WERA1007: Curly Top virus Biology, Transmission, Ecology, and Management
Statement of Issues and JustificationCurtoviruses 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.
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