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Rice (Oryza sativa L.) is one of the most important staple foods and it has been estimated that 50% of the human population depends on it as main source of nutrition (White 1994). It is particularly important for people living in the monsoon areas of Asia where it has a long history of cultivation.

In the 1960s, the rapid expansion of the world population and dramatic decrease in cultivated lands raised concerns that food production would not meet the growing demand, leading to a global food crisis. Recognizing the problem, the International Rice Research Institute (IRRI) developed a high-yielding semi-dwarf variety of rice, IR8, known as ‘miracle rice’. Widespread adoption of IR8 led to major increases in rice production and, as a result, the feared food shortages were averted in Asia. This remarkable achievement was referred to as ‘green revolution’(Hargrove and Cabanilla 1979, Dalrymple 1986, Khush 1999). The short stature of IR8 (Fig. 1-2) was due to the sd1 mutation, which played an important role for rice growth. Generally speaking, nitrogen fertilization is essential to increase grain production, but it also induces culm elongation, resulting in an overall increase in the height of crop plants. Tall crop plants are easily flattened by wind and rain and consequently dramatic yield losses may occur. IR8 was bred by the crossing with a Taiwanese native semi-dwarf variety, Dee-geo-woo-gen, which carries the semi-dwarf 1 (sd1) gene, and an Indonesian good-taste variety, Peta (Hargrove and Cabanilla 1979, Dalrymple 1986). The resultant IR8 variety showed the semi-dwarf phenotype caused by