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PLANT GENETIC RESOURCES

Genetic Base of Japanese Soybean Cultivars Released during 1950 to 1988

^a Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695-7631 USA
^b USDA-ARS and Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695-7631 USA
^c National Institute of Agrobiological Resources, Tsukuba, Japan

tommy_carter{at}ncsu.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Plant breeding success is dependent, in part, upon the genetic diversity found within applied breeding programs. To characterize genetic diversity in applied breeding, plant breeders have invoked the concept of genetic base, which can be defined as the ancestral pool from which breeding is derived. The genetic base of modern Japanese soybean [Glycine max (L.) Merr.] cultivars is not well characterized. The objective of this study was to quantify the genetic base of Japanese soybean cultivars by coefficient of parentage (CP) analysis, to compare the genetic bases of major growing regions and release eras in Japan, and to compare the Japanese base with that of other countries. Seventy-four ancestors were identified in the pedigrees of 86 public Japanese cultivars registered from 1950 to 1988. Ancestors originating from Japan contributed 76% of the genes to the Japanese breeding, while exotic ancestors from the USA and Canada (US-CAN), China, and Korea contributed 2, 5, and 2%, respectively. The remaining portion of the base was of unknown, but presumed Japanese origin. Three major growing regions of Japan displayed very distinct genetic bases with at least 50% of the ancestral contribution unique to each region. Comparisons revealed that the Japanese base was more diverse than that of the US-CAN. The more diverse genetic base was exemplified by (i) more ancestors accounting for 50 and 80% of the genes in Japanese breeding; (ii) a continual expansion of the genetic base since 1950, while the US-CAN base remained relatively static; and (iii) a higher ratio of ancestors employed to cultivars released. The number of ancestors contributing to breeding in Japan was much smaller than that for China in terms of number of ancestors, even though both genetic bases expanded with time. The long history of soybean breeding in Japan, its diverse genetic base and its relative isolation from US-CAN and China suggest that Japanese, Chinese, and North American breeding pools may serve as important reservoirs of diversity for each other. Twelve Japanese cultivars released from 1950 through 1988 derived at least 25% of their pedigree from improved U.S. or Chinese breeding materials.

Abbreviations: CP, coefficient of parentage • CJ, central Japan • NJ, northern Japan • SJ, southern Japan

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
PLANT BREEDING SUCCESS is extensive in agriculture and a key to meeting global demands for food and fiber. However, the predicted decline in global crop hectarage and increase in human population will place unparallel demands upon plant breeding this century (Carter and Wilson, 1998). The ability of plant breeders to meet these demands is uncertain, because long-term breeding progress cannot be predicted accurately. Progress is dependent in part upon crop diversity and there is no universally accepted measure of agronomic crop diversity (Gizlice et al., 1993b). Thus, a fundamental question in breeding remains unanswered: "Is there sufficient genetic diversity to sustain long term advances in applied plant breeding?"

To address this problem, breeders have developed the concept of genetic base to compare, in a relative way, the diversity of contrasting applied breeding programs (Delannay et al., 1983; Gizlice et al., 1994; Song et al., 2000). Genetic base has been defined as all genetic stocks that have contributed to cultivar development (Cui et al., 2000). Quantification of genetic base (i.e., calculation of the proportional contributions of ancestors to the base) has been achieved to date primarily through pedigree analysis of cultivars by means of coefficient of parentage (CP), a form of numerical taxonomy (Cox et al., 1985a,b; Murphy et al., 1986; Knauft and Gorbet, 1989; Souza and Sorrells, 1989; Dilday, 1990; Smith et al., 1990; Smith and Smith, 1992; Martin et al., 1991; Cuevas-Perez et al., 1992; McClean et al., 1993; Gizlice et al., 1994; Hintum and Haalman, 1994; Voysest et al., 1994; Cui et al., 2000).

