2006 Annual Report 4d.Progress report. Project 6618-22000-024-01S is a cooperative agreement, 'Cooperative Research on Citrus Tristeza Virus and other Exotic Citrus Diseases. This project was previously based on funding destined for the University of Florida for research on Citrus Tristeza Virus and other Exotic Citrus Diseases'. The project was terminated by ARS and no funds added in early FY2006, thus the report indicated below constitutes the final report. The parent project is 6618-22000-024-00D, Cooperative Research on Citrus Tristeza Virus and Other Exotic Citrus Diseases. The objective of this Specific Cooperative Agreement with the University of Florida is to determine genetic, epidemiological, biochemical, biological, and serological characteristics of citrus tristeza virus (CTV) and other exotic citrus pathogens, so as to improve citrus productivity and to support regulatory actions. Specific virus genes were shown to be necessary for CTV infection and disease development in citrus and insect transmission of CTV was shown to be variable. Progress was made on the studies of natural and artificial genes giving resistance to CTV. The pathogen that causes the citrus greening disease was shown to cause symptoms when transmitted by insects from Florida. The CTV SCA is funded on a year by year basis. The funding focuses now on research on stem-pitting strains of CTV, citrus leprosis virus and Phaeoramularia leaf spot. There are no specific goals for the next three years.