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Evolution of North American dent corn from public to proprietary germplasm.

AS PARENTS of F1 corn hybrids have transitioned from public to private inbred lines, predominant sources of germplasm for new product development have shifted from public to private germplasm. A 1985 seed industry survey documented the accelerating use of private sector inbred lines and the concurrent rapidly diminishing role of public germplasm in commercial corn hybrids (Darrah and Zuber, 1986). Only the public inbred B73 still had significant use, but its role was declining. This is well illustrated in Smith (1988) and Smith and Smith (1991) who analyzed the diversity of key commercial dent corn hybrids of the mid-1980s. Smith, through isozyme and/or RFLP genomic markers, determined that commercial hybrids from most seed companies other than Pioneer Hi-Bred had a number of inbred parents in common. Foundation inbred lines, particularly those from Holden's Foundation Seeds, were becoming widely used in branded hybrids marketed by many seed companies. This was the transition period from public germplasm to private germplasm for many of these companies. B73, and to a lesser extent Mo17, were the only public inbreds used in hybrids. For most companies, with the exception of Pioneer Hi-Bred, inbreds from foundation seed companies allowed them to remain competitive during the transition from public to private germplasm. Smaller companies that do not have plant breeders still depend on foundation seed companies to supply inbreds as parents for their commercial hybrids. Today the effort in private companies for inbred line development and evaluation greatly exceeds that in the public sector.

North American dent corn is composed of multiple heterotic groups that when crossed together can optimize hybrid performance. The nomenclature of heterotic groups is somewhat subjective (Tracy and Chandler, 2005). Heterotic groups in dent corn have been subdivided into Iowa Stiff Stalk Synthetic (BSSS) and non-BSSS (Lu and Bernardo, 2001). A similar grouping consists of Reid Yellow Dent (includes BSSS), Lancaster, and miscellaneous heterotic groups (Gethi et al., 2002). Troyer (1999) divided corn into five genetic backgrounds: Reid Yellow Dent (Iodent Reid and BSSS), Minnesota 13 (W153R and SD105), Northwestern Dent (A48, A509, and A78), Lancaster Sure Crop (Mo17 and Oh43), and Learning Corn (Oh07). The Reid Yellow Dent group is the largest group and made significant contributions to commercial hybrids. Smith and Smith (1989) constructed a more detailed list of dent corn pedigrees describing seven backgrounds. Their classification includes Pioneer Hi-Bred's proprietary germplasm base and identifies several new groups consisting of broad base Iodent, non-Stiff Stalk, and Stiff Stalk backgrounds.

To understand present day corn germplasm and its lineage through the past two decades, we examined the protected proprietary corn lines of Dekalb Genetics, Holden's Foundation Seeds, Pioneer Hi-Bred International, Inc., and Syngenta (includes through consolidation Novartis and Northrup King). Together these lines account for approximately 80% of protected germplasm and formulate approximately 90% of the commercial hybrid seed sold. Representative of the era of this study, U.S. corn hybrid market share of these four companies was estimated to be Pioneer Hi-Bred 42%, Holden's Foundation Seeds 35%, Dekalb Genetics 11%, and Novartis (now Syngenta) 8% (Fairley, 1998; Fritsch, 1997). An undetermined quantity of Holden's Foundation Seeds germplasm is present in its licensees Dekalb Genetics and Novartis market share. These protected registered corn inbred lines are traceable within the public domain through U.S. Patent and/or U.S. PVPA records. Seed of corn inbreds protected at the beginning of the patent and PVPA protection programs is now becoming available to all breeders as protection expires. These inbreds could be useful to broaden germplasm in the public domain that over the last 20 yr has become increasingly constrained by the restrictions imposed through protection of corn inbreds. An understanding of the genetic relationships among these protected inbreds is essential to their effective use in breeding.

Our first objective was to gain a greater understanding of corn germplasm protected from 1980 to 2004 by: (i) querying the U.S. Patent database to identify the inbreds most often referred to in comparisons within patents of new lines, (ii) creating and querying our own proprietary pedigree database (PD) consisting of derivations of 685 protected inbred lines to identify those lines most often used in recombinant populations for the development of new inbreds, and (iii) using PD to identify the types of germplasm and parental populations used for line development. Our second major objective was to use the information gained from Objective 1 to describe today's germplasm as it has changed during the last four cycles of selection and group it by relation and novelty into informative family backgrounds. This greater understanding of the corn germplasm base and heterotic groups should assist plant breeders in using this material as it becomes available for unrestricted use when U.S. Patent and/or U.S. PVPA protection expires.

MATERIALS AND METHODS

In 1970 the U.S. Congress passed the PVPA to facilitate the protection of plant germplasm, but corn breeders rarely used it until the early 1980s. In 1985 the U.S. Patent and Trademark Office (internal decision) allowed the patenting of corn inbred lines and hybrids (Janis and Kesan, 2001). The onset of extensive use of U.S. PVPA and/or U.S. Patent protection of corn inbreds coincides with the transition of parentage of commercial seed corn hybrids from public to proprietary inbred lines. The protection of corn lines by PVPA and/or patent facilitates public access to their description, performance, and pedigree information. To study these lines we created a PD by mining both the U.S. PVPA certificates and U.S. Patent database for protected corn lines and their pedigree derivation. The PD contains the protected corn lines and their derivations from Dekalb Genetics (160 lines), Holden's Foundation Seeds (134 lines), Pioneer Hi-Bred International (336 lines), and Syngenta (55 lines from Syngenta, Novartis, and Northrup King), or, in sum, 685 lines. Surprisingly, not all protected lines have their pedigree derivation divulged; for example, some U.S. patented inbred lines do not declare their pedigree derivation. All lines protected by U.S. PVPA show the pedigree derivation of the protected line. The PD consists of only those lines that have their pedigree declared in either a PVPA certificate and/or a patent. Because some lines are protected by PVPA only, some by patent only, and some are dual protected, lines protected by patent were cross checked with those lines protected by PVPA, and vice versa, to ensure that each inbred was counted only once. In addition, transgenic and/or conventional trait isoline conversions of the original line were not counted. Not represented in our search are abandoned, withdrawn, and pending applications as these records are closed and not accessible to the public. Protected inbreds were counted and tabulated by originating company within patent and PVPA records.

Within the description of each U.S. patented inbred line are other inbred line(s) used for comparative purposes to establish the novelty of the newly patented line both as an inbred and/or in a hybrid formula. These comparative inbreds are typically the most commercially elite lines of appropriate maturity and usage to which the patent assignee has access. As commercial corn lines are sold as branded hybrids, there is no direct way to judge the merits and extent of use of these lines. To measure the relative importance of commercial lines, we queried the U.S. Patent Database for all of the known proprietary and public inbred corn lines of this era to determine the number of patents in which each line is used for phenotypic comparisons. We refer to these occurrences as patent hits. Inbreds with larger numbers of patent hits were inferred to be more commercially valuable or elite. The U.S. Patent Office database is web accessible (http://patft.uspto. gov/netahtml/search-bool.html) with a search engine built into the database interface; thus, it is ideal for performing queries. Unfortunately, the U.S. PVPA records are not in a digital database, but rather exist as papers filed at one restricted site and cannot be electronically queried. To determine the importance of these protected lines we used the cumulative number of patent hits for each line in the PD. For the lines identified with the most patent hits we show the family background, pedigree derivation, and estimated cycle of recombination.

A second determination of the importance of a line is the number of times it is recombined or occurred in the pedigree derivation of another line. The cumulative number of occurrences in the pedigree of other lines in the PD was summed for each inbred. Each line's family background, pedigree derivation, and estimated cycle of recombination was determined.

To facilitate an understanding of chronology of development of the inbreds we estimated their "age" by cycle of recombinant selection. Cycle 0 inbreds consist of the public and proprietary inbred corn lines available at the beginning of this time period (1980). Subsequent recombination of Cycle 0 lines creates Cycle 1 progeny, and recombination of Cycle 1 lines creates Cycle 2 progeny, and so forth. This paper covers corn inbred lines protected from 1980 through 2004 and spans approximately four cycles of recombination.

