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The Other Side of Seed Saving: Preserving Genetic Diversity

Courtesy of Seed Savers Exchange

When we think of saving heirloom seeds, we tend to do what humans often do: We think of our own needs and desires first. We save heirloom cultivars because of their taste, form, and connection to our family or culture. And I’m not one to stand between someone and their favorite tomato; I have a few hundred favorites of my own. But beyond a personal connection, or an affinity for a cultivar’s taste or fragrance, we also keep heirloom cultivars because they’re comprised of genes that allow a species and, more specifically, a cultivar, to adapt to changing conditions in the world around us, ensuring that they have a chance of being in our gardens for generations to come.

The Nerve to Preserve

As seed savers and lovers of open-pollinated plants, we should do our share to help preserve the genes of time-honored cultivars. In the last issue of Heirloom Gardener (“Bountiful Blossom Bagging,” Summer 2019), we talked about manipulating a cultivar’s pollination to maintain its beloved traits, such as the form and taste of ‘Dr. Wyche’s Yellow’ tomato or the shape and color of ‘Black Barlow’ columbine. By ensuring that an heirloom cultivar was cross-pollinated by the same cultivar — and in the case of blossom bagging, by the same flower itself — we keep these cherished traits stable.

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Corn is prone to inbreeding depression, so collect seeds from a large number of plants to maintain the health of the cultivar.
Photo by Getty Images/ryasick

But there’s a second aspect to maintaining an heirloom variety, and that’s maintaining its vigor and adaptability by safeguarding and managing its genetic health. While there are many visible crop characteristics, there are other genes within each cultivar for traits that are latent, and that vary from seed to seed within the cultivar, such as disease resistance and drought tolerance. These traits allow the cultivar to adapt to changing conditions over time and are just as essential — or perhaps even more so — for keeping a cultivar in the world for the long run. Prioritizing genes that protect a cultivar over ones that enhance taste, for example, doesn’t discount our own passion for that taste inasmuch as it ensures that this particular great tasting cultivar will remain with us.

Vigorous Vines

Managing a cultivar’s genetic breadth is relatively simple, and requires a method that isn’t unfamiliar to dog breeders: Work with a large enough population size to ensure that inbreeding doesn’t damage the species with which you’re working. Unlike hybrids, which are strictly produced to have very little genetic variation, heirloom cultivars evolve­, like humans, over time and from generation to generation. By using a larger population of a particular cultivar from which to collect seeds, we help to ensure its long-term health.

As a beagle owner, I’m happy to say that beagles are considered to be a very healthy breed and, to a large extent, that’s due to the large breeding pool from which beagles are bred. Other breeds have a smaller pool of potential mating partners, and often see undesirable traits passed on due to a lack of genetic diversity within the breed.

To ensure genetic preservation in particular cultivars, we seed savers need to increase the population size of each cultivar from which we plan to collect seeds. The recommended population size varies from species to species due to the nature of the species themselves. Some crops, such as corn, are known to suffer from “inbreeding depression,” and without seed being collected across a larger population size, the health and vigor of the cultivar will decline.

Preserve your favorite cultivars, such as ‘Dr. Wyche’s Yellow’ tomato, by ensuring their genes are adaptable. 
Courtesy of Seed Savers Exchange

As a general rule, crops that are primarily self-pollinating can be collected from a smaller population size, whereas cross-pollinators benefit from being collected from a larger population. Many home gardeners collect seed from a small population for personal use, and if they see a decline in the performance of their seed, they simply buy new seed and begin again (provided that it’s a cultivar that can be easily obtained). While this isn’t the most effective method of genetic preservation, all the people saving seeds from the same cultivar are helping to maintain its genetic breadth. Generally, the hope is that the breed is being maintained as broadly as possible so we can all continue to enjoy a long-cherished pepper or cabbage cultivar.

On a higher level, though, we’re saving something more than the cultivar itself. While the beloved traits of a cultivar are often specific to it — the sweet, low-acid flavor of the aforementioned ‘Dr. Wyche’s Yellow’ tomato, for example — these unseen traits relating to vigor and adaptability are significant beyond that cultivar. These traits, whether held by a ‘Green Zebra’ or a ‘Trucker’s Favorite’ tomato, are valuable for maintaining the species, and are also a boon for breeders creating new cultivars with traits that may be essential to the genetic health of that species. For instance, a resistance to tomato blight found in one cultivar can be bred into another, or the drought tolerance of one cultivar can be crossed with another cultivar with great flavor to create a brand-new cultivar that will taste delicious and easily adapt to changing environmental conditions.

Tending to Traits

We preserve cultivars because of what we love about them, but just like anything we care for, we should also make sure we take care of the traits, seen and unseen, that’ll keep them around for decades. And if I need a reminder of why this work is so critical, I simply head out to the vegetable garden with my beagle, Fred, in tow to be surrounded by all the cultivars that I cherish and hope to have in my life for years to come.


Population Size for Seed Saving

Common Onion

Viable Seeds: 5 plants

Genetic Preservation: 80+ plants

Pepper

Viable Seeds: 1 plant

Genetic Preservation: 50+ plants

Cucumber

Viable Seeds: 1 plant

Genetic Preservation: 25+ plants

Summer Squash

 Viable Seeds: 1 plant

Genetic Preservation: 25+ plants

Carrot

Viable Seeds: 5 plants

Genetic Preservation: 80+ plants

Lettuce

Viable Seeds: 1 plant

Genetic Preservation: 20+ plants

Pea

Viable Seeds: 1 plant

Genetic Preservation: 20+ plants

Tomato

Viable Seeds: 1 plant

Genetic Preservation: 20+ plants

Corn (Maize)

Viable Seeds: 10 plants

Genetic Preservation 200+ plants


Lee Buttala is the former executive director of Seed Savers Exchange. He’s an Emmy Award-winning producer of “Martha Stewart Living,” and the creator, director, and producer of PBS’s “Cultivating Life.” He is the co-editor of The Seed Garden: The Art and Practice of Seed Saving.

Published on Aug 27, 2019

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