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Tar spot of corn is an emerging plant disease in the continental United States and Canada caused by the fungal pathogen Phyllachora maydis Maubl. Tar spot has been known to occur in Mexico, the Caribbean, and Central and South America since the early to mid-1900s. In 2015, it was reported for the first time in the continental United States. Since that time, tar spot has spread across corn-producing areas in the United States with epidemics as recent as 2021 resulting in significant yield losses. Although tar spot has been known to affect corn for over a century in the Americas, the biology of the pathogen, etiology, and epidemiology of the disease are not well understood. Additionally, symptoms and signs of tar spot resemble other foliar diseases and abiotic disorders of corn, which may lead to misdiagnosis. In this paper, we provide a brief description of current knowledge about tar spot of corn, including pathogen taxonomy, host range, symptoms and signs, specimen storage, pathogenicity testing, diagnostic protocols, and geographic distribution. This information will be useful to diagnosticians, researchers, and other professionals working with this disease.

The aggregation of gold nanoparticles (AuNPs) is known to induce an enhancement of localized surface plasmon resonance due to the coupling of plasmonic fields of adjacent nanoparticles. Here we show that AuNPs aggregation also causes a significant enhancement of chemiluminescence in the presence of luminophores. The phenomenon is used to introduce a rapid and sensitive DNA detection method that does not require amplification. DNA probes conjugated to AuNPs were used to detect a DNA target sequence specific to the fungus Ceratocystis fagacearum, causal agent of oak wilt. The hybridization of the DNA target with the DNA probes results in instantaneous aggregation of AuNPs into nanoballs, leading to a significant enhancement of luminol chemiluminescence. The enhancement reveals a linear correlation (R2 = 0.98) to the target DNA concentration, with a limit of detection down to 260 fM (260 × 10−15 M), two orders of magnitude higher than the performance obtained with plasmonic colorimetry and absorption spectrometry of single gold nanoparticles. Furthermore, the detection can be performed within 22 min using only a portable luminometer.

Naturally-occurring disease-suppressive soils provide control of plant pathogens via the activities of indigenous microbes. While all soils contain antagonistic microbes, there is little systematic understanding of the correlates of variation in indigenous antagonist populations and on their relationships with plant diseases. We characterized the population densities, inhibitory capacities, and phylogenetic composition of soil streptomycete communities in a potato field over time in relation to edaphic factors, antagonist inoculation, and potato common scab severities. Antagonistic Streptomyces populations were highly variable in time and space. Similarly, metagenomic analyses of streptomycete communities showed extensive spatial and temporal variation in composition. Soil characteristics (pH, potassium, organic matter, nitrate, and phosphorous) sometimes explained up to 50% of the spatial variation in Streptomyces population densities, proportion of inhibitory isolates, or pathogen suppressive capacity among locations in the field. Soil pH was positively correlated with common scab severity, and negatively correlated with the proportion of pathogen-inhibitory Streptomyces among locations in the field. This suggests that high pH may have direct beneficial effects on pathogen populations and disease development, and/or indirect effects on pathogen populations via reductions in pathogen-inhibitory Streptomyces populations. Mean pathogen suppressive capacity of antagonistic Streptomyces was negatively correlated with common scab disease. Streptomyces inoculants had no discernible effect on streptomycete community composition, antagonistic capacities, or potato common scab severities, likely reflecting poor colonization of inoculants. Further understanding of the relationships between indigenous antagonist populations and plant diseases will be important to harnessing the potential of indigenous communities to contribute to sustainable disease management.

Background and aims Plant impacts on soil microbial community composition and function are believed to be important but remain poorly understood. We looked at thebacterialcommunityeffectsofgrowingtwodifferent plant species in soils with differing plant growth histories. Methods Big bluestem (Andropogon gerardii: Ag) and cereal rye (Secale cereale: Sc) plants were grown in six soils with different planting and management histories for 14 weeks in a greenhouse study. Both prior to planting and harvesting, soil was collected for analysis. Bacterial community DNA was extracted and analyzed via 454 pyrosequencing and soil edaphic characteristics were also measured. Results Significant shifts in composition were observed between pre-plant and post-plant bacterial communities in 23 of the 40 most abundant orders but only one order (Nitrospirales) differed significantly between the two plant species treatments (Ag vs. Sc). Compared to preplant communities, post-plant communities increased significantly in alpha diversity (within community) but exhibited an overall decrease in beta diversity (between community), indicating that soil communities became more similar after growth of either Ag or Sc. Soil pH was the strongest predictor of bacterial community ordination, followed by percent carbon, organic matter, phosphorous, nitrogen, and potassium. Conclusions Overall, the relative lack of significant differences between the soil bacterial communities of Ag- and Sc-planted soils suggests that potential plantspecies-specific effects are strongly modulated by growth conditions and edaphic soil characteristics.