Pedigree lineages of inbred lines identified as most significant through U.S. Patent hits and recombination events were graphically linked together by descent. Results are presented in separate figures for Stiff Stalk, Lancaster/Oh07-Midland/Oh43, and Iodent related lines. Arrows originating at parent and pointing to progeny depict lineage of the inbred lines. A best effort was made to trace the lineages of the proprietary lines back to a public line or publicly recognized population or synthetic.

The preponderant pedigree backgrounds of the inbred lines are categorized and summarized. Criteria for grouping lines into pedigree background were their prevalent lineages by descent. Key founder lines for each lineage background are listed.

The types of populations from which PD lines were developed are categorized as: two parent inbred A x inbred B; backcross one (A x B) x B; backcross two or greater [(A x B) x B] x B; three parent (A x B) x C; four or more parents; synthetic or broad base population; synthetic or broad base population crossed to inbred(s); and commercial hybrid. If a commercial hybrid was crossed to an inbred it was considered a three-parent population. The overall composition of proprietary germplasm is summarized as to proportion of corn inbred lines originating from public, Pioneer Hi-Bred, Holden's Foundation, Dekalb Genetics, and Syngenta derived germplasm.

RESULTS AND DISCUSSION

For ease of presentation, the U.S. PVPA certificate number, U.S. Patent number, or other sources containing the derivation or description of origin of the inbreds mentioned in this paper either in a table, figure, or in the text are shown in Table 1.

Pedigrees of public and some of the foundation seed company, but not proprietary, corn inbred lines of this era have been published in sources such as Henderson (1983), Gerdes et al. (1993), and Mike Brayton Seeds Genetics LLC (Anonymous, 2003). In these sources the inbred derivation of known foundation seed company corn inbred lines is frequently gleaned from sales information and commonly does not name the specific inbreds in the derived lines pedigree. For example, in Gerdes et al. (1993) the derivation of LH195 is shown to be B37, B73 and in Mike Brayton Seed Genetics (Anonymous, 2003) its derivation is shown to be B73, LH1; whereas the actual derivation of LH195 is found to be LH117 x LH132 as per U.S. PVPA and patent records (Table 1). Establishing the correct pedigree derivation of LH195 allows its lineage to be established and therefore a greater understanding of its true background. The pedigree data assembled in this paper are from U.S. Patent and U.S. PVPA records and not from anecdotal and/or generic sales information. There is no previously published summary of proprietary lines of this era that discusses collectively their backgrounds, lineage, origin, and significance.

Thirty-three companies were identified that had inbred lines protected through U.S. Patent, PVPA, or both (Table 2). In total, 908 unique inbred lines were protected in the period of this study. Of these, 685 lines (78%) are in the PD. This database consists of lines and their pedigree derivations from Dekalb Genetics, Holden's Foundation Seeds, Pioneer Hi-Bred, and Syngenta. We focused on the inbred pedigrees from these four larger companies as they make up approximately 90% of U.S. corn hybrids and are continuously represented throughout this era.

Important Lines

Of the 43 inbred lines identified as having the most patent hits, three are CO or founder public inbred lines (Table 3) and in descending number of patent hits are: B73 (Stiff Stalk), A632 (early maturity Stiff Stalk), and Mo17 (Lancaster). B73 incurred the most patent hits of any inbred line, either public or proprietary, and is pivotal in the development of Stiff Stalk lines for all of the proprietary programs surveyed. The significance of Mo17 surely is underestimated due to the presence of Holden's Foundation Seed inbred LH51, which originated from a backcross recovery of Mo17 and is shown to be approximately 97% Mo17. Of the 43 inbreds identified as most elite by patent hits in Table 3, 20, or nearly half, are of Stiff Stalk backgrounds.

Significant lines identified in Tables 3 and 4 are shown graphically in Fig. 1-3 that group the lines by Stiff Stalk, Lancaster/Oh43/Oh07-Midland, and Iodent backgrounds, respectively. Additional lines from the PD were added to link together lines by pedigree derivation where necessary to unify the figures. When possible, the lineage of these lines is traced back to publicly recognizable ancestors.

[FIGURES 1-3 OMITTED]

We have formulated a grouping of lineage backgrounds to reflect how today's germplasm has evolved as a result of the past four cycles of recombination (Table 5). Seven major groups are designated: Oh43, Lancaster, Oh07-Midland, Iodent, Commercial hybrid derived, Maiz Amargo, and Stiff Stalk, as well as subgroups created from recombination between groups. Intergroup recombination has been successful between groups that each independently combines well opposite a common background in commercial hybrids. This essentially conserves combining ability of the derived group. For example the Oh43 x Lancaster subgroup is derived from two heterotic groups that each combine well with Stiff Stalk lines to make commercial hybrids. Thus, combining ability is preserved, but germplasm diversity is enhanced by the new recombinant subgroups. It is also true of the Iodent x Oh07-Midland group, as they both combine well with Stiff Stalk lines to produce commercial hybrids. The Stiff Stalk x Iodent subgroup works well in crosses to Oh43 lines, as both independently combine well with Oh43 lineage lines. With this in mind, we postulate that a Stiff Stalk x Oh43 derived subgroup may work well in commercial hybrid formulas opposite Iodent. The numerous subgroups within the Stiff Stalks are successful as they still maintain performance when crossed with Oh43, Lancaster, Oh07-Midland, commercial hybrid derived, or Iodent backgrounds to produce commercial hybrids. Thus, Stiff Stalk germplasm plays a significant role in many hybrids. Broadening the germplasm base of Stiff Stalk lines would have an immediate effect on expanding the diversity of commercial hybrids. Diversity among Stiff Stalk lines may have decreased with the emergence of B73 lineage as the dominant Stiff Stalk source along with concurrent loss of purebred B14 and B37 lineages.

Overall, in all programs hybrids have been improved as a result of intercrossing within heterotic groups, introgression of exotic germplasm, and tapping germplasm from other programs and using it in unfamiliar ways. During this period, increased hybrid diversity originated from the new groups derived from Maiz Amargo and Commercial Hybrid derived (germplasm from Pioneer Hi-Bred hybrids 3737, 3535, and 3558).

Oh43 Background

The Oh43 group has over the last several cycles of recombination lost its purebred identity. This lineage played a role in the development of numerous significant inbred lines through recombination with Oh07-Midland and Lancaster groups in Pioneer Hi-Bred and Holden's Foundation Seeds germplasm, respectively. An Oh43 progenitor within Pioneer Hi-Bred is the inbred line PH041 that is derived from Oh43 x (Iodent x WF9). It is broad based in origin, but is one-half Oh43 derived (Smith and Smith, 1987). Although the line PH041 was only found to be a parent of three new lines in our study, one of its direct progeny, PHG47, was found to be recombined 11 times in the development of new protected corn lines. PHG47 is derived from PH041 x MKSDTE Cycle 10. The background of MKSDTE is unknown, but is presumed to be a broad-based population. PHG47 was recombined primarily with Oh43 and Oh07-Midland, but also Stiff Stalk and Iodent, derived lines to develop new corn lines. It was through recombination of PHG47 with the Oh07-Midland derived line PHG35 that the significant line PHK56 was developed. Within Holden's Foundation Seeds Oh43 germplasm is present in LH59 and LH168, which were derived from recombination of Oh43 derived lines with Lancaster and Pioneer hybrid 3558 (LH82) derived backgrounds, respectively.

Lancaster Background

The public line Mo17 is the founder line that along with LH51 (itself a C1 Mo17 derivative and near Mo17 isoline) is the predominant lineage of Lancaster germplasm outside of Pioneer Hi-Bred. Mo17 and LH51 were widely used in new line development within Holden's Foundation Seeds and its licensees. Thus it was used by nearly all seed companies in the USA (Smith, 1988; Smith and Smith, 1991). Recombination of LH51 led to the development of 15 C2 lines that include the elite lines LH210, LH213, and LH216 (Table 4). Lancasters were recombined with lines from Lancaster, Oh43, and Commercial Hybrid derived backgrounds to create new commercial corn lines. Nowhere in the U.S. PVPA records or U.S. Patent database was a Pioneer Hi-Bred (336 Pioneer Hi-Bred lines) line found that was directly developed from Mo17 or LH51. However, PH06B, an unprotected line derived from the three-parent cross (Mo17 x PHN82) x PHR03 or generalized by background as (Lancaster x Pioneer Iodent) x Pioneer Oh07-Midland is the parent of two protected lines, PH581 and PH8PG, as divulged in their PVPA certificates (Table 1). PH06B is a line that Pioneer Hi-Bred did not register by U.S. PVPA or U.S. Patent and is presumed not to have been a commercially used line but is the only known carrier of Mo17 into Pioneer Hi-Bred germplasm.

