Ryan C. Graebner

Quantitative Trait Loci Associated with the Tocochromanol (Vitamin E) Pathway in Barley

The Genome-Wide Association Studies approach was used to detect Quantitative Trait Loci associated with tocochromanol concentrations using a panel of 1,466 barley accessions. All major tocochromanol types- α-, β-, δ-, γ-tocopherol and tocotrienol- were assayed. We found 13 single nucleotide polymorphisms associated with the concentration of one or more of these tocochromanol forms in barley, seven of which were within 2 cM of sequences homologous to cloned genes associated with tocochromanol production in barley and/or other plants. These associations confirmed a prior report based on bi-parental QTL mapping. This knowledge will aid future efforts to better understand the role of tocochromanols in barley, with specific reference to abiotic stress resistance. It will also be useful in developing barley varieties with higher tocochromanol concentrations, although at current recommended daily consumption amounts, barley would not be an effective sole source of vitamin E. However, it could be an important contributor in the context of whole grains in a balanced diet.

A comparison of polymorphism information content and mean of transformed kinships as criteria for selecting informative subsets of barley (Hordeum vulgare L. s. l.) from the USDA Barley Core Collection

Recent advances in genetic technologies have given researchers the ability to characterize genetic marker data for large germplasm collections. While some studies are able to capitalize on entire germplasm collections, others, especially those that focus on traits that are difficult to phenotype, instead focus on a subset of the collection. Typically, subsets are selected using phenotypic or geographic data. One major hurdle in identifying favorable subsets is selecting a criterion that can be used to quantify the value of a subset. This study compares two such criteria, polymorphism information content, and a new criterion based on kinship matrices, which will be called the mean of transformed kinships. These criteria were explored in terms of their ability to select subsets that are favorable for genome wide association studies, and in their ability to select subsets that contain a high number of rare phenotypes. Using phenotypic and genotypic data that has been amassed from the USDA Barley Core Collection, evidence was found to support the hypotheses that subsets based on the mean of transformed kinships were well-suited to select subsets intended for genome-wide association studies, but the same was not found for polymorphism information content. Inversely, evidence was found to support the hypothesis that subsets based on polymorphism information content were well-suited to select subsets intended for rare-phenotype discovery, but the same was not found for subsets selected using the mean of transformed kinships criterion. Tools to select subsets using these two criteria have been released in the R package “GeneticSubsetter.”

Evidence for evolution of increased competitive ability for invasive Centaurea solstitialis, but not for naturalized C. calcitrapa

Congeneric species with the same native and non-native ranges, but exhibiting different invasiveness, provide opportunities to assess the relative importance of factors contributing to successful invasions. For example, comparing the competitive ability of such congeners against other species from the native and non-native regions of invasive species can provide insight into the role of evolutionary experience with different competitors. We selected two congeneric Centaurea species with overlapping native and non-native ranges but with strikingly different invasive success, Centaurea solstitialis and C. calcitrapa, and conducted experiments with populations from each region using a suite of different native grass species from each region. When grown with Spanish grass species, competitive responses were 32% stronger for C. calcitrapa and 30% stronger for C. solstitialis, than when in competition with grasses native to California. Centaurea solstitialis from California had 66% higher competitive effects on grasses, all species considered together, than Spanish C. solstitialis; whereas the competitive effects of C. calcitrapa on grasses were not significantly different between C. calcitrapa ranges. Our results are consistent with the prediction that the evolution of increased competitive ability (EICA) might contribute to the devastating success of C. solstitialis in California, and that its absence might contribute to the modest naturalization of the non-invasive C. calcitrapa. Escape from the strong competitive effects and responses of grasses from Spain may also contribute to invasive success in California. Our results suggest that studies of EICA should be based on competitive tests, since biomass alone is not always a good predictor of competitive ability.

Relationships among wood anatomy, hydraulic conductivity, density and shear parallel to the grain in the wood of 24-year-old Handroanthus vellosoi (Bignoniaceae)

We studied the relationships among wood anatomy, hydraulic conductivity, density and shear parallel to the grain in the stem of Handroanthus vellosoi trees with the goal to identify possible trade-offs between hydraulic conductivity and mechanical properties. For this study we felled 12 trees with 24-year-old and cut 10-cm-thick disks at three heights: base of the trunk, one meter in height, and two meters in height. We propose that the relationship between hydraulic conductivity and mechanical resistance found along the H. vellosoi trunk indicates greater mechanical investment in the wood at the base of the trunk compared with the other two heights (1 and 2 meters). Anatomically, this would be represented by smaller diameter vessels and fibers with thicker walls. Consequently, strength investment implies lower water conductivity at the stem base. However, more studies are needed to determine whether this lower value with respect to 1 and 2 meters represents a significant effect on water transport along the stem.