A blocking primer set based on the technique described by Vestheim and Jarman (2008) was developed to reduce amplification of non-target plant DNA when conducting metagenomic studies on bacterial endophyte communities. Bacterial amplification efficiency was increased 300-fold compared to standard PCR in an Illumina-based study of Sorghastrum nutans leaves.

High densities of antagonistic Streptomyces are associated with plant disease suppression in many soils. Here we review use of inoculation and organic matter amendments for enriching antagonistic Streptomyces populations to reduce plant disease and note that effective and consistent disease suppression in response to management has been elusive. We argue that shifting the focus of research from short-term disease suppression to the population ecology and evolutionary biology of antagonistic Streptomyces in soil will enhance prospects for effective management. A framework is presented for considering the impacts of short- and long-term management on competitive and coevolutionary dynamics among Streptomyces populations in relation to disease suppression.

This review summarizes research concerning Antarctic fungi at the century-old historic huts of the Heroic Period of exploration in the Ross Dependency 1898–1917 and fungi in pristine terrestrial locations. The motivation of the research was initially to identify potential fungal causes of degradation of the historic huts and artifacts. The research was extended to study fungal presence at pristine sites for comparison purposes and to consider the role of fungi in the respective ecosystems. We employed classical microbiology for isolation of viable organisms, and culture-independent DNA analyses. The research provided baseline data on microbial biodiversity. Principal findings were that there is significant overlap of the yeasts and filamentous fungi isolated from the historic sites, soil, and historic-introduced materials (i.e., wood, foodstuffs) and isolated from environmental samples in pristine locations. Aerial spore monitoring confirmed that winter spore counts were high and, in some cases, similar to those found in summer. Microbial diversity varied between the three Ross Island historic sites, and one historic site showed noticeably higher diversity, which led to the conclusion that this is a variable that should not be generalized. Cultured fungi were cold active, and the broader scientific significance of this finding was that climate change (warming) may not adversely affect these fungal species unless they were out-competed by new arrivals or unfavorable changes in ecosystem domination occur.

Fungal abundance and diversity were studied from 245 soil samples collected in 18 distinct ice-free locations in Antarctica including areas in the McMurdo Dry Valleys, Ross Sea Region, and the Antarctic Peninsula. Cultivable fungal abundance in soil was found to be most positively correlated with percent carbon and nitrogen based on a Spearman’s rank correlation test of six soil parameters. Soil moisture and C/N ratio were also positively correlated with fungal abundance while pH and conductivity were negatively correlated. These results suggest that nutrient limitations in these highly oligotrophic environments are a primary factor in determining the distribution and abundance of indigenous fungi. Other effects of the extreme Antarctic environment likely affect fungi indirectly by limiting the distribution and abundance of plant-derived sources of carbon.

Throughout the history of polar exploration and up to recent times, wood and other exotic materials have been brought to the Antarctic continent and left there. While the possible transportation of exotic fungal species on these materials is sometimes considered, the effects of these exotic substrates on indigenous fungal communities have not been previously evaluated. This study reports results from seven plots where organic materials were used in baiting studies to determine the fungal diversity present in soils. Four plots were on islands in the Palmer Archipelago on the Antarctic Peninsula and three at Ross Island, Antarctica. Samples of sterile wood and cellulose with and without nutrients added were buried in soil and left for either two or four years before being removed and evaluated for fungal colonization. There was a significant increase in fungal colony-forming units (CFU) from soil in direct contact with introduced, sterile wood and cellulose substrates compared to background soil levels. The type of substrate, 2 or 4 year incubation period in the field, or nutrient addition did not have a significant effect on culturable densities in soil. Fungal abundance on soil adhering to substrates was found to be similar to that found in non-polar soils indicating that lack of organic material may be the most significant limiting factor affecting densities of Antarctic fungal populations. Based on a high degree of colonization, these exotic substrates appear to have a significant effect on indigenous soil fungal abundance.

