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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Research Project #423228

Research Project: Biology, Epidemiology and Management of Vector-Borne Viruses of Sugarbeet and Vegetable Crops

Location: Crop Improvement and Protection Research

2015 Annual Report

1a. Objectives (from AD-416):
Objective 1: Identify specific genes associated with Beet necrotic yellow vein virus infection of sugarbeet that contribute to development of rhizomania disease and the ability of the virus to overcome resistance for use as potential targets for induced resistance. This will involve comparisons with other soil-borne pathogens using in-house funds. Completion within 5 years. Objective 2: Determine environmental and epidemiological factors contributing to the ability of sugarbeet and vegetable viruses to emerge and establish over competing viruses, to provide effective disease management recommendations and prolong the durability of resistance sources. Specifically: 2.A. Determine the effect of variation among Polymyxa betae isolates on prevalence and dominance of soil-borne viruses affecting sugarbeet, including evaluation of virus competitiveness through collaborative studies involving this project using both in-house funds and those of a local collaborator in NP308. Completion within 5 years. 2.B. Assess accumulation of CYSDV in different host plants in relation to transmission and in development of host resistance using both in-house funds and collaboration with ARS Salinas vegetable breeding program (NP301). Completion within 5 years. 2.C. Identification of factors influencing emergence and dominance of existing and new curtoviruses in North America through analysis of competitive virus accumulation in host plants. Research will involve in-house funds, with completion within 3 years. 2.D. Elucidate biological and environmental factors influencing mealybug transmission of grapevine leafroll-associated viruses in order to develop and test options for vector monitoring and management. Research will involve in-house funds with completion within 5 years. Objective 3: Determine environmental and cultural factors contributing to the ability of viruses to induce disease to facilitate breeding efforts for resistance to soil-borne and insect-transmitted viruses affecting lettuce. Completion of both subobjectives within 5 years using both in-house funds and collaboration with Salinas vegetable project (NP301). 3.A. Develop methods for greenhouse-based evaluation of lettuce for resistance to soilborne tombusviruses through identification of environmental factors influencing disease development, and application of this knowledge to germplasm evaluation using controlled environments. 3.B. Identify sources of tospovirus resistance through evaluation of lettuce and Lactuca germplasm using mechanical transmission and viruliferous thrips under greenhouse conditions, for further development by breeders.

1b. Approach (from AD-416):
Objective 1: Some defense genes will be common to general sugarbeet or plant defense against pathogens. Determine similarities and differences among pathogens for gene expression between infected and pathogen free host plants based on results of studies currently concluding. Results will be compared with others including BNYVV and other pathogens through parallel studies. Objective 2: 2.A. Isolates of the plasmodiophorid vector of BNYVV, Polymyxa betae, differ in their ability to transmit BNYVV to sugarbeet and this is associated with increased presence of resistance-breaking forms of BNYVV in sugarbeet production. Single spore isolates of P. betae will be tested for ability to transmit BNYVV to examine transmission efficiency and effect of vector isolate on virus competitiveness with virus titer determined by ELISA or qRT-PCR. 2.B. Resistance from the exotic melon (Cucumis melo) accession PI 313970 can enhance resistance to CYSDV in cultivated melon, and provide high levels of resistance when combined with resistance source TGR-1551. Exotic melon accessions will be evaluated in replicated field plantings and studies will examine transmission efficiency of CYSDV from resistant and susceptible melons in comparison with virus concentration using either qRT-PCR or ELISA. 2.C. Individual curtoviruses accumulate to higher or lower titers during single and mixed infections, and this varies by host plant, and this influences virus dominance in the field. Curtoviruses will be transmitted by beet leafhoppers from single and mixed infections and qPCR for virus titer determination. If needed Agro-based delivery of virus isolates to specific hosts, or leafhopper membrane feeding studies could be used for virus delivery. 2.D. The proposed studies will elucidate grapevine leafroll transmission by two mealybug species and explore options for monitoring and management of mealybugs. Greenhouse studies involving single-virus isolates and each mealybug species will be conducted to determine efficiency for transmission of grapevine leafroll associated viruses isolated from California vineyards using viruliferous mealybugs. RT-PCR or ELISA will be used to detect virus. Objective 3: 3.A. Long-day or high temperature treatment will induce development of tombusvirus symptoms on susceptible lettuce and can be used for selecting resistant and susceptible varieties. Growth chamber experiments will be used to determine optimal environmental conditions (light, temp, soil moisture etc.) for tombusvirus infection of lettuce using mechanical transmission experiments. Chamber and soil moisture and nutrition conditions can be modified as needed. 3.B. Resistance to Impatiens necrotic spot virus (INSV) and Tomato spotted wilt virus (TSWV)exists in wild or cultivated Lactuca germplasm and can be identified through greenhouse evaluation. Transmission of INSV and TSWV to Lactuca germplasm sources will be conducted using thrips vectors in the greenhouse. Virus detection will be performed using standard ELISA. If necessary, virus can be mechanically transmitted directly to lettuce from select hosts.

