Citrus Tissue Culture Practice Makes Perfect

I recently posted an article that outlined some challenges and opportunities related to tissue culture (TC) production of citrus scions. This issue was brought to the forefront as a result of overnight interest in the UF/IFAS 7-6-27 mandarin hybrid (FAST TRACK Suite III). Grower demand for budwood quickly exceeded supply and nurseries began to look to TC as a potential solution. While the wheels are in motion to address the regulatory aspects of producing scions through TC, labs and nurseries are being licensed and they are beginning the process of establishing material, developing lab procedures, and taking orders.

Citrus tissue culture sample
Photo courtesy of Agri-Starts

It is important that citrus nurseries and growers understand the fundamentals of the TC process, the opportunities, and any risks that may be present. DPI is working hard to protect industry interests without unnecessarily hindering variety introductions through technological advancements and the use of proven laboratory procedures.

I reached out to TC laboratories and nurseries to better understand the process and how this may be a useful tool to restore acreage and help achieve critical mass of new varieties. This is a technical issue. The details and specific procedures are important. However, to avoid breach of confidentiality and competitive advantage of the companies involved, we will top-line the issue. Hopefully, those most interested will elect to seek more information from their nursery partners and follow the issue in future research and trade publications.

Why consider TC?

Mathew Konrad of Citrific puts it like this: “At its very core, plant tissue culture is a collection of techniques used to maintain or grow plants under sterile conditions on a nutrient culture medium of known composition (think synthetic soil). That being said, the only difference between tissue culture and a greenhouse cutting operation is that tissue culture is done in a sterile environment, which allows for faster growth; the ability to use smaller size material; more potent and larger database of synthetic chemicals; and more control that leads to a higher and faster success rate than one might get in a cuttings operation.”

Process Overview

David Lawson of Agri-Starts explains there are two traditional means of regenerating plants from TC. Indirect Organogenesis: “The plant is taken through a callus stage (undifferentiated cells, the cells have not chosen an organ to develop into) and then, by adding select hormones, you tell those cells to regenerate into shoots or embryos. This is one method where you get single cell regeneration. Typically, it has been shown this type of method increases the chances for off types or variations. However, it is still widely used as the percent of off types is typically so low that the risk does not outweigh the benefits. The best example of this is coffee. The majority of coffee trees worldwide are propagated this way. They generate embryonic callus the same as breeders do when they are doing transformations. These turn into plant embryos and eventually an entire plant.”

Direct Shoot Organogenesis: “New plants are regenerated from existing organs. Cells do not go through a callus stage. This process is considered the safer route to avoid mutation. It still encompasses regeneration from single cells of plants as long as they do not enter a callus stage. This typically takes higher concentrations of hormones to accomplish. Most cautious labs do not increase hormone concentrations to high enough levels for mutations to happen. Instead the propagators increase hormone levels just enough to break apical dominance without having to mechanically prune the plant. By doing this you can promote lateral growth from existing meristems (buds) much more rapidly than conventional methods ex vivo (in a greenhouse).”

Click on the following pages to read the Q&A with our plant nursery insiders.

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