Three Methods of Plant Breeding

The definitions below are intended to clarify the difference between the Three Methods of Plant Breeding.

1) Open-pollination: Open-pollinated or “standard” varieties of seeds breed true to their type. Seeds saved from such plants will produce a crop resembling their parents. While open-pollinated varieties may have originated from a genetic mutation, or a chance cross in the field, they have been stabilized and improved through years of selection by farmers and/or breeders choosing for desirable traits such as adaptability to climate and soil conditions, storage, disease and insect resistance, beauty, taste, ripening, and sugar content.

2) Hybridization: Hybrids are the result of the deliberate crossing of two different parent varieties, usually inbreds. Typically, a corn variety will be crossed with a different corn variety and the result will always be a corn. Commercial growers look for “hybrid vigor” (synergistic effort which occurs when two diverse varieties are crossed), uniformity for mechanical harvesting and shipping, widespread adaptability to different climates and conditions, disease resistance, high yields, etc. Interspecific hybrids occur rarely in nature and genus boundaries are never crossed. Thus, it is not possible through sexual reproduction to cross a corn plant with a squash or a pig. Seed saved from hybrid plants is unstable. Traits from parents will segregate out in various combinations in the next generation. A fresh cross of the inbred seed lines will be required to maintain the variety.

3) Genetic Engineering: Unlike open-pollination and hybridization, which occur in nature, genetic engineering requires human intervention in a laboratory setting directly manipulating DNA. Genetic engineers insert a foreign gene into the host DNA usually using one of two different methods: 1) ballistic — in which a gun injects foreign DNA, and 2) biological — in which a biological vector, usually a virus, carries the foreign gene into the DNA. Genetic engineering has the ability to cross all natural species boundaries and its products are often called “transgenic” (literally across genus boundaries). It is possible to insert a fish gene into a tomato or a pig gene into a corn — which would never occur in nature without human intervention.

According to Barry Commoner in Harper’s Magazine, February 2002, the biotech industry mistakenly assumed that altering a single gene would lead to a single precise change in the host organism. Geneticist and backyard breeder Carol Deppe, author of Breed Your Own Vegetable Varieties, says the engineers forgot to account for pleiotropy. Pleiotropy is the genetic version of the ancient Taoist understanding that you cannot do just one thing. A change in any gene in a tomato plant will affect every other characteristic, not just the targeted trait. Thus, the creators of Flav'r Sav'r, the first transgenic fresh tomato, engineered primarily for longer shelf life, were dismayed to discover that it also had a horrendous flavor that left an undesirable after-taste!

In the case of genetic engineering, nature’s unpredictability is reinforced by our still-limited understanding of genomics and our still-imprecise technology. With present methods it is uncertain where inserted genes will connect on the host’s DNA and each insertion will be different from the one before it and the one after it.

Contributors:
Seed to Seed by Suzanne Ashworth
CR Lawn of FEDCO Seeds
Co-op Voices Unite
28 March 2003