What is a “clean” plant? What process does the Clean Plant Center Northwest use to ensure fruit tree, grape, and hop plants (or root stocks) are clean?

At the Clean Plant Center Northwest (CPCNW), we follow a rigorous testing, propagative, maintenance, and retention process to ensure our plant materials are free from known virus and virus-like pathogens.

The stages of the clean plant process are as follows:

Introduction: A specific cultivar is submitted to the CPCNW (budwood or plant). When it arrives it is given a tag with an accession number, plant identification number, and its variety name. This ensures each piece of plant material can be tracked as it moves through the clean plant process. Fruit tree buds are propagated onto appropriate rootstock, while grapes and hops are rooted or repotted. All three are placed into their respective greenhouses and allowed to grow. Once green tissue is available the testing process can begin.

Testing and therapy: For each of the commodities we work with the pathogen screening starts with a combination of high throughput sequencing (HTS), PCR and ELISA tests. From here the process varies slightly depending on the commodity and its viral status.

Fruit trees that test negative for virus or virus-like agents will begin testing via indexing in the greenhouse (all fruit trees) and field (apples, pears and quince only). Greenhouse indexing involves both herbaceous and woody indexing this process takes approximately 90 – 120 days to complete. Field indexing however, requires observation over three growing seasons. Final testing by HTS and/or PCR/ELISA occurs at least 60 – 90 days after the first round of testing is complete. This process takes approximately two to three years to complete depending on the fruit tree variety.

Fruit trees that test positive for virus or virus-like agents enter into therapy. Currently the CPCNW uses thermotherapy and tissue culture to remove viruses and virus-like agents from fruit trees. Once the virus elimination process has been completed, greenhouse and field indexing begins. Also, after a minimum period of sixty to 90 days following virus elimination, the plants are tested via PCR and/or ELISA for the virus or virus-like agents originally detected. If the variety is found free of virus or virus-like agents, it is maintained under screenhouse for at least 150 – 180 days before undergoing final testing. Final testing is done by HTS and/or PCR/ELISA. This process takes 3+ years to complete depending on the fruit tree variety.

Grapevines that test negative for virus or virus-like agents will be maintained under screenhouse for 150 – 180 days before undergoing final testing. Final testing is done by HTS and/or PCR/ELISA. This process takes 12 – 18 months to complete depending on the grape variety.

Grapevines that test positive for virus or virus like agents enters into therapy. Currently the CPCNW uses meristem and shoot-tip culture to remove viruses and virus-like agents from grapevines. Sixty to 90 days after virus elimination has been completed the plants are tested via PCR and/or ELISA for the virus or virus-like agents originally detected. If the variety is found free of virus or virus-like agents, it is maintained under screenhouse for 150 – 180 days before undergoing final testing. Final testing is done by HTS and/or PCR/ELISA. This process takes approximately 18 to 24 months to complete depending on the grape variety.

Hops that test negative for virus or virus-like agents will be maintained under screenhouse for 150 – 180 days before undergoing final testing. Final testing is done by HTS and/or PCR/ELISA. This process takes 12 – 18 months to complete depending on the hop variety.

Hops that test positive for virus or virus like agents enters into therapy. Currently the CPCNW uses meristem and shoot-tip culture to remove viruses and virus-like agents from grapevines. Sixty to 90 days after virus elimination has been completed, the plants are tested via PCR and/or ELISA for the virus or virus-like agents originally detected. If the variety is found free of virus or virus-like agents, it is maintained under screenhouse for at least 150 – 180 days before undergoing final testing by HTS and/or PCR/ELISA. This process takes approximately 18 to 24 months to complete depending on the hop variety.

Selection of ‘mother plants’: We identify two plants that are free of virus and virus-like agents to serve as the ‘mother’ plant.

Release: Once the testing process is complete, test results are sent to USDA-APHIS.  Depending on the plant type (fruit tree, grape, or hop) we release healthy plant materials (budwood, dormant cuttings, propagative green cuttings or whole plants) through an ordering and distribution process that meets all phytosanitary requirements.

Retention and Maintenance: We retain two Mother plants per cultivar in our designated retention screen houses. Mother plants undergo regular testing to verify their pathogen-free status.

Distribution: The CPCNW sells clean propagation material to the US fruit tree, grapevine and hop industries during regularly scheduled sale periods. For more information about sales CLICK HERE