In plants, a hybrid is the result of cross-breeding between two different non-hybrid plants. There are several reasons for hybridization, including increased productivity or disease resistance in food plants, and improved color or other visual attributes in decorative plants. Huge improvements in agriculture and horticulture have been made possible by combining or concentrating the characteristics of non-hybrid plants. Modern varieties of wheat, for example, are the result of thousands of years of hybridization--bread wheat (Triticum aestivum) is a hexaploid hybrid of three wild grasses. Some wheat species have two sets of chromosomes (diploid), but many have four sets of chromosomes (tetraploid) or even six sets (hexaploid).
The first offspring of a hybrid cross is known as a F1 hybrid, which is short for Filial 1. It is the first generation resulting from the crossing of two distinctly different parents.
The seed of F1 hybrids will not reliably produce plants with the same features. Plants grown from the seed of F1 hybrids may have the characteristics of one parent, both parents, or an unpredictable combination of the two. To produce F1 hybrid seed, it is necessary to repeat the cross-pollination of the parent plants every season.
Heirloom and Open-Pollinated Plants
Non-hybrid plants are known as heirloom or open-pollinated (OP) varieties. An heirloom is an open-pollinated plant that has been passed down through generations of farmers or gardeners. Just how old a plant must be to qualify as an heirloom is hotly debated, but most agree that an heirloom must have existed as a stable variety before the 1945 to 1951 period when commercial hybrids were first widely used in agriculture and horticulture.
Advantages of Hybrids
The primary advantages of hybrids are the characteristics that result from the cross. In food plants, these include increased productivity, more uniform shape and size of the fruit, consistent (and sometimes faster) development to maturity, resistance to (or at least tolerance of) diseases, improved ability to withstand hot or cold temperatures, or a delayed bolting to seed that allows an extended harvest period.
In horticulture, the advantages of hybrids can include the production of larger and more colorful flowers, more consistent blooming patterns, and more uniform growth. The hybrid creation of new colors and more attractive bloom shapes results in the introduction of exciting new cultivars every year.
Many hybrid plants have one additional advantage, technically called heterosis but commonly known as hybrid vigor. A hybrid will often produce more or grow more vigorously than either of its parents. There are competing theories about what causes it, but plant breeders and growers agree that it exists.
Hybrid vigor is the opposite of inbreeding depression, where the repeated breeding of related individuals results in a decline in plant performance.
Advantages of Non-Hybrids
Non-hybrid open-pollinated and heirloom vegetable varieties are valued for their taste and unique appearance. For example, some gardeners insist that hybrid tomatoes lack the "real" tomato taste of heirloom varieties.
The seeds of non-hybrids can be saved from year to year, because those varieties will breed "true," unlike hybrids. Farmers all over the world traditionally save seed from which to grow next year's crop. These varieties have become adapted to certain climates, soils and other growing conditions, and are economically important to farmers in developing nations.
Non-hybrids are, of course, the parents of hybrids. When an heirloom variety is lost, its unique combination of characteristics is forever lost to the gene pool.