How a Gene from Japan Revolutionized the World of Wheat: CIMMYT's Quest for Combining Genes to Mitigate Threats to Global Food Security

In 1935, the work of Japanese scientist Gonjiro Inazuka to cross a semi-dwarf Japanese wheat landrace with two American varieties resulted in an improved semidwarf variety, known as Norin 10. Unlike other varieties, which stood taller than 150 cm, the Rht1 and Rht2 genes present in Norin 10 reduced its height to 60–110 cm. In the late 1940s Orville Vogel at Washington State University used Norin 10 to help produce high-yielding, semi-dwarf winter wheat varieties. Eventually, Vogel's varieties ended up in the hands of Norman Borlaug, who was working to develop rustresistant wheat in Mexico.

In 1953, Borlaug began crossing Vogel's semi-dwarf varieties with Mexican varieties. The result was a new type of spring wheat: short and stiff-strawed varieties that tillered profusely, produced more grain per head, and were less likely to lodge. After a series of crosses and re-crosses, the semi-dwarf Mexican wheat progeny began to be distributed nationally, and within 7 years, average wheat yields in Mexico had doubled. Borlaug named two of the most successful varieties Sonora 64 and Lerma Rojo 64, and it was these two varieties that led to the Green Revolution in India, Pakistan and other countries. This international exchange of ideas and germplasm – starting with genetic resources from Japan – ultimately saved hundreds of millions of people from starvation.

Fifty years on, farmers and societies face new challenges to feed rising populations, and wheat, along with its production and trade, epitomize the difficulties. The world's climate is changing; temperatures are rising in major wheat-growing areas and extreme weather events are becoming more common; natural resources are being depleted; new diseases are emerging; and yields are stagnating. Coupled with these difficulties, ever-increasing demand for wheat from a growing worldwide population and changing diets put pressure on grain markets, pushing up prices, disrupting free trade when drought or floods threaten crops in wheat-producing nations.

With offices and research stations in 14 countries including its headquarters in Mexico, the International Maize and Wheat Improvement Center (CIMMYT) is working to address these challenges through scientific research. CIMMYT's research is focused on sustainably increasing wheat and maize productivity, which includes actively contributing to a better understanding of the genetic basis of yield, as well as drought, heat and disease resistance. Through the Seeds of Discovery (SeeD) initiative, and other collaborations, CIMMYT is also broadening genetic variability and discovering new genes that will help increase yields and prevent crop losses to climate change or disease.

The Origins of Norin 10

Upon hearing of Orville Vogel's successes in incorporating the semi-dwarf genes from the Japanese Norin 10 variety into winter wheat, Norman Borlaug wrote to him in 1952 requesting that genetic materials containing the Norin 10 genes be used as parental lines in the Mexican wheat breeding program. A few months later a small number of seeds arrived in Mexico from three different F2 plants originating from the cross Norin 10 × Baart and a small number of seeds from each of the five F2 plants from the cross Norin 10 × Brevor (Reynolds and Borlaug 2006). With this simple exchange of communication and germplasm, so began one of the most extraordinary agricultural revolutions in history.

The journey of semi-dwarf wheat from Japan to Mexico may have begun in Korea in the third or fourth century, where short wheat varieties may have originated (Cho et al. 1993). From East Asia, wheat breeders in Italy, the USA and elsewhere began to seek and utilize dwarfing genes to breed for high yield, resistance to lodging and ability to produce more tillers than traditional varieties.

The lineage of the Norin 10 can be traced back to Daruma, a native Japanese short-straw variety (see Fig. 2.1) crossed with one soft “Fultz” and one hard wheat “Turkey Red” variety from the United States. 'Fultz' was first introduced to Japan

Fig. 2.1 Pedigree of Norin 10 (Reitz and Salmon 1968)

from the USA around 1892. The exact year that 'Turkey Red' arrived in Japan is unknown but it is thought to have been around the same time (Reitz and Salmon 1968). Fultz and Turkey Red were used in two significant crosses at the Central Agricultural Experiment Station in Nishigahara, Tokyo during the early twentieth century leading to the creation of Norin 10. First, in 1917 a variety called 'Glassy Fultz' was isolated from the 'Fultz' variety, and then crossed with Daruma to create 'Fultz-Daruma.' Then, in 1924 Fultz Daruma was crossed with Turkey Red (Inazuku1971). Pedigree lines were then transferred to the Konosu Branch Station, Saitama Prefecture where an F2 plant was selected in 1926 and then sent to the Iwate-Ken Prefectural Station, in northeast Japan where the F3 was grown and final selections of this lineage were made. The final selection was released in 1935 and named Norin 10.

The term Norin is an acronym of the first letter of each word of the Japanese Agricultural Experiment Station as spelled out using Latin letters. The successes of Norin 10 are attributed to Mr. Gonjiro Inazuka, a Japanese wheat breeder who was chief of the Wheat Breeding Program at Iwate from 1930–1935 (Iwanaga 2009).

According to Reitz and Salmon (1968) records from the Iwate-Ken Prefectural Station show that Norin 10 was 55 cm tall – 13 cm shorter than the control variety Norin 1. Despite being seeded in rows 50 cm apart and on land that was heavily fertilized and irrigated, the plants only grew about 60 cm high and did not lodge (Reitz and Salmon 1968).

The semi-dwarf stature of the Norin 10 cultivar is controlled by the Rht1 and Rht2 genes (Pinthus and Levy 1983). Rht1 (Rht-B1b) and Rht2 (Rht-D1b) have been used extensively over the last 60 years to develop high-yielding varieties that reduce plant height and resist lodging. The Rht genes produce shorter cultivars by 'decreasing the sensitivity of reproductive and somatic tissues to endogenous gibberellin' (Sial et al. 2002) which results in decreased internode length and reduced plant height.

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