Browsing by Author "Clark, Matthew Daniel"

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    Characterizing the host response and genetic control in 'Honeycrisp' to apple scab (Venturia inaequalis)
    (2014-01) Clark, Matthew Daniel
    Two novel apple scab resistance loci have been identified in the apple cultivar Honeycrisp, an emerging cultivar in North America that is utilized in apple breeding programs worldwide. Greenhouse inoculation experiments with the apple scab fungal pathogen, Venturia inaequalis, identified a resistance defense response in `Honeycrisp' and its ancestors `Keepsake', `Frostbite', and `Northern Spy' seven days after inoculation. The defense response ranged from necrotic and chlorotic lesions to stellate necrosis and class 3b lesions (with sporulation). A hallmark of the resistance defense response is autofluorescence at the infection site in cleared leaf tissue. Several `Honeycrisp' progeny populations were screened with monoconidial isolates of V. inaequalis and segregated 3:1 for resistance, suggesting two resistance genes inherited from `Honeycrisp'. A consensus `Honeycrisp' linkage map with 1091 SNP markers was constructed for use in mapping. Two resistance loci were mapped using linkage mapping and quantitative trait loci mapping approaches. Marker haplotypes were constructed to trace the inheritance of resistance loci. Rvi19 mapped on linkage group 1 at ~50 cM. In the Rvi19 haplotype, the 138 bp allele for the Ch-Vf1 marker cosegregates with resistance, and is identical by state (IBS) with the Rvi17 resistance in `Antonovka'. Rvi19 is transmitted from `Frostbite' to `Keepsake' to `Honeycrisp', and into the resistant progeny of `Honeycrisp'. The other locus, Rvi20, mapped onto linkage group 15, and is IBS with a marker haplotype found in the susceptible cultivar Golden Delicious. Rvi20 is transmitted to `Honeycrisp' from an unknown parent. Molecular marker haplotypes were used to identify advanced selections in the University of Minnesota breeding program with pyramided scab resistance. Candidate genes were identified at each haplotype that can serve as starting points for identifying the functional genes conferring resistance. A collection of V. inaequalis isolates was assembled and curated from six locations in Minnesota for screening scab resistance. These 80+ isolates were examined for genetic diversity and population structure and provide a snapshot of the diversity of the pathogen present at this time.
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    Evaluation of the genetic potential of prairie junegrass (Koeleria macrantha) for use as a low-input turfgrass
    (2010-05) Clark, Matthew Daniel
    Prairie junegrass [Koeleria macrantha (Ledeb.) Shultes] is a perennial, shortgrass prairie species distributed throughout the Northern Hemisphere. This species demonstrates tolerance to many environmental stresses found in Minnesota. In June 2007, 48 K. macrantha accessions from the United States National Plant Germplasm System (NPGS) were grown and evaluated in two experiments; (i) seed production characteristics and (ii) turf quality characteristics in 2 locations (St. Paul, MN and Becker, MN). In the seed production experiment, seed was harvested in 2008, and significant variation was found among accessions for several seed production traits including harvest date, plant height, seedhead number, and seed yield. A significant correlation between seedhead number and seed yield was found, which can be utilized for indirect selection in the production nursery. Plant growth and seed yield were highest at the Becker location demonstrating the species’ preference for well drained soils. In the turf quality experiment, mowed space plants were evaluated from 2007- 2009, nineteen accessions at Becker and 30 accessions at St. Paul performed with an adequate turf quality rating of 5.0 or higher when averaged over the three-year study, suggesting the potential for use in low-input areas. Prairie junegrass from northern collection regions displayed the highest ratings in spring green-up which is an important turf trait in northern climates. There was a strong negative correlation between this trait and mowing quality at Becker (r = -0.44) and at St. Paul (r = -0.34). Several accessions demonstrated acceptable mowing quality and would be candidates for integration into a native prairie junegrass breeding program. In June 2007 a third experiment was conducted. Three hundred genotypes representing crossing blocks derived from Colorado, Nebraska, and Minnesota germplasm were grown and evaluated for turf quality characteristics in a randomized complete block design with five clonal replications at 2 locations (St. Paul and Becker) and evaluated for three years. Following establishment, plots received no supplemental irrigation or fertility and were mowed weekly to a height of 6.4 cm. Broad-sense heritability estimates were calculated on a clonal mean (Hc) and single plant (Hsp) basis for turf quality (Hc = 0.62, Hsp = 0.13), crown density (Hc = 0.55, Hsp = 0.09), mowing quality (Hc = 0.59, Hsp = 0.09), and genetic color (Hc=0.45, Hsp = 0.06). The heritability estimates indicate that selection for these traits should result in significant gains in germplasm improvement. Differences were observed for means and variances among clones, crossing blocks, and/or collection regions for many of the traits evaluated including rust (incidence and severity), spring green-up, plant height, lateral spread, vertical re-growth, and flowering traits. The positive correlations among some of these traits and those with moderate heritability estimates will allow for multi-trait selection in cultivar development. Rust (unknown Puccinia species) was present at both locations.