POPULATION SIZESeed Savers Exchange

Grant Olson

Our mission is to save North America’s diverse, but endangered, garden heritage for future generations by building a network of people committed to collecting, conserving, and sharing heirloom seeds and plants, while educating people about the value of genetic and cultural diversity.

population size

inbreeders and outbreeders

inbreeders are primarily self-pollinating:

pea, bean, tomato, lettuce

outbreeders are primarily pollinated by other plants:

cabbage, carrot, onion, melon

generally, outbreeders require larger populations

inbreeding depression

deleterious alleles

genetic driftimage source: gringer

over-selection

extreme inbreeders: 10-20 plants

moderate inbreeders: 40 plants

outbreeders: 80 plants

outbreeders sensitive to depression: 200 plants

outbreeders not sensitive to depression: 10-20

varietal history and population size

planting size vs population size

home vs commercial scale

reacquiring genetic diversity

use the SSE Yearbook to locate other growers maintaining your variety

contact SSE directly for potential sources

contact seed companies who have offered the variety in the past

contact other seed banks or use USDA’s on-line GRIN database (www.ars-grin.gov/)

additional resources

for more information:

Breed your own Vegetable Varieties, Carol Deppe

Seed to Seed, Suzanne Ashworth

The Organic Seed Grower,John Navazio

A Seed Saving Guide for Gardeners and Farmers, OSAwww.seedalliance.org/publications