Wheat Breeding

Until the 1960s breeding new varieties of wheat and other plants was confined to research institutions. This changed with the introduction of the 1964 Plant Varieties and Seeds Act, which allowed breeders to be paid royalties for the varieties they developed, known as plant breeders rights. As a result, most plant breeding is now carried out in the private sector, while the basic research is still carried out by institutions. Breeding new wheat varieties is also funded by a system of payments collected from farmers who collect and save seed from one year to the next. Patents are sometimes used to fund research, for example when a technology has been applied to more than one variety. Collection of payments and government representation is carried out by the British Society of Plant Breeders, founded in 1966.

Creating new wheat varieties is achieved using conventional artificial selection. In artificial selection breeders cultivate wheat plants and select only the specimens with the features deemed to be desirable for further cultivation. The first generation of offspring, the F1 generation, are uniform but F2 and later generations show an enormous diversity of different gene combinations. Therefore, generations of wheat plants are cultivated and with each generation the plants with the best combination of characters are selected for further breeding. This continues until only those with the best traits remain and undesirable features cease to emerge, a process that can take up to 12 years. Characteristics that might be selected for include crop yield, physical characteristics like height, the timing of crop maturation and resistance to disease, pests and environmental stress. The efforts of breeders have resulted in the recent appearance of ‘Alternative Wheats’ that can be planted in both winter and spring growing seasons. Artificial selection has also been used to shorten the life cycle of wheat, allowing it to be grown at higher latitudes with shorter growing seasons;

Some genetic technologies are now being used to streamline the process of artificial selection. Mapping the location of a desirable gene in wheat allows breeders to work out from an early stage whether or not it is present in an individual. Marker assisted breeding uses genes to label a desirable characteristic and determine whether or not it is present in a plant.

Genetic modification offers precise manipulation of characteristics by changing or deleting genes, or inserting new genes from other organisms. This allows the inclusion of desirable traits in the genome of a cultivated plant without other less desirable traits that might be introduced. For more information on Wheat Genomic research, see the follow the link to the Research page.

Some breeders run parallel breeding programs in the northern and southern hemispheres, so that in a year they benefit from two growing seasons. Plants cultivated for breeding processes are grown under strictly controlled conditions that optimise their growing environment.

Breeders aim to reach a condition of complete homozygote wheat plants, ensuring that a variety is uniform across the population. This is achieved by a mode of reproduction called selfing, where the developing wheat seed is fertilised by the pollen of the same parent plant. However, eliminating heterozygote alleles is a lengthy process and may take many generations to perfect. Technological developments have accelerated the process by stimulating a phenomenon known as double haploidy.

To produce a double haploid wheat plant a specimen is crossed with another closely related cereal plant, such as maize, that stimulates the beginnings of cell differentiation. However, the difference between the two crossed species is sufficiently wide that the maize genome does not become involved, thus rendering the developing plant tissue haploid. Samples of this haploid plant tissue are cultured under laboratory conditions. The chromosomes are stimulated chemically into duplicating themselves, developing into a plant that bears two identical haploid genomes. This double haploid individual can then be selfed, becoming the parent for a pure line of homozygote diploid wheat plants. In effect, this achieves several generations of breeding in a single step. This technique is expensive, but to a breeder the time saved justifies the cost.

Virginia Polytechnic Institute and State University have a web site dedicated to crop genetics on which there is a nice short video decribing what plant breeders do. They have also published a Powerpoint presentation on the production of double haploids. A much more detailed description of the process is available in a 2010 issue of the Journal of American Science (J American Science 6(7): 139-148).

Once a new variety has been developed, it undergoes a series of trials in order to be considered for National Listing. The first phase of trials ensures that a new variety is distinct from previous ones, is uniform between individual plants, and is stable from one generation to the next. Criteria are very strict, even tiny details such as the shape of the glume tips are scrutinised. The slightest inconsistency can lead to the failure of a new variety. The second phase of trials tests the Value for Cultivation and Use (VCU), ensuring that only those plants that have improved characteristics can be approved for sale. If the breeder is successful, the variety will have a published description catalogued on a national register of varieties approved for marketing. Further trails comparing performance with other varieties are carried out once the new variety is on the market. A set of guidelines to test for distinctness has been published by the International Union for the Protection of New Varieties of Plants.

After a wheat variety has been developed, it is cultivated for the production of seed that is of a certified quality. Approximately 9% of arable farmland in the UK is used for seed production, including wheat, and other cereals.

The development of wheat varieties is estimated to have increased crop value between £373 million and £445 million since 1982, measured in 2010 wheat prices. Since 1982 wheat production has increased by 57%, securing milling jobs and £300 million of annual milling turnover. Importantly, the increased production has allowed imports to decrease, reducing dependence on other wheat-producing nations and reducing the environmental impact of transporting grain. More in depth information on cereal breeding can be found on the Agriculture and Horticulture Development Board website.

The British Society of Plant Breeders have published a handbook describing how the plant breeding industry works. KWS are a company that have successfully bred some of the most profitable wheat varieties in the UK, and their website contains more information on their breeding practices, and product development.

Norman Borlaug and the Green Revolution

Norman Borlaug, born in Iowa in 1914, is sometimes referred to as ‘the father of the green revolution’ and is accredited for having used artificial selection to produce some of the commercially viable wheat varieties used today. One of Borlaug’s achievements was hybridizing existing wheat varieties in order to produce varieties of wheat that could be grown in each of the separate growing seasons in Mexico, thus boosting the quantity of grain produced over the course of a year. Later he used similar hybridisation to produce wheat that was resistant to a greater diversity of diseases, as many pureline wheat varieties are only resistant to a few pathogens.

Borlaug is also responsible for the height of modern wheat varieties, a characteristic that is of great economic importance. Before Borlaug’s work, some of the most productive wheat varieties tended to grow very tall, and would fall over under the weight of the ears of grain that would then rot. Borlaug hybridised these tall wheat plants with a mutant dwarf variety that was found in US-occupied Japan, called Norin 10. The result was more modern wheat varieties that produce a high yield of grain, but did not grow to very great height and therefore was at a lower risk of falling over. A small group of different varieties with these characteristics were produced, named Nainari 60, Pitic 62, Penjamo 62 and Sonora 64. The reduced height also improves compatibility with combine harvesters, and diverts the plant’s resources from vertical growth into the production of grain. The impact of the semi-dwarf wheat has been profound: twenty years after its introduction to Mexican farmers, the crop yield had increased six fold. There has not been a famine in India since the semi-dwarf wheat varieties were introduied. Further information on Norman Borlaug and his work can be found on the Nobel Prize website, the AgBioWorld Foundation website and the Norman Borlaug Foundation website.