How it began
Taichung Native 1, known as TN1, was bred at the Taichung District Agricultural Improvement Station in Taiwan. The cross was made in 1949 between two local varieties, Dee-geo-woo-gen and Tsai-yuan-chung. Dee-geo-woo-gen was the source of the short stature. Research papers in the journals Genomics and Botanical Studies describe TN1 as the world's first bred high-yield semidwarf rice cultivar and as the variety that initiated the Green Revolution in rice.
How it works
TN1 grows to about 80 to 90 centimeters. Its short stature comes from the sd1 gene inherited from Dee-geo-woo-gen. A 2022 study defined the mutation as a 382 base pair deletion in sd1 that disrupts the plant's synthesis of gibberellin, a growth hormone, which keeps the stem short. The Genomics paper gives its yield as 6 tons per hectare. Like IR8, TN1 is insensitive to day length.
How it spread
During the 1960s TN1 was taken up outside Taiwan, in India, Korea, the United States and the Philippines. The Genomics authors write that IR8, the variety released by the International Rice Research Institute in 1966 and nicknamed miracle rice, was conceptualized from TN1. Both varieties took their sd1 semidwarf gene from Dee-geo-woo-gen.
Who pushed back
TN1 had a clear weakness. The 2022 study in Botanical Studies found that it lacks the blast resistance gene Pi54, which helps explain its vulnerability to the rice blast fungus Pyricularia oryzae. The same study looked for genes under positive selection in TN1, including ones related to drought and stress response, with a view to breeding hardier rice.
Where it stands today
TN1 is now mainly a reference variety for research. In 2021 a team published a chromosome-level genome assembly of TN1, 409.5 megabases long, and compared it with IR8 to build what they called a Green Revolution pangenome. The sd1 gene it carried is known as the green revolution gene of rice.
