Older plant varieties (landraces)
Before the advent of modern plant breeding, farmers often developed genetically diverse ‘landraces’ of wheat. These are populations which are often highly variable in appearance, but they are each identifiable morphologically and have a certain genetic integrity. All components of the population are adapted to local climatic conditions, cultural practices, and disease and pests. Landraces are typically lower-yielding than modern wheat varieties, and many have plant structures that make them difficult to grow intensively, for example many will fall over (lodge) in wet and windy weather.
By the end of the 19th century plant breeding had advanced so that distinct, uniform and stable wheat varieties were being produced and sold to farmers. There are now many plant breeding companies throughout the world developing new varieties.
Modern plant breeding
The standard method of wheat breeding used by breeders is to produce new varieties (cultivars) by crossing two wheat lines using hand pollination, then ‘selfing’ or in-breeding the progeny. It often takes ten or more generations before selections are identified as a new variety.
Conventional plant breeding may also involve the creation of mutants by the use of chemicals or radioactivity, though in practice this is still rare in wheat breeding.
Developments in planting breeding have resulted in a number of new techniques which are all now being used to speed the development of new varieties. These include single seed descent; double haploid breeding, genomics and marker-assisted breeding.
Genetic modification and gene editing
Genetic modification is a laboratory based method where a very limited amount of genetic material, typically one of a few genes, is transferred to a plant to convey a very specific change in phenotype. It has the advantage that genes can be sourced from any species, unlike conventional breeding which is restricted to gene transfer either within the species or between closely related species.
Gene editing involves the use of proteins to make a small number of targeted modifications to a genome. This can be used to change the traits of some plants, for example greater resistance to a disease or a pest.
There are no genetically modfied or gene edited wheat varieties grown commercially.