2012 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 & 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.
Experiments to refine PVY ‘Best Management Practices’ to limit current season spread of the virus in seed potato were implemented using different application timing, application intervals, and tank mixes of mineral oils and selected feeding blockers in a PVY susceptible cultivar ‘Russet Norkotah’. Replicated field experiments were established at the Langlade County Research Station of the University of Wisconsin Cooperative Extension. To ensure an adequate and standard source of PVY inoculum for spread within plots maintained under different management regimes, PVY was established by sap-inoculating 2 plants centrally in the plot. Replicated sets of R. Norkotah were planted in 20 ft rows X 36” row (6 rows/ plot) and experimental replicates separated by 12’ spray alleys. Applications were initiated on 6 July, using a CO2 pressurized, tractor-mounted sprayer and incidence of PVY was surveyed at the end of the experimental interval by counting all symptomatic plants, and their relative position in each experimental plot. Total plot yield will be determined at the conclusion of the experiment from each plot. A subsample (N=40) of potentially infected tubers were sent to the post-harvest test in Homestead, FL (January 2013) for further evaluation.
Field experiments were established in 2011 to determine the effect of various levels of seed borne PVY on yield and grade of potatoes intended for seed. Treatments consisted of several levels of seed borne PVY including 0, 2, 5, 10% present in different potato cultivars of regional importance. Treatment combinations of cultivar and inoculation level were replicated four times in a randomized complete block design (RCBD). Seed was obtained from the Wisconsin Certified Seed Program and plants were mechanically-sap inoculated in the field at the 3-4 true leaf stage with all tubers harvested from healthy and infected plants at the end of the 2011 season. Virus levels in the plots were determined after inoculation and final PVY incidence determined by visual inspection during the January, 2012, post-harvest test in Homestead, FL. Infected tuber incidence was determined by testing a subset of 200 harvested tubers. Yield, grade and PVY incidence data from plots starting with differing levels of PVY are being analyzed.
Experiments with the ARS and University potato breeders are examining the effects of PVY resistance on yield and quality due to the prevailing belief among breeders that PVY resistance genes are linked to poor quality and yield. In 2012, tubers were planted with and without the marker linked to PVY resistance from two crosses with a PVY-resistant parent (White Lady). The progeny will be evaluated for yield and quality. Researchers are generating diploid tubers from White Lady X GM10. These tubers will be planted in 2013 and assessed for yield and quality. Curiously, although White Lady gives round white tubers, the only tubers obtained so far are long white fingerlings or round tubers with purple stripes.