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    Field Crops Research 119 (2010) 277289

    Contents lists available at ScienceDirect

    Field Crops Research

    journa l homepage: www.e lsev ier .com/ locate / fc r

    stablishing a soybean germplasm core collection

    arcelo F. Oliveiraa,, Randall L. Nelsonb, Isaias O. Geraldi c, Cosme D. Cruzd,os Francisco F. de Toledoa

    Embrapa Soybean, P.O. Box 231, Londrina, PR 86001-970, BrazilUSDA-Agricultural Research Service, Soybean/Maize Germplasm, Pathology, and Genetics Research Unit, Dept. of Crop Sciences, 1101 W. Peabody Dr., Univ. of Illinois, Urbana, IL1801, United StatesUniversity of So Paulo-Faculdade de Agronomia-ESALQ, Dept. of Genetics, P.O. Box 83, Piracicaba, SP 13400-970, BrazilFederal University of Vicosa, Faculdade de Agronomia, Avenida Peter Henry Rolfs, s/n Campus Universitrio, Vicosa, MG 36570-000, Brazil

    r t i c l e i n f o

    rticle history:eceived 9 March 2010eceived in revised form 23 July 2010ccepted 25 July 2010

    eywords:lycine maxenetic diversity

    a b s t r a c t

    Core collections are of strategic importance as they allow the use of a small part of a germplasm collectionthat is representative of the total collection. The objective of this study was to develop a soybean corecollection of the USDA Soybean Germplasm Collection by comparing the results of random, proportional,logarithmic, multivariate proportional and multivariate logarithmic sampling strategies. All but the ran-dom sampling strategy used stratification of the entire collection based on passport data and maturitygroup classification. The multivariate proportional and multivariate logarithmic strategies made furtheruse of qualitative and quantitative trait data to select diverse accessions within each stratum. The 18

    ermplasm bankampling strategies

    quantitative trait data distribution parameters were calculated for each core and for the entire collectionfor pairwise comparison to validate the sampling strategies. All strategies were adequate for assemblinga core collection. The random core collection best represented the entire collection in statistical terms.Proportional and logarithmic strategies did not maximize statistical representation but were better inselecting maximum variability. Multivariate proportional and multivariate logarithmic strategies pro-duced the best core collections as measured by maximum variability conservation. The soybean core

    d usin

    collection was establishe

    . Introduction

    Access to genetic variability is critical for plant breeding.ermplasm conservation centers were created to preserve thevailable genetic variability before it is lost due to the widespreadse of modern, improved cultivars (Brown, 1989b). In the 1980s,he International Board for Plant Genetic Resources (IBPGR) pro-ided substantial financial support for germplasm preservationhat resulted in an increase in the number of collections. Themphasis placed on conservation led to the establishment andreservation of large collections, which were not totally or evenartially evaluated or characterized. Although large germplasmollections are desirable from the perspective of genetic variabil-ty preservation (Frankel and Bennett, 1970), their usefulness andccessibility can be inversely related to their size (Frankel and

    oul, 1981). The increase in the number of accessions that are notdequately evaluated can diminish the effectiveness of collectionsHolden, 1984; Marshall, 1989).

    Corresponding author. Tel.: +55 43 3371 6263; fax: +55 43 33716001.E-mail address: (M.F. Oliveira).

    378-4290/$ see front matter 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.fcr.2010.07.021

    g the multivariate proportional selection strategy. 2010 Elsevier B.V. All rights reserved.

    China has the largest Glycine collection, with approximately26,000 accessions of Glycine max and 6200 accessions of Glycinesoja, located in the Institute of Crop Germplasm Resources of theChinese Academy of Agricultural Science in Beijing (Chang et al.,1999; Carter et al., 2004) and has developed a core collection of thisaccessions (Zhang et al., 2003). A core collection of the perennialGlycine species has also been established (Brown et al., 1987).

    The soybean germplasm collection of the United States Depart-ment of Agriculture (USDA) is the second largest in the worldwith 16,999 accessions of introduced G. max, 1116 accessions ofG. soja and 919 accessions of perennial Glycine species. Detailedorigin data are available for most entries in the USDA SoybeanGermplasm Collection as are data for many descriptive, agronomic,and seed composition traits. For most germplasm collections, thereis a gap between the germplasm availability and its use (Peetersand Galwey, 1988) due to the collection size and financial limi-tations. In general, germplasm conservation programs have beenmore successful in ensuring long-term preservation then in facili-

    tating germplasm use.

