Dent corn (Zea mays L.) is a major field crop in the United

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1 RESEARCH Genetic Composition of Contemporary U.S. Commercial Dent Corn Germplasm Mark A. Mikel* ABSTRACT Germplasm of contemporary U.S. dent corn (Zea mays L.) is predominately from proprietary programs. Although publicly developed inbred lines contributed to the genetic foundation of these programs, their role is not known. The objective of this work is to identify and characterize major progenitors of contemporary proprietary germplasm through pedigree analysis of a set of 305 corn inbreds registered during the years 2004 through 2008 by U.S. Plant Variety Protection (PVP) and/or utility patent. Major progenitors found were the inbred lines Dekalb DK3IIH6 (12.2% genetic contribution), B73 (11.7%), and Pioneer Hi-Bred International (PHI) PH207 (9.5%). Using commercial hybrids as breeding germplasm was common during the 1980s and facilitated the introgression of PHI Iodent germplasm into competitor breeding programs. Of these, the PHI commercial hybrid 3737 has the greatest impact to contemporary germplasm by contributing 15.6% of the genes. Pedigree analysis of 1132 U.S. PVP and/or utility patent registered corn inbreds from 1984 through 2008 indicates that the genetic contribution of the public line Mo17 has decreased (from 8.6 to 1.7%) and the contribution of the public line Oh43 increased (from 1.5 to 3.9%), whereas the contribution of B73 remained constant. The contribution of Iodent germplasm increased concomitantly with use across commercial breeding programs. M.A. Mikel, Dep. of Crop Sciences and Roy J. Carver Biotechnology Center, Univ. of Illinois, 2608 Institute for Genomic Biology, 1206 W. Gregory Dr., Urbana, IL 61801, and Maize Lineage LLC, 3408 Mill Creek Ct., Champaign, IL Received 8 June *Corresponding author (mmikel@uiuc.edu). Abbreviations: BSSS, Iowa Stiff Stalk Synthetic; CP, coefficient of parentage; PHI, Pioneer Hi-Bred International; PVP, Plant Variety Protection; SNP, single nucleotide polymorphism; Y:M, grain yield:grain moisture ratio. Dent corn (Zea mays L.) is a major field crop in the United States, with approximately 35 million ha planted in 2009 (Anonymous, 2010). Today, corn grown in farmers fields mostly consists of single-cross hybrids between inbred lines (Mikel and Dudley, 2006). The inbred parents of a hybrid are generally unrelated and originate from different heterotic groups that when crossed maximize heterosis. Fifty years ago the origin of these inbreds was predominately from public programs, but today the formulation of contemporary U.S. commercial hybrids are entirely from proprietary programs (Darrah and Zuber, 1986; Mikel, 2008). The number of private breeding programs developing corn germplasm is decreasing as a result of corporate mergers and buyouts (Mikel and Dudley, 2006; Mikel, 2008). It would be useful to understand the composition of commercial germplasm currently grown in farmers fields. Such knowledge would benefit public research endeavors in areas such as improving germplasm, understanding heterosis and gene action, screening for herbicide and disease resistance, developing new molecular technologies, and providing relevant genetic platforms to access new traits. Once progenitors are identified, representative germplasm Published in Crop Sci. 51: (2011). doi: /cropsci Published online 27 Jan Crop Science Society of America 5585 Guilford Rd., Madison, WI USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher CROP SCIENCE, VOL. 51, MARCH APRIL 2011

2 can be readily accessed through the USDA North Central Regional Plant Introduction Station website (available at [verified 17 Dec. 2010]). This germplasm becomes available as a result of expiration of the applicable U.S. utility patent and U.S. Plant Variety Protection (PVP) (Mikel, 2006). Understanding the relation of this material to current commercial proprietary germplasm offers an avenue to package research for quicker utilization in commercial programs. The purpose of this work is to use pedigree analysis to identify and characterize major progenitors of contemporary proprietary corn germplasm by genetic contribution to facilitate their application to agricultural research. MATERIALS AND METHODS The pedigree breeding history of U.S. dent corn inbred lines is generally publicly available through registration documentation supporting U.S. PVP or utility patent. This frequently provides access to the genealogy of these inbreds for one or more