Duration: 10/01/2011 to 09/30/2016

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Curtoviruses are the most widespread geminiviruses in the United States. The viruses cause economic damage to a wide variety of crops including tomato, pepper, bean, sugarbeet, and leafy greens in the western U.S. Transmitted by the beet leafhopper Circulifer (=Neoalituras) tenellus, the viruses infect a broad host range from many plant families and the leafhopper vector also feeds and breeds on an extensive range of plant hosts. Curly top epidemiology in the western U.S. is dependent on area, climate, plant diversity and distribution, and cropping cycles. Generally, the beet leafhoppers overwinters on weed hosts, acquires virus from the weeds, and migrates into agricultural areas to feed on (and infect) crops and weeds. In some areas, leafhoppers migrate back to the overwintering areas in the fall.

Curtoviruses are monopartite geminiviruses and the type member is Beet curly top virus, BCTV. Recent work has shown that while BCTV is rarely identified in nature, Beet mild curly top virus BMCTV, Beet severe curly top virus BSCTV, Pepper curly top virus PeCTV, Spinach curly top virus SpCTV, Pepper yellow dwarf virus PeYDV and several new recombinant curtoviruses, have been reported in the western U.S.

Due to the ability of the virus to infect a large diversity of weeds and the ability of its insect vector to survive on a similarly large and diverse group of weeds, as well as migrate considerable distances, curtoviruses are endemic in the western U.S. Management of this viral pathogen and its leafhopper vector has proven difficult. California has long used a pesticide program to control the leafhopper using organophosphate sprays to uncultivated foothill breeding areas, although that program is now somewhat controversial. Plant resistance has been or is being developed for impacted crops. Cultural control has relied primarily on overseeding the crop or removing infected plants. Biocontrol, including releasing imported egg parasitoids to control the leafhopper vector was evaluated in California. Predictive models of disease have been developed for specific areas, but do not eliminate the disease. A sustainable management program is needed for this difficult pest/pathogen combination. Since leafhoppers migrate across state (and country) lines, management requires a coordinated effort between the different affected areas. Any approach to management requires an understanding of the genetic variability of the pathogen and vector among the different crop hosts of curtoviruses to be successful. Knowledge of the viral distribution within the region in wild and cultivated host plants, and the proximity of these virus reservoirs to commercial production fields is essential to reduce viral disease incidence. Only when many individuals work together will significant progress in management of this viral disease be possible.

We propose the continuation of the coordinating committee to address the problem. This committee will continue to meet to discuss, assess, and prioritize required research into curtovirus genetics, vector biology and genetics, weed ecology, and disease management. The committee will coordinate action plans to determine who will accomplish which aspects of the research, including who will work together to seek funding for the highest priority research. The group will also coordinate research to provide preliminary information needed to secure grant funding.

Objectives

Procedures and Activities

1. Individuals that are working on different aspects of curly top in the western US come together annually to improve communication among different disciplines. Those that have met with the group in the past include virologists, weed scientists, entomologists, plant breeders, and extension scientists, from New Mexico, Arizona, California, Colorado, Idaho, and Washington. The group has been approximately 25% each AES researchers, CES scientists, USDA scientists, and growers/industry representatives. Regional stakeholders with a commitment to the working group and its research include the New Mexico Chile Commission, the California Beet Sugar Association, and the Curly Top Eradication Board. The coordinating committee will meet yearly to discuss the status of curly top in the western US and present the latest developments in curly top research. At the annual meetings, the group will also discuss gaps in the knowledge of the disease and set priorities for research.

2. The ability to manage a virus disease requires an understanding of which virus is causing the disease. Committee members have demonstrated that viral genetic diversity is present in a variety of plant hosts and that new curtoviruses appear regularly. Within cooperating western states, there are efforts underway to study the virus incidence and diversity. These reports show that genetic diversity within curtoviruses is very high and will require a concerted effort to identify the tremendous virus diversity throughout the western US. The coordinating committee will share information on viral genetic diversity and encourage attempts to gain funding to study virus genetic diversity throughout the region by sequencing the genome of curtovirus isolates collected from different crops, weeds, and states.

While much research has been done to determine the leafhopper host range, the biology and ecology of the leafhopper in specific locations differs with cropping patterns and weed populations. Research to assess how the leafhoppers are overwintering has been done for some states, but not others and similarly, leafhopper flight patterns have been studied in some areas and not others. These research questions need to be expanded to additional areas in the western US.

Preliminary information suggests that beet leafhopper populations from different states vary genetically according to analysis of the mitochondrial DNA. The coordinating committee will encourage leafhopper collections from diverse populations to assess the vector leafhopper genetic variability. Leafhopper populations from the different breeding areas may be geographically isolated or interbreeding populations. If they are reproductively isolated, then there may be important differences in adaptation to local host plants, host range and preferences, and virus strain-vector specificity. If they are interbreeding populations which exhibit a similar phenotype, then it may be possible to devise broadly based disease control strategies.

There are many reports on the weeds hosts of BCTV and its leafhopper vector. However many of these reports are historical, and the weed populations have changed significantly in the last 50 to 80 years since the reports were published. Virus incidence in weeds has been reported for California and New Mexico. Similarly overwintering and key weed hosts have been studied in the two states. The group will encourage combining data for the leafhoppers and viruses into GIS mapping studies for each primary vector breeding area.

3. Curly top has proved very difficult to control. Coordinating committee members have studied a variety of methods to manage the disease including biocontrol of the leafhopper vector, impact of insecticide sprays, use of anti-transpirants to deter leafhopper feeding, effectiveness of trap crops, identification of plant resistance to virus and leafhoppers, engineered resistance, and predictive modeling to determine the likelihood of curly top in the next growing season and timing of leafhopper flights. The committee will continue to coordinate management tests in more than one location. The group will continue to help distribute management tools and products, such as resistant varieties and the predictive model. In addition, we anticipate that information about the genetics of the virus and vector may lead to novel management strategies applicable to many locations.

Expected Outcomes and Impacts

Projected Participation

View Appendix E: Participation

Educational Plan

All participants will be encouraged to disseminate information discussed at the meetings through grower and commodity board meetings as well as field days, pesticide applicator training, press releases, and extension and grower publications. Growers, crop consultants, processors, and extension personnel members of the group can help disseminate the information to their constituents and clientele. Transcripts of all meetings will be made available to all interested individuals upon request. Since the clientele has a large Hispanic base in New Mexico, Arizona, and Texas, transcripts will also be translated into Spanish. To address the needs of smaller growers such as Native Americans or organic producers, relevant information will be distributed to representatives of these groups, who will also be encouraged to participate more actively in the coordinating committee.

Organization/Governance

Dr. Rebecca Creamer will serve as the group coordinator, keeping the email listing of participants, writing reports, and maintaining all pertinent documentation. Local arrangements chairs for annual meetings will be rotated among participants. Major decisions will be made by group consensus.

Literature Cited

Attachments

Land Grant Participating States/Institutions

AZ, ID, NM, UT, WA

Non Land Grant Participating States/Institutions

The Amalgamated Sugar Company LLC, USDA-ARS/Idaho