Protocol (Modified Pedigree 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
GEM breeding protocol for developing S2 and S3
(seasons may vary)
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.
||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.
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.)
||Plant 250 S1 ears (ear to row) 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 among and within S1 families to obtain about 50 S2's. (For
example, choose 50 rows and 1 ear from each row or several ears may be saved
from superior rows depending on each breederís philosophy and style.)
Selection intensity of 20% is recommended, with a goal to save at least 50 S2
ears. Shell and maintain individual S2 ears. Do not treat
seed. (S2 should only be made in a summer nursery where selection
can be practiced.)
||Make 50 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
||Yield test all 50 S2 testcrosses (minimum of 6 locations, 1 rep
per location, need a minimum of 4 good locations for data summary). 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.
||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.
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.
||Make additional top
cross seed or seed increases as needed.
||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.
||The Coordinator will
write a release article to be published in Crop Science. 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 at random 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 400 kernels of the accession, necessary to cross a
minimum of 200 ears with pollen of the inbred line for making 50% breeding
crosses. For making 25% breeding crosses, we will send 200 kernels of the
50% breeding cross to be used as female for making 100 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 1000 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 6 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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