The origins of semi-dwarf wheat

Wheat

John Linnell, Wheat (1860)

The late summer landscape of 19th Century England, such as painted by John Linnell, was filled with fields of tall golden wheat ripening in the sun. Across the Atlantic the prairies of the midwest states inspired the words by Katharine Lee Bates to America the Beautiful,

O beautiful for halcyon skies,
For amber waves of grain,
For purple mountain majesties
Above the enameled plain!
America! America!
God shed His grace on thee,
Till souls wax fair as earth and air
And music-hearted sea!

In contrast today, on the prairies of the midwest or the fields of England, the wheat is unlikely to be so tall or waving in such a poetic manner. The wheat grown today is rather shorter and stockier, with stronger stems. This is a result of wheat breeding over the past hundred years to increase the yield of wheat by reducing plant height and make the plants resistant to lodging in conditions of intensive agriculture. Wheat breeders developed plants with shorter and stiffer straws, producing semi-dwarf, high-yielding varieties that were much better adapted to intensive agriculture. Before this time the traditional varieties of wheat grown were limited in the yield they could produce as adding more fertiliser resulted in the wheat stalks growing taller and weaker making them vulnerable to breaking.

The modern semi-dwarf varieties of wheat have recently come into public attention due to the publication of popular diet books blaming these new types of wheat for a plethora of modern health problems. However, rather than these alleged health issues, I was interested to know where these semi-dwarf wheats came from and the origin of the genes responsible. In an interesting article from 2005, Katarina and Ksenija Borojevic outline the history of the genes responsible for our modern dwarf wheat, with more of a focus on Europe, rather than the better known efforts in America that resulted in the Green Revolution.

The story starts further back than you might imagine, and to Korea, where naturally occurring short stemed wheat varieties were grown as far back as the third and fourth centuries A.D. The genes responsible were natural mutations rather than a production of any human intervention. These short varieties of wheat found there way to Japan as a result of the Korean-Japanese War during the sixteenth century. Semi-dwarf wheat varieties were widely grown in Japan by the 19th Century and served to provide the dwarfing genes for all our modern wheat varieties now grown around the world.

The variety Akakomugi, a 19th Century Japanese landrace of semi-dwarf wheat, provided the dwarfing genes first transferred to Europe in the early 20th Century. The Italian wheat breeder Nazareno Strampelli was to use this Japanese wheat, crossing Akakomugi with an Italian wheat by 1913 to produce a new shorter, lodging resistant Italians wheat. By 1918 a number of new semi-dwarf wheat varieties had been developed from this initial hybridisation which soon became very well known and were grown in Italy and South America, particularly in Argentina. By 1931 Nazareno Strampelli, using further hybridisations, had produced another improved variety called San Pastore that proved to be an extraordinary success and was widely grown in Italy and many other countries for more than 35 years.

These wheat breeding initiatives were supported and encouraged by the Italian government as they coincided with a drive for Italy to be self sufficient in food. This was known, as occurred during Mussolini’s time, as the Battle for Grain. These new semi-dwarf wheat hybrids enabled Italy to double its cereal production from 1922 to 1939 and and to become more or less self-sufficient in cereal production, where previously they had been heavily reliant on foreign imports.

After World War II, the Yugoslav government was also keen to encourage national self sufficiency and imported dwarf Italian wheat varieties during the 1950’s. These were widely grown, and through hybridisation with local wheats, enabled the development of new high-yielding winter wheat that were grown on a large-scale. Average yields increased from 1.36 tons of wheat per hectare up to 5.21 tones per hectare. Neighbouring countries including Hungary, Bulgaria, Romania, the former Czechoslovakia obtained similar results.

The gene responsible for reduced height originating in the Japanese Akakomugi wheat is known as Rht8 (abbreviated for reduced height 8). The function of this gene is still not clear but has been suggested to reduce sensitivity to brassinosteroids, a class of plant hormones that promote stem elongation and cell division. The identity of this Rht8 gene was only discovered at the end of the 20th Century and has been shown to have contributed its semi-dwarf characteristics of wheat across South Central Europe and the former USSR.