In soybean, the genetic base of Chinese soybean breeding has been described as broad and that of USA and Canadian (US-CAN) breeding as narrow (Gizlice et al., 1994; Cui et al., 2000). Coefficient of parentage analysis revealed that 35 and 339 ancestors contributed 50 and 90% of the genes in Chinese cultivars while only five and 26 ancestors contributed similar amounts to the US-CAN base. Each of the three major growing regions in China were almost independent in terms of genetic base and each had more contributing ancestors than did the whole of the US-CAN. The midwestern and southern growing regions of the US-CAN were quite distinct, on the basis of pedigrees, but less so than the major growing regions of China. Although most of the U.S. breeding base is derived from Chinese landraces, China and US-CAN cultivars share only a small degree of common ancestry based upon pedigree, and thus, have remained relatively isolated from each other in the 20th century.

The genetic base of modern Japanese soybean cultivars is not well characterized. Elucidation of this genetic base and its relation to Chinese and US-CAN breeding should facilitate the efficient use of Japanese cultivars in breeding and aid in determining the current status of genetic diversity in the crop. The objective of this study is to quantify the genetic base of Japanese soybean cultivars registered by the Ministry of Agriculture, Forestry and Fisheries between 1950 to 1988 by determining (i) the genetic contribution of each ancestor to the genetic base of Japanese soybean cultivars using CP analysis; (ii) the relative genetic diversity and relatedness of three major growing regions of Japan; (iii) the changes in the genetic base of Japanese cultivars over time; and (iv) the genetic structure of the Japanese base in comparison to those of the US-CAN and China.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Pedigree Data Base
Eighty-six publicly released cultivars were registered by Japanese Ministry of Agriculture, Forestry and Fisheries between 1950 and 1988 (Miyazaki et al., 1995a) (Table 1) . The pedigrees and related data for Japanese modern soybean cultivars were compiled by S. Miyazaki (1999, personal communication). Each cultivar was assigned to its primary growing region and release era. We defined the major growing regions of Japan as northern Japan (NJ, Hokkaido island), central Japan (CJ, Shikoku island from Nagano and Tokyo cities north), and southern Japan (SJ, Kyushu island) (Table 1). Release eras were defined as 1950s (1950–1959), 1960s (1960–1969), 1970s (1970–1979), and 1980s (1980–1988).

Genetic Contribution of Ancestors to Genetic Base and Assumptions
The genetic contribution of an ancestor to a modern cultivar was determined as the fraction of genes in the modern cultivar that could be traced to that ancestor through pedigree analysis (Gizlice et al., 1994; Cui et al., 2000). Coefficient of parentage was used to estimate this contribution. Coefficient of parentage between two individuals is defined as the probability that a random allele at a random locus in one individual is identical by descent to a random allele at the same locus in another individual (Malécot, 1948; Kempthorne, 1957). The average CP between an ancestor and all 86 cultivars in the study was taken as the overall genetic contribution of an ancestor to the genetic base of Japanese soybean (Gizlice et al., 1994). The ancestors did not have recorded common antecedents, and thus, total contributions of all ancestors to the genetic base summed to unity.

In the calculation of CP, we assumed the following: (i) all ancestors, cultivars, and parental breeding lines were homozygous and homogeneous; (ii) a cultivar or a breeding line derived from manual hybridization or natural outcrossing obtained 50% of its genes from each parent; (iii) the CP value between a naturally occurring or mutagen-induced mutation and its antecedent was 1.0; and (iv) the CP value between two full-sib inbreds from a cross of two unrelated parents was 0.5 if the two inbreds shared no common F₂ plant, 0.75 if two inbreds were derived from a common F₂ plant, or 1.0 if the two inbreds were derived from the same F₅ plant.

