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 healthy?

6DSC_0013healthy cluster 01Nice apples

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 virus-like pathogens. In addition to verifying the health of our plants, we also verify they are true-to-type through genotyping.

The stages of the clean plant process are as follows:

  1. Introduction: A specific cultivar is submitted to the CPCNW for testing (either a piece of budwood or rootstock, or plant) and labelled with a propagation number, plant identification number, and variety name to ensure each piece of plant material can be tracked as it moves through the clean plant process.
  1. Initial screening and therapy: For each of the commodities we work with, the pathogen screening (and subsequent therapy if needed) varies slightly. We test the plant material for an array of viruses and virus-like pathogens. If pathogens are detected, then the cleanup process begins.
    • In the fruit trees program, we use heat and cold therapy techniques.
    • In the grapes program, we employ microtip tissue culture processes to propagate a clean plant.
    • In the hops program, we also use several different tissue culture processes, including meristem culture, heat therapy and meristem culture, chemotherapy and meristem culture, and cold therapy and meristem culture.

Plants are grown under strict biosecurity conditions in growth chambers, greenhouses, and screen houses. For all commodities, the pathogen testing conducted at screening is repeated and if the plant is determined to be clean, it will move forward in the process.

  1. Selection of ‘mother plants’: We identify a healthy, true-to-type plant to serve as the ‘mother’ plant; propagative materials are derived from this plant and prepared for release to the public (typically nurseries and growers).
  1. Release: 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.
  1. Maintenance: Mother plants undergo annual testing to verify their pathogen-free status.
  1. Retention: We retain one to three plants per cultivar in our greenhouses, screen houses, and field blocks.