Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 173
Managing Global Genetic Resources: Agricultural Crop Issues and Policies 6 Using Genetic Resources The allelic variability within the various kinds of gene pools of all long-domesticated species has become very large. Nearly all domesticated species are now so different from their wild type progenitors that they can no longer survive in the wild. While there are great stores of genetic variation in wild-crop relatives, experience in breeding indicates that much of this variation is irrelevant to plant breeders. Plant breeders, the ultimate users of germplasm, generally agree that the need for genetic diversity within the economically important plant species has never been greater. The challenge is to detect and transfer those genes that will improve the cultivated species. AN EXAMPLE OF GERMPLASM USE The discovery of the Americas by Europeans set the stage for major developments in the recognition and use of crop germplasm. Explorers returned to Europe with New World species that greatly influenced European agriculture. The potato became one of the most important energy foods in Europe, and tomato and corn ultimately achieved status as major crops. Similarly, colonists to the Americas introduced the best germplasm available from their native lands. Introductions of wheat from England, The Netherlands, and Sweden were grown along the Atlantic coast of North America from 1621 to 1638 (Ball, 1930), and numerous additional introductions from a variety of places were made throughout the seventeenth, eighteenth, and
OCR for page 174
Managing Global Genetic Resources: Agricultural Crop Issues and Policies nineteenth centuries. These wheats provided the germplasm from which the soft red winter wheat of the eastern United States was developed. Cox et al. (1986, 1988b) have documented the ways in which twentieth century soft red winter wheat breeders took the great genetic diversity available in the large number of landraces that were grown in 1919, augmented this germplasm through hybridizations with other gene pools, and concentrated the best germplasm into approximately 100 different cultivars now grown commercially in the United States. Turkey wheat, a highly heterogeneous landrace brought to Kansas in 1883 by a group of settlers from the Crimean region of southern Russia, rapidly became the most widely grown variety in the vast hard red winter wheat area of the central Great Plains, where growing conditions are highly variable within seasons, from year to year, and from place to place. Turkey wheat reigned supreme throughout this region for a half century, remaining virtually unchanged. In the hard red winter wheat area, breeders firmly maintained the core of Turkey wheat germplasm over the years, thus preserving the basic adaptation, yield stability, and product quality of Turkey wheat while improving specific agronomic and quality characteristics. By 1984 the number of commercially grown varieties had increased to 164, but this increase was accompanied by higher than desirable genetic relatedness of the primary cultivars (cultivars that occupied 1 percent or more of the land planted to wheat) in the region. Cox et al. (1988b) evaluated the yields and various agronomic and quality traits of 38 of the major hard red winter cultivars released from 1874 to 1987 to estimate the genetic improvement achieved during that period (Table 6-1). Linear regression analyses of cultivar performance on the year of release showed steady increases in yields (about 1 percent per year) as well as steady improvement in various agronomic and quality traits. They found no indications that a yield plateau had developed. BREEDERS' PERCEPTIONS AND PRACTICES The most important scientific questions concerning the use of genetic variability involve (1) ways to identify useful variability and (2) methods to maximize availability to breeders while minimizing the danger of loss. There is general agreement among experienced breeders that the superior performance of modern cultivars has resulted from the accumulation of favorable alleles and the gradual assembly of these alleles into favorably interacting multilocus combinations. Breeders
OCR for page 175