Ancestors with Multiple Phenotypic Types in the Japanese Collection
Five ancestors (`Akasaya', `Ani', `Shirasaya', `Tamanishiki', `Tsuru No Ko') appeared as multiple phenotypic sources with identical names in the Japanese Germplasm Storage Center of the National Institute of Agrobiological Resources (Miyazaki et al., 1995b). Genetic relations among the multiple phenotypic sources were not clear from passport data. Multiple phenotypic sources for a single ancestor raised the possibility that more than one source of an ancestor was used as a parent in breeding and added a degree of uncertainty to pedigree relations. For two of the ancestors above (Ani, Tsuru No Ko), contrasting phenotypic sources of the single ancestor were collected from breeding stations. The ancestor Ani, for example, was collected at two different breeding stations while a third station actually developed a cultivar from it (source not specified). We adopted the following rules and assumptions for such cases. The multiple phenotypic types with a common ancestral name were assigned a CP value of 0.75 for all pairs to reflect an assumed similarity among the types. If a breeding station was the site of collection for an ancestral phenotype, we assumed that the station also used that same source in breeding. A breeding station which was not a collection site, but employed one of the multiple phenotypes in breeding, was assumed to use the source collected nearest to it. We further assumed that only one phenotypic ancestral source was used for breeding at any one station. We then counted each ancestral name as a single ancestor in the calculation of the genetic base.

Off-Type Variants Which Arose from Preexisting Strains
Twenty-three genotypes in the pedigree data base arose as selections from preexisting strains. Because of the uncertain pedigree associated with their development, these 23 genotypes could have arisen from mutation, natural outcrossing (via unknown male parents), or through mechanical mixing with the expected CP relation between selection and antecedent of 1.0, 0.5, or 0.0, respectively. Where phenotypic data were available, we examined conventional descriptive traits (flower, pubescence, maturity, and 100-seed weight) of the selection and its antecedent to help resolve pedigree uncertainties. Six of the 23 selections were compared with antecedents in this way. Phenotypic data were obtained from field evaluation of Japanese cultivars and available ancestors in 1994 and 1995 at Clayton, NC, from seed sources identified by Miyazaki et al. (1995a,b) from the Japanese Germplasm Storage Center of the National Institute of Agrobiological Resources (data not shown). Because of the rarity of multiple mutations in a single plant, we assumed an outcrossing event to be the origin of the variant if it differed from the preexisting strain by two or more of the four conventional descriptor traits and assigned a CP relation of 0.5 between the two in such cases. In the absence of evidence for outcrossing (i.e., no or only one phenotypic difference), a mutational event was assumed and a CP value of 1.0 was assigned. Employing this rationale, five selections were assigned a CP relation of 0.5 with their respective antecedents, and one selection was assigned a CP relation of 1.0. Four genotypes developed through irradiation were also compared phenotypically against their antecedents with no differences detected except for maturity dates.

In the absence of phenotypic data to clarify the origin of an off-type selection, we arbitrarily ignored the possibility of seed mixing and assigned a CP relation of 0.75 between the remaining 17 off-type genotypes and their preexisting source. The value 0.75 is the midpoint of the CP values associated with mutation or natural outcrossing as the origin of a selection. Murphy et al. (1986) assigned the identical value in a CP analysis of wheat (Triticum aestivum L.), and Cui et al. (2000) assigned a similar value of 0.87 for Chinese soybean on the basis of case studies of phenotypic difference between genotypes. For the five off-type selections deemed to have arisen from natural outcrossing and the 17 off-type selections with uncertain male pedigree, the category of assumed, but unknown, male parent (called pseudo ancestor hereafter) was employed to aid computational analysis of CP.

Analysis of Coefficient of Parentage
The pedigree information was recorded into a pedigree data base file with four column headings: progeny name, female and male parent, and a six or fewer letter abbreviation of progeny name. This file was checked extensively for typing errors against a hard copy. The CP matrix for ancestors and cultivars was computed by a FORTRAN program following the same procedures described in detail by Cui et al. (2000). Briefly, a first subroutine of the program assigned codes to ancestors and progeny. All ancestor codes were numerically smaller than all progeny codes, and the total number of ancestors was consistent with that derived via visual inspection of the original pedigree information. An overwrite file added pseudo ancestor relations and other relations not easily represented in the data base. The second subroutine took the output from the first subroutine and the overwrite file as input to calculate the CP matrix. Subsequently, the CP between Individuals X and Y was calculated as CP_XY = pxCP_XA + qxCP_XB, where Y was the progeny of A and B, X was a second strain but not a descendent of Y, and p and q were the percentage contribution of A and B to Y. If two parents, A and B, contributed equally to Y, then above formula was simplified to CP_XY = 1/2(CP_XA + CP_XB) which was the usual case. The average CP of each ancestor with all cultivars was then calculated.

