Made to order

One thing growers have in common with the makers of smartphones and other popular tech gadgets is they both need to anticipate what the consumer wants before it actually gets into their hands. In the meantime, there is an urgency to hunt out the best attributes of a product and have it ready as quickly as possible.

Top breeders across the country are searching the world—and their own backyards—to find plants with the best attributes. Once they make their selections, they can use tissue culture propagation to hasten the breeding and production of different plants. Growers have the option of investing in a tissue culture laboratory or contract those services out to an existing lab.
 

The process

Successful propagation via tissue culture is all about gaining the knowledge to do it successfully, says Mike Dobres, managing director at Nova Flora.

The process begins by taking cuttings off the terminal portion of the plant during active growth, says Megan Mathey, plant breeder with Spring Meadow Nursery in Grand Haven, Mich. “Sterile” will become a staple of your vocabulary throughout the process. Plant material that is being clipped to bring back to the lab must be clean at the time of the cutting and kept clean as you return to the lab. Snips and pruners must be kept sterile when taking multiple cuttings.

“We usually collect cuttings containing three nodes, then we bring them back to the lab to prepare for initiation,” Mathey says. “This is where the leaves are removed, the stem above each node is cut as close to the node as possible, and roughly a centimeter of stem is left below the node for easy insertion into the media. From this point the explant is ready for sterilization.”

Mathey says people have their own preferred method of sterilizing the explants, including a soaking in de-ionized water for a couple of hours, or running under tap water. She says they give their explants a quick zap in 70 percent ethanol (for 30 seconds) then they get rinsed in a beaker containing reverse osmosis water and placed on a stir plate and left to spin 30 to 40 minutes. They use a sterilization solution of sodium dichloroisocyanurate (NaDCC) or sometimes 10 percent bleach solution. Different concentrations of solutions and the time in the solution are used based on how woody the plant material is, or how likely it is to be burned under a solution.

“You have to find the right niche for each plant,” says Mathey.

After about 20 minutes in the sterilization solution the explants are then transported to a sterile, laminar flow hood. The sterilization solution is drained off and the explants are divided up into auto-claved, sterile de-ionized water.

Next is the initiation phase. The plants are placed in test tubes. The initiation media is water based with salt, sugar, hormones and vitamins—many powder formulas are available from lab supply companies.

If all goes well over the next two to four weeks the plant material should be multiplying. At this phase, propagators must watch for diseases. Success at this point depends on various environmental factors, including the time of year.

“It’s the frustrating part of the process, because some do really well, others don’t,” Mathey says.

The ones that make it will be moved on to a multiplication media, which contains a mixture of hormones that will produce prolific shoots. For each nodal shoot Mathey says they’ll get 4-5 plants and sometimes even more.

We’re not done yet. We need roots, which is why Mathey places the shoots on a rooting, or what is sometimes called an elongation media. In this phase the plants elongate with the assistance of a mix of different hormones. After roots are formed the plant then goes into a plug tray with peat-based media, then kept in a high humidity environment consisting usually of a dome and/or misting chamber, until fully acclimated. The final move to the greenhouse must be done carefully to avoid shocking tender plants that have been receiving special attention thus far.
 

Embryo rescue

Embryo rescue is a form of tissue culture used to facilitate crosses that would pollinate but not fully set seed before the embryo aborts. It can also be used for seed that is difficult to germinate.

Crosses are made, says Mathey, and then watched to see at what day they abort, which will allow you to come up with the day you can rescue the embryo. For instance, if the seed capsule swells then aborts on day 8, then the swollen capsule is harvested on day 7. From there the capsule is treated like an explant and put through the sterilization process. The capsule is then moved to the sterile flow hood and excised exposing the ovule, or the embryo—and either is then laid out on a media consisting of sugar and vitamins—no hormones—until they germinate.
 

Plant breeding and tissue culture

Breeders like Dan Heims at Terra Nova Nurseries travel abroad to collect breeding stock, coming up with some exotic varieties that have become perennial favorites with gardeners, such as Heuchera ‘Georgia Peach.’ Others, like Dobres at Nova Flora, find desirable crosses a little closer to home, part of a quest to cross plants that will be as appealing to the eye as they are sustainable in the environment.
 

Making the leap

“Plant breeding and especially tissue culture can require significant capital and knowledge depending on the size and scale of the startup business,” says Gary Hennen, president of Oglesby Plants International. “Both activities can be done on the hobby level with minimum investment and as you gain experience and expertise grow into something bigger.

“My recommendation is to do your homework and learn everything you can about the plant group or groups that interest you, where the breeding is heading and who the commercial players are, if any. Find a niche and dig in. It can be a long, fun ride.”

Neil Moran is a horticulturist and writer for GIE Media. Visit his website at www.neilmoran.com.