Managing Global Genetic Resources: Agricultural Crop Issues and Policies are consequently reluctant to introduce unadapted materials into their breeding stocks, because use of unadapted germplasm introduces unfavorable alleles and increases the likelihood that favorable combinations of alleles at different loci will be broken up by segregation and recombination. Breeders with established programs thus consider advanced materials in their own breeding nurseries, including commercially grown cultivars, advanced lines under evaluation for release, and sibling lines of such materials, to be the most useful germplasm available to them. They consequently make heavy use of such materials as parents in crosses so that past gains are less likely to be lost as a result of segregation and recombination. Breeders also regard advanced materials from breeders located in ecologically similar areas with favor, and they frequently use such materials as parents in crosses. Monitoring Advanced Materials Many breeders (including farmers who practice selection) regularly monitor advanced materials, especially commercially grown cultivars, for potentially useful variants; many useful alleles with major effects on characteristics such as early maturity, height, determinant versus indeterminant growth habit, cold or heat tolerance, and resistance to diseases and insects have been uncovered in this manner. The case of Periconia root rot of sorghum, which first appeared in Kansas in 1926, provides a dramatic example. The effects of this disease were catastrophic; the frequency of surviving plants in infected fields was on the order of only one in several hundreds or thousands. The disease soon appeared throughout the southern plains area of the United States and westward into California. Plant breeders throughout the affected area found the same low incidence of surviving plants in local varieties. The progency of some of these plants were free of disease, whereas others produced both healthy and diseased offspring. Breeders increased the numbers of seeds of resistant plants and were soon able to release resistant strains for commercial production that were indistinguishable from the parent variety but that could be grown in Periconia infested soil without any evidence of injury. Performance Advances It has been postulated that although reliance on advanced locally adapted materials improves prospects for continued modest improvements in performance (see above), it reduces the opportunity for major
OCR for page 176
Managing Global Genetic Resources: Agricultural Crop Issues and Policies Table 6-1 Year of Release and Means Over All Environments for Seven Traits of 38 Hard Red Winter Wheat Cultivars Released from 1874 to 1987 Lodging Cultivator Year Released Mean Grain Yield (kg/ha-1) Biomass Yield (kg/ha-1) Volume Weight (kg/m-3) Kernel Weighta (g) Heading Date (May) Height (cm) Scoreb Turkey 1874 1,609 8,533 708 24.5 16 117 2.0 Kharkof 1900 1,426 8,284 699 22.4 15 115 2.0 Blackhull 1917 2,031c 9,006c 760c 26.7c 13c 115c 2.0 Tenmarq 1932 1,589c 7,706c 722c 25.3c 14c 111c 2.0c Cheyenne 1933 1,547 8,054 693 22.9 15 110 1.8 Redchief 1940 1,854 8,742 758 26.9 13 120 1.7 Comanche 1942 1,823 7,766 717 25.2 12 112 2.0 Pawnee 1943 1,712 6,718 726 25.3 11 106 1.8 Wichita 1944 2,174 7,879 779 31.3 8 108 1.7 Ponca 1951 1,911 7,834 722 26.2 13 109 2.0 Bison 1956 1,944 7,715 728 27.2 13 111 1.8 Tascosa 1959 1,880 8,076 740 24.7 10 105 1.5 Warrior 1960 1,915 8,432 711 23.8 15 108 1.5 Kaw 61 1961 2,225 7,856 798 29.0 9 109 1.8 Lancer 1963 1,857 8,293 730 23.9 13 110 1.7 Triumph 64 1964 2,760 8,591 800 32.3 6 101 1.5 Scout 66 1966 2,286 8,662 758 28.9 10 109 2.0 Sturdy 1967 2,239 6,736 752 27.9 7 77 0.0 Shawnee 1967 1,996 8,089 738 23.8 13 109 1.7 Eagle 1970 2,194c 8,131c 732c 28.0c 10c 103c 1.7c
OCR for page 177
Managing Global Genetic Resources: Agricultural Crop Issues and Policies Larned 1976 2,396 8,354 758 28.6 11 105 1.3 Vona 1976 2,604 8,162 738 24.4 7 84 0.0 Newton 1977 2,134 7,811 720 24.4 10 90 0.5 Centurk 78 1978 2,367 8,227 749 24.2 10 99 1.5 Arkan 1982 2,494 7,645 740 27.2 7 88 0.7 Brule 1982 2,438 8,683 714 25.0 11 95 0.5 Hawk 1982 2,349 7,692 733 27.8 10 86 0.3 Chisholm 1983 2,761 7,632 779 30.4 6 84 0.0 Mustang 1984 2,389 7.094 759 29.7 8 83 0.0 Siouxland 1984 3,011 9,852 769 30.4 9 104 0.3 Stallion 1985 2,668 7,566 774 25.9 7 80 0.0 TAM 107 1985 2,727 8,034 735 28.6 6 83 0.0 TAM 108 1985 2,520 7,930 705 26.4 11 86 0.3 Victory 1985 2,733 8,524 745 29.4 9 89 0.3 Norkan 1986 2,404 8,482 749 26.3 10 90 0.0 Dodge 1986 2,531 8,015 754 28.8 9 88 0.0 Century 1986 2,982 8,668 765 27.4 9 87 0.3 TAM 200 1987 2,658 7,806 791 24.3 9 76 0.0 LSD (.05) 403 — 42 2.6 2 5 0.05 Change per yeard 16.2** 0.5 0.4* 0.04* -0.1** -0.5** -0.03** * ** Significantly different from zero at the .05 and .01 levels of significance, respectively. a From each plot, 200 kernels were weighed, and kernel weight was expressed in grams per thousand kernels. b Mean over 2 years at Manhattan, with 0 = no lodging, 2 = completely lodged. c Estimated 2-year mean for cultivars tested only in 1986. d Coefficients of regression of trait means on year of release. SOURCE: Cox, T. S., J.P. Shroyer, L. Ben-Hui, R. G. Sears, and T. J. Martin. 1988. Genetic improvement in agronomic traits of hard red winter wheat cultivars from 1919 to 1987. Crop Sci. 28:756–760. Reprinted with permission, ©1988 by Crop Science Society of America.