The Lancaster germplasm background was present in Pioneer Hi-Bred, composing approximately 4.5% of a set of U.S. central Corn Belt commercial hybrids during this period (Smith et al., 2004). The Lancaster background in Pioneer came from several sources. The Lancaster strain that is the progenitor of Mo17 was nearly absent in a set of Pioneer U.S. central Corn Belt hybrids of this era (1980 to 2004) (Smith et al., 2004). The presence of Lancaster in Pioneer's germplasm during this era was commingled within the PHG71 related Stiff Stalk lineage and the non-Stiff Stalk PH814 and PH848 related lineages (Smith and Smith, 1989).

Oh07-Midland Background

The core of Pioneer non-Stiff Stalk, non-Iodent germplasm traces to PH595 which has a diverse background consisting of 50% Female Composite (Pioneer Hi-Bred proprietary population), 25% Oh07, and 25% from a line described as from a Midland Yellow Dent background (Table 1). Oh07 is derived from Illinois Long Ear x Illinois Two Ear (Gerdes et al., 1993). Troyer (1999) describes Oh07 as being derived from the Learning Corn background. This background was not found anywhere else in the PD, thus Oh07 is unrelated to current germplasm. The same is true for Midland Yellow Dent. The background of Female Composite is unknown, but presumed to be genetically broad based and may or may not contain Lancaster. The best descriptive notation for the background of PH595 is Oh07-Midland. Recombination of PH595 led to the development of C1 lines PHG35, PHV78, and PHG84 and these C1 lines were recombined to develop the C2 lines PHK56, PHN46, and PHR03. All of these PH595 derived C2 lines are presumed elite, as measured by both patent hits and recombination events in this study. The most recombined Pioneer Hi-Bred proprietary line is PHR03, which is a direct progenitor of over 21 protected C3 corn lines. Non-Stiff Stalk, non-Mo17, and non-pure Iodents are characteristic of three groups of Pioneer germplasm that contain Lancaster and/or Oh07 (Smith and Smith, 1989). These are grouped into the PH814, PH848, and PH595 backgrounds. As seen in Fig. 2, the contributions of PH814 and PH848 are less than that of PH595. PH595 is at the center of several key lineages within Pioneer Hi-Bred line pedigrees. Through recombination, the PH595 lineage has established itself as the major non-Stiff Stalk non-Iodent group. With that being said, the recombination of PH814 and PH848 either with each other, with PH595, or with Iodent lineages has originated significant lines, but, as a result, purebred PH814 and PH848 lineages were lost. As would be expected, the inbred lines of the PH595 lineage were crossed to Stiff Stalk lines to produce commercial hybrids.

Iodent Background

The Iodent group is important and unique to Pioneer Hi-Bred and this background made up approximately 15% of the composition of a set Pioneer Hi-Bred U.S. central Corn Belt hybrids during the period of this study (Smith et al., 2004). Troyer (1999) presented an excellent overview of the origin of the Iodents. As a result of many cycles of selection Pioneer Hi-Bred optimized the performance of Iodents. In addition to Iodent, this group also has in its background a smaller proportion of Long Ear Open Pollinated Variety and Minnesota 13 (Smith and Smith, 1989; Smith et al., 1997). Much of the Iodent background of this era traces back to the founder line PH207 that was a parent in the development of 17 registered corn lines during this era. Significant C1 progeny of PH207 include the inbreds PHG29, PHG50, and PHR25 and the C2 inbreds PHJ90, PHN82, PHP02, and PHTD5. The lineage of Iodents and the role of PH207 as the main progenitor of Iodent germplasm within Pioneer Hi-Bred germplasm are shown in Fig. 3. Iodent germplasm may have been introduced into other proprietary programs through selfing and recombination from Pioneer Hi-Bred commercial F1 hybrids. Iodents have been crossed to lines from Oh43, Stiff Stalk, and Flint backgrounds to produce commercial F1 hybrids. Iodents have been recombined with lines from Iodent, Lancaster, and to a lesser extent Stiff Stalk backgrounds for new line development. Iodents and Stiff Stalks both trace back to Reid Yellow Dent and yet, although related in origin, crosses between them can produce commercially acceptable hybrids.

Commercial Hybrid Derived Background

During the era of this study new diversity has emerged from Argentine Maiz Amargo and Commercial Hybrid derived germplasm. These new sources of germplasm either originated within or were refined by Pioneer Hi-Bred. Commercial Hybrid germplasm sources were derived from Pioneer hybrids 3737, 3535, and 3558 and appear to be different from any established heterotic backgrounds within Pioneer Hi-Bred and these lines are typically crossed to Stiff Stalk lines to produce commercial F1 hybrids.

The Pioneer 3737 derived germplasm is represented by two Dekalb Genetics inbreds, DK3IIH6 and DK01IBH2, which were highly recombined within the Dekalb germplasm pool (Table 4). The Pioneer 3535 and Pioneer 3558 derived germplasm groups were developed by Holden's Foundation Seeds.

The Pioneer Hi-Bred hybrid 3558 group is represented by the line LH82 that was derived by Holden's Foundation Seeds from the lines LH07 and Holden line 610 (Table 1). LH07 is 75% Pioneer Hybrid 3558 and 25% public line N22A that is Krug derived. Holden line 610 is a W153R recovery presumed to be approximately half W153R (Gerdes et al., 1993). Thus, LH82, the progenitor line of the Pioneer 3558 group, is composed, in decreasing proportions, of Pioneer Hybrid 3558, W153R, and Krug. Holden's Foundation Seeds, in the patent of LH168 (U.S. Patent 5457,275), state that "LH82 is considered a family unto itself;" which reinforces the novelty of the LH82 background. The C1 line LH82 was recombined to develop the C2 lines LH168, LH172 and LH283. The derivatives of LH168 and LH172 involve recombination of LH82 with the Oh43 and Pioneer 3535 backgrounds, respectively. In the derivation of LH283, LH82 was recombined with the public inbred line Va99. It is worth mentioning that Va99 is derived from the cross Oh07B x Pa91 or the backgrounds Learning Corn x Wf9 (Gerdes et al., 1993). This is a rare example of Oh07 (Learning Corn) background outside of Pioneer Hi-Bred germplasm.

The Pioneer Hi-Bred hybrid 3535 group is represented by the line LH123 that was derived directly from selfing Pioneer Hybrid 3535 by Holden's Foundation Seeds and was a progenitor in the lineages of the lines LH185, LH211, LH212, LH213, and LH287. The Pioneer 3535 and 3558 groups have maintained their integrity by recombination within each group, although, on occasion, they have been crossed with each other, and with Lancaster derived lines (Fig. 2).

Other than for a few lines, the Lancaster lineage has not advanced as a purebred group during the most recent cycles of recombination. This has coincided with the emergence of the unique germplasm groups derived from the Commercial Hybrid (Pioneer Hi-Bred hybrids 3737, 3558, and 3535) derived group. Hybrid diversity has increased from interchanging these numerous Commercial Hybrid derived inbred corn lines in hybrid formulas with Stiff Stalk lines to produce new commercial hybrids. All three of these Commercial Hybrid derived groups introduced new unrelated sources of germplasm to companies outside of Pioneer Hi-Bred. Being derived from commercial F1 hybrids they also may be unique by being a composite of the known family groups within Pioneer Hi-Bred.

