Why There Are So Many Bacillus Thuringiensis Plants

The first commercial transgenic crops were planted in China during the early 1990s. These were primarily virus-resistant tobacco and tomato. In the United States, the first commercialized crop was Calgene's FLVR SAVR tomato in 1994. This product was not a commercial success in part because it did not pack well for shipping. Initially, a variety of transgenic crops were planted (Table Ia); by 1999, however, four crops dominated: soybean, corn, cotton, and canola. The primary traits of these GM plants are herbicide tolerance and insect resistance (Table Ib). In 1999, herbicide-tolerant soybeans, Bt (Bacillus thuringiensis) corn, herbicide-tolerant corn, Bt cotton, herbicide-tolerant cotton, and herbicide-tolerant canola accounted for over 99% of the commercial transgenic crops grown worldwide. All of the insecticidal-transgenic crops currently available are based on cry toxin genes from B. thuringiensis, and a few now under development are based on other toxin-coding genes from B. thuringiensis. The cry genes code for crystalline proteins that are toxic to some insects.

Bt genes have been incorporated into broccoli, cabbage, canola, cotton, corn, eggplant, poplar, potato, soybean, tobacco, and tomato, and the commercially available crops during 2001 in the United States are Bt corn and Bt cotton. Since their introduction during 1995, the cropping area of all of these transgenic crops has grown substantially (Table II). By 1999, Bt corn was grown on 9.6 million ha. Bt cotton lagged behind substantially in total area because about five times more corn than cotton is grown in the United States. Clearly, Bt corn in the United States is one of the dominant transgenic crops in the world today. Interestingly, Bt corn area has decreased during 2000, probably in response to market uncertainty. In contrast,

TABLE I Area of Transgenic Crops in the World from 1996 to 2000 (in Millions of Hectares)

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