OCR for page 178
Managing Global Genetic Resources: Agricultural Crop Issues and Policies advances in performance. Another more prevalent view is that modern-day pools of advanced, highly adapted germplasm are, in fact, vastly complex genetic systems containing great reserves of adapted and maximally exploitable genetic variability. There appears to be no solid basis for a choice between these hypotheses at present. Measured rates of progress appear to have been about the same for those gene pools that have been heavily introgressed with exotic germplasm as it has for those gene pools into which there has been only light introgression. Yield plateaus have not been detected in many major crops, even where there has been little or no introgression of exotic germplasm into the breeding populations in recent times. The gene pools in the U.S. Corn Belt from which high-yielding single crosses are produced (Duvick, 1984b) are good examples. When alleles are needed for specific improvements (for example, resistance to new races of diseases, various aspects of quality, and improved yield), and the needed alleles have not been found in locally adapted materials, the breeder and coworkers are forced to screen exotic germplasm in the search for the needed genetic variability. In this event, advanced exotic cultivars and advanced breeding lines, genetically enhanced germplasm pools, obsolete cultivars and landraces, and wild progenitors are screened, usually in this order. Numerous sought-after alleles have been identified in accessions from active collections. Recently, materials from national and regional trials, and trials conducted by international centers, have become increasingly important sources of exotic germplasm in recent years. Varieties and advanced lines undergoing evaluation in such trials are often used as sources of desirable alleles, because the substantial performance and evaluation data available from trials conducted under a range of environmental conditions help breeders to identify germplasm with the greatest potential value in their own area. Data from such trials are much more useful than descriptor data, because information about adaptation and productivity are specially helpful in choosing parental materials. Germplasm pools into which alleles for specific attributes have been introgressed into well-adapted genetic backgrounds are increasingly being used as sources of exotic genes. Breeders turn more and more frequently to such populations, because they often provide many different alleles for specifically sought-after traits concentrated from numerous sources into genetic backgrounds that provide adaptedness to specific ecological regions. Among the heaviest users of accessions from active collections are the breeders of those plant species that have little or no history of breeding improvement. Species that fall into this category include many forage species (grasses, legumes, and forbs) and other plants
OCR for page 179
Managing Global Genetic Resources: Agricultural Crop Issues and Policies used as root and industrial crops and medicinal plants. Breeders of the crops of marginal areas, which may have little history of breeding improvement, sometimes also find that primitive materials (including wild relatives) in active collections contribute useful alleles. Breeders who initiate plant improvement programs for such species or areas often have no alternative to evaluating primitive materials and selecting as parents either the more promising accessions or superior individuals within promising accessions. USERS' PERCEPTIONS OF THE GERMPLASM SYSTEM Duvick (1984b) has suggested that little more gain in yield in developed countries can be achieved from additional nonbreeding inputs. Among the reasons he cited are that it will be difficult to improve techniques of planting, weeding, and harvesting very much more and that gains from use of insecticides, fungicides, herbicides, and fertilizers appear to have plateaued. There is, on other hand, To ensure that only pollen from the desired male parent is applied, the flowers of a female pecan clone are enclosed in a bag at the W. R. Poage Pecan Field Station. A syringe is used to blow pollen into the bag to ensure fertilization. Credit: U.S. Department of Agriculture, Agricultural Research Service.
OCR for page 180