The historic expedition huts located in the Ross Sea Region of the Antarctic and the thousands of artifacts left behind by the early explorers represent important cultural heritage from the "Heroic Era" of Polar exploration. The hut at Cape Royds built by Ernest Shackleton and members of the 1907-1908 British Antarctic Expedition has survived the extreme Antarctic environment for over 100 years, but recent studies have shown many forms of deterioration are causing serious problems, and microbial degradation is evident in the historic wood. Conservation work to reduce moisture at the hut required removal of fodder, wood, and many different types of organic materials from the stables area on the north side of the structure allowing large numbers of samples to be obtained for these investigations. In addition, wood from historic food storage boxes exposed in a ravine adjacent to the hut were also sampled. Fungi were cultured on several different media, and pure cultures were obtained and identified by sequencing of the internal transcribed spacer region of rDNA. From the 69 cultures of filamentous fungi obtained, the most predominant genera were Cadophora (44%) followed by Thielavia (17%) and Geomyces (15%). Other fungi found included Cladosporium, Chaetomium, and isolates identified as being in Pezizomycotina, Onygenales, Nectriaceae, and others. No filamentous basidiomycetes were found. Phylogenetic analyses of the Cadophora species showed great species diversity present revealing Cadophora malorum, Cadophora luteo-olivacea, Cadophora fastigiata, as well as Cadophora sp. 4E71-1, a C. malorum-like species, and Cadophora sp. 7R16-1, a C. fastigiata-like species. Scanning electron microscopy showed extensive decay was present in the wood samples with type 1 and type 2 forms of soft rot evident in pine and birch wood, respectively. Fungi causing decay in the historic wooden structures and artifacts are of great concern, and this investigation provides insight into the identity and species diversity of fungi found at the site. The historic woods and other organic materials at this site represent a large input of carbon into the Antarctic environment. This as well as nutrient additions from the nearby Adélie penguin (Pygoscelis adeliae) colony and favorable conditions for fungal growth at Cape Royds appear responsible for the significant fungal diversity, and where extensive decay is taking place in wood in contact with the ground.

Investigations of microbial diversity in Antarctic are important to begin to understand ecosystem functioning and decomposition processes. This study documents fungi at 9 historic sites on the Antarctic Peninsula collected from wooden structures, other organic materials, and soils during a joint National Science Foundation and British Antarctic Survey expedition in 2007. Many of these sites had wooden structures built by the British during the World War II Operation Tabarin, but others visited included the American “East Base” on Stonington Island and the Swedish hut on Snow Hill Island. Fungi were cultured on several different media and pure cultures were obtained and identified by DNA sequencing of the internal transcribed spacer region. Cadophora species previously found to attack historic wooden structures on Ross Island, Antarctica, were found at all but 1 location sampled in the Peninsula region. Fungi causing decay in the historic wooden structures and artifacts and those causing mold problems inside the structures are of great concern, and conservation efforts are urgently needed to help preserve these important polar heritage structures. The results presented also expand our knowledge on the identity of fungi present throughout the Antarctic Peninsula region and provide insights into the organisms responsible for decomposition and nutrient recycling.

To survive in Antarctica, early explorers of Antarctica's Heroic Age erected wooden buildings and brought in large quantities of supplies. The introduction of wood and other organic materials may have provided new nutrient sources for fungi that were indigenous to Antarctica or were brought in with the materials. From 30 samples taken fromDiscoveryHut, 156 filamentous fungi were isolated on selective media. Of these, 108 were screened for hydrolytic activity on carboxymethyl cellulose, of which 29 demonstrated activities. Endo-1, 4-β-glucanase activity was confirmed in the extracellular supernatant from seven isolates when grown at 4°C, and also when they were grown at 15°C.Cladosporium oxysporumandGeomycessp. were shown to grow on a variety of synthetic cellulose substrates and to use cellulose as a nutrient source at temperate and cold temperatures. The research findings from the present study demonstrate that Antarctic filamentous fungi isolated from a variety of substrates (wood, straw, and food stuffs) are capable of cellulose degradation and can grow well at low temperatures.