generations. Commonly a one or two year hiatus occurs during processing before documents become publicly available. For this reason, the year 2008 is the most recent registration included in this work. KIN software (Tinker and Mather, 1993) was used to estimate coefficient of parentage (CP). Coefficient of parentage is the probability that two alleles at a randomly selected locus are identical by descent. Values for CP range from 0 to 1, with 0 indicating minimum and 1 indicating maximum relationship. To estimate genetic contribution, the relationships of a specific line to its ancestors were set to zero before analysis such that KIN would directly estimate each progenitor s cumulative genetic contribution. A progenitor s contribution to a set of descendents is the theoretical portion of genes that trace back to that specific progenitor (Mikel et al., 2010). Genes contributed from a progenitor will be counted in its own genetic contribution as well as in the contribution of its progeny. The percentage of descendents from a progenitor is the proportion of descendents among a set of registered lines. A progenitor s genetic contribution was calculated for the most recent five year period (2004 through 2008), defined as contemporary in this manuscript, and spanning 25 yr presented in five year increments: 1984 through 1988, 1989 through 1993, 1994 through 1998, 1999 through 2003, and 2004 through These applications of CP are based on the following assumptions: progeny inherit genes equally from both parents, parents are homozygous, parental ancestors with unknown pedigrees are unrelated, and backcross five or greater derived isolines are considered identical to the recurrent parent (Martin et al., 1991; Sneller, 1994; Van Beuningen and Busch, 1997; Wang and Lu, 2006). RESULTS Genetic Contribution Spanning 25 Years Evaluation of a progenitor s contribution over a period of 25 years (1984 through 2008) facilitates a historical chronology documenting importance and past use (Table 1). There were 1132 proprietary corn inbreds registered through U.S. PVP and/or utility patent originating from 48 seed companies. The genetic contribution of the public Iowa Stiff Stalk Synthetic (BSSS)- derived inbred B73 remained constant during the past 25 yr. The contribution of the Stiff Stalk lines B14 and B37 decreased. For Lancaster germplasm, the genetic contribution of the public inbred Mo17 decreased from 8.6 to 1.7%. The genetic contribution of Oh43 has increased from 1.5 to 3.9%. The Holden s (LH) line LH82 (Holden s Foundation Seeds, Inc., Williamsburg, IA) has steadily contributed approximately 2.5 to 2.8% of the genes to proprietary germplasm from 1994 through Among Iodents, the Pioneer Hi-Bred International (PHI) progenitor PH207 (Pioneer Hi-Bred International, Inc., Des Moines, IA) has maintained a genetic contribution of nearly 10%. The contribution of the PHG29, a descendent of PH207, has increased. The contribution of the Dekalb Iodent DK3IIH6 (Dekalb Genetics Corporation, Dekalb, IL) has increased concomitantly with that of PHG29 during the last 10 yr. Genetic Contribution of Commercial Hybrids as Breeding Germplasm Table 2 lists six PHI commercial hybrids with the greatest genetic contribution among the 49 PHI hybrids used as germplasm for breeding new lines in competitor programs from 1984 through In all cases, use of competitor hybrids as breeding germplasm was by programs other than PHI. The contribution of PHI hybrid PHI3737 is largest, and has nearly tripled during the most recent ten years (1999 through 2008). Hybrids PHI3180 and PHI3535 distantly follow that of PHI3737 with genetic contributions of 3.4 and 2.4%, respectively, to this set of contemporary proprietary germplasm. Progenitors of Contemporary Proprietary Germplasm Contemporary germplasm consists of 344 proprietary inbred corn lines registered (U.S. PVP and/or utility patent) from 2004 through Pedigree history was disclosed in 305 of the 344 registered inbreds during the application process. Of these 305, Monsanto (Monsanto Company, Creve Coeur, MO) and the contributions of its subsidiaries Dekalb Genetics, Asgrow Seed Company (Asgrow Seed Company LLC, Kalamazoo, MI), and Holden s Foundation Seeds developed 231 lines (76%), PHI 61 lines (20%), and Syngenta (Syngenta, Basel, Switzerland) 13 lines (4%) (data not shown). The discussion that follows will be predominately comparative of Monsanto and PHI germplasm, as they developed 96% of the lines with pedigree information. Common among proprietary programs is