3. Progress Report:
The Salinas, California, lab is recognized internationally as a leader in the study of insect-transmitted and soil-borne viruses affecting sugar beet and vegetable production, has characterized most of viruses in the genus Crinivirus, developed detection methods, and is actively working toward understanding the interacting epidemiological factors that drive emergence and establishment of these viruses. The lab works with breeding programs to improve and enhance the availability and performance of resistant varieties, and uses a wide range of applied, molecular and technological approaches to address emergence and epidemiology of sugar beet and vegetable viruses. Recently completed research examined whitefly gene expression differences in relation to virus infection in efforts to determine genes involved in transmission and to identify new strategies for whitefly control. Further completed studies conducted through this project identified protein changes in sugar beet associated with Beet necrotic yellow vein virus (BNYVV) infection and rhizomania disease, indicating specific biological pathways altered during infection of the plant, as well as a second study examining differences in protein expression between susceptible as well as resistant sugar beet. The projects involved a collaboration between ARS labs in Salinas, California, and Fort Collins, Colorado. Follow-up studies may lead to improved knowledge of how BNYVV causes disease, and to new approaches for control of rhizomania disease of sugarbeet. Separate research is examining efficiency of BNYVV acquisition by different isolates of Polymyxa betae, the soil-borne organism that transmits the virus; and comparing transmissibility of the virus by different P. betae isolates. Strategies were developed to efficiently evaluate lettuce and its wild relatives for resistance to two tospoviruses, Tomato spotted wilt virus and Impatiens necrotic spot virus. These viruses are an emerging problem for lettuce production in the western U.S., as well as many other parts of the world. Field evaluations are complicated by inconsistent disease incidence related to prevalence of their insect vector, thrips. Therefore, we successfully developed methods for greenhouse evaluation using a combination of thrips transmission and manual inoculation of virus to screen large collections of lettuce breeding material for infection and resistance to these viruses. The research will benefit our ongoing collaboration with the lettuce breeding program at ARS in Salinas as well as industry stakeholders. New variants of Beet curly top virus (BCTV) have been emerging and replacing traditional strains of the virus in several locations and crops in California’s San Joaquin Valley since 2013, and similar variants have been identified in Idaho and other areas of the Mountain West. The ARS Virology Lab in Salinas is examining competitiveness of these new variants in sugar beet and tomato to determine their potential for long-term persistence in the field and the importance of using these variants in evaluations for host plant resistance in sugar beet and disease management in tomato.

4. Accomplishments
1. Identification of Squash vein yellowing virus infecting cucurbits in the Imperial Valley of California. During the fall of 2014, ARS researchers in virology and vegetable breeding programs in Salinas, California, and collaborators at the University of California, identified the whitefly-transmitted ipomovirus, Squash vein yellowing virus (SqVYV) infecting pumpkin, squash, and cantaloupe in Imperial Valley, California. The virus was confirmed using SqVYV-specific molecular detection focused on two regions of the virus genome and susbsequent DNA sequence analysis. Follow-up studies confirmed the virus is still present in 2015 cucurbit crops, including watermelon, in which the virus can cause vine collapse. Continuing studies are evaluating whether the virus can overwinter in non-cucurbit weeds or other crops, potential impact on cucurbit production in the region, and to develop disease management strategies.

2. Methods to evaluate lettuce and Lactuca germplasm for resistance to Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV). TSWV and INSV are emerging as serious economic threats to production of lettuce (Lactuca sativa) in California and throughout the world; however, only limited sources of resistance have been identified. Methods were developed by the ARS researchers at the Virology Lab in Salinas, California, to evaluate lettuce and other Lactuca germplasm sources for resistance to these viruses under greenhouse conditions where virus transmission can be regulated more closely than in fields. These methods are being used to identify novel sources of resistance through collaboration between this project and the vegetable breeding program at ARS in Salinas. Results will benefit the lettuce industry in the U.S. and throughout the world through development of evaluation methods and identification of new sources of genetic resistance to these viruses.

