Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 28

In a review of plant breeding over the past 50 years Baenzinger and colleagues in 2006 revealed that while some aspects of how breeders conduct their operations have dramatically changed, others have stubbornly remained the same, being variations on a theme at best. Current plant breeding objectives still emphasize the following general areas:

 Higher yields of harvested produce or product.

 Improved quality of produce or product.

 Resistance to biotic stresses.

 Resistance to abiotic stresses.

 Wider adaptability of varieties.

A significant point to emphasize is that the focus of breeders within each of these general areas varies from one crop to another, as dictated by consumer preferences and production systems, among other factors.

Breeding objectives in the 1950s and 1960s and before appeared to focus on increasing crop productivity. Breeders concentrated on yield and adapting crops to their production environment. Resistance to diseases and pests was also priority. Quality traits for major field crops, such as improved fiber strength of cotton and milling and baking quality of wheat were important in the early breeding years. Attention was given to resistance to abiotic stresses like winter hardiness, and traits like lodging resistance, uniform ripening, and seed oil content of some species. Crop yield continued to be important throughout the 1990s. However, as analytical instrumentation that allowed high throughput, low cost, ease of analysis, and repeatability of results became more readily available, plant breeders began to include nutritional quality traits into their breeding objectives. These included forage quality traits like digestibility and neutral detergent fiber.

More importantly, with advanced technology, quality traits are becoming more narrowly defined in breeding objectives. Rather than high protein or high oil, breeders are breeding for specifics like low linolenic acid content, to meet consumer preferences of eating healthful foods (low linolenic acid in oil provides it with stability and enhanced flavor, and reduces the need for partial hydrogenation of the oil and production of trans fatty acids). Also, a specific quality trait like low phytate phosphorus in grains (e.g. corn, soybean) would increase feed efficiency and reduce phosphorus in animal waste, a major source of environmental degradation of lakes.

With advances in science and technology, breeding objectives are being achieved much quicker, as breeders are now able to utilize more efficient selection schemes to advance breeding programs. Instead of focusing on single genes, breeders access gene networks and target whole genomes in their research and applications. They are able to address more complex problems that heretofore were challenging. Perhaps no single technology has impacted breeding objectives in recent times more than biotechnology (actually, a collection of biological technologies). The subject of technological advances in breeding is discussed in detail in later chapters. Biotechnology has enabled breeders to develop a new generation of cultivars with genes included from genetically unrelated species (transgenic or GM cultivars). The most successful transgenic input traits to date have been herbicide resistance and insect resistance, which have been incorporated into major crop species like corn, cotton, soybean, and tobacco. According to a 2010 International Service for the Acquisition of Agri‐Biotech Crops (ISAAA), GM is far from being a global industry, with only six countries (US, Brazil, Argentina, India, Canada, and China) growing about 95% of the total global acreage (US leads with about 50%). The trend has changed, except that acreages in these countries in 2019 were significantly higher than in 2010. Some argue that biotechnology has become the tail that wags the plant breeding industry. Improvement in plant genetic manipulation technology has also encouraged the practice of gene stacking in plant breeding. Another significant contribution of biotechnology to changing breeding objectives is the creation of the “universal gene pool” whereby breeders, in theory, have limitless sources of diversity, and hence can be more creative and audacious in formulating breeding objectives.

In the push to reduce our carbon footprint and reduce environmental pollution, there is a drive toward the discovery and use of alternative fuel sources. Some traditional improvement of some crop species (e.g. corn) for food and feed is being changed to focus some attention on their industrial use, through increasing biomass for biofuel production, and as bioreactors for production of polymers and pharmaceuticals. In terms of reducing adverse environmental impact, one of the goals of modern breeding is to reduce the use of agrochemicals.