Safeguarding Citrus Stock

Tacy CalliesCitrus Greening, Regulation

Clean Plant Network

Budwood sources of quarantine-released varieties are maintained at the Lindcove Research and Extension Center in Exeter, California.

By Georgios Vidalakis

On March 30, 2007, I received a memorable phone call in my office at the University of California (UC), Riverside.

“Georgios,” said the caller, “The 2008 Farm Bill will establish the National Clean Plant Network (NCPN) for specialty crops. This program will be like no other because it will be driven from the ground up. The system will require the active participation of the industry in governance and funding recommendations. Citrus needs to be part of this.”

“Of course,” I responded, and the journey began.

Following the formation of the fruit tree and grape networks in 2009, the citrus network began its organization in February of the same year. After several meetings and in-depth discussions, the Citrus Clean Plant Network (CCPN) elected its governing board, a diverse group of citrus growers and nurserymen, scientists, Extension specialists and state agents from departments of agriculture. With the ratification of its operational chapter on March 23, 2010, the CCPN ( was officially formed.

Today, the CCPN connects 10 citrus centers in these nine U.S. states and territories: Hawaii, California, Arizona, Texas, Louisiana, Alabama, Maryland, Florida and Puerto Rico. The CCPN centers have the mission of “providing high quality asexually propagated citrus material free of target citrus pathogens and pests that cause economic loss.”

Clean Plant Network

This mission is achieved by diagnosing citrus diseases and detecting citrus pathogens in budwood and seed “mother” plants and applying therapy in order to “clean” these plants in preparation for their “increase” and use by industry. In a typical year, CCPN centers conduct over 75,000 diagnostic tests, distribute over 600,000 clean plant units, perform therapeutics on hundreds of plants and maintain hundreds of foundation plantings.

With the onset of the huanglongbing (HLB) epidemic in the United States, the CCPN centers became the only reliable source of HLB-tested citrus budwood for the citrus industry. In addition, the CCPN centers engaged in important research projects for the streamlining of the safe movement of citrus budwood in the post-HLB world. For example, in Florida, the citrus breeders had the unfortunate opportunity to screen naturally their varieties for HLB tolerance as the disease spread through their experimental plots.

Therefore, in 2014–15, two CCPN citrus centers, the California Citrus Clonal Protection Program (CCPP) and Florida’s Bureau of Citrus Budwood Registration, received funding from the California citrus industry (Citrus Research Board) and the U.S. Department of Agriculture’s (USDA) HLB Multi-Agency Coordination Group. The funding was to introduce into California more than 50 citrus varieties (scions and rootstocks, early and advanced breeding selections, public domain and protected varieties, etc.) from two Florida breeding programs, University of Florida’s Citrus Research and Education Center (CREC) and USDA’s Agricultural Research Service (ARS) in Fort Pierce.

In the first 18 months of this broadly collaborative project, the California Department of Food and Agriculture, USDA-Animal and Plant Health Inspection Service, UC Riverside, CREC and USDA-ARS compiled a 130-page protocol for the movement of citrus budwood from Florida to California. It includes federal and state permits, HLB-spread mitigation procedures and non-propagation and material-transfer agreements.


Currently, there are 23 citrus accessions in the introduction pipeline at the CCPP Rubidoux Quarantine Facility in Riverside. (Visit and select “Upcoming Citrus Varieties – Introductions” for real-time updates.) The citrus variety introduction pipeline includes pathogen detection and elimination via shoot-tip grafting followed by release of the variety from state and federal quarantine. Budwood sources of the quarantine-released varieties are maintained at the CCPP Protected Foundation Block at the Lindcove Research and Extension Center (LREC) in Exeter, California.

In addition, a small number of trees will be planted at the CCPP-LREC Evaluation Block for preliminary observation by growers, nurseries, scientists and the general public. Evaluation data will be disseminated to the industry in coordination with CREC and USDA-ARS. When a variety is ready for further evaluation or commercialization, additional entities such as the Florida Foundation Seed Producers and the New Varieties Development and Management Corporation will be invited to coordinate with all involved parties for the use of the introduced citrus varieties. This project will continue for the next two to five years, and the Florida and California collaborators will need the support of the citrus industry for the identification of cooperators for field trials in both states.

I would like to conclude this article by thanking all the members of the U.S. citrus industry. Without your leadership, vision and support, neither the NCPN nor the citrus centers across the nation could have successfully operated for the past decades. Thank you.

Georgios Vidalakis ( a University of California Cooperative Extension specialist and plant pathologist, director of the Citrus Clonal Protection Program and chair of the Citrus Clean Plant Network.

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