W150: Genetic Improvement of Beans (Phaseolus vulgaris L.) for Yield, Disease Resistance, and Food Value
Statement of Issues and Justification
I. STATEMENT OF THE PROBLEM:More efficient procedures are needed to transfer desirable traits to avoid unwanted phenotypic alterations often associated with conventional breeding strategies in plants. Although backcrossing is often used to transfer a single gene (or a few genes), breeders frequently cannot completely recover the phenotypic expression of the recurrent parent. Molecular biology techniques provide a tool to manipulate individual DNA sequences.
Relative to cereal grains, beans have low yields and suffer from several limitations. While the world average yield is 600 kg/ha, yields in the U.S. range from 100 kg/ha in the Upper Midwest to 2200 kg/ha in the Pacific Northwest. Problems affecting beans include susceptibility to many diseases, reduced productivity due to environmental stresses, reduced digestibility from antinutritional factors, and poor utilization of seed proteins. These problems are amenable to genetic solutions; however, it often is difficult to identify and incorporate appropriate traits. On a global scale, genetic diversity does not seem to be lacking, but the germplasm base in the U. S. is narrow (McClean, et al., 1993) with restricted exchange between temperate and tropical germplasm pools. In addition, some useful traits are available only by utilizing related species, such as P. ciccineus and P. acutifolius, or through genetic engineering technology.
Economic productivity can be increased by selecting genotypes with superior morphological characteristics. For example, yields can be improved if plants direct more photosynthate into seeds, due to either increased light penetration in the canopy, higher net CO2 fixation, or improved remobilization of stored carbon during periods of stress. This requires identification of genes controlling photosynthate partitioning and yield stability. Cultivars also must be disease-resistant, wholesome, with desirable culinary and nutritional qualities. Changes in nutritional guidelines and culinary habits portend a promise to increase domestic bean consumption.
II. JUSTIFICATION:
Extent of Problem
Some of the major factors affecting bean yield are: daylength, temperature, moisture, partitioning and remobilization of photosynthates, disease and insect pests, mineral deficiencies and toxicity and air pollutants. Although daylength and temperature strongly control maturation, the physiological basis underlying these mechanisms is not yet fully understood. More needs to be learned about the genetic processes that regulate adaptation, and about the genetic control of days to flowering and partitioning. Plant diseases can markedly decrease yield and can affect seed appearance and characteristics associated with quality. Consumers reject blemished and discolored pods and beans. Low yields often mean growers of beans are at a competitive disadvantage with growers of cereals and other foods. Moreover, there are additional losses if beans are unacceptable for purchase and consumption. The increased awareness of the nutritional value of beans in the diet should increase consumer demand.
Gastrointestinal discomfort, including flatulence and diarrhea, is the single most important factor that limits the consumption of dry beans in the diets of American consumers. The intestinal discomfort associated with eating beans is caused by microbial fermentation of particular compounds in the seed that pass into the lower gastrointestinal tract undigested. Factors that may limit digestibility and reduce the nutritional quality of food legumes include complexing of protein with natural polymers such as heat stable trypsin inhibitors, phytates, soluble dietary fiber and flavonoid compounds. Such reactants limit the bioavailability of nutrients and, thus, limit the nutritional potential derived from eating dry beans. It is not clear how flavonoids, fiber, and other complex carbohydrates interact in the bean seed to limit digestibility; however, there is good evidence suggesting that macromolecules form complexes in the seed. These complexes are genotype, post harvest age and storage environment dependent and are resistant to break down by digestive enzymes and/or inhibit the digestive enzyme themselves. Before digestibility can be improved through genetic intervention or food processing technology, a knowledge base needs to be established concerning the genetic and internal controls that restrict break down of bean seed reserve proteins and carbohydrates and render these important bionutrients unavailable in human diets. Studies of interactions between proteins, fiber and other carbohydrates, and flavonoids will provide the means to improve the digestibility of beans through genetic intervention and food processing technology.
Conventional breeding techniques and selection have been used to improve bean varieties. However, gene transfer promises to be the best method to improve disease, insect, and herbicide resistance; improve nutritional composition of bean; improve ease of cooking; and reduce flatulence. Additional research is warranted to identify the appropriate molecular genetic and biotechnological techniques that are required.
Need and Advantages of a Cooperative Approach
Since its initial approval in 1977, W-150 has established a rich history of procedures that are vital to a successful collaborative plant improvement project. The development and composition of the current revision was accomplished by the formation of three committees comprised of participants in the project. Each committee was composed of scientists with an expertise and interest in each of the three stated objectives. Each objective and subsequent supporting procedure was agreed upon by the membership of the regional committee. The planning was accomplished by joint input and consensus with collaboration as the vehicle by which the objectives were to be achieved.
No single research program or agency can conduct all the research necessary to improve beans as a food source. For example, the Agricultural Research Service of the USDA allocates 4.5 scientific years (SY) to in house research on beans under the aegis of National Programs 301, 302, 303, 306, and 107. Additional resources are required to solve the production, disease, and food?quality problems that currently limit the consumption of beans in human diets. These resources can be provided by a comprehensive approach involving regional collaboration to maintain germplasm and pathogen strains, exchange samples of seeds, pathogens and insects, pool information and equipment, and exchange research data. A coordinated effort will make the most efficient use of genetic resources and avoid duplication of research efforts.
Back to Top