Microorganisms play a dominant role in Antarctic ecosystems, yet little is known about how fungal diversity differs at sites with considerable human activity as compared to those that are remote and relatively pristine. Ross Island, Antarctica is the site of three historic expedition huts left by early explorers to the South Pole, Robert F. Scott and Ernest Shackleton. The fungal diversity of these wooden structures and surrounding soils was investigated with traditional culturing methods as well as with molecular methodology including denaturing gradient gel electrophoresis (DGGE) using the internal transcribed spacer (ITS) regions of ribosomal DNA for identification. From historic wood and artifact samples and soils adjacent to the huts as well as soil samples obtained from the Lake Fryxell Basin, a remote Dry Valley location, and remote sites at Mt. Fleming and the Allan Hills, 71 fungal taxa were identified. The historic huts and associated artifacts have been colonized and degraded by fungi to various extents. The most frequently isolated fungal genera from the historic woods sampled include Cadophora, Cladosporium and Geomyces. Similar genera were found in soil samples collected near the huts. Sampling of soils from locations in the Transantarctic Mountains and Lake Fryxell Basin at considerable distances from the huts and with different soil conditions revealed Cryptococcus spp., Epicoccum nigrum and Cladosporium cladosporioides as the most common fungi present and Cadophora species less commonly isolated. DGGE revealed 28 taxa not detected by culturing including four taxa which possibly have not been previously described since they have less than 50% ITS sequence identity to any GenBank accessions. Fungi capable of causing degradation in the wood and artifacts associated with the expedition huts appear to be similar to those present in Antarctic soils, both near and at more remote locations. These species of fungi are likely indigenous to Antarctica and were apparently greatly influenced by the introduction of organic matter brought by early explorers. Considerable degradation has occurred in the wood and other materials by these fungi.

Explorers to Antarctica during the Heroic Era of exploration built three wooden huts on Ross Island, Antarctica in 1902, 1908 and 1911. The structures were used as bases of operation while their occupants participated in scientific endeavors and strived to reach the South Pole. The huts, and the thousands of artifacts in and around them, have survived in the Antarctic environment for 9–10 decades, but deterioration has taken place. The successful preservation of these important historic structures and materials requires information on the agents causing deterioration and factors that influence microbial growth. Temperature and relative humidity (RH) were monitored in the expedition huts for several years. During the austral summer months of December and January it was common for temperatures to rise above 0 ∘ C and RH to exceed 80%. Extensive fungal growth was observed on wood and artifacts within the Cape Evans hut, and fungi isolated were identified as species of Cladosporium , Penicillium , Cadophora , Geomyces and Hormonema . The factors that influence RH within the huts and methods to control moisture and arrest microbial growth are discussed.

Twenty yeast strains, representing a selection from a wider group of more than 60 isolates were isolated from cold environments worldwide (Antarctica, Iceland, Russia, USA, Italian and French Alps, Apennines). The strains were grouped based on their common morphological and physiological characteristics. A phylogeny based on D1/D2 ribosomal DNA sequences placed them in an intermediate position between Cryptococcus saitoi and Cryptococcus friedmannii; the ITS1 and ITS2 rDNA phylogeny demonstrated that these strains belong to two related but hitherto unknown species within the order Filobasidiales, albidus clade. These two novel species are described with the names Cryptococcus vaughanmartiniae (type strain DBVPG 4736T) and Cryptococcus onofrii (type strain DBVPG 5303T).

Fungi have contributed to Antarctic ecosystems for >200 million years as, from the fossil record, it has been shown that fungi were present in Antarctica since at least the Triassic Period. Fungi have been reported from a wide variety of soils and substrates in far-ranging geographical locations and diverse habitats in Antarctica; the first reports being from as early as the beginning of the twentieth century. In Antarctic studies, non-lichenized fungi have generally been considered separately from lichenized forms and the list of non-lichenized fungi reported from Antarctic regions (including the sub-Antarctic) is extensive at +1,000 species. Fungi are notorious contaminants especially around sites of human activity, and it is crucial to acknowledge the difficulty of discerning transient/introduced versus indigenous and endemic fungi, and to understand their respective contributions to terrestrial biodiversity. To identify fungi, rigorous decontamination procedures on substrates are used along with conventional culturing methodologies and molecular technologies. This chapter focuses mainly on studies concerning terrestrial non-lichenized fungi published since 1993 and highlights specific taxonomic groups that are most important to Antarctic soil ecosystems.