the extensive use of BSSS and several publicly developed progenitors. In this set of contemporary germplasm, the Stiff Stalk line B73 contributes 11.7% of the genes across programs (12.0% within Monsanto, 8.6% within PHI, and 21.0% within Syngenta germplasm; Table 3). B73 has 126 descendents among this set of 305 contemporary proprietary lines. The contribution of the Stiff Stalk inbred B14 was similar within PHI and Monsanto; however, the Stiff Stalk inbred B37 was more prevalent within PHI germplasm. Neither of these two Stiff Stalks contributed nearly as much as B73. Mo17 contributes nearly 2% of the genes to this set of contemporary germplasm and was used more within Monsanto than within PHI. The inbred Oh43 contributes 3.9% of the genes but has more impact within Monsanto s germplasm. 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3 Table 1. Genetic contribution of progenitors to 1132 corn inbreds registered from 1984 through Year Mo17 Oh43 B73 B14 B37 PHG39 LH123 LH82 PH595 PHG29 DK3IIH6 PH207 Genetic contribution of each progenitor % 1.5% 13.6% 7.5% 2.4% 2.8% 2.2% 0.6% 8.8% % 2.9% 11.1% 4.8% 3.2% 2.6% 1.7% 1.2% 1.8% 2.3% 8.6% % 2.9% 12.5% 4.2% 4.3% 3.9% 3.2% 2.5% 1.5% 3.6% 0.8% 7.3% % 3.2% 11.6% 3.6% 3.4% 4.0% 2.3% 2.4% 1.7% 6.0% 2.6% 9.4% % 3.9% 11.7% 3.2% 1.5% 2.3% 2.1% 2.8% 0.6% 9.4% 12.1% 9.5% Genetic contribution is based on pedigree analysis and is the theoretical portion of genes contributed by the respective progenitor as determined by coeffi cient of parentage. Year inbred corn lines registered by U.S. Plant Variety Protection (PVP) or utility patent. The pedigree history of 1132 registered corn inbreds were analyzed from the following 5 yr periods: (90 registered inbreds), (184), (287), (266), and (305). Public inbreds are Mo17, Oh43, B73, B14, and B37. Proprietary inbreds are derived from Holden s Foundation Seeds, Inc. (LH; Williamsburg, IA), Pioneer Hi-Bred International, Inc. (PH; Des Moines, IA), and Monsanto/Dekalb Genetics (DK; Creve Coeur, MO). Table 2. Genetic contribution of commercial Pioneer Hi-Bred hybrids to registered corn inbred lines. Year PHI3737 PHI3180 PHI3535 PHI3558 PHI3901 PHI3378 Genetic contribution per progenitor % 0.4% 3.3% % 3.2% 0.5% 5.0% % 0.3% 3.7% 0.9% 1.9% 1.3% % 0.1% 3.2% 1.0% 0.7% 1.1% % 3.4% 2.4% 1.1% 1.4% 1.1% Genetic contribution is based on pedigree analysis and is the theoretical portion of genes contributed by the respective progenitor as determined by coeffi cient of parentage. Year inbred corn lines registered by U.S. Plant Variety Protection (PVP) or utility patent. The pedigree history of 1132 registered corn inbreds were analyzed from the following 5 yr periods: (90 registered inbreds), (184), (287), (266), and (305). The following are Pioneer Hi-Bred International, Inc. (PHI; Des Moines, IA) brand commercial hybrids: 3737, 3180, 3535, 3558, 3901, and In addition to these public lines, there are several significant Monsanto- and PHI-developed proprietary progenitors. Within PHI, the Iodent PH207 contributes 15.1% of the genes within their contemporary germplasm and PH207 descendents PHG29 and PHP02 also make large contributions. Within PHI Stiff Stalks, PHG39 is the most significant proprietary progenitor. Of PHI Lancasters, PH595 contributes 3% of the genes and PHR03 (a second cycle PH595 derivative) has a greater contribution of 7.5%. Approximately 30% of contemporary PHI lines are descendents of PH595. Within Monsanto s contemporary germplasm, the PHI3737 derivative DK3IIH6 is a major progenitor of non- Stiff Stalk germplasm. The genetic contribution of DK3IIH6 is 16.1% within Monsanto s germplasm. The Holden s line LH82 and its progeny LH283 contribute 3.7% and 3% of the genes, respectively, within Monsanto s contemporary germplasm. The public inbred B73 is the main progenitor of contemporary Monsanto Stiff Stalks. The B73 descendents DK90DJD28 (9.1% genetic contribution within Monsanto contemporary germplasm), DKFBLL (8.6%), and DK2FACC (5%) form the core of their proprietary Stiff Stalk germplasm. DISCUSSION Stiff Stalk Germplasm Among Stiff Stalks, generally corn breeders crossed within and between B14, B37, and B73 derivatives, but ultimately agronomic performance favored the B73 lineage. The most successful Stiff Stalk breeding populations involved intercrossing predominately B73 descendents. Thus gradually over time the contribution of B73 increased, whereas that of B14 and B37 germplasm decreased. Occasionally breeders crossed B73 with B14 germplasm to achieve earlier maturity or crossed