A clone has an identical genetic blueprint to its source organism. Few members of the animal kingdom reproduce naturally by cloning. Plants, however, often reproduce by cloning, establishing new units from cuttings, limbs bent to the ground and rooting, or suckers and shoots springing from the root system. Root division for replanting, such as with tulips, garlic and potatoes, also creates clones.
Cloned plants are uniform in appearance and growing habits. Once plant breeders develop desirable characteristics in a line of plants through traditional breeding methods, explains Jim Giovannoni, a plant molecular biologist at the Boyce Thompson Institute at Cornell University, allowing further sexual propagation would likely dilute the desired traits. Cloned plant reproduction has the advantage of locking those desired characteristics uniformly across the plants subsequently produced and distributed for sale. Some plants must be reproduced by this method to ensure uniformity; for example, apples will not reproduce true-to-type, so growing successive generations of Granny Smiths or Red Delicious apples requires cloning trees from prior specimens. Uniformity may have both positive and negative effects, however; genetically identical plants will flower or bear fruit at the same time, which may be an advantage in a commercial setting requiring large one-time harvests, but a disadvantage in the home or market garden or landscape where an extended bloom or harvest season is desired.
Disease resistance may be both an advantage and a disadvantage of cloned plants, according to botanist David Hershey writing for the MadSci Network botany division. Genetic uniformity across a wide region can mean that all of that particular type of plant may be wiped out by a particular pest or disease. Genetic diversity increases the odds that some plants will survive the infestation and go on to populate the area with more resistant strains. On the other hand, Hershey notes that cloned plants, particularly of the agricultural crop varieties, can be rapidly duplicated, so plant breeders can devise and clone sufficient blight-resistant tomatoes, for example, and distribute them throughout a growing region within a few growing seasons to ensure that food production systems and the agricultural industry can continue successfully in the face of pest and disease threats.
The Ohio State University Botany Department readings on plant propagation use the example of fall-planted bulbs--daffodils, tulips--as common cloned landscape plants. Commercial bulb breeders compete to see who can offer the next interesting color or growing habit variation in spring flowering bulbs. The ability to clone a tulip that has a new color combination allows bulb growers to develop proprietary lines which have high economic value. However, the ability of most hardy cloned varieties, like naturalizing daffodils, to be reproduced by their subsequent purchasers in their own landscapes means that the proprietary advantage of many cloned plants will only last a few years from their release. After that, the ease of reproducing plants by cloning will diminish the proprietary value of the variety, and the plant seller will have to look to the next advantageous characteristic to clone to boost sales.