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Genetic Base of Japanese Cultivars
Seventy-four ancestors were identified for the 86 Japanese soybean cultivars released during 1950 to 1988 (Table 2) . These ancestors accounted for 85% of the genetic base for Japanese soybean cultivars. The remaining 15% of the genes could not be traced to an ancestor because of incomplete pedigree records, including 23 variants that arose in preexisting strains. Phenotypic evaluation indicated that one of these variants likely derived from a mutational event. For the other 22 variants, the uncertainty in male pedigree was represented in our computations by the category of pseudo ancestor. Because pseudo ancestors are a computational device used only for CP analysis, this category was not included in the count of ancestors. Among the 74 ancestors, 16 were exotic: seven from China, six from US-CAN, two from Korea, and one from Sakhalin Island (Table 2 and 3) . The remaining 58 ancestors were Japanese landraces or, in cases where the name of the original landrace was unknown, selections from landraces. Japanese ancestors contributed 91% of the genes to Japanese soybean breeding (76% from pedigree records and 15% from pseudo ancestors assumed to be of Japanese origin), while the 16 exotic ancestors contributed 9% (Table 3). Most ancestors contributed only a small amount, individually, to Japanese soybean breeding. The two most important ancestors contributed 6 and 5%, while 28 additional ancestors each contributed from 1 to 5% of the genetic base (Table 2). The 18 most important ancestors contributed 50% of the total genetic base; and 53 ancestors contributed 80%.

The CJ region released twice as many cultivars as other regions and had a correspondingly larger base than the other regions of Japan. This larger genetic base for CJ is reflected in the total number of ancestors for the region and in the number of ancestors contributing 50% of the genetic base (twice as many as for the other two regions, Table 1). The NJ and SJ regions were similar in terms of number of releases and size of genetic base. However, exotic ancestors contributed 18% of the NJ base but only 2% of the SJ base (Table 3). The CJ region was intermediate in the use of exotic germplasm with 7% derived from exotic sources. The U.S. ancestors only contributed genes to the CJ and SJ base, while Chinese strains only contributed genes to the NJ and CJ bases. The ratio of ancestors employed to cultivars released and average number of ancestors used for each individual cultivar were relatively constant across regions, despite the larger number of releases in the CJ region (Table 1). These findings support the view that breeders from the contrasting regions tended to share a common philosophy which promoted the inclusion of a broad range of diversity in breeding.

Changes over Time in Japanese, Chinese, and US-CAN Genetic Bases
New Japanese cultivars were released in every decade since 1950, and the genetic base of Japanese soybean breeding expanded in a corresponding way (Tables 1 and 4) . The expansion of the base was exemplified by the relatively large percentage contribution of new ancestors added to the base in successive decades from 1950 (15, 12, 18, and 27%) and by the relatively stable ratio of ancestors used to cultivars released across decades (Tables 1 and 5) . There were only three ancestors that made sizable contribution to the genetic base for at least three of the four decades studied (Ani, Geden Shirazu, and Daizu Hon 326).

The three genetic bases of Japan, China, and the US-CAN were largely independent based upon pedigree analysis (Gizlice et al., 1994; Cui et al., 2000). Approximately 6% of the US-CAN and 3% of the Chinese genetic bases traced to Japanese stock. Only 5 and 2% of the Japanese base traced to China and the US-CAN, respectively. The genetic separateness of Japan cultivars from those in China and the US-CAN was confirmed recently by DNA-based genetic distance measures (Thompson et al., 1997; Nelson et al., 1998; Carter et al., 2000). The elite Japanese cultivars were the most distinct group as indicated by four types of molecular markers.