Managing Global Genetic Resources: Agricultural Crop Issues and Policies no indication of reduction in rate of increase that can be attributed to breeding. Germplasm exists that carries any needed traits, and present day breeding methods are quite capable of transferring these into elite material from which improved varieties can be selected (Duvick, 1984b). In developing countries opportunities still exist for improvement in crop productivity and stability from nonbreeding inputs, and at the same time, opportunities for inputs from breeding are also higher in developing countries than they are in developed countries. Thus, most countries, developed or not, accept the proposition that if the food, feed, fiber, and other agricultural needs of an ever-increasing world population are to be met, a significant part of the increase must come from genetic improvement of plants and that adequate supplies of useful germplasm are essential for genetic improvement. Nevertheless, despite the continuing need for genetic diversity, it has often been stated that only limited use is being made of the germplasm resources maintained in national, regional , and international collections. Thus, for example, according to the Five-Year Plan for Action, 1985–1989, of the Regional Committee for Southeast Asia under the auspices of the International Board for Plant Genetic Resources (1984a), very little of the sizable germplasm collections now available in that region has been used in breeding programs or research studies. Limited use is not confined to developing countries: in developed countries, the majority of breeders of principal crops mainly resort to their own working collections for breeding materials (Duvick, 1984b). Frankel (1985a) attributed the limited use of germplasm collections to management problems, such as lack of definition of objectives, excessive size of collections, inadequate evaluation, and lack of breeder participation. Chang (1985a) pointed out the poor communication between germplasm workers and users as the main handicap in using exotic germplasm. These topics are also discussed by Brown et al., (1989). There has been growing dissatisfaction among breeders with the international germplasm programs and some of the large national collections as they have expanded and grown more complex in recent decades. Some of the most frequently voiced criticisms of these systems are examined below, and an attempt is made to establish scientific criteria for structuring and managing collections to serve their intended purposes. BREEDERS' PERCEPTIONS OF ACTIVE COLLECTIONS It is a common perception among breeders that a disproportionate number of accessions in active and base collections are obsolete
OCR for page 181
Managing Global Genetic Resources: Agricultural Crop Issues and Policies and that the most modern and useful materials are too frequently not present in such collections. An important step in organizing the structure and management of collections is to identify the unit of utilization. From the breeder's standpoint, the primary dichotomy is weather accessions from collections are (1) used directly as sources of cultivars (individual genotypes, populations, ecotypes, species) or (2) whether they are sources of specific genetic elements (usually alleles of specific loci) to be transferred by breeding into locally adapted genotypes. The most common type of active collection, a breeding collection, is intended to serve as a reservoir of alleles governing specific traits to be transferred, by appropriate breeding methods, into locally adapted genotypes. Breeders' perceptions of active collections as they are now structured and maintained, together with some suggestions from breeders for improving their usefulness, are given below. Passport and Descriptor Information Accessions must be well documented to allow users the means for rationally examining collections. Without relevant data, users must screen accessions more or less blindly in their search for needed alleles. Unfortunately, accurate passport and descriptor information is often not available for many accessions. For initial screening, breeders prefer to identify those accessions best suited to their own production environment and to screen the remainder of the collection only if they do not find the needed alleles in the initial screening. Efforts have been made to aid plant explorers, germplasm bank managers, and curators by identifying those passport and descriptor data useful to users. The International Board for Plant Genetic Resources has published standard descriptor lists for many crops. However, this crucial information is often missing from the accession record. Traditional collections are often inadequate for population, ecologic, and evolutionary genetic studies of the structure of population, ecotypes, and species. Sampling strategies, sample sizes, and documentation have often been inadequate for such purposes. Scientists who undertake such population genetic studies consequently often find it necessary to organize their own collecting expeditions independent of the germplasm system. Maintenance, Rejuvenation, and Sample Size One of the most vehement criticisms of germplasm banks concerns failures in the maintenance and renewal (or regeneration) of
