cultural methods to suppress pest populations (Smith and Van denBosch 1967). IPM is an approach which manages pests by biologically integrated alternatives for pest control (US Congress 1947, as amended in the 1972 Federal Environmental Pesticide Control Act, section 136r(a)) and is “a sustainable approach to managing pests by combining biological, cultural, physical, and chemical tools in a way that minimizes economic, health, and environmental risks” (US Congress 1947, as amended by the 1996 Food Quality Protection Act, section 136r-1). Pesticides are used only as necessary and when other control methods have failed (Stern et al. 1959).

1.2 DIVERSE GENETIC MODIFICATION METHODS

To develop pest-resistant or tolerant cultivars, plant breeders have taken advantage of natural genetic variation or induced mutations. The methods that plant breeders use depend on the type of cultivar they want to improve (for example, an inbred line, a hybrid, or a population) and the reproductive biology of the plant (for example, self-pollinated or cross-pollinated) (Fehr 1987; Stoskopf et al. 1993).

An inbred line (or purebred) is phenotypically uniform1, and the progeny2 are identical with the parent. Many self-pollinated crops are released as inbred lines (for example, soybeans, Glycine max, and barley, Hordeum vulgare). A hybrid is the cross between two or more inbred lines; it can also be phenotypically uniform but not genetically identical with the parents. Many cross-pollinated crops are released as hybrids (for example, corn or maize, Zea mays). A plant population results from crossing a number of lines and is genetically and phenotypically diverse, although for key traits, a population can be phenotypically uniform (for example, every plant resistant to a pest).

All genetic modification methods for crop improvement consist of introducing variation, selecting useful variants, and field-testing the selected lines, hybrids, or populations to determine their merit. In the past, almost all commonly used plant breeding techniques began with artificial crosses, in which pollen from one plant is transferred to a reproductive organ of another, sexually compatible plant. Crossing allows for the combining of desirable traits, such as pest resistance and increased yield, from two or more plant cultivars.3 The objective is to combine these traits in a new cultivar that is superior to its parents. To overcome some of the

1  

Expressing the same phenotypes or traits.

2  

Offspring.

3  

Cultivated variety of plant.



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