B73 with B37 material for increased health as well as extension into fuller season environments. The background of PHI inbred PHG39 is 69% BSSSC0 and 25% exotic germplasm (Maiz Amargo) (Mikel and Dudley, 2006; U.S. PVP Exhibit A [U.S. PVP certificates are available at {verified 21 Dec. 2010}]; Smith et al., 1997). PHG39 is a major progenitor of contemporary PHI Stiff Stalk germplasm. When genotyped with molecular markers, PHG39 clusters distantly with BSSSC0 Stiff Stalks such as B14 and B37 but does not cluster with B73 (BSSSC5) (Kahler et al., 2010; Nelson et al., 2008; Smith et al., 1997). Within PHI germplasm the contribution of PHG39 and B73 have become synergistically coupled through the interbreeding of their descendents. Genetic distance among a cross section of PHI Stiff Stalk inbreds shows much diversity among this germplasm (Fig. 1 from Smith et al., 1997). The impact of PHG39 in breeding new germplasm can only be determined within PHI s program. PHG39 most likely has been serendipitously used in other programs through using PHI commercial hybrids as breeding germplasm. Monsanto Stiff Stalks are largely descendents of B73 frequently facilitated through breeding DKPB80, a second cycle B73 derivative, and the DKPB80 progeny DKFBLL and DK2FACC. However, B73 remains the largest contributor although the Monsanto line DK90DJD28 is a close second. DK90DJD28 was developed from the breeding cross DKFBLL PHI commercial hybrid It would be interesting to know the contribution of PHI3180 to the CROP SCIENCE, VOL. 51, MARCH APRIL 2011

4 Table 3. Progenitor contribution to 305 proprietary corn inbred lines with known pedigrees registered in the United States from 2004 through 2008 by U.S. Plant Variety Protection (PVP) or utility patent. Progenitor Pedigree Family Pedigree source contribution % Genetic Public: Over all programs Within Monsanto Within PHI Within Syngenta % of descendents, % Genetic (no. lines) contribution % of descendents, (no. lines) % Genetic contribution % of descendents, (no. lines) % Genetic contribution % of descendents, (no. lines) W153R Ia153/W8//Ia153 Minnesota 13 Gerdes et. al , (22) , (22) Mo17 C103/CI Lancaster Gerdes et. al , (47) , (45) , (2) Oh43 W8/Oh40B Oh43 Gerdes et. al , (153) , (115) , (36) , (2) B14 BSSS Stiff Stalk Gerdes et. al , (119) , (91) , (28) B37 BSSS Stiff Stalk Gerdes et. al , (54) , (19) , (27) , (8) B73 BSSSC5 Stiff Stalk Gerdes et. al , (126) , (95) , (23) , (8) PHI: PH207 PHB3BD2/PHG3RZ1 Iodent Mikel and Dudley , (120) , (90) , (29) , (1) PHG29 PH207 *2/PH806 Iodent Mikel and Dudley , (111) , (86) , (24) , (1) PHP02 PHG44/PHG29 Iodent Mikel and Dudley , (21) , (21) PHG47 (PH041/MKSDTE)C10 Oh43 Mikel and Dudley , (106) , (86) , (19) , (1) PH595 PHAN0/PH082 Lancaster U.S. PVP certifi cate , (18) , (18) no PHR03 PHT19/PHG84 Lancaster Mikel and Dudley , (14) , (14) PHG39 PHA33GB4/ Stiff Stalk Mikel and Dudley , (25) , (25) PHA34CB4 Monsanto: LH82 Holden s line 610/LH7 Minnesota 13 Mikel and Dudley , (22) , (22) LH283 Va99/LH82 Minnesota 13 U.S. PVP certifi cate , (14) , (14) no DK01IBH2 PHI3737 Iodent Mikel and Dudley , (36) , (36) DK3IIH6 PHI3737 Iodent Mikel and Dudley , (75) , (75) LH123 PHI3535 Lancaster Mikel and Dudley , (23) , (22) , (1) LH185 LH59/LH123 Lancaster Mikel and Dudley , (11) , (11) DKFBLL DK5B2C-A/DKPB80 Stiff Stalk Mikel and Dudley , (62) , (62) DK90DJD28 PHI3180/DKFBLL Stiff Stalk U.S. PVP certifi cate , (48) , (48) no DK2FACC DK4676A/DKPB80 Stiff Stalk Mikel and Dudley , (48) , (48) Number of registered proprietary corn inbreds ( ) over all programs, Monsanto (Creve Coeur, MO), Pioneer Hi-Bred International (PHI; Des Moines, IA), and Syngenta (Basel, Switzerland) were 305, 231, 61, and 13, respectively. Public inbreds denoted per Gerdes et al. 1993, Dekalb Genetics (DK; Dekalb, IL), Holden s Foundation Seeds (LH; Williamsburg, IA), and Pioneer Hi-Bred International (PH). Pedigree format written per Purdy et al Sources for pedigree determination are Mikel and Dudley (2006), Gerdes et al. (1993), and U.S. Plant Variety Protection (PVP) certifi cates. PVP certifi cates are available at fi eld [verifi ed 21 Dec. 2010]. Note that the pedigree for PH595 was found in the U.S. PVP of PH0V0 (U.S. PVP certifi cate no ). Genetic contribution is based on pedigree analysis and is the theoretical portion of genes contributed by the respective progenitor as determined by coeffi cient of parentage. Percent (and number) of lines descending from each respective progenitor. BSSS, Iowa Stiff Stalk Synthetic. CROP SCIENCE, VOL. 51, MARCH APRIL