OCR for page 182
Managing Global Genetic Resources: Agricultural Crop Issues and Policies accessions, which, in turn, have adverse effects on the quality and quantity of materials available to users. In some cases accessions known to be genetically uniform have become hybrid mixtures or swarms, and conversely, accessions known to be genetically diverse have suffered severe genetic erosion. The problems and challenges of adequate regeneration procedures are addressed in Chapter 5. Redundancy Many breeders believe that unacceptable levels of redundancy exist in collections. A survey of germplasm conservators and users on the world collections of barley, which contain more than 250,000 accessions, suggests that only about 50,000 are unique accessions (Lyman, 1984). Unnecessary duplication is often obvious and, hence, correctable; for example, adequate passport data often identify redundancy. In the case of barley, a large group of several thousand accessions from the National Small Grains Collection of the United States is duplicated in many collections around the world (Anishetty et al., 1982). It can be argued that such redundancy provides insurance against loss of important collections. However, it also leads to inflated and inaccurate estimates of the true extent of diversity contained in the world collections. Further, if passport data are unavailable, it is not possible to reliably determine which accessions are widely duplicated. New molecular technology (see Chapter 7), coupled with increased efforts to obtain basic passport and characterization information, may in part address the problem of redundancy. Where collections are large, management strategies, such as the designation of core subsets, may also be needed (see chapter 5). Obsolescence A disproportionate number of accessions in active collections are obsolete and are unlikely to serve as useful germplasm in modern breeding programs or in modern basic genetic, cytogenetic, or ecogenetic studies. This problem is discussed further below. Evaluation Germplasm systems have done virtually nothing to address the problem of evaluation, even though evaluation of performance (yield, components of quality, disease reaction) in specific habitats, and especially evaluation of prepotency (the capacity of a parent to produce
OCR for page 183
Managing Global Genetic Resources: Agricultural Crop Issues and Policies superior offspring) which provides the most useful information for identifying accessions with superior breeding potential. Unfortunately, the substantial information on performance and prepotency that was accumulated over the years has rarely been added to accessions records. Results of even the most simple evaluations are useful, and it is important that managers of active collections add such information to the record of accessions as it becomes available. Even though evaluation is more appropriately carried out by breeders and other researchers than by germplasm personnel, assembly of evaluation data should be a responsibility of the germplasm system. Germplasm collections should devote a portion of their resources to solicitation of evaluation by qualified breeders located in strategic environments, and to assurances that the information gathered is incorporated into the accessions records. Moreover, inadequate communication between germplasm workers and users in the past has impaired the use of unimproved germplasm (Chang, 1992). Core subsets, as described in Chapter 5, would allow collection managers to set priorities for their evaluation resources. MODERNIZATION OF ACTIVE COLLECTIONS Often, outstandingly useful modern materials do not find their way into germplasm collections. There are at least five main sources of new accessions: New elite lines and cultivars developed by breeders; Obsolete but historically important cultivars and stocks (including privately developed stocks) that should become generally available once they are obsolete; Genetically enhanced populations and germplasm stocks (discussed in the next section); Genetic, cytologic, cytoplasmic, and other stocks developed in basic genetic investigations; and Exotic germplasm, including landraces and wild relatives, obtained on collection expeditions. In North America a system has evolved that attempts to ensure that outstanding products of U. S. breeding programs and other categories of useful germplasm are made known both to curators of collections and to users of germplasm. In 1919 a plan for voluntary registration of field-crop cultivars was developed by the American Society of Agronomy and the Bureau of Plant Industry, U.S. Department of Agriculture (Committee on Varietal Standardization, 1920). This program was subsequently expanded to include the registration
