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 potent ial problem with the use of such crops is the possibility of insects a dapting to overcome the resistance mechanism. Strategies to minimize t his risk have included concepts of seed mixtures and crop rotations. T his may involve genotypes transformed with a series of genes encoding different resistance mechanisms and/or manipulating the manner in whic h these genes are expressed. The aim of this paper is to put these str ategies into perspective with respect to the limitations imposed by th e nature of plant transformation the traditional approaches to plant b reeding for cultivar development and seed marketing options for commer cial release of transgenic crops. The optimum strategy for any specifi c crop varies depending on whether the cultivar targeted for release i s a clone, an inbred line, a hybrid or an open pollinated population.