PLANT-BREEDING AND SEED MARKETING OPTIONS FOR THE INTRODUCTION OF TRANSGENIC INSECT-RESISTANT CROPS

Genetic engineering offers considerable potential for the development of insect-resistant crop plants through the transfer and expression of Bacillus thuringiensis genes encoding insecticidal proteins. A potential problem with the use of such crops is the possibility of insects adapting to overcome the resistance mechanism. Strategies to minimize this risk have included concepts of seed mixtures and crop rotations. This may involve genotypes transformed with a series of genes encoding different resistance mechanisms and/or manipulating the manner in which these genes are expressed. The aim of this paper is to put these strategies into perspective with respect to the limitations imposed by the nature of plant transformation the traditional approaches to plant breeding for cultivar development and seed marketing options for commercial release of transgenic crops. The optimum strategy for any specific crop varies depending on whether the cultivar targeted for release is a clone, an inbred line, a hybrid or an open pollinated population.