Implications to Breeding
The relative independence of applied breeding programs in Japan, China, and the USA suggests that each of these three breeding pools may serve as important reservoirs of genetic diversity for the others. Carter et al. (2000) proposed the use of foreign cultivars as sources of new yield genes for applied breeding in the USA, because applied soybean breeding was based primarily on a narrow genetic base of one dozen founding ancestors (source of 80% of genes) introduced prior to 1930 (Gizlice et al., 1994; Sneller, 1994). Gizlice et al. (1993a) reported that intensive selection upon this narrow base caused a decline in genetic diversity, noting that newer cultivars from the USA were as highly related as half sibs on the average. Some breeders have suggested that this decline could threaten future yield advances in U.S. breeding if left unchecked (Zhou et al., 1998). Because cultivars are usually more productive than random plant introductions from germplasm collections, Japanese and Chinese cultivars may be attractive potential sources of yield genes and other agronomically important diversity (Bernard et al., 1998; Carter et al., 2000). At present, however, Japanese cultivars are viewed by many U.S. breeders only as useful sources of desirable food processing traits for niche markets.

In China, there is not an apparent threat to genetic diversity in applied breeding because of the large genetic base and the tendency of Chinese breeders to avoid the mating of close relatives (Cui et al., 2000). However, Chinese breeders have demonstrated the ability to develop high-yielding, popular cultivars in recent years from the hybridization of traditional Chinese cultivars with cultivars from the USA. More than 20 cultivars with at least 25% U.S. cultivar pedigree are currently grown in China (J. Gai, 1999, personal communication). This important success story suggests that the U.S. and Chinese cultivars are mutually important to each other as a source of yield genes for breeding. In Japan, a narrow genetic base does not appear to be a serious hindrance to breeding progress, yet 12 cultivars have been released with 25% or greater U.S. or Chinese pedigree. These Japanese breeding successes indicate that all three contrasting gene pools may be economically important in applied breeding. Many Chinese, Japanese, and publicly derived U.S. cultivars are available freely as breeding stock from the USDA-ARS National Soybean Germplasm Collection.

At present, modern Japanese and Chinese cultivars have not made a great impact in U.S. soybean breeding. Duvick (1984) indicated that most U.S. soybean breeders preferred to use only elite U.S. cultivars as donor sources for pest resistance and stress tolerance, even though most of these same breeders supported the concept of expanding the soybean genetic base through germplasm introgression. A later survey by Frey (1996) indicated that 104 science-person years were devoted to U.S. soybean cultivar development, with only 26 responsible for germplasm enhancement. A more recent survey revealed that less than 1% of U.S. field breeding involves breeding lines using introductions not already part of the genetic base (T.E. Carter, 1998, unpublished data).

Marshall (1989) identified an important reason why exotic germplasm such as Japanese cultivars are seldomly used in mainstream U.S. breeding: unknown relations between the exotic germplasm and adapted cultivars. Breeders are reluctant to spend breeding capital on exotic germplasm unless there is a clear rationale. Providing a clear rationale for selecting one plant introduction over another has proven elusive in terms of yield improvement (Goodman, 1985). Recent development of molecular marker techniques in conjunction with detailed pedigree analysis, such as provided here, may provide breeders with useful tools to measure genetic diversity among cultivars. These techniques may enhance the use of exotic material in practical soybean breeding (Nelson et al., 1998; Thompson et al., 1998; Li 1999; Boerma and Rouf Mian, 1999; Carter et al., 2000).

Received for publication February 14, 2000.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 

