Potatoes and sweet potatoes are maintained in a tissue culture laboratory rather than in the field. Established in 1994, the tissue culture laboratory minimizes the amount of time, space, and labor required to maintain these plant types. Over 500 potato varieties and 90 sweet potato varieties are currently held in this way. Since both potatoes and sweet potatoes are propagated clonally, the varietal genetics remain constant even when small populations are maintained. This is very different from sexually propagated crops, where genetic drift and small population size is a constant consideration in maintaining each variety’s genetic diversity. With our in vitro Collection, just four individuals of every variety are maintained at a given time. To ensure against contamination or other cultural problems, the four individuals always consist of two sets of two. The two batches are sub-cultured at different dates, on different batches of media.
All tissue culture work is performed in aseptic laboratory conditions within a laminar flow hood. To induct a potato variety into tissue culture, a lab technician first separates a small nodal cutting from the parent plant or cuts off the apical end of a tuber sprout. This explant is disinfected, trimmed, and placed in a test tube with a purpose-specific growth medium. After 3-4 weeks, a new plantlet will have grown to the point that it can be sub-cultured. Plantlet nodes are then cut and placed into fresh growth media where they are monitored for health and vigor.
At the end of 3-4 months, four healthy plantlets of each variety are chosen for long-term storage in a specialized growth chamber. Nodes from these plantlets are transferred to test tubes containing media with growth-inhibiting hormones, which will slow growth and maximize the time before the variety must be sub-cultured again. Most varieties can be maintained in the growth chamber for 6-12 months before subsequent sub-culturing, and they are propagated in this way for many years.
In 2010, sweet potatoes were inducted in the tissue culture laboratory for the first time. The tissue culture process for sweet potatoes is similar to potatoes, though they require different media and temperatures for ideal long-term storage.
SSE is currently collaborating with the Wisconsin Seed Potato Certification Program and the Department of Plant Pathology at the University of Wisconsin-Madison to eliminate plant viruses from our potato collection. To learn more about this collaboration, see Collection Projects.