Genetically Modified Crops

Introduction

Genetically modified crops (GMCs) also known as transgenic crops are those in which a foreign genetic material (gene) has been introduced in order to gain additional specific trait (Somerville, 2000; Kotchoni & Bartels, 2003). The introduction of the foreign gene is generally performed by either an infection process of bacteria (Agrobacterium tumefaciens-mediated transformation) carrying the desired gene or by a direct shooting of microscopic pellets containing the transgene into the host-cells (Gachomo et al., 2003). The primary objective of genetic manipulation is to provide insight into the behaviour of plants in a given environment and further to generate plants that can tolerate/resist various biotic and abiotic stresses (Conrath et al., 2002; Ramanjulu & Bartels, 2002). GMC technology has become increasingly important since it aims to improve crop yield even under environmental challenges. For example, crop improvements have been realised in nutritional quality (James, 2003; Nap et al., 2003; Conner et al., 2003), insect and disease resistance (James, 2002; Chen et al., 2003), herbicide resistance (Hofte & Whiteley, 1989; Chen et al., 2003) and abiotic stress tolerance such as salt stress, drought, and heavy metal contamination (Gachomo et al., 2003; Shinozaki et al., 2003; Kroemer et al., 2004, Bartels & Sunkar, 2005). However, controversies continue to arise concerning the GMC risks on human health, high cost of GMC establishment and their threat to biodiversity. Europe is that part of the world where the introduction of genetically modified organisms (GMOs) is facing stiff opposition (Somerville, 2000). Somerville (2000) reported that the greatest threat to biodiversity is rather the expansion of agricultural land. In this regard any technology that can help to stop the expansion of agricultural land and minimize chemical inputs will probably be welcome. Farmers searching for more productive land cleared approximately 11 million ha of forest every year (Herrera-Estrella, 2000; James, 2003). Conversion of tropical forest land into agricultural land might have more adverse ecological consequences than the use of GMCs (Herrera-Estrella, 2000).

Knowing the coldness of the Europeans towards GMOs, the year 2004 can be viewed as a year of breakthrough for the GMC technology. This is because the European Union (EU) has approved the commercial production of 17 different transgenic maize MON 810 strains engineered by the big US biotech company Monsanto (www.agbios.com). The maize MON 810 (trade name yieldGrade®) was developed through a specific genetic modification to be resistant to the attack of European corn borer (ECB) Ostrinia nubilalis, a major insect pest of maize. This maize transgene produces a truncated form of the insecticidal protein, Cry1Ab, isolated from Bacillus thuringiensis (Nap et al., 2003). The introduction of transgenes into plants by Agrobacterium mediated transformation results in a stable random integration of one or a few copies of the genes (Gheysen et al., 1989) leading to different epigenetic effects in independent transgenic seed strains. The resulted transgenic seeds often show very different levels of trangene expression (Peach & Velten, 1991). The US has approved the commercial production of MON 810 in 1995, but it has taken ...