Maiz Amargo Background

Argentine Maiz Amargo is an exotic germplasm source whose introduction was instrumental in the creation of a unique germplasm within Pioneer Hi-Bred. This group emerged in the 1980s, with no significant use before 1980 (Smith et al., 2004). Maiz Amargo quickly established itself and with subsequent recombination within Pioneer Hi-Bred germplasm became a key component of their Stiff Stalk germplasm. Maiz Amargo was introduced through recombination with the public corn lines B96 and B64 that are 100 and 12.5% Maiz Amargo 41.2504B, respectively (Table 1). Though both PHG39 and PHG86 are Maiz Amargo recombinant lines, the PHG39 lineage is most significant in the introgression of Maiz Amargo into Pioneer Germplasm. PHG39 was a parent in the development of 12 protected corn lines. The background of PHG39 contains in decreasing proportions B37, B14, B96 (Argentine Maiz Amargo 41.2504B), and Iodent (U.S. PVPA 9500208). Notable first cycle recombinant lines from PHG39 are PHP38, PHR61, PHT11, and PHW52. These C1 lines are considered commercially significant because of the large number of reference hits in the U.S. Patent database (Table 3) and/or recombination events in the PD (Table 4). Significant second cycle recombinant lines of PHG39 include PHBW8, PHHB9, PHRE1, and PH07D. The Maiz Amargo lineage was perpetuated through the C1 derivative PHP38 that was a parent of 11 C2 lines and the C2 line PHHB9 that was the parent of 12 C3 corn lines (Table 4). Many Maiz Amargo derived lines were ultimately either directly or indirectly recombined with B73 and this facilitated a significant introgression of B73 concurrently with Maiz Amargo into Pioneer Hi-Bred germplasm. In fact, approximately 35% of Pioneer's U.S. central Corn Belt hybrids during this era were of Stiff Stalk (BSSS) background (Smith et al., 2004). Although the presence of Maiz Amargo is predominantly within Pioneer Hi-Bred it may have been serendipitously introduced into other proprietary germplasm sources through selfing and recombination of Pioneer Hi-Bred commercial hybrids or through using public lines such as B64, B68, or B96. However, the lineages of this era did not indicate a significant introduction of Maiz Amargo outside of Pioneer Hi-Bred through recombination of public lines. The U.S. PVPA protection of PHG39 has expired and the line is readily available for freedom-to-operate use.

Stiff Stalk Background

During the period covered by this study, improvement of Stiff Stalk inbreds was achieved largely through recombination either directly with the C0 inbred B73, its C1 derivatives DKPB80, LH74, LHll9, LH132, LH146, LH202, LH206, PHG86, and PHW52, or its C2 derivatives DKFBLL, DK2FACC, LH194, LH195, LH198, LH200, LH227, PHBW8, PHHB9, and SGH8431. The public founder line B73 was universally recombined within all proprietary programs to develop 33 protected C1 corn lines during this period. Therefore the lineage of most present day Stiff Stalk lines traces back to B73 (Fig. 1). The Stiff Stalk line DKFBLL was a parent of 22 new corn lines and played a key role in Dekalb Genetics Stiff Stalk germplasm. Early maturity Stiff Stalks were derived from recombination of the C0 B14 founder lines A632, A662, CB59G (Cornelius Hybrid Company), and CM105. Many of the B14 derivatives were recombined with B73 derived Stiff Stalks in subsequent cycles such as in the derivation of LH74 and LH202. Inbred lines derived directly from the B37 include LH1 and PHB47 and no instances in later cycles of recombination were found that preserved the B37 lineage (Fig. 1). The lineages of Stiff Stalks (B14, B37, and B73) are commingled as shown by recombination of B73 lineages with B37 and B14 derived lines. Presumably, the loss of purebred B14 and B37 lines is because of agronomic performance that was inferior to B73.

Breeding Methodology

Selfing in two-parent hybrid populations followed by pedigree selection was used in 77% of the 685 derivations in PD (Table 6). In most cases, two-parent inbred populations involved the recycling of elite, often related, inbred lines. Among proprietary breeding programs there were differences in magnitude of two-parent population use. Pioneer Hi-Bred used 90% two-parent populations, but Holden's and Syngenta used only approximately 50% two-parent populations (Table 5). Two-parent backcross one populations, followed by three-parent, and commercial hybrid are the next most common types of populations used in inbred development. Using commercial hybrids as germplasm was prevalent within Syngenta, Dekalb, and Holden's. Synthetics or Open Pollinated varieties either used separately or crossed to inbred(s) were rarely used.

PVPA or patent protected lines are commercially elite lines that warranted protection and their derivations are primarily found to be from the recycling of elite lines. Of course, for every line protected, there were hundreds if not thousands of lines developed and evaluated that failed during evaluation and consequently were not protected. For these failures, the type of recombinant breeding methods or germplasm is not known.

Pioneer Hi-Bred during the period of this study was a self-sustaining closed system using only its own germplasm and a very small number of public lines. The only public line Pioneer used more than once was B73, which was used in the development of 7 inbred lines. During this era, Holden's Foundation Seeds and Syngenta (Syngenta, Novartis, and Northrup King) used public inbreds in the derivation of nearly one fourth of their new inbred lines. Frequently used public lines in Holden's populations were B73 (10 times), Mo17 (9), CM105 (5), A662 (2), A665 (2), B84 (2), H99 (2), and ND246 (2). For Syngenta, frequently used public inbreds in line development are B73 (7), W117 (4), B37 (3), Mo17 (3), and B14 (2). Dekalb Genetics primarily used the two public Stiff Stalks B73 (9) and A634 (4) in their successful inbred line development projects. Overall, B73 and Mo17 were the public inbred lines used most extensively in line development.

Examination of the PD for the role of public lines in development of new inbreds from 1980 through 2004 shows 45% during 1980 to 1988 (dates are the years for PVPA filing), 10% from 1989 to 1996, and 2% from 1997 to 2004 of new lines having public inbred parent(s). Thus the number of new lines derived from public inbred parentage decreased from nearly half during the first third of this era to a minimal 2% during the last third of this era. Of the 55 elite public inbred lines of the late 1970s identified by Smith et al. (1985), only 11 were used more than once and only two (B73 and Mo17) were used more than 10 times in the derivations of the 685 lines in the PD. The role of these public lines was most significant at the beginning of this era (1980s) and quickly diminished in the 1990s. During the transition of decreased use of public inbreds in new inbred development projects, the use of Holden's Foundation inbred lines as a key source of germplasm was common in Dekalb, Syngenta, and nearly all other commercial seed companies, except for Pioneer Hi-Bred.

Another major source of germplasm used in development of new lines during this era for Holden's Foundation, Dekalb Genetics, Syngenta, and others was recombination of Pioneer Hi-Bred commercial hybrids. They were used either by direct selfing or by crossing the Pioneer commercial hybrid to inbred parents before selling and selection. In a few cases, as noted in the pedigree derivation of Dekalb inbred DKRDBQ2, a Pioneer Hi-Bred inbred is stated as being used rather than the actual F1 commercial hybrid in development of a new line (U.S. Patent 6037,531). Pioneer hybrids used most often in inbred development were 3737 (used in eight new inbred line developments), 3394 (5), 3378 (5), 3901 (4), 3535 (2), and 3475 (2). The use of Pioneer commercial hybrids as germplasm constituted 8% of new lines (non-Pioneer Hi-Bred lines) developed from 1980 through 1988 (dates are the years for PVPA filing), 22% of new lines from 1989 through 1996, and 10% of new lines from 1997 through 2004. The decrease in the third period is most likely a result of restrictions from the onset of U.S. Patent protection of both corn hybrids and inbreds.

CONCLUSIONS

Review of the pedigree derivations in this study suggests that plant breeders have been most successful in developing new products when they recombine the most elite material available. The propensity of breeders to work elite related material in recycling of inbred lines may over the long-term decrease genetic diversity. During the years of this study new diversity, within particular companies, emerged from exotic (Argentine Maiz Amargo) or diverse (Commercial Hybrid derived that contain multiple backgrounds in the hybrid formula) sources rather than from recycling closely related inbred lines.

During the period evaluated, proprietary corn inbred development programs have become closed systems due to the diminishing contribution of public inbreds in new inbred development projects. Intellectual property protection through U.S. Patent and U.S. PVPA has further restricted germplasm access. However, over time, patents and/or PVPA certificates expire and previously protected germplasm becomes available for general use Protection for some lines already has expired and the lines are presently available with no restrictions: LH123 (Pioneer 3535 background); LH82 (Pioneer 3558 background); and PHG39 and PHG86 (Maiz Amargo background). In addition, the Iodent lines PH207, PHG29, and PHG50; Oh07-Midland lines PHG35, PHG84, and PHZ51; Oh43 line PHG47; Lancaster line LH51; and Stiff Stalk lines LH74, LHll9, LH132, PHB09, PHB47, and PHJ40 have had their protection expire and are publicly available. Seed of PVPA protected lines is available from the North Central Regional Plant Introduction Station in Ames, IA, and seed of U.S. patented lines is available from the American Type Culture Collection in Manassas, VA. Hopefully, results from this study will assist corn breeders in understanding this germplasm and provide insight into its effective use in developing new corn inbreds. These previously protected lines may be a useful source of new germplasm, but the caveat is that these lines are antiquated by four cycles of recombination and selection. The challenge to breeders who have not previously had access to these lines is to find new ways to use this germplasm to generate unique germplasm that will within a cycle or two of recombination and selection create competitive, genetically diverse, commercially successful hybrids.

