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NCPN Citrus
NCPN Citrus
NCPN Citrus
University of California
NCPN Citrus

Dr Georgios Vidalakis

Photo of Dr Georgios Vidalakis
Professor & UC Extension Specialist in Plant Pathology - Director, Citrus Clonal Protection Program (CCPP)
Department of Plant Pathology & Microbiology
900 University Avenue
1463 Boyce Hall
Riverside, CA 92521
(951) 827-3763 Create VCard



Dr. Vidalakis completed his undergraduate studies in 1998 at the Agricultural University of Athens, Greece with concentration in plant protection and environment and specialization in plant virology. He became the director of Citrus Clonal Protection Program (CCPP) in the summer of 2005 a year after earning his Ph.D. from the Department of Plant Pathology at the University of California, Riverside, where he was the recipient of the Special Dean’s Fellowship Award for the duration of his doctoral studies. Funded by the Citrus Research Board, California Citrus Nursery Board, California Department Food and Agriculture, and the United States Department of Agriculture, Dr. Vidalakis has developed a diverse research and extension program that is serving all citrus producing states in the US via the citrus germplasm services of the National Clean Plant Network (NCPN) and the CCPP.

As an Extension Specialist Dr. Vidalakis has been working directly with the citrus industry, growers and nurseries, at a state and national level. His service to the citrus industry include, but is not limited to, the organization of industry supported events (e.g. Meeting the Challenge of the Asian Citrus Psyllid in Nurseries), participation in key industry organizations and committees (e.g. California Citrus Quality Council-Citrus Pest Management Strategic Plan) as well as state and national panels and workgroups (e.g. Recovery Plans for the National Plant Disease Recovery System and National Plant Diagnostic Network STAR-D Board).

As a researcher, Dr. Vidalakis has developed a program focused on the study of graft-transmissible pathogens of citrus with emphasis on viruses, viroids, and bacteria. Mixed viral infection and their effect to biodiagnosis of citrus diseases as well as the biological activity, molecular properties and intrapopulation structure of citrus viroids have been part of his work. He is also focusing on citrus diseases, such as Huanglongbing (HLB), and citrus associated microbes and their potential beneficial impacts on citrus production as well as the optimization of the functions of citrus germplasm programs, which include: diagnostics (bioindexing and laboratory), therapy (shoot tip grafting and thermotherapy), production, and distribution of citrus propagative materials (foundation blocks and variety management).

Dr. Vidalakis is also participating in several national and international programs. He is the Chair of the Citrus Network of the National Clean Plant Network (NCPN) for Specialty Crops and he is a member of the Laboratory Accreditation Board STAR-D of the USDA National Plant Diagnostic Network (NPDN). He is a member of the Viroid Study Group of the International Committee on Taxonomy of Viruses (ICTV) and he serves as the secretary and 2019 Chair-Elect of the International Organization of Citrus Virologists (IOCV).


Ph.D. Plant Pathology-Citrus Virology, University of California, Riverside. 2004
B.S. & M.Sc. Plant Protection & Environment, Agricultural University of Athens, Greece. 1998


Graft-transmissible diseases of citrus diagnosis and therapy & Citrus germplasm.

Areas of Expertise (click to see all ANR academics with this expertise)