OCR for page 184
Managing Global Genetic Resources: Agricultural Crop Issues and Policies of parental lines, elite germplasm, and genetic stocks and the incorporation of the registered materials into the U. S. National Plant Germplasm System (Crop Science Society of America, 1968; White et al., 1988). The materials registered are assigned plant introduction numbers, and the U.S. National Plant Germplasm System assumes responsibility, through the appropriate working collection, for maintaining and increasing the materials when they are no longer available from the developer or commercial sources. It is the policy of the U. S. National Plant Germplasm System that all plant materials in the system be freely distributed in small quantities for research purposes (there may be an embargo on distributing selected elite germplasm up to 7 years). Very large numbers of cultivars, parental lines, elite germplasm, and genetic stocks have been registered and distributed on a worldwide basis through this program since its inception, and the program has served a useful role in the modernization of many germplasm collections. The development of the registration programs for plant materials was important for gene resource conservation and utilization. In the United States, registration and publication of descriptive articles in the journal Crop Science provide a widely available and permanent record of the most useful modern elite materials. Registration also fosters greater utilization of the most modern materials and provides appropriate recognition for the developers of such materials and their institutions. Incorporation of the materials into the national germplasm systems attempts to preserve the materials for use in the future. Enhancement programs provide a cost-effective means of using large numbers of alleles previously scattered in hundreds of obscure accessions. Many additional enhancement programs are called for to concentrate and recombine useful genes into adaptive combinations that promote high performance and stability. EVOLUTIONARY PROCESSES AND GERMPLASM USE Evolutionary processes can be effective in concentrating and enhancing genetic variability from a small sample of selected materials. Two studies, one with barley and one with maize, indicated how these processes can be effective. These examples illustrate an essential step in using germplasm, which is the transfer of desired genetic traits into breeding lines that have agronomic, physiologic, and morphologic traits compatible with modern production systems. Other examples of such efforts include the Latin American Maize Project and the government, industry, and university cooperative effort in
OCR for page 185
Managing Global Genetic Resources: Agricultural Crop Issues and Policies the United States to adapt important tropical sorghum germplasm to more temperate daylength conditions (Maunder, 1992). Barley Harlan and Martini (1929) appear to have been the first to recognize the problems associated with obtaining useful alleles from large populations. They noted that most of the 5,000 items then available in the barley collection of the U. S. Department of Agriculture had been found to be of little value. However, they said that some barleys had promising qualities and that hybridization would allow the recombination of characters to produce superior offspring. They selected 28 outstanding accessions from the major barley-growing areas of the world, thus including materials that encompassed a wide range of ecological conditions. They crossed these 28 accessions in all possible pair combinations (378), mixed equal numbers of F2 hybrid seeds from each cross, and distributed the mixed hybrid population (Composite Cross II [CC II]) to barley breeders in various countries. They predicted that natural selection would eliminate many of the weaker combinations and that, at the end of 5 years, selections could be made with the reasonable hope of isolating superior types. This prediction was fulfilled. Within a few years many outstanding lines had been selected from CC II, including more than 50 lines that became named varieties, as well as numerous other lines that were used as parents in networks of subsequent