Although access to this germplasm provides new genetic resources to the companies to whom access was previously not permitted, it does not increase diversity of the total corn germplasm pool. We suggest two critical issues exist which need to be addressed to enhance diversity of corn germplasm. First, to continue to make gains in performance and diversity corn germplasm needs to be broadened through concerted efforts of both private and public research programs. Fortunately, such an effort is underway through the Germplasm Enhancement for Maize (GEM) program (Pollak, 2003). This program is a partnership of government and private researchers to increase diversity by identifying exotic corn germplasm and adapting it by crossing it with adapted elite private corn germplasm. Second, a measure of the diversity currently available to corn producers in the USA is needed. With the growing availability of formerly protected proprietary inbred corn lines, a molecular marker survey of those lines and current dent corn hybrids, done by a public agency or disinterested third party, could provide a measure of current genetic diversity and of shifts in diversity since the beginning of protection of lines. Such a survey might also be useful in identifying genomic regions in today's germplasm that have been conserved from key progenitor lines through multiple cycles of recombination and selection. These regions may contribute to increased performance stability and be valuable for use in future marker assisted selection projects.

ACKNOWLEDGMENTS

We wish to thank Robert Lambert and Richard Johnson for reviewing this manuscript and their suggestions for its improvement and Dennis Butler for assistance with our literature search. The assistance of Janice Strachan at the Plant Variety Protection Office for facilitating and providing copies of corn inbred PVPs is greatly appreciated. We thank the Roy J. Carver Biotechnology Center of the University of Illinois at Urbana-Champaign for financing the publication of this research.

REFERENCES

Anonymous. 2003. Genetic handbook. 30th ed. MBS Genetics, LLC., Story City, IA.

Darrah, L.L., and M.S. Zuber. 1986. 1985 United States farm maize germplasm base and commercial breeding strategies. Crop Sci. 26:1109-1113.

Fairley, P. 1998. Let the bidding begin. Chem. Week 160(7):9.

Fritsch, P. 1997. Monsanto to buy seller of corn seed. Wall Street Journal 7 Jan. 1997; A:3.

Gerdes, J.T., C.F. Behr, J.G. Coors, and W.F. Tracy. 1993. Compilation of North American maize breeding germplasm. CSSA, Madison, WI.

Gethi, J.G., J.A. Labate, K.R. Lamkey, M.E. Smith, and S. Kresovich. 2002. SSR variation in important U.S. maize inbred lines. Crop Sci. 42:951-957.

Henderson, C.B. 1983. Maize research and breeders manual. No. IX (Suppl.). Illinois Foundation Seeds, Champaign, IL.

Janis, M.D., and J.P. Kesan. 2001. Designing an optimal intellectual property system for plants: A U.S. Supreme Court debate. Nat. Biotechnol. 19:981-983.

Lu, H., and R. Bernardo. 2001. Molecular marker diversity among current and historical maize inbreds. Theor. Appl. Genet. 103: 613-617.

Pollak, L.M. 2003. The history and success of the public-private project on Germplasm Enhancement of Maize (GEM). Adv. Agron. 78:45-87.

Smith, J.S.C. 1988. Diversity of United States hybrid maize germplasm; isozymic and chromatographic evidence. Crop Sci. 28:63-69.

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. 1997. 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. 95:163-173.

Smith, J.S.C., D.N. Duvick, O.S. Smith, M. Cooper, and L. Feng. 2004. Changes in pedigree backgrounds of Pioneer brand maize hybrids widely grown from 1930 to 1999. Crop Sci. 44:1935-1946.

Smith, J.S.C., M.M. Goodman, and C.W. Stuber. 1985. Genetic variability within U.S. maize germplasm. II. Widely-used inbred lines 1970 to 1979. Crop Sci. 25:681-685.

Smith, J.S.C., and O.S. Smith. 1987. Associations among inbred lines of maize using electrophoretic, chromatographic, and pedigree data. 1. Multivariate and cluster analysis of data from 'Lancaster' Sure Crop derived lines. Theor. Appl. Genet. 73:654-664.

Smith, J.S.C., and O.S. Smith. 1989. The description and assessment of distance between inbred lines of maize: I. The use of morphological traits as descriptors. Maydica 34:141-150.

Smith, J.S.C., and O.S. Smith. 1991. Restriction fragment length polymorphisms can differentiate among U.S. maize hybrids. Crop Sci. 31:893-899.

Tracy, W.F., and M.A. Chandler. 2005. The historical and biological bases of the concept of heterotic patterns in 'Corn Belt' maize. Forty-First Annu. Illinois Corn Breeders School, Urbana, IL. University of Illinois, Urbana-Champaign.

Troyer, A.F. 1999. Background of U.S. hybrid corn. Crop Sci. 39: 601-626.

Abbreviations: DK, Dekalb Genetics; LH, Holden's Foundation Seeds; NK, Northrup King; PD, Patent Database; PH, Pioneer Hi-Bred International; PVPA, Plant Variety Protection Act; SG, Syngenta Seeds.

Mark A. Mikel * and John W. Dudley

M.A. Mikel, Roy J. Carver Biotechnology Center, Univ. of Ill., 901 S. Mathews Ave, Urbana, IL 61801 and Maize Lineage LLC, 3408 Mill Creek Ct., Champaign, IL 61822; J.W. Dudley, Department of Crop Sciences, Univ. of Ill., 1102 S. Goodwin Ave, Urbana, IL 61801. Received 12 Oct. 2005. * Corresponding author (mmikel@uiuc.edu).
Table 1. Citations for corn inbredline backgrounds.

Line                              Source of background ([dagger])

Public
A632 ([double dagger])            Gerdes et al., 1993
A634                              Gerdes et al., 1993
B73                               Gerdes et al., 1993
CM105                             Gerdes et al., 1993
H93                               Gerdes et al., 1993
Mo17                              Gerdes et al., 1993
N22A                              Gerdes et al., 1993
W117                              Gerdes et al., 1993

Cornelius Hybrid Seed Company
CB59G                             PVPA 9200250

Dekalb Genetics
DKO11BH2                          Pat. 6,855,877
DK2FACC                           PVPA 9000016
DK3AZA1                           Pat. 5,910,25
DK3IBZ2                           PVPA 9100223
DK3IIH6                           PVPA 9300087
DK4676A                           PVPA 8600092
DK5B2C-A                          PVPA 9100034
DK78551S                          PVPA 8800195
DK87916W                          PVPA 8800189
DKFBAB                            PVPA 8700173
DKFBLL                            PVPA 9100034
DKHBA1                            Pat. 4,594,810
DKIBC2                            PVPA 8700198
DKIBI                             PVPA 8700197
DKJ6                              PVPA 8700196
DKMM402A                          PVPA 9100222
DKMM501D                          PVPA 9300085
DKPB80                            PVPA 9100034
DKRDBQ2                           Pat. 6,037,531
DKZZZ38                           PVPA 9100223