• Bernard, R.L., C.R. Cremeens, R.L. Cooper, F.I. Collins, O.A. Krober, K.L. Athow, F.A. Laviolette, C.J. Coble, and R.L. Nelson. 1998. Evaluation of the USDA soybean germplasm collection: Maturity groups 000–IV. p. 1–16. USDA Tech. Bull. 1871. U.S. Govt. Print. Office, Washington, DC.
• Boerma, H.R., and M.A. Rouf Mian. 1999. Soybean quantitative loci and marker assisted breeding. In H. Kauffman (ed.) Proc. World Soybean Res. Conf. VI. p. 68–83. Superior Printing, Champaign, IL.
• Carter, T.E., Jr., R.L. Nelson, P.B. Cregan, H.R. Boerma, P. Manjarrez-Sandoval, X. Zhou, W.J. Kenworthy, and G.N. Ude. 2000. Project SAVE (Soybean Asian Variety Evaluation) – Potential new sources of yield genes with no strings from USB, public, and private cooperative research. p. 68–83. In B. Park (ed.) Proceedings of the 28th Soybean Seed Research Conference. 1998. American Seed Trade Association, Washington, DC.
• Carter, T.E., Jr., and R.F. Wilson. 1998. Soybean quality for human consumption. In A. James (ed.) Proceedings of the 10th Australian Soybean Conference. CSIRO Tropical Agriculture, Australia.
• Cox T.S., Kiang Y.T., Gorman M.B., Rodgers D.M. Relationship between coefficient of parentage and genetic similarity indices in the soybean. Crop Sci. 1985;25:529-532 a.[Abstract/Free Full Text]
• Cox T.S., Lookhart G.L., Walker D.E., Harrell L.G., Albers L.D., Rodgers D.M. Genetic relationships among hard red winter wheat cultivars as evaluated by pedigree analysis and gliadin polyacrylamide gel electrophoretic patterns. Crop Sci. 1985;25:1058-1063 b.[Abstract/Free Full Text]
• Cuevas-Perez F.E., Guimaraes E.P., Berrio L.E., Gonzalez D.I. Genetic base of irrigated rice in Latin American and the Caribbean, 1971 to 1989. Crop Sci. 1992;32:1054-1059.[Abstract/Free Full Text]
• Cui Z., Carter T.E., Jr., Burton J.W. Genetic base of 651 Chinese soybean cultivars released during 1923 to 1995. Crop Sci. 2000;40:1780-1793 (this issue).[Abstract/Free Full Text]
• Delannay X., Rodgers D.M., Palmer R.G. Relative genetic contribution among ancestral lines to North American soybean cultivars. Crop Sci. 1983;23:944-949.[Abstract/Free Full Text]
• Dilday R.H. Contribution of ancestral lines in the development of new cultivars of rice. Crop Sci. 1990;30:905-911.[Abstract/Free Full Text]
• Duvick D.N. Genetic diversity in major farm crops on the farm and in reserve. Econ. Bot. 1984;38:161-178.
• Frey K.J. National plant breeding study - I. Special Rep. 98. Ames, IA: Iowa State University, 1996.
• Gizlice Z., Carter T.E., Jr., Burton J.W. Genetic diversity in North American soybean: I. Multivariate analysis of founding stock and relation to coefficient of parentage. Crop Sci. 1993;33:614-620 a.[Abstract/Free Full Text]
• Gizlice Z., Carter T.E., Jr., Burton J.W. Genetic diversity in North American soybean: II. Prediction of heterosis in F₂ populations of southern founding stock using genetic similarity measures. Crop Sci. 1993;33:620-626 b.[Abstract/Free Full Text]
• Gizlice Z., Carter T.E., Jr., Burton J.W. Genetic base for North American public soybean cultivars released between 1947 and 1988. Crop Sci. 1994;34:1143-1151.[Abstract/Free Full Text]
• Goodman M.M. Exotic maize germplasm: status, prospects, and remedies. Iowa State J. of Research. 1985;59:497-527.
• Hintum T.J.L. van, Haalman D. Pedigree analysis for composing a core collection of modern cultivars, with examples from barley. Theor. Appl. Genet. 1994;88:70-74.
• Hymowitz, T., and R.L. Bernard. 1991. Origin of soybean and germplasm introduction and development in North America. In H.L. Shands and L.E. Wiesner (ed.) Use of plant introduction in cultivar development.Part I, Spec. Publ. 17. CSSA, Madison, WI.
• Kempthorne O. An introduction to genetic statistics. Ames, IA: Iowa State University Press, 1957.
