Modern bread wheat was born out of a chance crossing of just a few individuals from three grass species about 10,000 years ago. Many other grass species that were not part of this crossing are still around and are being used by scientists to provide modern wheat with a boost of useful genetic diversity.
Incorporating Desired Traits from Wheat’s Wild Relatives
CIMMYT scientists have been crossing durum wheat with wild relatives of wheat, such as goat grass, since the early 1990s. This cross creates synthetic wheats, which can easily be crossed with improved varieties to incorporate new, useful genes. The resulting wheats are improved varieties that also have desirable traits from the wild parents. CIMMYT has produced synthetic wheats and their derivatives with traits such as resistance to septoria and fusarium head blight and also tolerance to drought, heat, salt, or waterlogging.
Most improved wheat varieties lack high concentrations of iron or zinc. Although grain nutrient levels vary by location, CIMMYT scientists have identified grasses in northwestern Mexico that have high levels of these minerals. The grain of some wild relatives contains 1.5 times more iron and 1.8 times more zinc than average wheats. Because the inheritance of iron and zinc seems to be genetically linked, breeders can find both traits in the same synthetic wheat and cross it with a high yielding line.
A cross between a synthetic wheat and an improved variety has almost twice as much genetic diversity as its parents. The current challenge is to make the best use of this new diversity. CIMMYT possesses more than 1,000 synthetic wheats, and samples of all are available upon request. More than 25% of all new wheats that CIMMYT has distributed in the past three years to wheat improvement programs and farmers in developing countries in irrigated and low rainfall areas have been synthetic wheat derivatives.
The Evolution of Wheat
Modern wheat is a relatively young crop, with just 10,000 generations of evolution, which sprang from the crossing of a few individuals from three grasses. Humans have been domesticating this crop for thousands of years. Early on, they started selecting plants with the most desirable traits and taking care of them with irrigation, weeding, and other precautions. Partly in response to domestication, spikes became more compact and easier to harvest, seeds stopped sticking to plant petals and became free-threshing, and most seeds germinated around the same time after planting.
Domestication facilitated those changes in a short period of time. The proto-wheat became a different species, called emmer wheat, which crossed with a third grass in present-day Iran about 10,000 years ago. With domestication, this combination eventually became modern bread wheat. However, the story continues with the help of modern science. Genes found in grasses that are thousands of years old are helping scientists to increase genetic diversity in wheat and to fortify it with desired traits.
China and Spain Benefiting from Bridge Wheat Derivatives
Researchers in China recently crossed CIMMYT synthetic wheats with local wheats and released the results to farmers in 2003. Breeders in Sichuan province have been using the CIMMYT-developed synthetic hexaploid wheat since 1995 to improve quality, yield potential, and disease resistance. After crossing and backcrossing this wheat with high-yielding local varieties, they have developed several lines and are currently testing five more.
The synthetic wheats pass on beneficial traits such as large kernels, heavy spikes, and resistance to new races of Chinese stripe rust. During two years of yield trials, the two varieties derived from synthetic wheats had 20% to 35% higher yields than the commercial check variety. One of these varieties, named Chuanmai42, had the highest average yields – more than six tons per hectare – in the trials. Since it was released in Sichuan in 2003, Chuanmai42 has been recommended by the government to farmers and has been delivered to most wheat breeding research programs in China.
In 2003, Spain registered a CIMMYT synthetic wheat derivative under the name Carmona. This fast-growing variety matures and provides seed in a shorter period than most commercial cultivars, which is valuable for wheat growers who often plant late in the year in southern Spain. Carmona has better grain quality and is suited to zero-tillage systems, where it resists foliar diseases and produces higher yields.