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United States Department of Agriculture

Agricultural Research Service

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Location: Emerging Pests and Pathogens Research

2011 Annual Report

1a. Objectives (from AD-416)
Potato virus Y (PVY), once managed effectively by strict seed certification practices, has reemerged as a serious disease problem in the seed potato crop. The seed potato industry has identified PVY as its most serious disease problem and has set goals to reduce PVY incidence below tolerance limits set by seed certification programs, and to eliminate the new tuber necrotic isolates. Our overall objective in this proposal is to refine the current PVY management strategies used by growers and seed certification agencies to reduce virus levels in seed stocks and spread of virus within the crop. Specifically, we will: a) Assist seed certification agencies to amend current practices and improve their ability to detect, monitor and eliminate PVY from seed stocks. b) Assist breeding programs to develop improved methods to screen for PVY resistance and symptom expression. c) Assist growers to develop cost effective, on-farm virus control strategies. Reducing the overall incidence of PVY to manageable levels and eliminating the tuber necrotic strains will require an adjustment of seed certification practices and a more aggressive use of on-farm management strategies by both seed and commercial potato growers. Similar strategies have been successful in eliminating other potato pathogens from seed production by learning important control points for each of the pathogens, implementing control measures on farms, and making appropriate changes in seed certification and regulatory practices. The goal of this proposal is to achieve a similar level of control for PVY. The expected outcomes and deliverables of our proposed research include: 1. Improved diagnostic tests capable of differentiating all the PVY strains affecting U.S. potatoes. 2. Educational training aids for seed inspectors and growers to recognize all the various foliar and tuber symptoms caused by the new PVY strains. 3. Information back to each participating seed programs on the PVY strains collected from their state. 4. Alternatives to current post harvest test methods, including a comprehensive economic analyses of the different methods currently in use and for those developed in this proposal. 5. Knowledge of the susceptibility of the major U.S. potato varieties to potato tuber necrotic ringspot disease cause by the recently introduced necrotic and recombinant strains of PVY. 6. Establishment of regional trials to evaluate susceptibility, symptom expression, and resistance in varieties and advanced breeding lines to the range of PVY isolates now present in the U.S. 7. Improved minituber production methods that would allow varieties to reach the market earlier and reduce the potential for PVY infection of minituber crops planted in the field. 8. Forecast and economic models that relate the levels of PVY in seed lots of major cultivars to the levels of PVY incidence determined in the field and harvested tubers. 9. New information on the aphid transmission efficiency of the new PVY strains to help predict the likelihood of spread of these strains within and between crops. 10. New information on the efficacy of new antifeedant compounds that could prevent aphid inoculation of PVY to potato.

1b. Approach (from AD-416)
Efforts to improve the effectiveness of seed certification will include the development of new training materials to help inspectors better identify virus infections. This will also include evaluations of diagnostic methods that are being developed in this and other projects. Improvements to post harvest test procedures will focus on new lighting systems that may allow operations to move out of the field and into controlled environments that would allow more uniform growth and faster testing. An economic analysis of various post harvest test methods will provide certification agencies with short and long term cost savings projections if they choose to implement new testing procedures. Potato tuber necrosis is the most serious aspect of the emerging PVY strains. Field and greenhouse evaluations of existing cultivars and breeding lines for their susceptibility to tuber necrosis and their reactions to all PVY strains will provide valuable risk assessment information. Regional trials of material should also identify new sources of resistance to PVY that can be introduced into breeding populations. Finally, studies to improve on-farm management options will focus on reducing initial inoculum and reducing the spread of PVY into and within a crop. Both the mechanics and economics of identifying maximum threshold levels of PVY that will still allow satisfactory disease management and high economic return are featured aspects of these studies. Epidemiological studies on reducing virus spread in the field will focus on aphid vector phenologies and control, as well as weed reservoir management. A cost-benefit analysis will be conducted for each of the scientific recommendations when appropriate to assist the industry and regulatory agencies in deciding acceptance of any proposed changes to the national plans. Cost-benefit analyses also can assist state certification and regulatory agencies and individual growers in determining whether to adopt individual practices that are not mandated at the federal level. Each of the outlined objectives of this proposal meets current needs as defined by the industry. To ensure the research continues to address relevant issues, growers, industry representatives, seed certification officials, and federal regulatory officials meet annually with the Co-Investigators on the proposal to discuss research findings and potential recommendations to modify the current Management Plan, as well as changes in direction and scope of proposed research needs. In addition, Seed Certification officials from each of the 16 seed producing states meet in December with scientists and grower representatives to focus on seed certification issues. A WERA-089 meeting held each March brings together scientists working on virus and phytoplasma diseases of potato. These are often attended by seed certification, regulatory and industry representatives. Technology and information is also transferred to stakeholders at regional and national grower meetings, farm and field- day events, statewide vegetable newsletters, and through popular press and scientific articles.

3. Progress Report
Potato virus Y is the most important disease affecting seed potatoes in Idaho and the emerging necrotic strains are threatening the commercial crop. Surveys of seed and commercial acreage have determined that the ordinary strain of PVY is no longer the predominant strain. The recombinant PVYN-Wi strain is now detected in a majority of potato samples and the recombinant tuber necrotic strain now comprises about 20% of the total. The level of tuber necrotic strain has remained steady over the past several years. The use of serological tests to determine virus levels in seed lots, a change we were able to implement last year, has resulted in a reduction in the overall levels of PVY in the crop and a reduction in the number of seed lots rejected for certification. Breeding for PVY resistant potato cultivars has also become a priority for the western region breeding programs. Two different sets of clones and cultivars were tested for Potato Virus Y (PVY) R-gene markers. The first set of eighteen breeding clones/cultivars were selected based on Solanum tuberosum ssp. andigena, S. stoloniferum background, or known PVY resistance. R-genes in these species are reported to confer resistance against all PVY strains (extreme resistance). These clones/cultivars have been utilized in the breeding program as parents in a PVY resistance crossing block. A second set of clones derived from other parents with evidence of PVY resistance were selected based on acceptable agronomic characteristics. Both sets of were tested with SCAR marker RYSC3 for Ryadg and an SSR marker STM0003 for Rysto. All entries were further characterized by their PVY reactions in the field or by grafting in the greenhouse. Strategies to hybridize marker-confirmed PVY resistant parents with superior agronomic parents should result in higher frequencies of selected clones with extreme PVY resistance and desirable agronomic traits. Confirming PVY markers after initial agronomic selection would eliminate the need for greenhouse and field bioassays to determine resistance to individual PVY strains. Results show initial selection of ten russet types for processing or fresh pack and one for specialty. Of these eleven selections, three have markers for Ryadg and Rysto genes, while the remainders have a marker for either one of the genes. Additional research is being conducted to investigate the influence the initial level of PVY in seed stocks has on overall PVY incidence in the commercial crop and on yield reduction. A second year of field trials was planted and data from the first year is being analyzed. Progress is monitored via bi-monthly conference calls, tri-annual written reports and an annual project meeting as well as by frequent emails.

4. Accomplishments

Last Modified: 10/19/2017
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