• Knauft D.A., Gorbet D.W. Genetic diversity among peanut cultivars. Crop Sci. 1989;29:1417-1422.[Abstract/Free Full Text]
• Li Z. Applications of RAPD markers in soybean: Genetic diversity and linkage analysis. Ph.D. diss. (Diss. Abstr. no. 9953080). Urbana, IL: University of Illinois, 1999.
• Malécot, G. 1948. Les mathematiques de l'hérédité. Masson, Paris. English translation. The mathematics of heredity. 1969. W.H. Freeman and Co., San Francisco, CA.
• Marshall D.R. Limitations to the use of germplasm collections. In: Brown A.H.D., et al. , ed. The use of plant genetic resources. New York: Cambridge University Press, 1989:105-120.
• Martin J.M., Blake T.K., Hockett E.A. Diversity among North American spring barley cultivars based on coefficient of parentage. Crop Sci. 1991;31:1131-1137.[Abstract/Free Full Text]
• McClean P.E., Myers J.R., Hammond J.J. Coefficient of parentage and cluster analysis of North American dry bean cultivars. Crop Sci. 1993;33:190-197.[Abstract/Free Full Text]
• Miyazaki, S., T.E. Carter, Jr., S. Hattori, H. Nemoto, T. Shina, E. Yamaguchi, S. Miyashita, and Y. Kunihiro. 1995a. Identification of representative accessions of Japanese soybean varieties registered by Ministry of Agriculture, Forestry and Fisheries, Based on passport data analysis. No. 8. Misce. Publ. of National Ins. of Agrobiological Resources (Japan).
• Miyazaki, S., T.E. Carter, Jr., S. Hattori, T. Shina, T. Chibana, S. Miyashita, and Y. Kunihiro. 1995b. Identification of representative accessions of old cultivars that contribute to the pedigree of modern Japanese soybean varieties, Based on passport data analysis. No. 8. Misce. Publ. of National Ins. of Agrobiological Resources (Japan).
• Murphy J.P., Cox T.S., Rodgers D.M. Cluster analysis of red winter wheat cultivars based upon coefficient of parentage. Crop Sci. 1986;26:672-676.[Abstract/Free Full Text]
• Nelson, R.L., P.B. Cregan, H.R. Borma, T.E. Carter, Jr., C.V. Quigley, M.M. Welsh, J. Alvernaz, and R. Main. 1998. DNA marker diversity among modern North American, Chinese and Japanese soybean cultivars. p. 164. In Agronomy Abstracts. ASA, Madison, WI.
• Smith O.S., Smith J.S.C. Measurement of genetic diversity among maize hybrid, a comparison of isozymic, RFLP, pedigree, and heterosis data. Maydica 1992;37:53-60.
• Smith O.S., Smith J.S.C., Bowen S.L., Tenborg R.A., Wall S.J. Similarities among a group of elite maize inbreeds as measured by pedigree, F₁ grain yield, grain yield, heterosis, and RFLPs. Theor. Appl. Genet. 1990;80:833-840.[ISI]
• Sneller C.H. Pedigree analysis of elite soybean lines. Crop Sci. 1994;34:1515-1522.[Abstract/Free Full Text]
• Song Q.J., Quigley C.V., Nelson R.L., Carter T.E., Jr., Boerma H.R., Strachan J.L., Cregan P.B. A selected set of trinucleotide simple sequence repeat markers for soybean cultivar identification. Plant Varieties and Seeds 2000;in press.
• Souza E., Sorrells M.E. Pedigree analysis of North American oat cultivars released from 1951 to 1985. Crop Sci. 1989;29:595-601.[Abstract/Free Full Text]
• Thompson J.A., Nelson R.L., Vodkin L.O. Identification of diverse soybean germplasm using RAPD markers. Crop Sci. 1998;38:1348-1355.[Abstract/Free Full Text]
• Thompson, J.A., L. Qiu, R.L. Nelson, and Z. Li. 1997. Genetic diversity of U.S. and Chinese ancestral soybean lines. p. 160. In Agronomy Abstracts. ASA, Madison, WI.
• Voysest O., Valencia M.C., Amezquita M.C. Genetic diversity among Latin American Andean and Mesoamerican common bean cultivar. Crop Sci. 1994;34:1100-1110.[Abstract/Free Full Text]
• Zhou, X., T.E. Carter, Jr., R.L. Nelson, H.R. Boerma, and B.R. McCollum. 1998. Breeding progress vs breeding efforts: The road ahead in soybean variety development. p. 81. In Agronomy Abstracts. ASA, Madison, WI.

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