Steven R. Larson

Characterization of fructan biosynthesis in big bluegrass (Poa secunda)

Summary Most cool-season grasses contain multiple types of fructans. One exception is big bluegrass (Poa secunda Presl.). When grown under specific controlled environmental conditions it synthesizes only β-2,6-linked fructans. This study analyzed fructan accumulations, enzyme activities and gene expression in big bluegrass. Detachment/illumination and cool treatments effectively induced the accumulation of fructans in leaf tissues. Enzyme assays indicated that 6-SST (sucrose : sucrose 6-fruc tosyltransferase)- and 6-SFT (sucrose : fructan 6-fructosyltransferase)-like activities were the major enzyme activities involved in fructan biosynthesis in big bluegrass leaves. A full-length cDNA of the putative 6-SFT gene was cloned using RT-PCR and RACE techniques. The deduced amino acid sequence showed 69 percnt; identity with barley 6-SFT. Homology was also high with other fructosyltransferases and some invertases. The abundance of putative 6-SFT mRNA showed a coincidence with fructan accumulation and 6-SFT activity. We suggest that 6-SFT is the major enzyme involved in fructan biosynthesis in big bluegrass but it may also exhibit limited 6-SST activity.

Phylogeography of North American mountain bromes

Although native grasses are often desired and used for revegetation of disturbed areas, genetic differences may exist within and among natural and cultivated germplasm sources. This phylogeographic study compares geographic origin and genealogical linkages of 25 natural and cultivated germplasm sources of mountain brome (Bromus carinatus Hook. & Arn. [Poaceae]) from western North America. Significant variation among accessions (FST = 0.70) was detected by analysis of molecular variance (AMOVA), based on the number of amplified fragment length polymorphisms (AFLPs) between individual plants. Likewise, significant differences among 4 hierarchical genotypic groups, encompassing all but 5 unique accessions, were also detected (FCT = 0.47). This study identified at least one well-defined genealogical lineage, comprising 8 accessions, distributed over a broad geographic region and different ecosystems of western North America. Two other hierarchical groups, comprising 6 accessions and 3 accessions, were located within or near specific ecoregions. Results of this study indicate that natural genealogical lineages of cultivars, such as Garnet mountain brome, have dispersed and succeeded over broad geographical regions. However, more research and plant material work are needed before specific recommendations can be made over the entire species distribution.

Native Grasses for Biomass Production at High Elevations

Herbaceous perennial grasses as lignocellulosic resources are a preferred feedstock source for biofuels because they have a neutral carbon budget, require few agronomic inputs, can be readily managed to be environmentally friendly, and have the potential to be grown on a variety of lands, soils, and crop production situations. The Mountain West at elevations of 1,200 m, and higher, typically have unique and variable conditions typified by dry climates, cold-season precipitation, cold winter temperatures, hot summers with cool nights, large areas of public land, long distances to markets, large variations in soil types, variable soil quality such as salinity, changing field topography, and other factors. Large regions of the Mountain West are dominated by cool-season grasses that could be a desirable source for biofuel production. Tall-statured, cool-season perennial grasses including basin wildrye, creeping x basin wildrye hybrids, intermediate wheatgrass, and tall wheatgrass are viable candidates for lignocellulosic biomass production in this region. Developing a locally grown biomass and biofuel products could provide economic diversification to rural communities in the Mountain West. Establishing a regional supply chain for biofuel production could diversify fuel sources and provide a degree of energy security. Cool-season biomass grasses are not currently cost-competitive with other biomass feedstocks or other Mountain West energy sources. Policies that encourage market development, energy diversification and security could jump-start the market for cool-season biomass grasses, although long-term market viability hinges on their production at competitive costs. Furthermore, commercial production of cool-season perennial grass species will require considerable genetic improvement to develop these plant species for suitable biomass production.

Association of candidate genes with heading date in a diverse Dactylis glomerata population

Flowering occurs in response to cues from both temperature and photoperiod elicitors in cool-season, long-day forage grasses, and genes involved in sensing the elicitors and inducing downstream flowering responses have been associated with heading date and flowering time in perennial forage grasses as well as cereal grasses. In this study we test for association between orchardgrass (Dactylis glomerata L.) heading date and polymorphisms in the CONSTANS (DgCO1), FLOWERING TIME (DgFT1), a VRN1 like MADS-box (DgMADS), and PHOTOPERIOD (DgPPD1-like) containing genes. A diverse population of 150 genotypes was measured for heading date across three years, genotyped, and candidate genes sequenced. Although pairwise population kinship values were generally low, the genotypes fit into a two-group structure model. Linkage disequilibrium decayed rapidly, reaching r2 levels below 0.2 within the 500bp of each gene. SNPs significantly associated with heading date were detected in equal-dose and tetraploid dosage models. The DgCO1 gene had the most significant polymorphisms and those with the largest effects, while DgMADS had several significant polymorphisms in its first intron with smaller effects. These polymorphisms can be used for further validation, selection, and development of breeding lines of orchardgrass.

Tall fescue forage mass in a grass-legume mixture: predicted efficiency of indirect selection

High fertilizer prices and improved environmental stewardship have increased interest in grass-legume mixed pastures. It has been hypothesized, but not validated, that the ecological combining ability between grasses and legumes can be improved by breeding specifically for mixture performance. This experiment examined the predicted efficiency of selection in a grass monoculture environment to indirectly improve tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) forage mass in a grass-legume mixture. Heritability, genetic and rank correlations, and selection efficiencies were estimated for forage mass in a tall fescue half-sib population grown as spaced-plants overseeded with either turf-type tall fescue (monoculture) or alfalfa (mixture). Heritability for tall fescue forage mass in monoculture ranged from 0.32 to 0.70 and were always similar or greater than those in mixture (range 0.27–0.55) for four successive harvests and annual total. Genetic correlations between monoculture and mixture tall fescue forage mass varied with values of 0.48, 0.92, −0.31, 0.70, and 0.25 in June, July, August, October, and annual total, respectively. Indirect selection efficiencies exceeded or approached direct selection for mixtures only in July and October (1.29, and 0.73, respectively). Whereas, indirect selection efficiencies were low in June, August, and annual forage mass (0.58, −0.31, and 0.28, respectively). Moreover, low Spearman’s rank correlations (−0.03 to 0.35) indicated differing half-sib family performance between the monoculture and mixture environments. Results indicate that direct selection should be used to improve tall fescue forage mass in a grass-legume mixture, and support the hypothesis of increasing ecological combining ability by breeding for mixtures per se.