5 agronomic performance of DK90DJD28 and its descendents. The parentage of PHI3180 is not publicly known but putatively contributes germplasm from two unrelated heterotic groups that formulate the hybrid. This use of PHI3180 as germplasm facilitated introgression of a novel combination of alleles not otherwise available outside of PHI and most likely not a breeding cross commonly used within PHI. Iodent Germplasm Iodents are increasing in use across commercial programs. Pioneer Hi-Bred International Iodents are major contributors to contemporary germplasm. Iodents have long been recognized through anecdotal stories and publication but not really understood (Smith et al., 1997). It is known that Iodents are of Reid Yellow Dent background and named for Iowa Experiment Station Reid Yellow Dent (Troyer, 2004). Iodent germplasm has been improved and extensively used by PHI. Troyer (1999) gives an excellent overview of the first six cycles of Iodent breeding within PHI that was initiated in the 1940s. The first cycle began with the Iodent lines Idt and I205 that were initially crossed with Minnesota 13 (Minn13)-derived germplasm followed by several recurrent backcrosses to Iodent germplasm. Current PHI Iodent germplasm has been developed predominately through recycling related Iodent lines, thus the progeny of each cycle appear genetically similar. Genetic distance studies using molecular markers confirm the close relationship among PHI Iodents (Kahler et al., 2010; Nelson et al., 2008; Smith et al., 1997). The Iodent PH207 is the major progenitor within PHI germplasm and its descendents include nearly half of PHI contemporary inbreds. Other Iodent progenitors are the PH207 descendents PHG29 (a PH207 first breeding cycle descendent) and PHP02 (a PHG29 first cycle descendent). Pioneer Hi-Bred International Commercial Hybrid 3737 Germplasm Competitor programs accessed PHI Iodent germplasm by breeding with Pioneer Hi-Bred commercial hybrids. Many PHI commercial hybrids have been used as breeding germplasm, but the greatest impact is from the hybrid PHI3737 (Mikel and Dudley, 2006; Troyer and Mikel, 2010). PHI3737 facilitated the introduction of PHI Iodent into competitor programs through the Iodent line PHG29 that is one of the two inbred parents of PHI3737 ([Idt]5A in Fig. 3 from Troyer, 1999; A.F. Troyer, personal communication, 2009; Troyer and Mikel, 2010). The further introgression of PHI Iodent germplasm within Monsanto is primarily through the two PHI3737-derived Dekalb inbreds DK3IIH6 and DK01IBH2. DK3IIH6 was used successfully in more breeding crosses than DK01IBH2. The use of Iodent germplasm has increased rapidly within Monsanto and become the primary non-stiff Stalk heterotic group used with Stiff Stalks in commercial hybrid formulas. Breeding PHI3737 descendents also contributes to the increasing contribution of Oh43 germplasm over the last 25 yr. PHG47, an inbred parent of PHI3737, is a descendent of Oh43 as well as a mix of other backgrounds (A.F. Troyer, personal communication, 2008; U.S. PVP certificate no , Smith and Smith, 1987; Troyer and Mikel, 2010). The background of PHG47 is 50% from the broad base synthetic MKSDTEC10, 25% Oh43, 12.5% WF9, and 12.5% Iodent (U.S. PVP certificate no ; Smith and Smith, 1987). In the U.S. PVP for PHG47, it is stated by the originator that PHG47 is most similar to the public inbred Oh43. Functionally, PHG47 is an Oh43 regarding background and similarity to Oh43. Within contemporary (registered 2004 through 2008) Monsanto germplasm, 115 lines are Oh43 descendents and this is primarily facilitated through PHG47 as accessed through PHI3737. Oh43 impacts a large number of inbreds, but the cumulative genetic contribution remains small. Ironically, the breeding of PHI3737 germplasm within Monsanto led to PHG47 having a higher genetic contribution within Monsanto than within PHI germplasm. Minnesota 13 Germplasm The Holden s inbred LH82 is a descendent of Minnesota 13 (Minn13) through W153R. Minnesota 13 germplasm contributes fast dry down and stress tolerance to LH82 (Troyer, 1999). The inbred LH82 carries an undetermined composition of PHI germplasm derived from PHI3558 in its pedigree. Judging by genetic distance determined from single nucleotide polymorphism (SNP) (Nelson et al., 2008) and microsatellite (Kahler et al., 2010) analysis, LH82 appears related to the PHI Iodents. It is not clear if this relationship is derived from Iodent and/or Minn13 germplasm. Breeding of LH283 (a LH82 first cycle