Browsing by Author "D. Michael Benson, Committee Member"

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    Biology and Management of Fairy Rings on Golf Putting Greens
    (2010-04-23) Miller, Gerald Leo Jr; Lane P. Tredway, Committee Co-Chair; Larry F. Grand, Committee Co-Chair; Marc A. Cubeta, Committee Member; Michael A. Fidanza, Committee Member; D. Michael Benson, Committee Member
    Fairy ring is a severe disease problem on golf putting greens in North Carolina and throughout the United States. Pathogen identification is difficult and very little is known about the etiology and management of this disease. Basidiocarps and soil samples were collected from 15 bermudagrass and 30 bentgrass greens exhibiting fairy ring symptoms in CA, FL, HI, IL, OK, NC, SC and WI. Genomic DNA was extracted from 122 total samples. Extractions were made from mycelium isolated from puffball or mushroom context tissue, from mycelium isolated from a soil block, or through direct DNA extraction from infested soil. DNA was also extracted from 16 type isolates for comparison to unknowns. The internal transcribed spacer (ITS) region of ribosomal (r)DNA was amplified and sequenced using the basidiomycete-specific primer sets ITS1f/ITS4b and Basid0001/2R. Most ITS sequences grouped into one of three clades corresponding to species within the Family Lycoperdaceae: Arachnion album, Bovista dermoxantha, and Vascellum curtisii. This is the first report of Arachnion album in association with fairy ring formation. Molecular identification was confirmed with morphological characterization of mature basidiocarps. Although many basidiomycete fungi have been associated with fairy ring on turfgrass, only 5 fairy ring forming species were detected in this survey of golf putting greens. Soil DNA extraction and a PCR detection assay was also specifically evaluated for diagnosis and identification of fairy ring pathogens. Genomic DNA was extracted from five soil samples from putting greens infested with fairy ring. The ITS region was amplified and directly sequenced from soil DNA extracts, yielding a consensus ITS sequence for four of the five samples. Four to eight cloned PCR fragments were sequenced per sample. Clones showed high sequence similarity (99%) to directly sequenced ITS fragments, indicating homogeneity in the resultant amplicon sequence. Target rDNA sequences were amplified successfully using primers specific to Vascellum curtisii and Bovista dermoxantha from both extracted soil DNA and DNA from known isolates. However, several false positive amplifications also occurred. Due to this variability in PCR detection assays, sequencing of extracted soil DNA may be a more viable alternative for detecting and identifying fairy ring pathogens. Field experiments were conducted to evaluate the impact of application rate, application timing, fungicide + surfactant tank-mix, and irrigation timing on the efficacy of preventive DMI fungicide applications for fairy ring control. No statistical difference was observed between the level of control afforded by single applications of low and high rates of triadimefon and tebuconazole. Single applications suppressed fairy ring early in the season, but did not provide season long control. No statistical difference was detected between application timing events based on average 5-day soil temperature thresholds, but a data trend showed lower disease severity in plots treated with fungicide at 13°C and 16°C. Two spring applications of triadimefon or triticonazole provided less residual control when tank-mixed with a surfactant than when applied alone. Irrigation timing treatments did not affect preventive fungicide control. An in vitro mycelial growth assay was used to determine the sensitivity [% 50 effective concentration (EC50)] of 16 isolates representing major fairy ring species to the fungicides flutolanil, propiconazole, tebuconazole, triadimefon, and triticonazole. No significant differences in fungicide sensitivity were detected among fairy ring species. Differences in in vitro sensitivity of isolates were detected among fungicides. Isolates were most sensitive to tebuconazole (EC50 = 0.149) and triticonazole (EC50 = 0.263), moderately sensitive to propiconazole (EC50 = 0.371) and flutolanil (EC50 = 0.546) and least sensitive to triadimefon (EC50 = 0.821).
