Plant breeding, insect resistance

Several trophic levels must be considered. Breeding plants with greater allomone content in some cases causes specialist herbivores to accumulate higher levels of these compounds and discourages parasites that normally control herbivore levels (36). The presence of secondary compounds may also alter the usefulness of the crop plant to man or his domestic animals. Lines of cotton with high gossypol content have increased insect resistance with regard to a nunter of insects, but have reduced value as food materials for livestock. 

Breeders have selected celery with relatively high amounts of psoralens because farmers prefer to grow insect resistant plants and consumers prefer to buy undamaged produce. Unfortunately, workers who harvest such celery sometimes develop a severe skin rash (NAS 2004), an unintended consequence of this conventional breeding. It is possible that if the gene encoding the toxic protein had been cloned and studied before being introduced into the new varieties, farm workers would have learned of the harmful effects before exposure. 

Practical implications of a full elucidation of biochemical bases of insect resistance in plants are tremendous. Identification of the chemicals that confer resistance or susceptibility, and study of their inheritance in crop plants, would greatly improve breeding for resistant varieties. If resistance involves more than one defense chemical, it may be possible to develop a relatively stable type of resistance since pests are not likely to overcome sensitivity to several substances simultaneously. It would also open new avenues for manipulation of insect behavior for use in pest management programs. 

During the last decade our knowledge of the bases and genetics of resistance of solanaceous crop plants to insects (see other chapters in this volume) has increased markedly. Resistance has been primarily based on the enhancement of the levels of one or two constitutive chemical and/or physical resistance-conferring characteristics in commercial varieties via breeding with exotic germplasm (see other chapters in the volume). The predominant mode... 

Guthrie, W. D. (1974) Techniques, accomplishments and future potential of breeding for resistance to European corn borers in com. In Proceedings of the Summer Institute on Biological Control of Plant Insects and Diseases (Maxwell, F. G. and Harris, F. A., eds). University Mississippi Press, Jackson. 

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