Soybeans are grown on approximately 60 million acres annually in the U.S. and ranks second in value only to corn among all U.S. crops. Soybeans provide one-fourth of the world's fats and oils, about two-thirds of the world's protein-concentrate animal feeds, and three-fourths of the total world trade in high protein meals. From about 20 percent of the total U.S. crop acreage, farmers harvest almost two-thirds of the world's total soybean production, worth billions of dollars in domestic and export markets. Because of the magnitude of the crop in the U.S. and the importance of soybeans and soybean products in world trade, major soybean pest problems and end-use quality characteristics of soybeans can have a significant impact upon the economy of the nation. Continued manipulation of the germplasm base will be essential for meeting future demands for changes in soybean seed composition, seed yield, and pest resistance in a timely manner. Because of the preeminence of the U.S. in world soybean production, the major responsibility for maintaining the world's soybean germplasm rests upon the U.S.
The crop originated in China, and until this century its production was restricted almost exclusively to Eastern Asia in an area extending from the Far East region of the Soviet Union through China, Japan, and Korea and into Indonesia. Except for a few reports of weedy types in China the soybean is known only as a cultivated crop. Its close relative, the wild soybean, is quite distinct morphologically and occurs in China, Taiwan, eastern Russia, Japan, and Korea. The much more distant relatives, the perennial Glycine, are all native to Australia.
USDA Soybean Germplasm Collection currently contains 14,287 introduced G. max, 1,098 G. soja, and 887 perennial Glycine representing 16 species. In addition there are 151 lines in the Genetic Type Collection, 564 near-isogenic lines, 210 pre-1945 public cultivars, 381 modern U.S. and Canadian public cultivars, 35 privately developed cultivars, and 130 Crop Science registered germplasm releases for a current total of 17,743. The Collection has more than tripled in size during the past 20 years. Despite the large size and rapid recent growth, more accessions are still needed. Based on information from other collections, especially from China, and our research on genetic diversity, we estimated that the USDA Collection could contain more than 30,000 G. max accessions without risk of excessive duplication. The G. soja collection could reach a similar size since there are many opportunities still remaining for field collecting even though the total current world inventory is far below that number. The Australian perennial Glycine collection contains accessions not in the U.S. and additional field collecting is occurring in 1996.
Storage and distribution of all accessions is done at Urbana, IL, but seed increase plots are also grown at Stoneville, MS, and Isabela, PR. Staff, laboratory, and cold-storage facilities are provided by the USDA. Greenhouse space and land for grow-outs and evaluations are provided by the respective state experiment stations.
Sources of resistance have been identified for Phytophthora rot, brown stem rot, powdery mildew, downy mildew, bacterial pustule, frogeye leafspot, Phomopsis seed decay, stem canker, soybean mosaic virus, Meloidogyne incognita, Meloidogyne arenaria, Meloidogyne javanica, soybean cyst nematode, and leaf feeding insects. Commercial cultivars are available with resistances to most of these pests. Resistance has been found absent or inadequate for Sclerotinia stem rot, Septoria brown spot, Charcoal rot, Rhizoctonia aerial blight, and sudden death syndrome.
Like all other major crops, the nation's commercial soybean varieties are descended from a small number of ancestral strains. Thirty-five ancestral lines account for over 95% of the genes in all commercial varieties grown in the U.S.
Recent acquisitions from China have greatly increased the representation from central and south China in the Collection. At this time, it seems likely that this process will continue for the foreseeable future. This is filling a major void in the Collection and continuing this acquisition should be a high priority. We should continue to monitor the Glycine accessions in other national collections including India, Japan, South Korea, and Russia. The collection in AVRDC is also a potential source of germplasm. Germplasm has been obtained from all of these collections in the past but it is important to periodically review the current inventory of these collections. Newly released enhanced germplasm and modern cultivars from Asia should also be considered in germplasm exchanges.
Field collection is possible and desirable in certain areas of south Asia. Vietnam should be a high priority for collection. Soybeans have been cultivated here for several hundred years and there is a great diversity of primitive varieties still used in production. Opportunities to collect in other Asian countries from Laos to Afghanistan should be considered.