Semi-dwarf wheat reached the Americas via a completely separate route and through unrelated genes. Japanese wheat breeders, continuing their work on reduced height wheat, produced a new variety in 1932 that became known as Norin 10. This was produced by crossing an old Japanese dwarf landrace wheat called Daruma with American wheat varieties. Norin 10 grew to just two feet tall, instead of the usual four.

Norin 10 was never an important variety in Japan but found its way to the USA due to the occupying US army after the Second World War. S. D. Salmon, a scientist working on wheat research with the U.S. Department of Agriculture (USDA) was serving as an advisor of the occupation army when he made a  visit to the Marioka Agriculture Research Station on Honshu in Japan. He returned to the US, with wheat samples, given by Japanese scientists during his visit, Norin 10 was among these samples.  The genes making Norin 10 a short wheat  are the Rht1 and Rht2 genes that make the wheat plant insensitive to another type of plant growth hormones called gibberellins.

In 1952, an agronomist working at Washington State University called O. A.Vogel used this Norin 10 to cross with a popular wheat variety grown in Washington at the time. The resulting variety called Gaines became the predominant wheat variety in the Pacific Northwest in the late 1960s with farmers producing record wheat yields. It was from Washington State that Norin 10 was acquired by Norman Bourlag at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico where new dwarf  wheat varieties were developed and later spread around the world, resulting in the Green Revolution and earning Norman Bourlag the 1970 Nobel Peace Prize. Adding the dwarfing genes in Norin 10 to their wheat breeding enabled the development of high yielding wheat varieties that could stand high levels of added fertiliser. These varieties developed at the CIMMYT dramatically increased wheat yields around the world, first enabling Mexico to become self sufficient in wheat and later countries like India and Pakistan.

It is clear the genes responsible for dwarfism in wheat plants have a long history and a complex route has taken them from ancient Korea into modern wheat plants in Europe and the rest of the world. While the work North America and the green revolution has attracted most of the attention, in Europe at least, genes introduced in the early 20th Century have also been important in the development of of modern wheat. It is also interesting that parts of Europe have been eating semi-dwarf hybrid wheat since the 1920s. Whatever the alleged health implications of these modern wheat varieties, the genes that make make them shorter have a long history and appeared spontaneously long before the work of modern genetics and crop manipulation.

 

Sources:

Borojevic K. and Borojevic K. (2005) The Transfer and History of “Reduced Height Genes” (Rht) in Wheat from Japan to Europe. Journal of Heredity96(4):455-459.

“Wheat is the main crop and often a strategic crop in many European countries. From a historical perspective, we describe the transfer of “reduced height genes” (Rht genes) from Japanese wheat varieties to wheat varieties in Europe and their influence on the increase of the total wheat production in the last century. Historic pathways of Rht genes were influenced directly or indirectly by wheat breeders exchanging seed samples and by some governments importing large quantities of wheat during historically critical periods for their countries.”

Borojevic K. and Borojevic K. (2005) Historic Role of the Wheat Variety Akakomugi in Southern and Central European Wheat Breeding Programs. Breeding Science. 55(3):253-256

“The old semidwarf, not very attractive, Japanese wheat variety Akakomugi was the source of the dwarfing gene Rht8 and photoperiodic insensitive gene PpD1 to many semidwarf wheat varieties in South and Central Europe in the 20th century. Integrating the Rht8 and PpD1genes in wheat varieties offered the best opportunities for reducing plant height, accelerating time of flowering, improving grain fill before the onset of dry summer conditions, enhancing spikelet fertility, and consequently increasing yields. Many breeders from South and Central Europe and from the former Soviet Union were creating winter short high yielding wheat varieties without knowing at the time that Akakomugi was the donor of such important genes. At the end of the 20th century, it was discovered that dwarfing gene Rht8 and photoperiodic insensitive gene PpD1 are located on the short arm of chromosome 2D in wheat. Microsatellite analyses proved that Akakomugi is the source for the Rht8 and PpD1 genes in many short wheat varieties in South and Central Europe.”

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