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Browsing by Author "Koski, Anthony, advisor"

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    Chromosome races and polypoid cytoforms in Distichlis spicata
    (Colorado State University. Libraries, 2001) Reid, Scott D., author; Hughes, Harrison G., advisor; Koski, Anthony, advisor
    Saltgrass (Distichlis spicata [L.] Greene) is a salt-tolerant C4 grass native to the Americas that is currently being evaluated for use as a turfgrass species. Saltgrass has a highly variable morphology in different regional occurrences, and this has led some botanists to consider it as two species or as comprising several botanical varieties over its wide distribution in the U.S. west of the Mississippi River and along coastal regions. Chromosome numbers of 160 saltgrass accessions, primarily from nine western states, were determined. A 38-chromosome saltgrass race with distributions separate from the previously known 40-chromosome type has been identified. Both races are fertile and hybridize readily. The distribution pattern and the cytological behavior of hybrids between the races suggest they are adaptively different. No aneuploidy in the 38-chromosome race has been found, and no deficient aneuploids have been found in the 40-chromosome race. Meiotic irregularities in the 40-chromosome race suggest a pathway for the evolution of the 38-chromosome race, dependant on hypothesized genetic changes that allow fitness in individuals lacking the pair of homologues defining the difference between the races. More research is needed to evaluate broad but varied morphological differences between the races. The consequences of intermating the two cytoraces in breeding efforts are unknown, but karyotypic instability may result in some cases. An octaploid saltgrass cytotype, previously considered rare, has been found to occur more commonly, distributed among both of the cytoraces. One accession, believed to be a 6x cytotype, represents a ploidy level previously undescribed in saltgrass. Screening to identify individuals of different ploidy levels among collections made for the turfgrass breeding program is advisable. Aneuploidy and multivalent associations in meiosis suggest the higher-order polyploid cytoforms may reproduce with less efficiency sexually, but this has not been adequately studied. Two ca. 74-chromosome accessions showed high estimated pollen viability. B chromosomes are reported for the first time in saltgrass, occurring in some individuals of all three cytotypes.
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    Heritability estimates, accession evaluation, and digital imaging in Distichlis spicata
    (Colorado State University. Libraries, 2009) Christensen, Dana K., author; Koski, Anthony, advisor; Holm, David, advisor
    Conserving water in the landscape is critical to inhabiting the arid portions of the western United States. Native accessions of the inland form of saltgrass [Distichlis spicata var stricta (Torr.) Beetle] remained green, while turfgrass lines of blue grama, buffalograss, crested wheatgrass, and bermudagrass went dormant from lack of rainfall during the drought of 2000 and 2001 in Colorado. Since saltgrass is non-domesticated, this research selected plants for four traits needing improvement to make saltgrass more turf like. Resistance to leaf rust (Puccinia aristidae Tracy), short height, high shoot density, and high seed yield were traits that made up a selection index which ranked all 158 accessions collected from the Front Range of Colorado, the Great Basin, South Dakota, and Nebraska. The top 14 females and 12 males of these were topcrossed, and progenies were evaluated. Response to selection was recorded for all four traits. Realized heritability, narrow sense heritability from half-sib analysis, narrow sense heritability from parent-offspring regression, and broad sense heritability were very high for height and shoot density. Broad sense heritability and narrow sense heritability from half-sib analysis were high for seed yield, but narrow sense heritability from parent-offspring regression and realized heritability were moderate. A major gene for rust resistance was inferred. Negative heterosis measured on the midparent for height and seed yield were noted. Positive heterosis occurred for shoot density.