| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a 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
b Department of Crop Sciences, Univ. of Ill., 1102 S. Goodwin Ave, Urbana, IL 61801
* Corresponding author (mmikel{at}uiuc.edu)
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
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
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
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 Leaming 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 |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
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 |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
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.
|
|
–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.
|
|
|
|
|
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 Leaming 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 Leaming Corn x Wf9 (Gerdes et al., 1993). This is a rare example of Oh07 (Leaming 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, LH119, 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.
|
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 selfing 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 |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
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, LH119, 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 |
|---|
Received for publication October 12, 2005.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  S. Smith Intellectual Property Protection for Plant Varieties in the 21st Century Crop Sci., July 1, 2008; 48(4): 1277 - 1290. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Mikel and F. L. Kolb Genetic Diversity of Contemporary North American Barley Crop Sci., July 1, 2008; 48(4): 1399 - 1407. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. T. Nelson and M. M. Goodman Evaluation of Elite Exotic Maize Inbreds for Use in Temperate Breeding Crop Sci., January 16, 2008; 48(1): 85 - 92. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. A. Lee and M. Tollenaar Physiological Basis of Successful Breeding Strategies for Maize Grain Yield Crop Sci., December 18, 2007; 47(Supplement_3): S-202 - S-215. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Smith Pedigree Background Changes in U.S. Hybrid Maize between 1980 and 2004 Crop Sci., September 1, 2007; 47(5): 1914 - 1926. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. F. Troyer and L. G. Hendrickson Background and Importance of 'Minnesota 13' Corn Crop Sci., May 31, 2007; 47(3): 905 - 914. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Mikel Availability and Analysis of Proprietary Dent Corn Inbred Lines with Expired U.S. Plant Variety Protection Crop Sci., November 21, 2006; 46(6): 2555 - 2560. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
