Duration: 10/01/2006 to 09/30/2011

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Beet curly top virus (BCTV) is the most widespread geminivirus in the United States. The virus has caused economic damage to a wide variety of crops including tomato, pepper, melon, bean, sugarbeet, and spinach in the western U.S. Transmitted by the beet leafhopper Circulifer tenellus, the virus infects a broad host range from many plant families and the leafhopper vector also feeds and breeds on an extensive range of plant hosts . BCTV 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. Leafhoppers migrate back to the overwintering areas in the fall.

BCTV is a monopartite geminivirus and the type member of the genus Curtovirus. Early molecular characterization of BCTV in sugarbeet demonstrated that the virus primarily exists as three viruses and genotypic variants of these viruses. Recent work from New Mexico and California has shown that two of those viruses (CFH and Worland) commonly infect a variety of plants types, and several new curly top viruses and recombinants are present in the field.

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, BCTV is endemic in the western U.S. Management of this viral pathogen and its leafhopper vector has proven difficult. California has long used a costly pesticide program to control the leafhopper using organophosphate sprays to uncultivated foothill breeding areas. 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 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 BCTV 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 development of a coordinating committee to address the problem. This committee will meet to discuss, assess, and prioritize required research into curly top virus 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. Assemble a group which will include university, government, extension, and commodity-based individuals to assess the current status of curly top and set priorities for research on beet curly top virus. Over 40 individuals that are working on different aspects of curly top in the western US have already begun working together on curly top. Those already committed to joining the group include university and government virologists, weed scientists, entomologists, plant breeders, a statistical modeler, and extension scientists, from New Mexico, Arizona, California, Colorado, Texas, Idaho, and Washington. Regional stakeholders with a commitment to the working group and its research include the New Mexico Chile Task Force, 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. The objectives that are presented below were named as likely research topics by potential committee members.

2. Organize research on beet curly top virus genetics in the western US. The ability to manage a virus disease requires an understanding of which virus is causing the disease. Preliminary data from New Mexico and California suggests that viral genetic diversity is present in a variety of plant hosts and that new curly top viruses appear regularly. Within both states, there are efforts underway to study the virus incidence and diversity. These scattered reports suggest that genetic diversity within curly top viruses may be tremendous and will require a concerted effort to identify 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 large numbers of BCTV isolates collected from different crops, weeds, and states.

3. Organize research to assess the genetics and biology of populations of the beet leafhopper vector, Circulifer tenellus within the western US. While much research has been done to determine the leafhopper host range, the biology and ecology of the leafhopper in specific locations has changed with alterations in cropping patterns and weed populations. Work is underway to assess how the leafhoppers are overwintering, and whether different populations have different feeding preferences at a statewide level, but this work needs to be expanded to include the entire vector breeding area. Similarly, leafhopper flight patterns have been studied in New Mexico, but 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.

4. Organize research to study the role of weed hosts in curly top in the western US. 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. Members of the proposed coordinating committee have begun studying the weed populations in vector breeding areas, although little is known of the distribution of key weed hosts. The group will encourage combining data for the leafhoppers and viruses into GIS mapping studies. Work in New Mexico is also focusing on the ability of annual mustards to serve as overwintering hosts of the leafhopper and virus. These overwintering weed hosts need to be determined for each primary vector breeding area.

5. Organize research to examine strategies for managing curly top. Curly top has proved very difficult to control. Coordinating committee members are studying 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 be able to coordinate management tests in more than one location. 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

Standard Description.

Literature Cited

Attachments

Land Grant Participating States/Institutions

AZ, CA, CO, NM

Non Land Grant Participating States/Institutions