Holden's Foundation Seeds
610                               Gerdes et al., 1993; Pat. 5,773,683
LH1                               PVPA 7600047
LH7                               Gerdes et al., 1993
LH24                              Gerdes et al., 1993
LH51                              PVPA 8200062
LH53                              Gerdes et al., 1993
LH59                              PVPA 8700213
LH74                              PVPA 8200063
LH82                              PVPA 8500037
LH85                              PVPA 8700088
LH105                             Pat. 5,457,275
LH117                             Gerdes et al., 1993
LH119                             PVPA 8200064
LH122                             Gerdes et al., 1993
LH123                             PVPA 8400030
LH132                             PVPA 8300148
LH146                             PVPA 8700089
LH168                             Pat. 5,457,275
LH172                             Pat. 5,276,266
LH176                             Pat. 5,491,296
LH181                             Pat. 5,304,713
LH185                             Pat. 5,491,294
LH194                             PVPA 9000125
LH195                             Pat. 5,059,745; PVPA 9000047
LH198                             Pat. 5,304,717
LH200                             Pat. 5,285,005
LH202                             PVPA 9000126
LH206                             PVPA 9000126
LH210                             Pat. 5,276,262
LH211                             Pat. 5,387,743
LH212                             Pat. 5,276,260
LH213                             Pat. 5,276,259
LH216                             Pat. 5,276,263
LH227                             Pat. 5,633,429
LH235                             Pat. 5,639,942
LH283                             Pat. 5,773,683
LH287                             Pat. 6,281,414

Pioneer Hi-Bred
PH041                             Smith and Smith, 1987
PH06B                             PVPA 200100250, 200200190
PH07D                             PVPA 9700214
PH09B                             PVPA 9700218
PH207                             PVPA 8300144
PH24E                             PVPA 9600204
PH581                             PVPA 200100250
PH595                             PVPA 9800383
PH814                             Smith et al., 1997
PH848                             Smith et al., 1997
PH8PG                             PVPA 200200190
PHAA0                             PVPA 9400091
PHAC54                            PVPA 8700214
PHB09                             Smith et al., 1997
PHB47                             PVPA 8300141
PHBE2                             PVPA 9500200
PHBW8                             PVPA 9200079
PHG29                             PVPA 8600047
PHG35                             PVPA 8300140
PHG39                             PVPA 8300115, 9500208
PHG3BD2                           Smith et al., 1997; PVPA 8300144
PHG3RZ1                           Smith et al., 1997; PVPA 9700226
PHG42                             Smith et al., 1995
PHG44                             PVPA CN 9700226
PHG47                             PVPA CN 8600131
PHG50                             PVPA CN 8300143
PHG69                             Smith et al., 1997
PHG71                             PVPA CN 8400157
PHG84                             PVPA CN 8600130
PHG86                             PVPA CN 8700170
PHH93                             PVPA 8800216
PHHB9                             PVPA 9300108
PHJ40                             PVPA 8600133
PHJ90                             PVPA 9100093
PHK05                             PVPA 8800001
PHK29                             PVPA 8700214
PHK42                             PVPA 9100093
PHK56                             PVPA 9000247
PHK76                             PVPA 8800036
PHKM5                             PVPA 9400097
PHKW3                             PVPA 9500209
PHM10                             PVPA 8900312
PHMK0                             PVPA 9300112
PHN18                             PVPA 9200086
PHN46                             PVPA 9000249
PHN82                             PVPA 8900317
PHP02                             PVPA 8800212
PHP38                             PVPA 9000250
PHR03                             PVPA 9100097
PHR25                             PVPA 8800002
PHR47                             PVPA 8800213
PHR61                             PVPA 9100100
PHRE1                             PVPA 9300114
PHT11                             PVPA 9100101
PHTD5                             PVPA 9400095
PHV78                             PVPA 8800003
PHW52                             PVPA 8800215
PHZ51                             PVPA 8600132

Syngenta and Novartis
NK347                             PVPA 8800152
NK377                             PVPA 8800152
NKB386                            PVPA 8800152
SGH8431                           PVPA 8800152

([dagger]) PVPA refers to U.S. Plant Variety Protection Act (PVPA)
certificate number and Pat. refers to U.S. Patent number.

([double dagger]) Public inbred lines are denoted by published prefix
of origin. All other lines are prefixed as CB, DK, LH, NK, PH, SG are
Cornelius Hybrid Seed Company, Dekalb Genetics, Holden's Foundation
Seeds, Northrup King, Pioneer Hi-Bred, Syngenta (includes Novartis,
Northrup King, and Ciba), respectively.

Table 2. U.S. Patent and U.S. PVPA registration of corn inbred
lines.

                                    Number of inbred lines

                            U.S.         U.S.           Nonredundant
Assignee                   Patent   PVPA ([dagger])   ([double dagger])

Pioneer Hi-Bred             223           336                340
  International, Inc.
Dekalb Genetics Corp.       103           134                163
Holden's Foundation          75           134                134
  Seeds, LLC
Novartis AG                  26            34                 52
Advanta Technology, Ltd.      9            23                 32
Syngenta Seeds AG            17             8                 18
Asgrow Seed Company,         15             4                 17
  LLC
United AgriSeeds, Inc.        0            15                 15
Agrigenetics Inc.            14             2                 14
J.C. Robinson Seed            9            14                 14
  Company
Limagrain Genetics Corp.      7             7                 14
NDSU Research Foundation      0            10                 10
Standard Oil Company          1            10                 10
Monsanto Technology, LLC      8             0                  8
Zeneca Ltd.                   8             0                  8
FFR Cooperative               6             1                  7
Illinois Foundation           6             1                  7
  Seeds, Inc.
KWS Kleinwanzlebener          5             2                  6
  Saatzucht AG
DowElanco                     0             5                  5
Wilson Hybrids, Inc.          0             5                  5
Entities with 4 or fewer     28            13                 29
  nonredundant lines
  ([section])
Total                       560           758                908

([dagger]) United States Plant Variety Protection Act (PVPA).

([double dagger]) Nonredundant factors out lines that are double
protected in both U.S. Patent and U.S. PVPA databases and ensure
that each line is counted once.

([section]) Cargill Inc. (4 lines), Hogemeyer Hybrids (4), Rustica
Prograin Genetique (4), Golden Seed Company, LLC (3), Lifaco Seed
Corp. (3), Garst Seed Company (2), Iowa State University (2),
Sandoz Ltd (2), Edward J. Funk (1), Funk Seeds International,
Inc. (1), Mycogen Corp (1), Quality Research Associates (1), and
Stine Seed Farms (1).

Table 3. Most referenced corn inbred lines for phenotypic comparisons
in the U.S. Patent database.

Inbred                  Hits ([dagger])        Cycle ([double dagger])

B73 ([paragraph])              63                         C0
LH185                          63                         C2
LH132                          60                         C1
LH198                          59                         C2
LH51                           54                         C1
LH195                          48                         C2
PHP38                          47                         C1
PHP02                          41                         C2
PHRE1                          40                         C2
LH172                          38                         C2
LH200                          37                         C2
PHN46                          37                         C2
LH82                           36                         C1
LH74                           35                         C1
PHW52                          34                         C1
LH59                           34                         C1
DKFBLL                         33                         C2
LH212                          33                         C2
PHR03                          33                         C2
PHTD5                          33                         C2
PH24E                          32                         C3
LH216                          30                         C3
DK3IIH6                        29                         C2
A632                           27                         C0
PHHB9                          27                         C2
LH210                          27                         C2
PH09B                          26                         C3
PHK56                          26                         C2
LH202                          26                         C1
PHAA0                          25                         C2
LH176                          25                         C2
Mo17                           25                         C0
LH168                          24                         C2
DK2FACC                        24                         C2
DK01IBH2                       24                         C2
LH119                          23                         C1
LH146                          22                         C1
LH235                          22                         C3
PHBE2                          21                         C3
LH85                           21                         C1
LH213                          21                         C2
PHR25                          21                         C1
LH227                          20                         C2

