2012 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.
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):
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.
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.
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.
Plant viruses cause millions of dollars in damage to vegetable and sugarbeet production each year through decreased yield, quality, and plant longevity. Management of virus diseases requires knowledge of virus-host-vector interactions, and knowledge of ecology and epidemiology of insect transmitted and soil-borne viruses, as well as host resistance. This project, which began in April 2012, is targeted toward these goals. Research is in progress on all aspects of proposed research, with progress made toward all milestones. New projects and projects building on previous studies are examining 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, and are determining environmental and cultural factors contributing to ability of viruses to induce disease to facilitate breeding efforts for resistance to soil-borne and insect-transmitted viruses affecting lettuce.
Molecular and applied biological approaches will be used to address current problems associated with emerging and re-emerging viruses affecting sugarbeet and vegetable production in the United States, including, but not limited to BNYVV and its vector, Polymyxa betae, insect-transmitted viruses in the family Closteroviridae, and soil-borne viruses affecting lettuce production. This will result in new detection technologies for these viruses, knowledge of the biology of infection, factors driving emergence of new virus strains and species, improved methods for disease management integrating resistance with cultural practices, and improved sources of resistance.