Peer Reviewed

  • Silva, D.; Lovatt, C.; Vidalakis, G.; Roose, M. (2014). Citrus. California Master Gardener Handbook. UC ANR.
  • Kwon, S.; Tan, S.; Vidalakis, G. (2014). "Complete nucleotide sequence and genome organization of an endornavirus from bottle gourd (Lagenaria siceraria) in California, U.S.A." Virus Genes: 6.
  • Bostock, R.; Thomas, C.; Hoenisch, R.; Golino, D.; Vidalakis, G. (2014). "Diagnostics in Plant Health: How Diagnostic Networks and Inter-Agency Partnerships Protect Plant Systems from Pests and Pathogens." California Agriculture
  • Polek, M.; Vidalakis, G. (2014). Invasive Pests: Exotic Plant Pathogens. Citrus Production Manual.L. Ferguson and E. Grafton-Cardwell. UC ANR.: 347-360.
  • Shi, J.; Pagliaccia, D.; Morgan, R.; Qiao, Y.; Vidalakis, G.; Ma, W. (2014). "Novel Diagnosis for Citrus Stubborn Disease by Detection of a Spiroplasma citri-Secreted Protein." Phytopathology 104(2): 188-195.
  • Kahn, T.; Vidalakis, G. (2014). Scion Cultivars. Citrus Production Manual.L. Ferguson and E. Grafton-Cardwell. UC ANR.: 63-94.
  • Vidalakis, G.; Gumpf, D.; Polek, M.; Bash, J. (2014). The California Citrus Clonal Protection Program. Citrus Production Manual.L. Ferguson and E. Grafton-Cardwell. UC ANR.: 117-130.
  • Gumpf, D.; Polek, M.; Vidalakis, G. (2014). Virus and Viroid Diseases. Citrus Production Manual.L. Ferguson and E. Grafton-Cardwell. UC ANR.: 337-346.
  • Osman, F.; Hodzic, E.; Kwon, S.; Wang, J.; Vidalakis, G. (2013). "Development and validation of a multiplex reverse transcription quantitative PCR (RT-qPCR) assay for the rapid detection of Citrus tristeza virus, Citrus psorosis virus, and Citrus leaf blotch virus." Journal of Virological Methods
  • Wang, J.; Boubourakas, I.; Voloudakis, A.; Agorastou, T.; Magripis, G.; Kyriakopoulou, P.; Vidalakis, G. (2013). "Identification and Characterization of Viroids in the Greek National Citrus Germplasm Collection Reveals Novel Viroid Variants and Threats to the Industry." European Journal of Plant Pathology 137: 17-27.
  • Wang, J.; Bozan, O.; Kwon, S.; Dang, T.; Rucker, T.; Yokomi, R.; Lee, R.; Folimonova, S.; Krueger, R.; Bash, J.; Greer, G.; Diaz, J.; Serna, R.; Vidalakis, G. (2013). "Past and future of a century old Citrus tristeza virus collection: a California citrus germplasm tale." Frontiers in Microbiology 4(366): 1-13.
  • Zhao, H.; Sun, R.; Albrecht, U.; Padmanabhan, C.; Wang, A.; Coffey, M.; Girke, T.; Wang, Z.; Close, T.; Roose, M.; Yokomi, R.; Folimonova, S.; Vidalakis, G.; Rouse, R.; Bowman, K.; Jin, H. (2013). "Small RNA profiling reveals phosphorus deficiency as a contributing factor in symptom expression for citrus Huanglongbing disease." Molecular Plant 6: 301-310.
  • Parrano, L.; Afunian, M.; Pagliaccia, D.; Douhan, G.; Vidalakis, G. (2012). "Characterization of viruses associated with garlic plants propagated from different reproductive tissues from Italy and other geographic regions." Phytopathologia Mediterranea 51(3): 549-565.
  • Vidalakis, G. (2012). Diseases. Integrated Pest Management for Citrus. UC ANR. 3303: 39-84.
  • Hajeri, S.; Ramadugu, C.; Manjunath, J.; Ng, J.; Lee, R.; Vidalakis, G. (2011). "In vivo generated Citrus exocortis viroid progeny variants display a range of phenotypes with altered levels of replication, systemic accumulation and pathogenicity." Virology 417(2): 400-409.
  • DiSerio, F.; Randels, J.; Flores, R.; Owens, R.; Sano, T.; Li, S.; Vidalakis, G.; Pallas, V. (2011). Viroids. Virus Taxonomy.A. King, M. Adams, E. Carstens and E. Lefkowitz. Oxford, Elsevier.: 1221-1234.
  • Vidalakis, G.; Pagliaccia, D.; Bash, J.; Afunian, M.; Semancik, J. (2010). "Effects of Citrus Dwarfing viroid, a transmissible small nuclear RNA on tree size and scion performance specific to poncirus trifoliata rootstock with applications for high density planting." Annals of Applied Biology 158: 204-217.
  • Vidalakis, G.; Pagliaccia, D.; Bash, J.; Semancik, J. (2010). "Effects of mixtures of citrus viroids as transmissible small nuclear RNA (TsnRNA) on tree dwarfing andd commercial scion performance on carrizo citrange rootstock." Annals of Applied Biology 157: 415-423.
  • Hajeri, S.; Ramadugu, C.; Keremane, M.; Vidalakis, G.; Lee, R. (2010). "Nucleotide Sequence and Genome Organization of Dweet mottle virus and Its Relationship to Members of the Family Betaflexiviridae." Archives of Virology 155: 1523-1527.
  • Polek, M.; Vidalakis, G.; Godfrey, K. (2007). Citrus Bacterial Canker Disease and Huanglongbing (Citrus Greening). UC ANR. 8218: 12.
  • Szychowski, J.; Vidalakis, G.; Semancik, J. (2005). "Host directed processing of Citrus exocortis viroid." Journal of General Virology 86: 473-477.
  • Vidalakis, G.; Davis, J.; Semancik, J. (2005). "Intra-population diversity between citrus viroid II variants described as agents of cachexia disease." Annals of Applied Biology 146: 449-458.
  • Semancik, J.; Vidalakis, G. (2005). "The question of Citrus viroid IV as a Cocadviroid." Archives of Virology 150: 1059-1067.
  • Vidalakis, G.; Gumpf, D.; Bash, J.; Semancik, J. (2004). ""Finger Imprint" of Poncirus trifoliata: A Specific Interaction of a Viroid, a Host, and Irrigation." Plant Disease 88: 709-713.
  • Onelge, N.; Cinar, A.; Szychowski, J.; Vidalakis, G.; Semancik, J. (2004). "Citrus Viroid II Variants Associated with "Gummy Bark" Disease." European Journal of Plant Pathology 110: 1047-1052.
  • Vidalakis, G.; Garnsey, S.; Bash, J.; Greer, G.; Gumpf, D. (2004). "Efficacy of Bioindexing for Graft-Transmissible Citrus Pathogens in Mixed Infections." Plant Disease 88: 1328-1334.

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