1a.Objectives (from AD-416):
The overall objective of this proposal is to refine the current management strategies based on industry needs to reduce overall levels of PVY and prevent the continued spread of necrotic and recombinant strains.
1b.Approach (from AD-416):
Our overall objective in this proposal is to refine the current management strategies used by the certification agencies to reduce the initial virus inoculum planted in the field and those used by growers to reduce the spread of virus within the crop. Specifically, we will
1. Work with seed certification agencies to monitor PVY strains and develop new diagnostic and training tools to better identify and eliminate PVY from seed stocks.
"Specialty Crops Research Initiative"
2. Work with breeding programs to better recognize and screen for virus resistance and symptom expression.
3. Work with growers to develop cost effective virus control strategies for both minituber and conventional seed production that can be implemented on the farm.
Continuing surveys of PVY strains present in seed lots and commercial fields from many seed production states indicated that the ordinary strain of PVY is no longer the predominant strain in most seed production areas. The recombinant tobacco necrotic strain predominates in most of the states surveyed. The tuber necrotic strain is present in nearly all production areas but remains associated with a limited number of seed lots. This has led Certification agencies to conduct more laboratory testing, especially for the tuber necrotic strain, to better evaluate PVY incidence in seed lots. Growers are urged not to reenter into certification those seed lots infected with the tuber necrotic strains and not to plant that seed in seed production areas. Our research has driven in part the adoption of new national standards for the movement of seed potatoes between states and Canada. Many state Certification agencies ask growers to abide by the same rules for seed moving within a state and many states have adopted strict seed laws that require certified seed for planting. Negotiations are ongoing to amend the bi-national PVY management plan adopted by Canada and the US in 2004 to include the updated standards. The identification of PVY strain variants that can be misidentified by current diagnostic protocols has led to the development of revised diagnostic testing protocols that have been adopted by Certification testing labs. These changes have also been submitted to NAPPO and are undergoing review prior to adoption by Canada, U.S. and Mexico. Four advanced breeding lines from public programs were identified as resistant to all strains of PVY and several lines from the private program also show promise. The evaluation of symptom expression on multiple cultivars induced by multiple isolates representing each of the PVY strains indicates that in general the emerging recombinant strains induce milder and often transient foliar symptoms whereas the nonrecombinant ordinary strain induces more severe foliar symptoms. However, many cultivars are asymptomatic when infected with most PVY isolates, and isolates within a strain can cause a range of symptom types and severity within a cultivar. This necessitates testing using multiple isolates within a strain to adequately evaluate cultivar reactions. Furthermore, tuber necrosis is not restricted to the tuber necrotic strain of PVY, but can be induced by isolates of the virus classified in other strain groups. Analyses of seed certification data identified Russet Burbank, Russet Norkotah and Atlantic as cultivars that cannot be evaluated for PVY incidence by summer field inspections and that require visual and laboratory post harvest testing. Economic modeling of yield effects of PVY indicate that on average the fresh market income per acre will fall by $8.32 for each percent of PVY in the Russet Burbank crop.