2007 Annual Report 1a.Objectives (from AD-416) The objectives of this cooperative research project is to: 1) Identify how the genetic diversity of PLRV and PVY affect virus movement within and among plant hosts. 2) Develop improved diagnostics to accurately detect and monitor the range of genetic variants of PVY known to affect the potato crop. 1b.Approach (from AD-416) The potato industry is plagued by virus diseases; the most serious are Potato Virus Y and Potato Leafroll virus and the virus populations are genetically diverse. Our continuing research will define the diversity of virus populations using serological, biological and nucleic acid based assays. Research will also investigate how the genetic diversity in specific virus genes can effect the ability of the virus to cause systemic disease in plants and to be transmitted by aphid vectors between plants. This information is used to develop improved diagnostic capabilities and to design more effective control strategies that prevent the movement of viruses within or between hosts. Novel control strategies will be designed to interfere with the normal virus transmission and infection process. 3.Progress Report This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Cornell University. In FY07 we concluded and published a study identifying specific regions of the Potato leafroll virus capsid protein involved in virus assembly, virus movement in plant hosts and virus transmission by aphid vectors. Virus assembly and structural integrity were required for the virus to spread in a plant. This is in contrast to many plant viruses whose genetic material can spread in a plant without being surrounded by the capsid proteins. Also surface features of the virus particle were identified that interact with unknown components of aphid vectors and allow the virus to be transmitted. Understanding how a virus moves within and between plants provides potential targets for novel control strategies. Additionally, the transmission efficiency of multiple isolates of PVYO and PVYN:O, the predominant virus strains affecting the U.S. seed potato crop, were determined using colonizing and noncolonizing aphid species. No differences in transmission efficiency were observed among isolates using a colonizing aphid species. The transmission efficiency of noncolonizing species was too low to allow for any meaningful analysis of the data. These studies help to understand what is driving the re-emergence of PVY as a potato disease problem and why more aggressive strains of the virus are emerging. Progress is monitored via monthly lab meetings.