Hybrids
A hybrid results from the controlled pollination of one genetically uniform variety with the pollen from another genetically uniform variety. A grower (seed company or hybridizer) chooses male and female parents with specific traits and characteristics to produce a brand new offspring variety.
Parents may be selected for disease resistance, earliness, unformity, color or flavour depending on the qualities sought after for the new variety. The pollination is done by hand, and it is very labor intensive to produce the quantities of seed needed for mass marketing. That is one reason that hybrid seed is usually more expensive than open-pollinated varieties.
F1 hybrid
Is the first generation offspring of the controlled pollination of the two parents.
This is the seed that you buy, and plant.
This generation usually has a vigor that is not present in open-pollinated varieties, and can result in higher yields.
The one downside of hybrids is that they don’t “breed true”.
If you plant the seeds you save from a hybrid they will not be the same as they were the first year, and in fact may be totally different, reverting to ancestral forms.
For that reason, hybrid seed must be purchased from the seed company. The original cross pollination of the two parent varieties must be repeated every year in order to produce the hybrid seed.
Common home tomato varieties like Early Girl, Tumbler, Mamma Mia and Sunsugar are all hybrids.
Open-Pollinated
These varieties are strains that originally resulted either by chance or by human selections for their desirable traits. These varieties will breed true, and the offspring will remain fairly close to their parents, but with less uniformity than F1 hybrids.
The seed source of O.P. varieties is kept “true” by utilizing the proper isolation of seed plants from each other to prevent cross-pollination by bees or wind.
With these seeds cross-pollination with other varieties is not desirable, which can result in ‘off” types.
Home gardeners can save seed from open pollinated varieties as long as recommended practices for each species are followed.
Heirloom
The definition of an heirloom variety differs between experts.
Generally speaking you can think of heirlooms as antique open-pollinated varieties.
Heirloom varieties have sometimes been handed down from generation to generation, or have been carried by people as they move and settle in new places.
Heirlooms have generally been around for at least 50 years, though some have been around much longer.
GMO
Seeds labeled GMO—the acronym for “genetically modified organism”—result from one of the industry’s most controversial practices. GMO seeds are bred not in a garden but in a laboratory using modern biotechnology techniques like gene splicing.
Hybrids should not be confused with GMOs. While hybrids are crossed manually in the field, GMOs are created using high-tech methods such as gene splicing, sometimes combining genes from different species to yield organisms that could not occur in nature.