progeny) with PHI3737 progeny has facilitated the development of the commercial Monsanto inbreds I (U.S. PVP certificate no ) and I (U.S. PVP certificate no ). The major contribution of Minn13 is in the formulation of PHI Iodent germplasm. Lancaster Germplasm The presence of Mo17 in contemporary germplasm is largely outside of PHI. Overall, the genetic contribution of Mo17 has decreased since the mid 1980s. Before this decline, Mo17 was extensively used crossed to Stiff Stalks in commercial hybrids. The most recognized Mo17 hybrid is B73 Mo17, which peaked in commercial use around 1980 (Zuber and Darah, 1980). The contribution of Mo17 to contemporary germplasm is much less today than 25 yr ago. Though its genetic contribution has decreased substantially, Mo17 still has a genetic imprint in 47 contemporary inbreds. Within Monsanto germplasm the contribution of Mo17 has largely been replaced by PHI3737-derived Iodents CROP SCIENCE, VOL. 51, MARCH APRIL 2011

6 Pioneer Hi-Bred International took a different approach from its competitors by using Mo17 much less as germplasm for Lancaster improvement. Pedigree distance (Fig. 1 from Smith et al., 1997) indicates virtually no relationship of Mo17 with a set of 47 diverse PHI inbreds. Only minor use of some second cycle Mo17 derivatives could be found within PHI registered inbreds, such as PH8PG and PH581 (Mikel and Dudley, 2006) and later in their descendents PHDWA and PHC5H (U.S. PVP certificate no and U.S. PVP certificate no ). Pioneer Hi- Bred International used other material such as PH595 and Iodent related germplasm, rather than Mo17, crossed to Stiff Stalks to formulate middle maturity commercial hybrids. The background of the PHI Lancaster PH595 is extremely diverse, with 50% originating from PHI broad base Female Composite and 25% each from Midland Yellow Dent and Oh07 (pedigree disclosed in U.S. PVP certificate no Exhibit A). The contribution of PHR03, a second cycle PH595 progeny, is large within contemporary PHI germplasm. The lineage of PH595 presents unique phenotypic and genetic diversity for germplasm improvement in other programs. Though PH595 is not available, many PH595 descendents have been released by the USDA through expired U.S. PVP and/or utility patent and are publicly available (Mikel, 2006). The Oh43/Lancaster related inbred line LH123 contributes to Monsanto germplasm directly and through its progeny LH185 and LH287. LH123 was selfed from the hybrid PHI3535, which has an unknown pedigree. However, LH123 is somewhat related to Oh43 germplasm based on microsatellite and SNP genetic distance (Kahler et al., 2010; Nelson et al., 2008). Prospects for Germplasm Improvement Current practice for commercial corn breeding is high throughput recycling of closely related elite lines within heterotic families. Subsequently, newly developed hybrids are similar to the hybrids they replace. One aspect of increasing functional diversity would be expansion of existing and/or development of new heterotic families. Breeding progress can be increased through using more diverse breeding crosses by intercrossing between heterotic families. Germplasm available from the USDA from expired U.S. PVP and/or utility patent protection furnish germplasm and often heterotic families previously unavailable outside of the program of origin. This offers opportunity for corn breeders to develop new material by selectively using commercially elite germplasm from other programs. To better understand the proprietary germplasm available, Johnson (2008) examined combining ability for grain yield of a diallel cross of a diverse set of twelve public and proprietary lines. Several inbreds exhibited promising hybrid performance in multiple crosses by achieving a grain yield:grain moisture ratio (Y:M) equal to or greater than the widely used hybrid standard B73 Mo17: PHG47 (nine hybrid crosses with greater Y:M than B73 Mo17), PHZ51 (nine), B73 (seven), PHG35 (seven), LH82 (seven), LH123 (five), PHJ40 (five), Mo17 (four), PHG39 (four), PH207 (two), PHG84 (two), and LH1 (one). As expected, the Stiff Stalk B73 showed broad combining ability across Lancaster germplasm but interestingly also with the PHI Stiff Stalks PHG39 and PHJ40. Several non-stiff Stalk (LH123, LH82, PHG35, PHG47, and PHZ51) lines exhibited good hybrid performance when crossed with other non-stiff Stalk lines as well as with Stiff Stalk lines. This preliminary study indicates that there are resources available for breeders to explore new crosses between heterotic groups. All of