Browsing by Subject "fungus"

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    Factors Controlling the Decomposition of Ectomycorrhizal Fungal Tissue and the Formation of Soil Organic Matter
    (2019-06) Ryan, Maeve Elizabeth
    The turnover of ectomycorrhizal (ECM) fungi accounts for up to half of the organic carbon found in forest soils and therefore represents an important pathway for the removal of carbon from the atmosphere to be stored belowground as long-lived soil organic matter (SOM). Understanding the flux of fungal necromass inputs to SOM, and their subsequent stabilization potential in forest soils, requires an understanding of the chemical changes that occur during the degradation of fungal tissue. Additionally, it is hypothesized that degradation of fungal necromass is slowed by high melanin content and accelerated by high nitrogen content. A field degradation study was carried out at the Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota. Necromass from four species of ECM fungi with varying degrees of melanization was buried in litter bags in a Pinus-dominated forest below the soil litter layer, allowed to degrade naturally, and harvested nine times over a period of 90 days. Harvest was more frequent during the first week to gain insight into the dynamic early decomposition period. Elemental analysis (EA), Fourier-transform infrared spectroscopy (FTIR), and thermochemolysis-gas chromatography-mass spectrometry (pyGCMS), including novel methods of quantifying the contribution from various types of biopolymers to the total remaining tissue, supplement mass loss data to provide an overview of the chemical changes that occur as fungal necromass decomposes. Each of the four species lost a significant amount of mass in the first seven days of incubation but, at the end of the three-month degradation sequence, a significant fraction of fungal necromass remained. This necromass was chemically distinct from undegraded necromass, containing more aromatic compounds, suggesting that the relative abundance of melanin, which is highly aromatic, increased as other cellular components degraded away. Although melanin content was hypothesized to slow degradation, a high-melanin species degraded at effectively the same rate as the two low-melanin species. Differences in degradation rates across species can be attributed to initial nitrogen content, while melanin content could explain differences in degradation rate within a species.
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    A new and effective method to induce infection of Phyllachora maydis into corn for tar spot studies in controlled environments
    (Plant Methods, 2023) Solórzano, José E.; Issendorf, Shea E.; Drott, Milton T.; Check, Jill C.; Roggenkamp, Emily M.; Cruz, C. D.; Kleczewski, Nathan M.; Gongóra-Canul, Carlos C.; Malvick, Dean K.
    Background Tar spot of corn is a significant and spreading disease in the continental U.S. and Canada caused by the obligate biotrophic fungus Phyllachora maydis. As of 2023, tar spot had been reported in 18 U.S. states and one Canadian Province. The symptoms of tar spot include chlorotic flecking followed by the formation of black stromata where conidia and ascospores are produced. Advancements in research and management for tar spot have been limited by a need for a reliable method to inoculate plants to enable the study of the disease. The goal of this study was to develop a reliable method to induce tar spot in controlled conditions. Results We induced infection of corn by P. maydis in 100% of inoculated plants with a new inoculation method. This method includes the use of vacuum-collection tools to extract ascospores from field-infected corn leaves, application of spores to leaves, and induction of the disease in the dark at high humidity and moderate temperatures. Infection and disease development were consistently achieved in four independent experiments on different corn hybrids and under different environmental conditions in a greenhouse and growth chamber. Disease induction was impacted by the source and storage conditions of spores, as tar spot was not induced with ascospores from leaves stored dry at 25 degrees C for 5 months but was induced using ascospores from infected leaves stored at -20 degrees C for 5 months. The time from inoculation to stromata formation was 10 to 12 days and ascospores were present 19 days after inoculation throughout our experiments. In addition to providing techniques that enable in-vitro experimentation, our research also provides fundamental insights into the conditions that favor tar spot epidemics. Conclusions We developed a method to reliably inoculate corn with P. maydis. The method was validated by multiple independent experiments in which infection was induced in 100% of the plants, demonstrating its consistency in controlled conditions. This new method facilitates research on tar spot and provides opportunities to study the biology of P. maydis, the epidemiology of tar spot, and for identifying host resistance.