There are few accessions from North Korea in the collection and they were either obtained more than 60 years ago or more recently received through third parties. We have no direct contact with scientists there and have no information on status or even existence of a soybean germplasm collection in that country. Some North Korean germplasm does exist in Germany and was requested without success.
The wild soybean ranges through eastern Asia from Siberia to south China including Japan and the Korean peninsula. The G. soja collection is small compared to the G. max collection. It is still very difficult to obtain any G. soja accessions from China and that remains a high priority. No G. soja accessions have ever been obtained from North Korea. Additional G. soja collecting in South Korea, Russia, and Japan would be possible and could benefit the Collection. The islands surrounding South Korea would be a high priority for collecting as would Shikoku, eastern Kyushu, southern Honshu, and the smaller islands of Japan. Cooperative ventures to collect from these regions should be explored. Before additional collecting is conducted, exchanges of G. soja accessions already existing in collections should be attempted. G. soja exists in the national collections of these countries as well as in individual scientist's collections.
Only a few accessions are available for many of the perennial species. Additional accessions could be obtained from the Australian collection. A collection trip into the northwestern part of the continent was conducted in 1993. A collection trip into north central Australia funded by the USDA is planned for 1996. Continued efforts to expand the diversity of this collection are needed. Perennial Glycine species should receive less emphasis than the annual species. The perennials are difficult and expensive to maintain because they require greenhouse facilities for grow-outs. The cooperative relationship with Australia has been productive and successful and should be continued and encouraged.
General evaluation data is routinely collected for all G. max accessions except those in the Genetic Type and Private Cultivar Collection. Field evaluations of all accessions in maturity groups VI (816), VII (474), VIII (370), IX (356) and X (276) and 1,371 recent acquisitions in maturity groups 000 to IV have been conducted in the past four years. Laboratory data remains to be collected on some accessions. This evaluation includes data on 13 descriptive characteristics, 11 agronomic characteristics, and 7 seed composition characteristics. Evaluation tests are conducted at Isabela, PR (maturity groups IX and X), Stoneville, MS (maturity groups V, VI, VII, and VIII), Urbana, IL (maturity groups I, II, III and IV) and St. Paul, MN (maturity groups 000, 00, and 0). Yield data is not collected for accessions evaluated in Puerto Rico. After completion, all data will be published in USDA technical bulletins and entered into the GRIN. Currently there are 5 technical bulletins of evaluation data available and one is currently in press.
Cooperation with USDA, university and private company soybean scientists is critical for obtaining specific evaluation data especially for identifying resistance to diseases, insects, and nematodes. Major screening programs are currently underway for Phytophthora rot, brown stem rot, soybean mosaic virus, soybean cyst nematode, Sclerotinia white mold, Septoria brown spot, Rhizoctonia aerial blight, sudden death syndrome, leaf feeding insects, and drought tolerance using accessions from the Collection.
There are some deficiencies in the current evaluation scheme. There are proven techniques established for screening for resistance to soybean rust, northern root knot nematode and silverleaf whitefly but no evaluations are underway or planned partially because of the high cost of these procedures. There are no good screening procedures for charcoal rot, and pod feeding by stinkbugs, bean leaf beetles and corn earworm and other lepidopterous pod feeders. It is possible to screen for resistance to frogeye leafspot, but because the diversity of the pathogen is not well categorized, the results are not as useful as they could be.
It would be desirable to locate DNA markers closely linked with pest resistant loci especially for those resistances that are multigenic. These linked markers could facilitate transfer of genes from primitive accessions to modern cultivars or could be used to indirectly select for resistance to pests such as soybean rust that require expensive containment-facility evaluation.
During the past 15 years, scientists from ARS, university and private industry have cooperated in evaluation of many germplasm accessions and improved germplasm derived from those accessions. This work has identified high-yielding germplasm through multilocation testing. As high-yielding germplasm accessions and derived lines are identified, it becomes increasingly important to be able to determine if these genotypes actually contain desirable genes not currently in commercially used gene pools. Measuring genetic diversity at the DNA level is now possible and is beginning to be used to assess genetic diversity.
