbsp; The following curly top related publications were published during the last year:</p><br /> <p>&nbsp;</p><br /> <p>Strausbaugh, C.A., Majumdar, R., Wenninger, E.J. 2023. Foliar insecticides for the control of curly top in Idaho sugar beet, 2022. Plant Disease Management Reports. 17. Article ST004.</p><br /> <p>&nbsp;</p><br /> <p>Strausbaugh, C.A., Eric, W., Jackson, L.K., Vincill, E.D. 2023. Beet leafhopper and BCTV strain survey 2022 progress report. The Sugarbeet. p.50-52.</p><br /> <p>&nbsp;</p><br /> <p>Gorman, C.J., Crowder, D.W., Swisher Grimm, K.D. 2023. A high-throughput plate method for nucleic acid extraction from beet leafhopper (Hemiptera: Cicadellidae) and potato psyllid (Hemiptera: Triozidae) for pathogen detection. J. Econ. Entomol. Doi:10.1093/jee/toad153</p><br /> <p>&nbsp;</p><br /> <p>Swisher Grimm, K.D., Gorman, C. Crosslin, J. 2023. New Assays for rapid detection of beet leafhopper associated plant pathogens, Candidatus <em>Phytoplasma</em> <em>trifolii</em>, <em>Beet curly top virus</em>, and <em>Spiroplasma citri</em>. Plant Disease doi: 10.1094/PDIS-04-23-0769-RE</p><br /> <p>&nbsp;</p><br /> <p>Creamer, R., Simpson, A., Rheay, H.T., Brewer, C.E. 2023. Interactions fo beet leafhopper (Hemiptera:Cicadellidae) vector of beet curly top virus and hemp in New Mexico. Environmental Entomology&nbsp; doi.org/10.1093/ee/nvad069</p>

Impact Statements

1. Curly top is an economically important disease in many states in the western U.S. Members of the WERA1007 group increased the knowledge of the virus biology, its transmission, and the management of the disease. The range of virus strains was expanded in California, Colorado, Washington, and New Mexico. The resistance to curly top in sugarbeets was assessed, aspects of the curly top virus transmission were characterized, and the use of foliar insecticides for vector control was tested. These findings should help improve the management of curly top in sugar beet and other affected crops in the western U.S.

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