Investigations of microbial diversity in Antarctic are important to begin to understand ecosystem functioning and decomposition processes. This study documents fungi at 9 historic sites on the Antarctic Peninsula collected from wooden structures, other organic materials, and soils during a joint National Science Foundation and British Antarctic Survey expedition in 2007. Many of these sites had wooden structures built by the British during the World War II Operation Tabarin, but others visited included the American "East Base" on Stonington Island and the Swedish hut on Snow Hill Island. Fungi were cultured on several different media and pure cultures were obtained and identified by DNA sequencing of the internal transcribed spacer region. Cadophora species previously found to attack historic wooden structures on Ross Island, Antarctica, were found at all but 1 location sampled in the Peninsula region. Fungi causing decay in the historic wooden structures and artifacts and those causing mold problems inside the structures are of great concern, and conservation efforts are urgently needed to help preserve these important polar heritage structures. The results presented also expand our knowledge on the identity of fungi present throughout the Antarctic Peninsula region and provide insights into the organisms responsible for decomposition and nutrient recycling.

Early explorers of Antarctica's Heroic Era erected wooden buildings and brought large quantities of supplies to survive in Antarctica. The introduction of wood and other organic materials provided nutrient sources for fungi that were indigenous to Antarctica or were brought in with the materials and adapted to the harsh conditions. Seventy-two isolates of filamentous fungi were cultured on selective media from interior structural wood of the Cape Evans historic hut and 27 of these screened positive for the ability to degrade carboxymethyl cellulose (CMC). Four non-CMC-degrading isolates were added to a group of 14 CMC-degrading isolates for further study, and endo-1, 4-beta-glucanase activity was demonstrated in the extracellular supernatant from all of these 18 isolates when grown at 4 degrees C, and also when they were grown at 15 degrees C. Isolates of Penicillium roquefortii and Cadophora malorum showed preference for growth at 15 degrees C rather than 25 degrees C or 4 degrees C indicating psychrotrophic characteristics. These results demonstrate that cellulolytic filamentous fungi found in Antarctica are capable of growth at cold temperatures and possess the ability to produce extracellular endo-1, 4-beta-glucanase when cultured at cold and temperate temperatures.

Tar spot, caused by Phyllachora maydis Maubl., can be a significant disease of corn (Zea mays L.). Commercial corn hybrids with typical signs and symptoms of tar spot were observed and collected in fields from Fillmore and Winona Counties, Minnesota, in late September and early October 2019. The disease in Fillmore County appeared to be focused in one area of the field about 10 m in diameter with incidence estimated at 90% and severity on individual leaves at and above the ear ranging from 1 to 34%. The field in Winona County had leaves with a similar level of severity on field edges. Signs and symptoms on the epidermis of leaves in both fields consisted of small black, raised, circular stroma (0.5 to 4 mm), primarily on the upper surfaces of leaves. All lesions were assessed, and less than 3% of tar spots were associated with fisheye lesions or chlorotic halos. Microscopic examination of the stroma from both locations revealed asci and oval to ovoid, hyaline ascospores of characteristic size and appearance for P. maydis as described by Parbery (1967). Specifically, 40 randomly selected stroma were dissected from the Fillmore County sample, and ascospores within had an average length of 9.8 μm and width of 6.6 μm. Identity of the stroma from samples in both counties was further confirmed by DNA sequencing. Genomic DNA was extracted from stroma, and a portion of the RNA gene (491 bases) was amplified by PCR using ITS4/ITS5 or ITS1F/ITS4 primers (White et al. 1990). The sequence similarity using BLASTN for all samples was 96 to 100% for four accessions of P. maydis (NCBI GenBank accessions MG881846.1, MG881847.1, KU184459.1, and MK184990.1). Due to the biotrophic, obligate nature of P. maydis, Koch’s postulates were not conducted (Parbery 1967). This confirms for the first time that tar spot of corn caused by P. maydis occurs in Minnesota. These results document an increased distribution of tar spot in the United States since it was first found in 2015 (Ruhl et al. 2016), which includes at least two counties in Minnesota, where it could cause significant economic losses for corn producers.