Recent research clearly demonstrates the limited genetic base of the U.S. soybean crop. Extensive germplasm exchange among programs has been the key factor for continuous incremental yield gains. As the impact of commercial varieties increases in the market place, and variety patenting becomes commonplace, germplasm exchange and yield advances are threatened as never before. Public field-oriented programs must expand their role in the creation of germplasm with desirable combinations of genetically diverse alleles for agronomically important traits. The ability of new molecular technologies to improve previously intractable traits, i.e. high yield and drought tolerance, will require continued field evaluations prior to use by commercial breeding organizations.
An important component of the germplasm collection at Urbana is the soybean isoline collection. With these genetic resources, specific genes controlling traits of potential economic importance or of potential research value are transferred to a common genetic background. The transfer of one- or two-gene traits from unadapted germplasm increases the usefulness of the traits in the development of commercial cultivars and provides researchers with a new tool for genetic research. Such unique germplasm is not available through any other collection. Both the large number of requests received for this germplasm and the many research publications based on the use of isolines attest to the value of these lines. Additional isolines are being developed by scientists associated with the Collection and efforts are being made to acquire isolines developed by other scientists.
Adequate storage facilities exist at Urbana for the near term but the recent consolidation of the Collections and acquisition of large numbers of new accessions has consumed much of the available space. Chemical desiccation units have been added to two of the cold storage rooms in Urbana. Recent research has shown that reducing the relative humidity can improve seed vigor and longevity. All germplasm accessions are now stored at 10 C and 25% relative humidity. Currently G. max accessions are regrown every 10 years and G. soja accessions every 15 years. Future research will determine how much the regeneration cycle can be extended with the improved storage conditions. New, more space-efficient storage containers have allowed for an almost doubling of the amount of seed stored in only 10% more space. This has reduced the number of accessions that must be regrown because of low seed supply.
As soon as sufficient quantities of seed are available, back-up samples are sent to the National Seed Storage Laboratory at Ft. Collins, CO.
The current basic program for germplasm maintenance, agronomic evaluation, and seed distribution is good but does have some deficiencies. To achieve a fully adequate national program in soybean germplasm, we recommend the following priority of actions:
Priority 1. Additional Staff: The most limiting constraint on the current collection is insufficient staff. Urbana still has the same level of staffing as existed when that location was responsible for less than half of the accessions in the current collection. To compensate for this imbalance, available technical staff have been shifted from research to germplasm activities, a permanent back log of work has become standard, and much that could and should be done is not attempted. Expanded evaluation and acquisition, although desirable, is not possible without more people.
Priority 2. Germplasm acquisition: This is an activity uniquely associated with the Collection and must always remain a high priority as long as voids remain in the Collection. Because G. max is a domesticated species, those lines not in formal collections are generally more vulnerable to human decisions than other Glycine species and can be lost very quickly. Highest priority should be given to field collection of G. max, where possible. Many opportunities exist for additional collection of G. soja and perennial Glycine and they should be actively pursued. Germplasm exchange has been and still remains the key method of acquisition and should not be overlooked.
Priority 3. Germplasm enhancement - Germplasm enhancement of quantitatively controlled traits will require the cooperative efforts of high-quality research teams, development of techniques for assessing genetic diversity, additional funding, and much hard work. This will be long-term, high-risk research, but the results of such cooperative efforts have the potential of being very significant.
Priority 4. Identification and genetic analysis of needed resistance to soybean
pests - Although not many soybean pests are devastating a major portion of the
crop because of a lack of genetic resistance, there are some areas in which
additional screening is still important and should be addressed. The development
of previously unimportant diseases and the identification of new strains of
diseases that have long been recognized as important requires that this research
be a permanent part of the germplasm agenda. New accessions need to be evaluated
for resistance to all of the major pests, especially for pests for which known
resistance is represented by few accessions or does not exist.