In agriculture and gardening, hybrid seed is seed produced by cross-pollinated plants. In hybrid seed production, the crosses are specific and controlled. The advantage of growing hybrid seed compared to inbred lines comes from heterosis. To produce hybrid seed, elite inbred varieties are crossed with well-documented and consistent phenotypes (such as yield) and the resulting hybrid seed is collected. Another factor that is important in hybrid seed production is the combining ability of the parent plants.
Although two elite inbred parent plant varieties may produce the highest yields of their crop, it does not necessarily mean that crossing these inbreds will result in the highest yielding hybrid. The level of heterosis that the parents will generate in the resultant seed is called “combining ability. ” Higher combining ability between the parents results in increased performance in the resulting hybrid seed. Hybrids are bred to improve the characteristics of the resulting plants, such as better yield, greater uniformity, improved color, disease resistance, and so forth.
Today, hybrid seed production is predominant in agriculture and home gardening, and is one of the main contributing factors to the dramatic rise in agricultural output during the last half of the 20th century. In the US, the commercial market was launched in the 1920s, with the first hybrid maize. All of the hybrid seeds planted by the farmer will be the same hybrid while the seeds from the hybrids planted will not consistently have the desired characteristics. This is why hybrid seed is constantly repurchased by growers for each planting season.
Crop yield Using the techniques of modern biotechnology, one or two genes (Smartstax from Monsanto in collaboration with Dow AgroSciences will use eight, starting in 2010) may be transferred to a highly developed crop variety to impart a new character that would increase its yield.  However, while increases in crop yield are the most obvious applications of modern biotechnology in agriculture, they are also the most difficult ones. Current genetic engineering techniques work best for effects that are controlled by a single gene.
Many of the genetic characteristics associated with yield (e. g. , enhanced growth) are controlled by a large number of genes, each of which has a minimal effect on the overall yield.  There is, therefore, much scientific work to be done in this area. Reduced vulnerability of crops to environmental stresses Crops containing genes that will enable them to withstand biotic and abiotic stresses may be developed. For example, drought and excessively salty soil are two important limiting factors in crop productivity.
Biotechnologists work to find genes that enable some plants to cope with these extreme conditions and eventually to transfer these genes to the more productive crops. One of the latest developments is the identification of a plant gene, At-DBF2, from Arabidopsis thaliana. Arabidopsis thaliana is a tiny weed often used for plant research because it is very easy to grow. Its genetic code, approximately 115 Mb of the 125 Mb genome, which has been sequenced and interpreted and which can be manipulated in many ways. Improved taste, texture or appearance of food
Modern biotechnology can be used to slow down the process of spoilage. Modified fruit can ripen longer on the plant and then be transported to the consumer with less risk of spoilage, and a still-reasonable shelf life. Production of novel substances in crop plants Biotechnology is finding novel uses beyond food. For example, oilseed can be modified to produce fatty acids for detergents, substitute fuels and petrochemicals. Potatoes, tomatoes, rice, tobacco, lettuce, safflowers, and other plants have been genetically engineered to produce insulin and certain vaccines.
If future clinical trials prove successful, the advantages of edible vaccines would be enormous, especially for developing countries. Seed enhancement Seed enhancement is a range of treatments of seeds that improves their performance after harvesting and conditioned, but before they are sown. They include priming, steeping, hardening, pregermination, pelleting, encrusting, film-coating, tagging and others, but excludes treatments for control of seed born pathogens.  They are used to improve seed sowing, germination and seedling growth by altering seed vigor and/or the physiological state of the seed.
The alteration may improve vigor or the physiological state of the seed by enhancing uniformity of germination. Treatments may include hydration treatments, such as priming, steeping, hardening, and pre-germination. Other treatment include the use of chemicals that trigger systemic acquired resistance or improve stress tolerance. The use of antioxidants. Enhancements like pelleting, coating and encrusting improve seed handling and planting. Some treatments enhance nutrient availability or provide inoculates by delivering materials (other than pesticides) needed during sowing, germination and seedling establishment.
In agriculture, precision seeding is a method of seeding that involves placing seed at a precise spacing and depth. This is in contrast to broadcast seeding, where seed is scattered over an area. Although precise hand placement would qualify, precision seeding usually refers to a mechanical process. A wide range of hand-push and powered precision seeders are available for small- to large-scale jobs. Using a variety of actions, they all open the soil, place the seed, then cover it, to create rows. The depth and spacing vary depending on the type of crop and the desired plant density.
In commercial production, precision seeding is an alternative to placing larger quantities of seed in a row, by dribbling seed or setting several seeds in each position. Depending on the device, precision seeders may place only one, or a very few seeds per position. This is an advantage, in that it saves seed and it avoids crowding, or the need for thinning, allowing plants the space to grow efficiently. On the downside, by placing fewer seeds, a very high germination rate is required to make full use of the seeded area.
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