Inbred              Background ([section])     Derivation

B73 ([paragraph])   SSS                        Iowa Stiff Stalk
                                                 Synthetic C5
LH185               Pioneer Hybrid 3535        LH59 x LH123
LH132               SSS                        (H93 x B73) x B73
LH198               SSS                        (LH132 x B84) x LH132
LH51                Lancaster                  Mo17 backcross 5
                                                 recovery
LH195               SSS                        LH117 x LH132
PHP38               Amargo/SSS                 PHG39 x PHK29
PHP02               Indent                     PHG44 x PHG29
PHRE1               Amargo/SSS                 PHJ40 x PHR47
LH172               Pioneer Hybrid 3558/       (LH82 x LH122) x LH82
                      Pioneer Hybrid 3535
LH200               SSS                        LH117 x LH132
PHN46               Oh07-Midland               PHZ51 x PHV78
LH82                Pioneer Hybrid 3558        Holden private fine
                                                 610 x LH7
LH74                SSS                        A632 x B73
PHW52               Amargo/SSS                 B73 x PHG39
LH59                Lancaster/OH43             (Mo17 x H99) x LH53
DKFBLL              SSS                        DK5B2C-A x DKPB80
LH212               Pioneer Hybrid 3535/       (LH24 x LH123) X LH123
                      Lancaster
PHR03               Oh07-Midland               PHT19 x PHG84
PHTD5               Indent                     PHH93 x PHR25
PH24E               Indent                     PHP02 x PHN82
LH216               Lancaster/Pioneer          [(LH51 x LH123) x LH51]
                      Hybrid 3535                x LH51
DK3IIH6             Pioneer Hybrid 3737        Pioneer Hybrid 3737
A632                SSS                        [(Mt42 x B14) x B141
                                                 x B14
PHHB9               Amargo/SSS                 PHG86 x PHW52
LH210               Lancaster                  LH51 x BSll
PH09B               Amargo/SSS                 PHP38 x PHHB9
PHK56               OhO7-Midland/Oh43          PHG47 X PHG35
LH202               SSS                        [(A662 x B73) x B73]
                                                 x B73
PHAA0               SSS                        PHW03 x PHJ40
LH176               Pioneer Hybrid 3558        Pioneer Hybrid 3704
                                                 x LH82
Mo17                Lancaster                  C.1.187-2 x C103
LH168               Pioneer Hybrid 3558/Oh43   LH82 x LH105
DK2FACC             SSS                        DK4676A x DKPB80
DK01IBH2            Pioneer Hybrid 3737        Pioneer Hybrid 3737
LH119               SSS                        (1193 X B73) x B73
LH146               SSS                        (B73 x CM105) X CM105
LH235               SSS                        LH194 x LH195
PHBE2               Oh07-Midland               PHR03 x PHN46
LH85                unknown                    Pioneer Hybrid 3978
LH213               Pioneer Hybrid 3535/       LH123 x LH51
                      Lancaster
PHR25               Indent                     PHB83 x PH207
LH227               SSS                        (LH145 x LH146) x LH119

([dagger]) Hits are the cumulative number of references for a given
line in the patents of other corn inbred lines in the U.S. Patent
database.

([double dagger]) Cycles of recombination are estimated cycles of
recombination past the base genetics available when pedigrees began to
be published through U.S. Plant Variety Protection and U.S. Patents.

([section]) Background shown is an estimate of the most predominant
background. The derivation of some inbred lines can be from a
commingling of several backgrounds. Backgrounds are Oh43, Lancaster,
Oh07-Midland, Indent, Commercial hybrid (Pioneer Hybrid 3737, 3558,
and 3535 derived), Maize Amargo (Amargo), and Stiff Stalk (SSS)
derived. Some lines are significantly derived from multiple backgrounds
that are shown separated by a "I" with the predominant background shown
first.

([paragraph]) Corn inbred lines are prefixed with DK (Dekalb Genetics),
LH (Holden's Foundation Seeds), and PH (Pioneer Hi-Bred International)
proprietary lines. All other lines are public inbred corn lines and are
denoted by conventional recognized format.

Table 4. Most recombined corn inbred lines within the pedigree
database. ([dagger])

                Number of times used
Title        as parent ([double dagger])    Cycle ([section])

B73 (#)                  33                        C0
DKFBLL                   22                        C2
PHR03                    21                        C2
PH207                    17                        C0
PHP02                    16                        C2
LH51                     15                        C1
PHW52                    15                        C1
LH123                    14                        C1
PHJ40                    14                        C1
DK3IIH6                  14                        C2
Mo17                     13                        C0
LH132                    13                        C1
LH82                     13                        C1
PHG39                    12                        C0
DK01IBH2                 12                        C2
DK2FACC                  12                        C2
PHHB9                    12                        C2
PHG47                    11                        C1
PHP38                    11                        C1
PHK29                    10                        C0
LH74                     10                        C1
DK3IBZ2                  10                        C2
LH59                      9                        C1
PHR25                     9                        C1
PH595                     8                        C0
DKMM501D                  8                        C2
PHN46                     8                        C2
PHRE1                     8                        C2
PHTD5                     8                        C2
PHK76                     7                        C0
DK87916W                  7                        C1
SGH8431                   7                        C2
LH194                     7                        C2
LH195                     7                        C2
PHN82                     7                        C2
CB59G                     6                        C0
DKHBA1                    6                        C1
DKMM402A                  6                        C1
PHG50                     6                        C1
PHKM5                     6                        C1
LH213                     6                        C2
PHBW8                     6                        C2
LH38                      6                        ??
DK3AZA1                   5                        ??
CM105                     5                        C0
PH814                     5                        C0
DK78551S                  5                        C1
DKFBAB                    5                        C1
DKIBC2                    5                        C1
LH85                      5                        C1
PHG29                     5                        C1
PHN18                     5                        C1
PHT11                     5                        C1
LH210                     5                        C2
PH09B                     5                        C2
PHKW3                     5                        C3
A634                      4                        C0
W117                      4                        C0
DKIBI                     4                        C1
LH119                     4                        C1
PHG35                     4                        C1
PHK05                     4                        C1
PHM10                     4                        C1
LH172                     4                        C2
LH181                     4                        C2
LH198                     4                        C2
LH211                     4                        C2
LH212                     4                        C2
PH07D                     4                        C2
PHJ90                     4                        C2

Title       Background ([paragraph])        Derivation

B73#        SSS                             Iowa Stiff Stalk Synthetic
                                              C5
DKFBLL      SSS                             DK5B2C-A x DKPB80
PHR03       Oh07-Midland                    PHT19 x PHG84
PH207       Iodent                          PHG3BD2 x PHG3RZ1
PHP02       Iodent                          PHG44 x PHG29
LH51        Lancaster                       Mo17 backcross 5 recovery
PHW52       Amargo/SSS                      B73 x PHG39
LH123       Pioneer Hybrid 3535             Pioneer Hybrid 3535
PHJ40       SSS                             PHB09 X PHB36
DK3IIH6     Pioneer Hybrid 3737             Pioneer Hybrid 3737
Mo17        Lancaster                       C.I.187-2 x C103
LH132       SSS                             (B73 x H93) x B73
LH82        Pioneer Hybrid 3558             Holden line 610 x LH7
PHG39       Amargo                          A33GB4 x A34CB4
DK01IBH2    Pioneer Hybrid 3737             Pioneer Hybrid 3737
DK2FACC     SSS                             DK4676A x DKPB80
PHHB9       Amargo/SSS                      PHG86 x PHW52
PHG47       Oh43                            PH041 x MKSDTE Cycle 10
PHP38       Amargo/SSS                      PHG39 x PHK29
PHK29       SSS                             PHB47 x PHAC54
LH74        SSS                             A632 x B73
DK3IBZ2     unknown                         DKIBC2 x DKZZZ38
LH59        Lancaster/Oh43                  (Mo17 x H99) x LH53
PHR25       Iodent                          PHB83 x PH207
PH595       Oh07-Midland                    Fem Comp, OhO7, Midland OP#
DKMM501D    unknown                         LH38 x DK88121A
PHN46       Oh07-Midland                    PHZ51 x PHV78
PHRE1       Amargo/SSS                      PHJ40 x PHR47
PHTD5       Iodent                          PHH93 x PHR25
PHK76       unknown                         PHAD18 x PHB02
DK87916W    SSS                             [(DKW37-2 x B73) x B73]
                                              x B73
SGH8431     SSS                             (NK377 x NKB386) x NK347
LH194       SSS                             LH77 x LHE137
LH195       SSS                             LH117 X LH132
PHN82       Iodent                          PHG29 x PHHD38
CB59G       SSS                             [(B14A x R168) X B59] x B59
DKHBA1      unknown                         Pioneer Hybrids 3195 x 3199
DKMM402A    unknown                         LH38 X DKMANS
PHG50       Iodent                          PH848 x PH207
PHKM5       unknown                         PHK70 x PHG96
LH213       Pioneer Hybrid 3535/Lancaster   LH123 x LH51
PHBW8       Amargo/SSS                      PHJ40 x PHW52
LH38        unknown                         unavailable
DK3AZA1     unknown                         DKAQA3 x DKQFAR
CM105       SSS                             (V3 x B14) x B14
PH814       Lancaster                       Broad base Lancaster
DK78551S    unknown                         DK78060A x LH38
DKFBAB      SSS/Lancaster?                  B14 x LH23
DKIBC2      Lancaster                       DKJ6 x MoI7Ht
LH85        unknown                         Pioneer Hybrid 3978
PHG29       Iodent                          (PH207 x PH806) x PH207
PHN18       unknown                         PHDK6 x PHNN2
PHT11       Amargo/SSS                      PHG39 x PHG69
LH210       Lancaster                       LH51 X BS11
PH09B       Amargo/SSS                      PHP38 x PHHB9
PHKW3       Iodent                          PHN82 x PHN63
A634        SSS                             {[(Mt42 x B14) x B14) x
                                              B14] x B14
W117        Minnesota 13                    643 x Minnesota 13
DKIBI       unknown                         Pioneer Hybrid 3901
LH119       SSS                             (H93 x B73) x B73
PHG35       Oh07-Midland/Iodent             PHG3BD2 x PH595
PHK05       Flint                           CM7 x PH051
PHM10       Iodent/Amargo                   PHG39 x PH207
LH172       Pioneer Hybrid 3558/ Pioneer    (LH82 x LH122) x LH82
              Hybrid 3535
LH181       Pioneer Hybrid 3535/Lancaster   LH58 x LH122
LH198       SSS                             (LH132 x B84) x LH132
LH211       Pioneer Hybrid 3535/Lancaster   LH58 X LH123
LH212       Pioneer Hybrid 3535/Laucaster   (LH24 X LH123) x LH123
PH07D       Amargo/SSS                      PHMK0 x PHR61
PHJ90       Iodent                          PHG50 x PHK42

