Crop plants, insect resistance

In addition, naturally growing plants resist plant pathogen and Insect attack because resistance develops over time via natural selection (35). Also, most natural and crop plants have, as a part of their basic physical and chemical makeup, a wide array of mechanisms that help them resist pest attack. These Include chemical toxicants, repellents, altered plant nutrients, hairiness, thorns, and diverse combinations of these (35). 

The levels of antifeedants can be raised safely only in plants such as forest trees or fiber crops, not in food plants for humans or livestock. Such problems have arisen inadvertently. For instance, a new insect-resistant potato cultivarhad to be withdrawn from the market because it contained high levels of the carcinogens solanine and chaconine (Renwick etal, 1984). In another example, an insect-resistant celery had 10 times the usual concentration of the carcinogen 8-methoxypsoralen (and related psoralens), which caused dermatitis in produce handlers (Seligman etal, 1987). 

Interactions Among Allelochemicals and Insect Resistance in Crop Plants... 

Such a strong impact on survivorship or fecundity, and on the fitness of individuals, means exerting strong natural selection on herbivorous insects. This should favor the rapid evolution of insect adaptations which overcome it. This is, of course, a common occurrence in the application of pesticides or the development of resistant crop plant cultivars (11). The supposition that plant defenses select for detoxication adaptations in insects is the foundation of the concept of coevolution (12). 

The Importance of developing crop plants that are resistant to major Insect pests has created a need for detailed examination of the mechanisms Involved In resistance. The widely recognized classification proposed by Painter W appears to provide an acceptable break-down of the possible bases of resistance for most purposes. However, some modification of the terminology may be desirable before beginning to analyze the Individual mechanisms Involved. The term "nonpreference" refers to a behavioral response of the Insect to a plant, whereas "antibiosis" and "tolerance" refer to plant characteristics. This anomaly has been addressed by Kogan and Ortman ( ), who suggested the term "antlxenosls" to describe the plant properties responsible for nonpreference. 

Painter, R. H. "Insect Resistance in Crop Plants" University Press of Kansas Lawrence/London, 1951 520... 

In the coevolutionary interactions of plants and animals, lipids play a major role. They function as ecomones (pheromones, allomones and kairomones) and have been classified by their function. Host plant resistance is partially dependent on these chemical constituents. Lipids may be subdivided into two types. Volatile lipids are generally involved in long distance interactions whereas non-volatile lipids are generally involved after the insect has contacted the host plant. Several examples of each are reviewed. Utilization of these compounds to promote increased host plant resistance could be accomplished by selection of plants rich in allomones, lacking kairomones for a particular pest or those with inducible systems of defense. Another approach is to isolate the defensive compounds of one plant and apply them to crop plants. Trap crops could also be used to lure insects away from other crops. 

There are a number of possibilities for using plant secondary chemistry to control herbivory in crop plants. One possibility is to select for insect resistant lines and though it has been done in only a few cases, select for specific allomones. There are, however, some potential problems with this approach. There is a cost for the production of the secondary compounds which may be useful for defense ( ). Insect resistant soybean cultivars produce lower yields of seeds and accumulate nitrogen at a slower rate than insect susceptible varieties in the absence of herbivores 3 ). Conversely, varieties of crop plants selected for high yield are often more susceptible to insects, pathogens, and weeds (35). 

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. 

Price, P. W. "Insect Ecology", Wiley, New York, 1975. Dethier, V. G. XH "Chemical Ecology" (E. Sondheimer and J. B. Simeone, eds.) 83-102. Academic Press, New York, 1970. Painter, R. H. "Insect Resistance in Crop Plants",... 

The successful transfer of recombinant DNA into plants was vividly illustrated by an experiment in which the luciferase gene from fireflies was introduced into the cells of a tobacco plant (Fig. 9-29)—a favorite plant for transformation experiments because its cells are particularly easy to transform with Agrobacterium. The potential of this technology is not limited to the production of glow-in-the-dark plants, of course. The same approach has been used to produce crop plants that are resistant to herbicides, plant viruses, and insect pests (Fig. 9-30). Potential benefits include increased yields and less need for environmentally harmful agricultural chemicals. 

In China, the results are dramatic an 80% reduction in pesticide use on small farms planted with GE insect-resistant cotton (Huang et al. 2005 see box 5.3). Similarly, the USDA Economic Research Service reports that pesticide use on corn, soybeans, and cotton declined by about 2.5 million pounds in the United States since the introduction of GE crops in 1996 (Fernandez-Cornejo and Caswell 2006). These results support the notion that GE may radically reduce the negative impacts of farming practices on the environment and spare more land for wildlife (figure 8.1). 

One model for coexistence between GE and non-GE crops is the program established for publicly owned land in Boulder County, Colorado (Byrne and Fromherz, 2003). The county leases about 4,000 acres of cropland to farmers, some of whom have chosen to grown insect resistant or herbicide tolerant GE corn. An advisory committee of farmers, scientists, and concerned citizens developed a set of protocols to minimize cross-pollination to nearby non-GE corn fields. The protocols include grower notification to the county of their planting intentions, communication among neighboring farmers to work out an acceptable coexistence plan, and establishment of a 150-foot buffer zone between fields to minimize cross-pollination. 

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