Approaches to Plant Breeding and Genetic Engineering
Successful plant breeding efforts have specific and well-defined objectives. In most applied breeding programs (programs which develop new varieties or cultivars that will be used directly by farmers), objectives are determined primarily by economic considerations, with emphasis placed on plant characteristics most likely to produce added income to the user of the new cultivar. The primary objective in these programs is usually increased yield, because yield generally has the most direct influence on producer income and thus grower acceptance and economic success of a new cultivar. Depending on the crop, quality of the product (e.g., nutritional content, shelf life, suitability for industrial processing) may also be a major breeding objective. Pest resistance, in applied breeding programs, is pursued as a high-priority objective only if resistance enhances yield or quality, or if resistance can significantly reduce the cost of production by replacing crop-protection chemicals without sacrificing yield or quality. It should be noted that breeding for high yielding ability per se often confers a level of tolerance-type resistance even when breeding is conducted under nonchallenged conditions [21,92]. In many situations, particularly with relatively low-value crops, appropriate pesticides are not available or are prohibitively expensive. These situations make genetic resistance essential, as in the case of disease resistance in wheat and soybeans. In such cases, a pest's impact on yield often makes pest resistance the primary breeding objective. Cultivars that are only partially resistant can increase net crop value by responding more efficiently to pesticides [114,145,150]. Even in applied breeding programs, resistance can, in some circumstance, stand with yield and quality as a top breeding priority.