the proprietary germplasm (and often many of their progeny) in this diallel are publicly available with freedom to operate as a result of expiration of applicable U.S. PVP and utility patents. This germplasm offers opportunity to use interprogram breeding crosses to tap previously unavailable material from other programs. Breeding exotic germplasm offers great potential for increasing breeding progress. The caveat is that this approach is long term, more prone to failure, and may take numerous breeding cycles before U.S. cornbelt commercialization (Duvick, 2005). There are few examples of successful improvement of proprietary corn germplasm through breeding exotic material. Breeding exotic germplasm resulted in the development of PHG39 from breeding Maiz Amargo with Stiff Stalk germplasm. In non-stiff Stalk improvement, the composite Suwan 1 cycle 4 has been bred into PHI germplasm for over five breeding cycles, resulting in the development of PH2MW (U.S. PVP certificate no ) and PH8T0 (U.S. PVP certificate no ). The diverse CIMMYT composite TGCR28 crossed with PHN46 resulted in the development of the registered inbred PH14T (U.S. PVP certificate no ). There are no inbred line registrations for failed breeding projects using exotic germplasm, so it is difficult to estimate the extent proprietary programs have used exotic germplasm. From the successful projects we do know of, there is no doubt that using exotic germplasm in temperate breeding programs can work, albeit at a lower probability of developing competitive material. To increase diversity, a concerted commitment is required to increase use of both inter-program and exotic breeding crosses. SUMMARY This work uses pedigree analysis to facilitate an overview and understanding of proprietary corn germplasm. This strategy has limitations. First, as a result of inbreeding and selection, each parent may not contribute genes equally to their progeny. Parental genetic contributions to their progeny can be characterized further by molecular genotyping. A second caveat is extending these results to determine what germplasm is actually grown in farmers CROP SCIENCE, VOL. 51, MARCH APRIL

7 fields. The pedigrees of hundreds of registered commercial corn lines were analyzed, but there is no information linking pedigree to amount of commercial use. Some inbreds were extensively used and others rarely if at all. However, through pedigree analysis, we do gain insight as to which inbred lines and lineages are used most in breeding programs and from this the overall composition and background of contemporary germplasm. Among public germplasm the importance of the Stiff Stalk B73 is well known. It has been previously assumed that Mo17 would be the principle non-bsss progenitor, largely as a result of the dominance of the commercial F 1 hybrid B73 Mo17 in the 1970s and early 1980s. The genetic contribution of B73 is without a doubt enormous but in contrast the contribution of Mo17 is relatively small. This is partially due to minimal use of Mo17 in PHI germplasm as well as a diminishing role for Mo17 within Monsanto germplasm during past 20 yr. This void has been fi lled by Iodents that are now the most significant group of non- Stiff Stalk germplasm. An extension of this work is the identification of progenitors that are representative of current germplasm for genomic sequencing. B73 was the first corn genome to be sequenced and assembled (Wei et al., 2009). What are other publicly available candidates for genomic sequencing that are representative of contemporary commercial germplasm? The following progenitors warrant consideration: the Iodent lines PH207 and PHG29, the Oh43 line PHG47, the Stiff Stalk/Maiz Amargo line PHG39, the Stiff Stalk DK2FACC, the Minn13 line LH82, and the Lancaster PH595-derived inbred PHG84, as well as the Lancaster Mo17 for historical context. Unfortunately, the PHI3737-derived DK3IIH6 and Lancaster PHR03 are not available at the time of this writing due to ongoing U.S. PVP and/or utility patent protection. Today, the proprietary germplasm formulating U.S. commercial corn hybrids in farmers fields originate predominately from several sources. These are large robust programs that have developed and registered 305 elite inbred lines from 2004 through However, proprietary breeding programs are in practice primarily breeding new germplasm through recycling closely related inbred lines within their respective germplasm pools. Despite well-intentioned effort to broaden genetic diversity, pedigree records show