    The establishment of core collections, as proposed by Frankeland Brown (1984), is an effective strategy to optimize human, mate-rial, and financial resources by providing greater efficiency in theuse of germplasm collections (Spagnoletti-Zeuli and Qualset, 1993;

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    78 M.F. Oliveira et al. / Field Cro

    an Hintum et al., 2000). A core collection is formed by selectingsmall percentage of the original collection that will representost of the total genetic variation with a minimum of redundancy

    Brown, 1995). Those accessions not retained in the core collec-ion are still maintained to preserve rare and potentially importantombinations of alleles. Core collections are not necessarily staticBrown et al., 1987) and accessions may be added over time to rep-esent new geographical areas or taxons, or to replace accessionsf questionable value. Ideally, changes in the core collection shoulde infrequent as one of the goals of a core collection is to constructn extensive data base on these reference accessions (Brown et al.,987). The general steps to establish a core collection are: (a) deter-ine the size of the core; (b) divide the collection in distinct groups;

    nd (c) select entries in each group to form the core. The complexityf establishing a core is a function of the available data and sam-ling procedure used (Brown, 1989a,b; Brown and Spillane, 1999).he established core collection must be validated to ensure its ade-uacy and usefulness by assessing whether the characteristics andariability of the entire collection have been maintained. A compar-son of the entire and core collection properties is accomplishedsing mean, variance, frequency, and distribution data of severalorphological traits or molecular markers. The objective of this

    esearch was to develop a core collection of the G. max accessionsf the USDA Soybean Germplasm Collection based on the resultsrom five selection strategies.

    . Materials and methods

    .1. Data tabulation

    The entire introduced G. max sub-collection of the USDA Soy-ean Germplasm Collection consists of 16,999 accessions, but only5,558, the entire collection in this work, have been evaluated forny quantitative traits. A majority of those accessions not evalu-ted (960) are in maturity groups IX and X, which are not adaptedo any location in the continental US Only the evaluated accessionsere subjected to the five sampling strategies. In addition to pass-ort information, evaluation data gathered from 1963 to 2005 inne of four locations where specific accessions are adapted weresed. The 000, 00, 0 and I maturity group accessions were charac-erized and assessed in the State of de Minnesota; the I, II, III andV maturity group accessions were characterized and assessed inhe State of Illinois; the V, VI, VII and VIII maturity group acces-ions were characterized and assessed in the State of Mississipi;nd the IX and X maturity group accessions were characterized andssessed in the territory of Porto Rico. The evaluation data wereollected over two years of testing, assessed in the field plots withour 3.6 m long rows, spaced at 0.76 m and classified in two cat-gories, qualitative and quantitative (one replication in each yearor qualitative traits an two replications in each year for quantita-ive traits). The qualitative data included flower color, pod color,eed coat color, hilum color, pubescence color, pubescence form,ubescence density, seed coat luster, plant growth habit, maturityroup, and origin (Hill et al., 2005). The quantitative data, averagedver the two years, included flowering date recorded as days afterlanting when 50% of the plants have one flower; maturity dateecorded as days after planting when 95% of the pods have reachednal color; plant height recorded at maturity; lodging score ratedn a scale from 1 (erect) to 5 (prostrate); stem termination scoreecorded on a scale from 1 to 5 with 1 representing very abrupt

    tem termination and 5 being very viney; shattering score recordedn the date of maturity and 2 weeks after maturity on a scale of5 with 1 equal no shattering, 2 equal 110% open pods, 3 equal025% open pods, 4 equal 2550% open pods and 5 equal greaterhan 50% open pods; seed quality score on a scale of 15 considering

    search 119 (2010) 277289

    wrinkling, defective seed coat, greenish or diseased seeds; mottlingscore on a scale of 15 with 1 equal no mottling, 2 equal 110% ofseed coat mottled, 3 equal 1025% of seed coat mottled, 4 equal2550% of seed coat mottled, and 5 equal greater than 50% of seedcoa


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