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    Development of a Genetic Linkage Map in Abies nordmanniana Accession 9M
    (2005-06-15) Hudson, Emily Elizabeth; D. Michael Benson, Committee Member; Henry V. Amerson, Committee Co-Chair; L. John Frampton, Committee Co-Chair
    Genetic linkage maps have been constructed for many species of conifers; however, none has been previously published for an Abies species. A genetic linkage map of Nordmann fir (Abies nordmanniana (Steven) Spach) open-pollinated family 9M was constructed using AFLP and RAPD markers developed from megagametophytic DNA. In all, 556 markers were grouped at LOD ≥ 5.0, θ = 0.30, into 19 linkage groups that covered 1977 cM (Kosambi). Framework maps were ordered with interval support ≥ 3.0 for each linkage group. Accessory markers were attached to the nearest framework marker based on LOD scores and recombination fractions. Significant linkage distortion (approximately 10% of the 556 markers based on a chi-square test at p ≤ 0.05) from the expected 1:1 Mendelian segregation ratio was recognized. The genome size was estimated to be 2471 cM, and this map provided 80% coverage of the genome. Attempts to map a trait locus (based on disease phenotype in an inoculated mapping population) for disease resistance to Phytophthora cinnamomi Rands were unsuccessful. This Abies linkage map will be important to the Christmas tree industry for marker-assisted selection of useful traits such as pest resistance, branching characteristics, height, growth rate, and post-harvest needle retention.
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    Factors affecting susceptibility to - and management of - postharvest soft rot of sweetpotatoes caused by Rhizopus stolonifer.
    (2008-11-25) Edmunds, Brooke Aurora; James W. Moyer, Committee Member; D. Michael Benson, Committee Member; Gerald J. Holmes, Committee Chair; Lee-Ann Jaykus, Committee Member
    Studies were undertaken to explore the relationship of R. stolonifer susceptibility with preharvest growing conditions and postharvest handling of sweetpotatoes. Additional studies were also completed to identify effective decay control products. A three-year study investigated the effect of preharvest conditions on R. stolonifer and Erwinia chrysanthemi susceptibility. Roots were harvested from 75 sweetpotato fields and information collected including soil samples, weather during the growing season, weed density, and insect injury (153 predictors). Roots were inoculated after 100 days in storage. Mean R. stolonifer incidence was 34.9% (standard deviation=31.7%) and mean E. chrysanthemi incidence was 51.0% (standard deviation=30.5%). Predictive models were developed using forward stepwise regression to identify predictors of interest, followed by mixed model analysis (p-value<0.05) to produce a final model. R. stolonifer susceptibility is best predicted by soil calcium (% CEC), plant-available soil phosphorus, soil humic matter (%), mean air temperature, mean volumetric soil moisture at 40 cm, and mean soil temperature at 2 cm (all over the growing season). E. chrysanthemi susceptibility is best predicted by soil pH and days that soil temperature exceeds 32 ºC (14 days pre- harvest). Studies were also conducted to define the relationship between postharvest handling and susceptibility to R. stolonifer. Experiments designed to simulate packingline handling found root ends are more susceptible that mid-sections and that increasing the number of time a root is dropped as well as increasing the impact force resulted in increased decay susceptibility. ‘Hernandez’ roots were significantly more susceptible than ‘Beauregard’ in all experiments. To confirm the relationship of impacts and disease development, Beauregard roots were sampled from locations along commercial packinglines. High decay in inoculated as compared to non-inoculated roots indicates that wounding is occurring that could result in disease if the pathogen was present at higher levels. Evaluations of reduced-risk fungicides, bio-fungicides and generally recognized as safe products for efficacy against R. stolonifer found that reduced-risk chemistries boscalid+pyraclostrobin and fludioxonil significantly reduced R. stolonifer development and performed similarly to dicloran. Pseudomonas syringae based products were moderately effective although results were extremely variable among tests. Generally recognized as safe treatments were ineffective by testing methods used.