3. Sugarbeet proteome differences characterized between resistant and susceptible sugar beet in response to infection by Beet necrotic yellow vein virus (BNYVV). Rhizomania, caused by BNYVV, severely impacts sugarbeet (Beta vulgaris) production throughout the world. Sugarbeet varieties resistant to ‘traditional’ strains of BNYVV are susceptible to recently emerged resistance-breaking strains of the virus. ARS researchers in Salinas, California, and Fort Collins, Colorado, with collaboration from Colorado State University, identified proteins associated with infection of resistant and susceptible sugarbeet by ‘traditional’ and resistance-breaking strains of BNYVV using mass spectrometry. They identified pathways, as evidenced by changes in protein expression, that may be altered during infection and resistance. These proteins can be exploited to develop novel and environmentally friendly disease control strategies for management of this very serious threat to sugarbeet production.

4. Resistance of melon to Cucurbit yellow stunting disorder virus (CYSDV) and whiteflies. CYSDV impacts production of melon and other cucurbit crops in the southwestern U.S., Florida and Texas. ARS scientists in Salinas, California, in collaboration with University of California, Division of Agriculture and Natural Resources (ANR), Holtville, California, characterized epidemiology of the virus in the Southwest and identified new sources of resistance in melon. Continuing studies are examining the impact of resistant melon on the ability of CYSDV to move to additional crop plants by examining both virus titer in resistant and susceptible melon and how this relates to transmission. Results will lead to development of improved virus resistance and enhance management practices through more effective pest management incorporating enhanced resistance to CYSDV.

5. Transcriptome analysis of whitefly species in response to virus infection. Semi-persistent whitefly-transmitted viruses significantly decrease agricultural productivity throughout the world through reduced yields and plant longevity, yet very little information exists on the specific interactions between virus and insect that determine whether a virus can be transmitted by a whitefly or how the insect is influenced by the presence of the virus in a host plant. ARS researchers at virology program in Salinas, California, and researchers at the Boyce Thompson Institute in Ithaca, New York, compared differences in whitefly gene expression between whiteflies fed on healthy plants and plants infected with the semi-persistent virus, Tomato chlorosis virus (ToCV). Results identified several proteins and potential pathways that are altered in whiteflies as a result of feeding on ToCV-infected tomato plants. Follow-up studies will focus on further evaluation of the involvement of key proteins and pathways in transmission of ToCV and other semi-persistent whitefly-transmitted viruses. This will lead to development of targeted approaches for control semi-persistent plant viruses and will be used in coordination with studies on the whitefly genome to develop in targeted strategies for control of both virus and vector.

6. Sequenced genome of Bemisia tabaci MEAM1. Whiteflies and whitefly-transmitted viruses result in significantly decreased agricultural productivity throughout the world through reduced yields and plant longevity. The ARS scientists at the virology program in Salinas, California, in collaboration with ARS scientists in Charleston, South Carolina, and the Boyce Thompson Institute in Ithaca, New York, sequenced the genome of the whitefly, Bemisia tabaci MEAM1, and are currently annotating the genome. These studies will lead to identification of specific genes and genetic pathways activated in common during feeding of whiteflies on plants infected with different types of plant viruses. This will lead to development of targeted approaches for control of the whitefly vector through plant biotechnology and other targeted strategies.

Review Publications
Lapidot, M., Legg, J.P., Wintermantel, W.M., Polston, J.E. 2014. Management of whitefly-transmitted viruses in open-field production systems. Advances in Virus Research. 90:147-206.
Van Der Vlugt, R.A., Verbeek, M., Dullemans, A.M., Wintermantel, W.M., Cuellar, W.J., Fox, A., Thompson, J.R. 2015. Torradoviruses. Annual Review of Phytopathology. doi: 10.1146/annurev-phyto-080614-120021.
Batuman, O., Natwick, E.T., Wintermantel, W.M., Tian, T., Mccreight, J.D., Hladky, L.L., Gilbertson, R.L. 2015. First report of an ipomovirus infecting cucurbits in the Imperial Valley of California. Plant Disease. doi: 10.1094/PDIS-12-14-1248-PDN.
Wintermantel, W.M., Gilbertson, R.L., Mccreight, J.D., Natwick, E.T. 2015. Host-specific relationship between virus titer and whitefly transmission of Cucurbit yellow stunting disorder virus. Plant Disease. doi: 10.1094/PDIS-11-14-1119-RE.
Webb, K.M., Wintermantel, W.M., Kaur, N., Prenni, J., Broccardo, C., Wolfe, L., Hladky, L.L. 2015. Differential abundance of proteins in response to Beet necrotic yellow vein virus during compatible and incompatible interactions in sugar beet containing Rz1 or Rz2. Physiological and Molecular Plant Pathology. 91:96-105.