Germplasm Enhancement of Maize

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 GEM Protocol (Modified SSD Method):

The Germplasm Enhancement of Maize project is a cooperative effort of the United States Department of Agricultureís Agricultural Research Service, universities, and industry.  Our objective: via conventional intercrossing and selection methods, widen the germplasm base of commercial hybrid corn in the United States through the introduction and incorporation of novel and useful germplasm gathered from around the globe.


Develop lines from Elite Corn Belt/Exotic germplasm crosses.

The basic protocol of GEM is a modified pedigree breeding system to develop S2 lines (private sector) or S3 lines (public sector).  The Coordinator assigns materials and heterotic pattern to be used in this procedure to the participating cooperators.

It is understood that any seed or data generated as a result of in kind support shall be returned to the GEM Coordinator.  Such seed and/or data shall be shared with other GEM Cooperators, who shall have the right to freely use such seed and/or data.

GEM breeding protocol for developing S2 and S3 lines.

Season Breeding Activity (seasons may vary) 
Winter 1 Private cooperator crosses the assigned accessions with a proprietary line of the same heterotic group to form the breeding cross.  The nursery in which the breeding cross is made needs to be inspected and a copy of the inspection sent to the Coordinator along with the seed.  This is so the Coordinator can obtain a phytosanitary certificate if necessary.  Do not treat seed.
Summer 1 A different private cooperator crosses the accession x proprietary line breeding crosses with their proprietary line of the same heterotic group to form the three-way cross.  The nursery in which the breeding cross is made needs to be inspected and a copy of the inspection sent to the Coordinator along with the seed.  This is so the Coordinator can obtain a phytosanitary certificate if necessary.  Do not treat seed.
Winter 2 The resulting breeding cross (S0) is selfed to generate 300 pollinations.  The ultimate goal is obtaining 250 S1 ears.  Mild selection is made to avoid smut, very late flowering, and non-adapted or unattractive phenotypes. Shell S1 seed from each ear separately (do not bulk seed). Do not treat seed.  Send all seed to the Coordinator, but maintain enough remnant seed to plant one row of each ear the next generation.  Coordinator may assign the same material to the cooperator to make S2ís in summer.  (S1ís can be made in either a winter or summer nursery.)
Summer 2 Plant a balanced bulk (BBK) of 250 S1 ears (2 kernels per ear=500 kernels) to make the S2.   Handle this material in the nursery as you would any of your own breeding projects (such as inoculating for diseases, selection procedures, etc.).  Select the best plants for selfing before and post pollination with a goal to have about 70 selfed ears that are individually identified.  Shell and maintain individual S2 ears.  Do not treat seed.  (S2 should only be made in a summer nursery where selection can be practiced.)
Winter 3 Make 70 S2 topcrosses with one appropriate elite inbred tester of the opposite heterotic group.  If the private cooperator does not have in-kind winter nursery rows available, contact the Coordinator to get the crosses made.
Summer 3 Yield test all 70 S2 testcrosses (minimum of 5 locations, 1 rep per location).  If the cooperator does not have enough in-kind yield trial plots to fully test their testcrosses, contact the Coordinator to organize these yield trials.   Each cooperator will send the data by e-mail attachment to the GEM IT Specialist.  Seed of the best S2 lines based on topcross yield data (about 10 lines; but will vary based on performance relative to check means), should be returned to the Coordinator.  Some remnant seed of each S2 line may be kept by the cooperator.
Winter 4 Make S3 increases of the 10 best selected S2 lines based on S2 topcross data. Ears are bulked on a per row basis beginning at the harvested S3 generation. Public cooperators should return S3 generation seed.
Summer 4 Begin lab quality trait evaluation of S3 bulk lines after harvest in summer nursery.  Evaluate the S3 lines for general appearance, disease and insect resistance, etc., using in kind support of the cooperators who expressed an interest in these traits.  Cross the S3 lines to 2 testers not used previously for evaluation in second year trials.
Winter 5 Make additional top cross seed or seed increases as needed.
Summer 5 Conduct second year yield trials on two testers at 8 locations. Continue lab quality trait evaluation of the lines, and other traits such as disease, insect, and stress resistance to obtain second year data.
Winter 6 The Coordinator will write a release article to be published in Crop Science within 2 years after germplasm is made available to GEM Cooperators. When the article is published, the Coordinator will release GEM designated lines and all relevant data to NCRPIS (North Central Regional Plant Introduction Station) for maintenance and distribution.

The accessions that are used for breeding crosses will be assigned to the cooperators by the Coordinator.  The Coordinator will recommend the selected material to use for breeding to each group.  If the number of nursery rows or yield trial plots for a given company is too few to handle an entire project, the Coordinator will split the project into parts to accommodate those numbers.

Requests for seed of the accessions can be made directly through NCRPIS, and the Coordinator may assist in obtaining seed if desired. Seed of breeding and testcrosses are made through the Coordinator.  The distribution of the seed will be according to the utilization of the material:

a)    Breeding crosses

We will send 250 kernels of the accession, necessary to cross 60 ears with pollen of the inbred line for making 50% breeding crosses.  For making 25% breeding crosses, we will send 250 kernels of the 50% breeding cross to be used as female for making 60 crossed ears.  The cooperator will send seed of balanced bulks of the shelled ear seed (untreated) to the Coordinator

b)    Breeding procedure

We will send 1200 kernels of the breeding cross (S0 generation).  The goal is to self 300 plants with an objective to have 250 selfed ears.  Public sector cooperators will send seed of their selected S3 lines to the Coordinator, and private sector cooperators will send the Coordinator their selected S2 lines.

c)    Yield testing

Each first year experiment will require 5 locations, 1 replication, 2 rows/plot, and enough kernels based on individual cooperator requirements.  Second year experiments require 8 locations.  Seed of 5 standard commercial check hybrids will also be distributed by the Coordinator for including in each experiment.  Each cooperator will send the GEM IT Specialist an e-mail attachment of the data as soon as possible after harvesting.

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We are grateful to our Cooperators for their support!


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Contact us | Home | USDA | ARS | NCRPIS | ISU | Corn Breeding | March 03, 2011