([dagger]) Pedigree database (PD) consists of all of the protected corn
lines protected in the U.S. Patent and U.S. Plant Variety Protection
Act with known pedigree derivations. These lines were from Dekalb
Genetics, Holden's Foundation Seeds, Pioneer Hi-Bred International, and
Syngenta (Syngenta, Novartis, and Northrup King) or in sum 685 lines.
Lines are prefixed as CB, DK, LH, PH, SG are Cornelius Hybrid Seed
Company, Dekalb Genetics, Holden's Foundation Seeds, Pioneer Hi-Bred,
Syngenta (includes Novartis, Northrup King, and Ciba), respectively.
All other lines are public inbred lines denoted by published prefix.

([double dagger]) Number of times used as parent is the cumulative
number of times within the PD that a line is cited as a parent in the
pedigree of another line.

([section]) Cycles of recombination are estimated number of cycles of
recombination past the base genetics available at the beginning of
this era (approximately 1980).

([paragraph]) Background shown is an estimate of the most predominant
background. The derivation of some inbred lines can be from a
commingling of several backgrounds. Backgrounds are Oh43, Lancaster,
Oh07-Midland, Iodent, Commercial hybrid (Pioneer Hybrid 3737, 3558, and
3535 derived), Maize Amargo (Amargo), Stiff Stalk (SSS), Flint, and
Minnesota 13 derived. Some lines are significantly derived from
multiple backgrounds that are shown separated by a "I" with the
predominant background shown first.

(#) Pioneer Female Composite is a proprietary composite of Pioneer
Hi-Bred, Midland is an Open Pollinated variety.

Table 5. Grouping of dent corn inbred backgrounds based on
pedigree lineage.
                                Main progenitor
Background ([dagger])           line(s) ([double dagger])

Oh43 related
  Oh43                          PH041 and PHG47
  Oh43 x Lancaster              LH59
Lancaster related               Mo17 and LH51
Oh07-Midland related            PH595
  Oh07-Midland x Oh43           PHK56
Indent related
  Indent                        PH207
  Indent x Midland/OhO7         PHG35
  Indent x stiff stalk          PHG71 and PHM10
Commercial hybrid derived
  Pioneer hybrid 3737           DK3HH6 and DKOIIBH2
  Pioneer hybrid 3535           LH123
  Pioneer hybrid 3558           LH82
Maiz Amargo 41.2504b            PHG39
  Maiz Amargo 41.2504b x B73    PHW52
Stiff Stalk related
  B14                           CM105 and A632
  B37                           PHB47
  B37 x B73                     LH117 and PHK29
  B73                           B73
  B73 x B14                     LH74 and LH202

([dagger]) Backgrounds are subjectively grouped on the basis of
prevalence of pedigree lineage. Public inbred lines are noted in
published format, Dekalb Genetics (DK), Holden's Foundation Seeds (LH),
and Pioneer Hi-Bred International (PH).

([double dagger]) Main progenitor lines are those which play an
important founder lines in the lineages of each background.

Table 6. Types of recombinant populations used in developed of
corn inbred lines from 1980 to 2004.

                                       Pioneer
                                    Hi-Bred Int.

Populationt           No. lines ([double dagger])    % ([section])

Two-parent                          303                    90
BC1 (2 inbreds)                      17                     5
BC2+ (2 inbreds)                      4                     1
Three-parent                          7                     2
Four or more                          0                     0
  different parents
Synthetic                             2                     1
Synthetic X inbred                    3                     1
Commercial Hybrid                     0                     0
Total                               336                   100
Germplasm sourcel
Public                           14 of 336                  4
Pioneer Hi-Bred                 333 of 336                 99
Holden's                             0
  Foundation
Dekalb Genetics                      0
Syngenta/Novartis                    0

                             Holden's
                            Foundation               Dekalb Genetics

Populationt            No. lines         %         No. lines         %

Two-parent                 73            54           126           79
BCl (2 inbreds)            17            13            18            11
BC2+ (2 inbreds)            6             4             1             1
Three-parent               16            12             5             3
Four or more               10             7             1             1
  different parents
Synthetic                   1             1             1             1
Synthetic X inbred          5             4             1             1
Commercial Hybrid           6             4             7             4
Total                     134           100           160           100
Germplasm sourcel
Public                 34 of 134         25         12 of 160         8
Pioneer Hi-Bred        13 of 134         10         31 of 160        19
Holden's              111 of 134         83         18 of 160        11
  Foundation
Dekalb Genetics            0                       145 of 160        91
Syngenta/Novartis          0                           0

                        Syngenta/Novartis            Combined Average

Populationt            No. lines         %         No. lines         %

Two-parent                26            47           528            77
BCl (2 inbreds)           11            20            63             9
BC2+ (2 inbreds)           0             0            11             2
Three-parent               3             5            31             5
Four or more               4             7            15             2
  different parents
Synthetic                  0             0             4             1
Synthetic X inbred         3             5            12             2
Commercial Hybrid          8            15            21             3
Total                     55           100           685           100
Germplasm sourcel
Public                 15 of 55         27         75 of 685        11
Pioneer Hi-Bred        12 of 55         22        389 of 685        57
Holden's               12 of 55         22        141 of 685        21
  Foundation
Dekalb Genetics            0                      145 of 685        21
Syngenta/Novartis      35 of 55         64         35 of 685         5

([dagger]) Population types: two-parent, inbred A x inbred B; backcross
one, (A x B) x B; backcross two or more, [(A x B) x B] x B;
three-parent (A x B) x C; four-parent or more (A x B) x (C x D);
synthetic or broad base population; synthetic or broad base population
crossed to inbred(s); and commercial hybrid. If commercial hybrid was
crossed to an inbred corn line it was considered a three-parent
population.

([double dagger]) Number of lines derived from each respective
population type.

([section]) Percentage of total published pedigrees derived from
each respective population.

([paragraph]) Population composition shows representation of public,
Pioneer Hi-Bred, Holden's Foundation, Dekalb Genetics, and Syngenta
(including Novartis, Northrup King, and Ciba) germplasm. Germplasm
source used was inbred corn tines, except for Pioneer Hi-Bred
germplasm which used as corn inbred lines in Pioneer's breeding
program, but was used in the form of Pioneer Hi-Bred commercial
hybrids in Dekalb Genetics, Holden's Foundation Seeds, and Syngenta
breeding programs.
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Author:Mikel, Mark A.; Dudley, John W.
Publication:Crop Science
Geographic Code:100NA
Date:May 1, 2006
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