Browsing by Subject "Fusarium virguliforme"

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    Distribution and Traits of the Fungal Pathogen Fusarium virguliforme that Influence Spread and Survival in Minnesota
    (2021-08) Hall, Rebecca
    Fusarium virguliforme is an invasive fungal pathogen responsible for soybean sudden death syndrome (SDS) and root rot of other legumes. Despite a previous study that suggested the pathogen would not survive in Minnesota due to winter cold stress, the pathogen was found in southern Minnesota in 2002 and has continued to spread throughout the state since its discovery. While much has been learned about the SDS pathogen in the United States, more work is needed to better understand the distribution of F. virguliforme in soybean and other crop fields and the strategies the pathogen uses to survive and spread in northern climates. This thesis includes studies of key traits that may aid in the survival of F. virguliforme, including 1) the asymptomatic and symptomatic host range of this fungus in a field setting, 2) the cold temperature limits of the pathogen’s survival, and 3) the unique nutrient use profiles of F. virguliforme. This work sought to expand our knowledge of the distribution of the pathogen within Minnesota. A distribution study in soybean fields was conducted in 2018 and 2019 based on SDS symptoms and the use of a specific qPCR assay. SDS and F. virguliforme were confirmed for the first time in Rice, Isanti, and Stevens counties; and the pathogen was confirmed for the first time in Clay, Douglas, Hubbard, and Pope counties. Cold temperature limits of the pathogen that may influence the spread and survival of F. virguliforme in Minnesota’s current and future climate were explored. It was determined that the pathogen can survive to temperatures of -40°C and thus survival is not likely limited by cold temperatures in Minnesota. The host range of the pathogen was studied to define which plant species may be vulnerable to disease development and potentially help the survival of F. virguliforme. Eleven species of dry edible beans, native legumes, prairie grasses, and prairie flowers common in the Midwestern United States were selected for field and greenhouse studies. It was determined that black bean, pinto bean, kidney bean, and pea are symptomatic hosts, whereas alfalfa, showy tick trefoil, black-eyed Susan, Indiangrass, partridge pea, and white clover are asymptomatic hosts. Lastly, the nutrients that support the growth of F. virguliforme, as well as the relative nutrient preferences and competitive abilities of F. virguliforme compared to other fungal and oomycete species commonly found in soil or soybean roots was explored within this thesis. The results suggest that F. virguliforme utilizes a larger number of carbon and nitrogen sources, both of which are potentially released from germinating seeds and crop residue and are strong stimulants of F. virguliforme growth. Additionally, it was determined that F. virguliforme is more competitive for these nutrients than the other species included in this study.
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    The host range of Fusarium virguliforme on rotational crops and common plant species and its survival and growth on crop residue.
    (2010-03) Kolander, Tammy Mae
    Sudden death syndrome (SDS), caused by Fusarium virguliforme (Fv), is an important soybean (Glycine max) disease. Crop rotation is not an effective management strategy, suggesting that the pathogen may survive long periods in the soil or may infect or be sustained on weeds or crops other than soybean. Minimal research has been conducted to understand Fv survival or its host range and ability to grow on different plants. The objectives of this thesis research were to determine the host range of Fv, the best methods for extracting Fv DNA from crop residue and macrocondia, and to determine how long Fv DNA can be detected on crop residue after burial in a field. Fifteen plant species were inoculated in a greenhouse to determine the host range of Fv. In at least one experiment, soybean, alfalfa (Medicago sativa), pinto bean and navy bean (Phaseolus vulgaris), white clover (Trifolium repens), red clover (T. pretense), pea (Pisum sativum), and Canadian milk vetch (Astragalus canadensis) developed foliar and/or root symptoms. In at least one experiment, corn (Zea mays), wheat (Triticum aestivum), ryegrass (Lolium perenne), pigweed (Amaranthus retroflexus), sugar beet (Beta vulgaris), lambsquarters (Chenopodium album), and canola (Brassica napus) appeared to be asymptomatic hosts for Fv. Thus, multiple plant species may be negatively affected by Fv and/or promote its survival and growth. Three commercial DNA extraction kits were compared to determine which would yield the greatest purity and quantity of Fv DNA from crop residue and macroconidia. The FastDNA® kit was generally most effective for extracting Fv DNA from crop residue and the MO BIO PowerSoil™ kit was superior for extracting Fv DNA from macroconidia. This knowledge was used to determine if Fv DNA can be detected on soybean, corn, alfalfa and wheat residue over time after placement in three crop fields and whether different inoculation methods influence the duration of detection. Soybean and corn tissue that was infected while growing retained detectable amounts of Fv DNA for at least 8 months after burial in the field. Dead tissues inoculated with Fv macroconidia typically did not retain quantifiable amounts of Fv DNA after burial. Results from this study suggest that the inoculation method is important for survival and detection of Fv DNA, and that Fv DNA remains detectable on crop residue from fall into the following summer.
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    Substrates from Soybean and Corn Influence Pathogenesis and Growth of Fusarium virguliforme
    (2014-04) Freed, Gretchen Marie
    Symptoms of sudden death syndrome of soybean (SDS), caused by Fusarium virguliforme, include root rot and leaf scorch symptoms The goal of this study was to understand the roles of inoculum rate, crop residues, and seed exudates on growth of F. virguliforme and the development of SDS. The first study was a greenhouse experiment to investigate the influence of inoculum rate and crop substrate on disease development using moderately resistant and susceptible soybean cultivars to SDS. Soybean seeds were planted in soil mix containing an inoculum at four rates (0, 101, 102, or 103 conidia/cc) and with one of seven crop residue substrate treatments (none, soybean seed, corn seed, sorghum seed, corn stalk, corn root, or soybean stem) incorporated into the soil mix. Root rot severity was assessed 15 and 50 days after inoculation (dai) and foliar disease severity and fresh biomass were assessed 50 dai. Root rot and foliar symptom severity were positively associated with the increase of inoculum rate, especially in cultivar MN1410 Plants grown with no added substrate exhibited very low to no disease severity. Disease severity was greater in the treatments with the soybean, corn, and sorghum seed substrates compared to the other treatments examined. Early root rot severity (15 dai) corresponded with the foliar disease severity for all treatments examined. In the second study, the influence of seed exudates on the growth of F. virguliforme was investigated. Seed exudates from four soybean cultivars, two moderately resistant and two susceptible to SDS, and one corn hybrid, which is an asymptomatic host, were collected at different time points during seed germination. These seed exudates were transferred to the wells of a 96-well plate along with macroconidia of one of four F. virguliforme isolates or one Fusarium solani isolate. Optical density values, used as an indication of fungal growth, were recorded after five days of incubation. Soybean seed exudates of the SDS moderately resistant cultivar MN1606, collected just prior to radicle emergence, triggered significantly (p<0.001) more fungal growth compared to all other exudates studied. Exudates from soybean cultivars susceptible to SDS did not promote greater growth of F. virguliforme than the moderately resistant cultivars tested. The effect of corn exudates on fungal growth was similar to the moderately resistant and susceptible soybean cultivars tested. Overall, these findings indicate that organic substrates from soybean and corn promote the growth of F. virguliforme, seedling root infection and the development of SDS in soybean.