Abstract
Farmers and growers, already under pressure to produce food under tighter constraints, face the omnipresent threat of new pests and diseases caused by new strains of fungal, bacterial or viral pathogens or their vectors, such as insects. The whitefly Bemisia tabaci is an example of such a threat in Europe (Bedford and Markham, 1993). It is feared that over-use of pesticides, fertilizers and growth regulators could create major environmental problems, but to survive without them will require other strategies, broadly referred to as ‘sustainable agriculture ’. Traditionally, durable disease resistance has required ingenious breeding programmes to introduce natural resistance genes from crop-related wild species into crops. However, we can now exploit the power, flexibility and specificity of recombinant DNA techniques (genetic manipulation) either to identify existing natural resistance genes and transfer them between unrelated crop species, or to create new and more effective resistance genes against one or more pathogens or pests. The rationale behind many of these ‘designer genes ’ has arisen from empirical field observations or from our deeper understanding of molecular and genetical aspects of the natural life-cycle of the pathogen.
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