Principles of Plant Genetics and Breeding

BREEDING SORGHUM 513
Kansas State University, Texas A&M University, and USDA. These public programs do not produce or sell hybrids, but they
develop parental lines and germplasms that are used by private industry in commercial hybrid production. In addition, public
research programs in sorghum conduct research in long-term projects such as the introgression and development of new
germplasm that may provide useful traits in the future.
The Texas Agricultural Experiment Station (TAES) sorghum breeding program located at Texas A&M University in College
Station, Texas is part of a multiproject, multilocation sorghum improvement program supported by the TAES. Sorghum breeders
work in conjunction with plant pathologists, entomologists, and grain quality and molecular geneticists to create an effective and
important research and application oriented team. In terms of the sorghum breeding program at College Station, the breeding
program has several objectives: (i) develop and release germplasm and parental lines with improved adaptability, yield, quality,
and stress resistances; (ii) conduct research that increases our understanding and knowledge of sorghum breeding and genetics;
and (iii) train undergraduate and graduate students in plant breeding.
Methodology of the TAES sorghum breeding program at College Station
For improved hybrids, new and improved parental lines must be developed. First, genetic variability must be developed through
the selection and hybridization of parent material. This is a crucial step in the process. Usually elite germplasm is crossed to other
material (elite lines, germplasm, genetic stocks) to correct a perceived deficiency in the elite material. For example, if an otherwise
good A/B pair is susceptible to lodging, it will be
Summer Year 0
Winter Year 0
Summer Year 1
Summer Year 2
Summer Year 3
Summer Year 4
Breeding crosses are made;
∼200 annually
Weslaco, Texas
self-pollinated;
∼200 annually
College Station (CS), Beeville, Texas
200 populations and 15 rows/population;
∼3,000 plots annually
One environment/per selection
Either CS, Corpus Christi (CC)
or Lubbock (LB), Texas
∼5,000 plots annually
Genotypes are shifted among
environments (CS or CC)
∼2,000 plots annually
Multiple environments (CC, CS, and LB)
Testcross hybrids made in CS, and
sterilization (for B-lines) begun in CS
∼500 lines annually
P 1 × P 2
Figure 2 Pedigree breeding scheme used by the TAES
sorghum breeding program at College Station, Texas. This
scheme is used for the development of new B- and R-lines and
germplasm. Initial crosses are made using either plastic bag
crosses or hand emasculations. Open-pollinated selections are
made in each generation until the F 5 where the plot is selfpollinated
and used to make testcross hybrids. At the F 5
generation, new B-lines enter sterilization and testcrossing while
new R-lines are evaluated in testcrosses.
F 1
F 2
F 2:3
F 3:4
F 4:5
hybridized with several different sources of lodging
resistance with the goal of producing a new A/B pair
with improved lodging resistance. In our program, the
A/B program is managed separately from the R-line
program to maintain heterosis between the two groups
and keep the fertility restoration and maintenance
genetics separate. Based on the considerations listed
above, specific crosses are made using the methodology
described by Rooney (2004). These F 1 progeny are
self-pollinated to produce an F 2 population.
Once F 2 populations are created, our program utilizes
a pedigree breeding approach for the development
of inbred lines (Figure 2). From the F 2 generation
until the F 5 generation (in which uniform lines are
selected), the progeny rows are grown and panicles in
the rows are visually selected on the basis of agronomic
desirability, pest resistance, and abiotic stress
tolerance. F 5 lines that are phenotypically uniform are
testcrossed to measure their general and specific combining
ability and their suitability as parent lines in
hybrid combinations.
The appropriate time for the selection of specific
traits is dependent on the heritability of the trait and
the environments in which the selection occurs. In
our program, traits with higher heritability (maturity,
height, grain color, etc.) are selected in the early generations
while traits with lower heritability (yield,
drought tolerance, disease and insect resistance) are
selected in more advanced generations. These more
complexly inherited traits must also be screened in
multiple environments, because these traits may not
be expressed in any given environment. Evaluation in
multiple environments is crucial to the development
of widely adapted sorghum genotypes. In our program,
we use three basic regions for inbred selection:
south Texas, central Texas, and the Texas high plains
(Figure 3). These regions are each unique and force
different selection pressures on the material grown
therein. For example, our south Texas nurseries are
rainfed and subject to drought stress and consistent
disease pressure. In addition, this region is good for
selecting genotypes that perform well in subtropical