Environmental Engineering Reference
In-Depth Information
simplest would be a SNP marker located within a functional gene or EST combined with phenotypic
evaluations of plants containing alternate forms of the polymorphism identifying which allele
is favorable. In this case, one nucleotide polymorphism within one gene is focused on one trait,
analogous to the brown-midrib genetic mutations involved in the phenylpropanoid pathway and
their effect on lignin (Vignols et al. 1995). Second, QTL discovery, using either linkage mapping
or association mapping, would identify random DNA markers flanking a QTL of interest. Selection
would be based on the flanking markers associated with favorable phenotype, and (hopefully)
a small probability of crossover between the flanking markers and the QTL of interest. Third,
selection could target several genes for one or more traits, seeking to pyramid multiple favorable
genes together into a population using multiple SNP markers. Fourth, marker-assisted recurrent
selection (MARS) expands the DNA markers used as selection tools to a broader genomic coverage
focused on regions of the genome known to contain QTL of interest, typically based on linkage
or association mapping (Johnson 2001, 2004). Least squares and/or maximal likelihood statistical
methods are used to develop a marker selection index that is related to plant phenotype in a predictive
capacity. Fifth, genome-wide selection goes one step further to saturate the genome with markers,
and using best linear unbiased prediction (BLUP) methods to develop a marker index predictive of
plant phenotype (Bernardo and Yu 2007).
Any of the above marker selection strategies can be effectively combined with existing selection
methodology to implement marker selection for specific plant traits in switchgrass. For phenotypic
selection, markers and traits are measured on the same plants to develop the BLUP equations. Plants
selected in the first generation are intercrossed to create a new generation for marker evaluation and
BLUP selection, eliminating the need for phenotyping in every generation. For among-and-within-
family selection, marker scores or indices would be used as the within-family selection criterion
on an individual plant basis, whereas biomass yield or other field-based phenotypic traits would be
used as the among-family selection criterion.
22.8 sWItchGrass as a BIoenerGy croP
Designation of switchgrass as an herbaceous model species for bioenergy feedstock development
has transformed this species from obscurity to celebrity status. Before the BFDP, switchgrass
was used principally for conservation and restoration of tallgrass prairie habitats and livestock
production, the latter largely restricted to the Great Plains region of the United States. With the
increase in research activity during the BFDP and subsequent USDA-ARS and U.S.-DOE research
programs (Bouton 2007; Sanderson et al. 2007), interest in switchgrass research has grown to
many public institutions in North America, Europe, and Asia and to some very high-profile
commercial research efforts. In 1992, switchgrass breeding was conducted by the USDA-ARS in
Lincoln, Nebraska and by South Dakota State University in Brookings, South Dakota. During the
BFDP, Oklahoma State University, University of Georgia, and University of Wisconsin (combined
with USDA-ARS) initiated new switchgrass breeding programs targeted to different regions and
hardiness zones within the United States. During this period, a switchgrass breeding program
was also initiated in the private sector near Ottawa, Canada, and a research program focused on
molecular genetics was initiated at the University of Tennessee. Since the completion of the BFDP
and the rapid expansion of feedstock research in 2005-2008, new breeding and genetics initiatives
have been established at Iowa State University, University of Illinois, Texas A&M University,
and the Noble Foundation, Ardmore, OK, whereas new private breeding programs have been
established at Auburn, AL, and Bryan, TX.
The boom in switchgrass research can be viewed as a double-edged sword. One side of the sword
cuts in favor of creating a vast database on basic biology, genetics, and production information
to reduce production costs and improve conversion efficiency of switchgrass feedstock to various
forms of energy. Vast amounts of funding have brought basic and applied scientists together and
formed partnerships between public and private organizations, all working toward the goal of
