Propagation Notes: To Seed or To Clone?
The most popular horticulture debate of the year 2015: seeds or cuttings? Our horticulturists and restoration practitioners have their favorite plant materials, but perhaps the real solution lies somewhere in between.
Here’s some background. At our Native Plant Nursery in Patagonia, AZ, plants are produced from two types of plant materials, seeds and cuttings. The seed, produced by sexual reproduction, contains a mash up of genetic information from the two parent plants. Because of the separation and recombination of genes during the process, each seed contains genetic blueprints that are unique, and will produce plants with unique traits. Plants produced from cuttings, on the other hand, are genetic clones of the parent material.
The question: how are we affecting the gene bank of a wild plant population with our restoration efforts? While we don’t yet know the answer on extended time scales, we can make observations and educated assumptions about each.
The success of offspring produced from sexual reproduction varies among individual plants. Next time you’re out wandering in the wild, pay attention to some of the reproduction strategies utilized by plants: some produce thousands of seeds per plant, while others invest their energy in a small number of seeds. This is generally an adaptation the plant has developed to maximize its seedling survival in relation to the amount of energy it invests in the seed. Of course the relationship can’t be defined by a simple equation: there are myriad other factors to consider, including the length of the life cycle (annual, biennial, perennial), the size of the organism, competition for resources…the list goes on. The same patterns are visible across kingdoms, Pacific salmon, which produce thousands of eggs at one time and then die, to human beings, who produce a few offspring over the course of decades. Remarkably, ecologists have developed a theory that can identify and give reason to the patterns of different organisms’ life histories.
Each year, we at Borderlands Restoration, in concert with federal agencies across the southwest, collect thousands upon thousands of seeds from native plants on public and private lands. Many of these seeds are then grown out at our greenhouses, and re-planted back in the wild. In the artificial, moist, sun-shaded and insulated environment of the greenhouse, seeds will germinate that may not have had the same chances out in the wild. When we out-plant, we then introduce these “genetic outliers” into the gene bank of the landscape, broadening the gene pool but perhaps working against the natural process of selection and competition.
To ensure that a plant propagated at our greenhouses in Patagonia will succeed in the wild, perhaps it’s easiest to take a cutting from a successful wild plant. That plant contains genetic information that was shaped and refined over years of competition and selection, and is specifically adapted to that place. In fact, it’s not unusual for plant populations to spread and colonize by clones – using runners, rhizomes, or other creative methods (as illustrated by the desert chollas, whose arms will break off and attach to passing animals, to be deposited in another spot where they can root and grow an entirely new plant). When we propagate plant populations for restoration primarily from cuttings, are we decreasing the genetic diversity of the population to a significant extent?
SO, WHAT’S THE ANSWER?
In our restoration practices, current thinking revolves around a compromise between the two. In nature, as well, it’s not unusual to see a plant use both strategies (seeds and clones) to colonize new areas and ensure seedling success.
Our best tools for ensuring we are making the most informed, educated decisions in our restoration practices lie in national protocols and good observational science. All of our plant materials are collected following Seeds of Success protocols, which involve sampling large populations to make sure we are gathering a representative genetic selection. The protocol for cuttings was adapted from these guidelines by BR professionals, and similarly mandates a minimum sampling size. Every collection and grow-out is accompanied by meticulous recording of data, which will enable us in future years to monitor and increase our knowledge on the topic.
BR restoration practitioners, seed collectors, and horticulturists are excited to be working in a field where so much is unknown, so much that we want to share in the journey with others! We recognize that the process of scientific inquiry is most effective when shared and discussed broadly.
We are currently seeking volunteers for our propagation and seed curation teams! Check out our Volunteer and Internship Opportunities and our Calendar (on the homepage) for upcoming events and to learn how to get involved.