that new germplasm remains largely derived from breeding a small subset of elite inbreds within the same heterotic families. With the market and germplasm dominance of a few large proprietary programs, it would be challenging for an emerging program to develop the competitive germplasm required to establish a significant commercial presence. As a result, the genetic improvement of U.S. commercial germplasm may be perpetually dependent on the productivity of several established programs. Acknowledgments I am extremely grateful to Nicholas Tinker for his generosity in adapting the software KIN to accommodate larger databases. The assistance of Janice Strachan of the Plant Variety Protection Office in accessing U.S. PVP certificates is greatly appreciated. I wish to thank the Roy J. Carver Biotechnology Center of the University of Illinois for financing the publication of this work. References Anonymous Corn acreage up from previous estimates. Available at news/0630-corn-acreage-increases/ (verified 17 Dec. 2010). Corn and Soybean Digest, Minneapolis, MN. Darrah, L.L., and M.S. Zuber United States farm maize germplasm base and commercial breeding strategies. Crop Sci. 26: Duvick, D.N The contribution of breeding to yield advances in maize (Zea mays L.). Adv. Agron. 86: Gerdes, J.T., C.F. Behr, J.G. Coors, and W.F. Tracy Compilation of North American maize breeding germplasm. CSSA, Madison, WI. Johnson, G.R Development of a commercial-grade hybrid maize mapping population. 44th Annu. Illinois Corn Breeders School, Urbana, IL. University of Illinois, Urbana-Champaign, IL. Kahler, L., J. Kahler, S.A. Thompson, R.S. Ferriss, E.S. Jones, B.K. Nelson, M.A. Mikel, and S. Smith North American study on essential derivation in maize: II. Selection and evaluation of a panel of simple sequence repeat loci. Crop Sci. 50: Martin, J.M., T.K. Blake, and E.A. Hockett Diversity among North American spring barley cultivars based on coefficients of parentage. Crop Sci. 31: Mikel, M.A Availability and analysis of proprietary dent corn inbred lines with expired U.S. plant variety protection. Crop Sci. 46: Mikel, M.A Genetic diversity and improvement of contemporary proprietary North American dent corn. Crop Sci. 48: Mikel, M.A., B.W. Diers, R.L. Nelson, and H.H. Smith Genetic diversity and agronomic improvement of North American soybean germplasm. Crop Sci. 50: Mikel, M.A., and J.W. Dudley Evolution of North American dent corn from public to proprietary germplasm. Crop Sci. 46: Nelson, P.T., N.D. Coles, J.B. Holland, D.M. Bubeck, S. Smith, and M.M. Goodman Molecular characterization of maize inbreds with expired U.S. plant variety protection. Crop Sci. 48: Smith, J.S.C., E.C.L. Chin, H. Shu, O.S. Smith, S.J. Wall, M.L. Senior, S.E. Mitchell, S. Kresovich, and J. Ziegle An evaluation of the utility of SSR loci as molecular markers in maize (Zea mays L.): Comparisons with data from RFLPs and pedigree. Theor. Appl. Genet. 95: Smith, J.S.C., and O.S. Smith Associations among inbred lines of maize using electrophoretic, chromatographic, and pedigree data. 1. Multivariate and cluster analysis of data from Lancaster sure crop derivatives. Theor. Appl. Genet. 73: Sneller, C.H Pedigree analysis of elite soybean lines. Crop Sci. 34: CROP SCIENCE, VOL. 51, MARCH APRIL 2011

8 Tinker, N.A., and D.E. Mather KIN: Software for computing kinship coefficients. J. Hered. 84:238. Troyer, A.F Background of U.S. hybrid corn. Crop Sci. 39: Troyer, A.F Background of U.S. hybrid corn II: Breeding, climate, and food. Crop Sci. 44: Troyer, A.F., and M.A. Mikel Minnesota corn breeding history: Department of agronomy and plant genetics centennial. Crop Sci. 50: Van Beuningen, L.T., and R.H. Busch Genetic diversity among North American spring wheat cultivars: I. Analysis of the coefficient of parentage matrix. Crop Sci. 37: Wang, S., and Z. Lu Genetic diversity among parental lines of Indica hybrid rice (Oryza sativa L.) in China based on coefficient of parentage. Plant Breed. 125: Wei, F., J. Zhang, S. Zhou, R. He, M. Schaeffer, K. Collura, D. Kudrna, B.P. Faga, M. Wissotski, W. Golser, S.M. Rock, T.A. Graves, R.S. Fulton, E. Coe, P.S. Schnable, D.C. Schwartz, D. Ware, S.W. Clifton, R.K. Wilson, and R.A. Wing The physical and genetic framework of the maize B73 genome. PLoS Genet 5(11): E doi: /journal. pgen Zuber, M.S., and L.L. Darah U.S. corn germplasm base. p In Proc. 35th Annu. Corn and Sorghum Industry Res. Conf., Chicago, IL Dec American Seed Trade Association, Washington, DC. CROP SCIENCE, VOL. 51, MARCH APRIL