successful crosses. Furthermore, long-term genetic studies have shown that the 28 parents of CC II contributed much of the total agriculturally relevant variability of the entire barley species to the population and that very useful evolutionary changes continued in CC II for more than 50 generations when it was grown under standard agricultural conditions in each of a number of ecogeographic regions (Allard, 1988). Maize The Iowa Stiff Stalk Synthetic population of maize was synthesized in 1933 and 1934 by Sprague and Jenkins (1943) from 16 inbred lines. They noted that many inbred lines of maize posses important desirable characteristics but, because of some specific fault, are unsuited for use as parents in commercial hybrids. They also noted that such lines might be of use as sources of desirable gene combinations in reservoirs synthesized from a number of selected lines. A large number of inbred lines that have been extracted from Iowa Stiff Stalk Synthetic were outstanding in their performance in hybrid combinations,
OCR for page 186
Managing Global Genetic Resources: Agricultural Crop Issues and Policies both in yield and in resistance to lodging. Lines selected from it have, over the years, been used extensively in hybrids in the Corn Belt and elsewhere, and lines extracted from it are still widely used in source populations in selection programs. The usefulness of the barley CC II and the maize Iowa Stiff Stalk Synthetic populations as sources of germplasm has stimulated the initiation of many different kinds of germplasm enhancement programs based on carefully selected materials in a number of different species. As enhanced germplasm has become more widely known and available, breeders have increasingly turned to such sources and away from traditional collections, in which variability is stored in a static state. RECOMMENDATIONS Germplasm collections are only valuable if they are used. The acquisition and compilation of a minimal set of data are required to locate the accessions most likely to contain the traits of interest. Efforts must also be made to enhance the ability to access important traits contained within exotic accessions. Programs of genetic enhancement should be developed to make a diversity of germplasm resources useful to crop breeders Germplasm collections are of little value unless useful alleles for disease resistance and tolerance to stresses such as cold, heat, and drought, including alleles from primitive sources, are introgressed and assimilated into appropriate genetic backgrounds. Significant enhancement (prebreeding) programs have been undertaken in the past by publicly supported universities, especially in North America, and by the Agricultural Research Service of the U.S. Department of Agriculture. Some of the commodity-oriented international agricultural research centers, such as the International Rice Research Institute and the Centro Internacional de Mejoramiento de Maíz y Trigo, have also made large numbers of crosses involving exotic germplasm. Useful germplasm often reaches germplasm collections via regional and international testing networks of the international centers. Enhancement activities are also pursued in many large private-sector breeding programs. The products of these efforts are increasingly become generally available through national registration programs. Private groups should be encouraged to participate in these programs, making available obsolete lines of historical importance for possible use by other countries.
OCR for page 187
Managing Global Genetic Resources: Agricultural Crop Issues and Policies Increased efforts are needed to evaluate and document germplasm accessions. Breeders and other researchers do not generally have the resources or facilities to screen large collections. There is, however, considerable information for many collections, but this information is often not readily available. Managers of collections must make increased efforts to gather this information and make it available with seeds or plant parts from accessions to aid in selection and use of germplasm. At a minimum, the basic information about the origins and habitat of accessions is needed. Such information is essential to germplasm use and can aid management by reducing redundancy and enabling the establishment of core subsets as outlined in the previous chapter. Germplasm workers should strive to become active partners in germplasm evaluation, enhancement, and use by contributing their knowledge on and experience with unimproved germplasm.
OCR for page 188
Managing Global Genetic Resources: Agricultural Crop Issues and Policies This page in the original is blank.
Representative terms from entire chapter: