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Target spot, caused by Corynespora cassiicola, is a common lower canopy soybean disease in the southern United States. Recently, target spot has resurged in importance especially following the identification of resistance to the quinone outside inhibitor (QoI) fungicides. As a result, a survey of C. cassiicola from soybean throughout Mississippi began in 2018. A total of 819 C. cassiicola monoconidial isolates were obtained from 228 fields in 75 counties. The molecular mechanism of QoI resistance was determined, resulting from an amino acid substitution from glycine (G) to alanine (A) at position 143, using a PCR-RFLP method and comparing nucleotide sequences of the cytochrome b gene. Five previously defined geographic regions were used to present the distribution of the G143A substitution and included the Capital, Coast, Delta, Hills, and Pines. The Capital had the greatest proportion of G143A-containing isolates (95.0%) followed by the Coast (92.9%), Delta (89.8%), Pines (78.8%), and Hills (69.4%). In all, 85.8% of the C. cassiicola isolates carried the G143A substitution. In addition, the effective fungicide concentration (EC50) of randomly selected C. cassiicola isolates to azoxystrobin was used to characterize isolates as resistant (n=14), based on presence of the G143A susbstitution and EC50 values > 52 μg/ml, or sensitive (n=11), based on absence of the G143A susbstitution and EC50 values < 46 μg/ml. The EC50 values varied among isolates (p < 0.0001) with QoI-sensitive isolates exhibiting lower EC50 values than QoI-resistant. The current study revealed that a reduction in sensitivity to QoI fungicides has likely resulted based on the percentage of C. cassiicola isolates containg the G143A substitution identified in Mississippi.

Quinone outside inhibitor (QoI) fungicides have been widely used to manage diseases of soybean including target spot caused by

The genus Gaeumannomyces (Magnaporthaceae, Magnaporthales, Sordariomycetes, Ascomycota) includes root-infecting pathogens, saprobes, and endophytes. Morphological, biological, and phylogenetic analyses were employed to identify fungal isolates derived from turfgrass roots colonized with ectotrophic, dark runner hyphae. Phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions and of the minichromosome maintenance complex 7 (MCM7), largest subunit of RNA polymerase II (RPB1), and translation elongation factor 1-alpha (TEF1) genes were obtained via maximum likelihood and Bayesian methods. Our isolates consistently formed a distinct and highly supported clade within Gaeumannomyces. Common and distinctive biological and morphological characters reinforced these findings. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davey), its native host, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, Gaeumannomyces nanograminis, associated with rotted roots of ultradwarf bermudagrass.

Target spot, caused by Corynespora cassiicola, is a foliar disease of soybean in the Midsouthern United States. Increased target spot incidence and severity have been observed across parts of Arkansas and Mississippi regularly since 2007. Because target spot resistant cultivars are not available to manage target spot, soybean farmers rely on fungicides to reduce the potential yield losses associated with the disease. In general, fungicides within the quinone outside inhibitor (QoI) class have been the most widely used products for target spot management. As a result of increased and more widespread target spot during the 2016 season, a brief study was conducted using C. cassiicola monoconidial isolates derived from infected leaf tissue from Arkansas (n = 2) and Mississippi (n = 56) soybean to determine whether isolates were resistant to the QoI fungicides. In all, 27 isolates, one from Arkansas and 26 from Mississippi, were determined to contain the G143A substitution that confers complete resistance to the QoI fungicides.

Taproot decline (TRD) is a disease of soybean that has been reported recently from the southern United States (U.S.). Symptoms of TRD include foliar interveinal chlorosis followed by necrosis. Darkened, charcoal-colored areas of thin stromatic tissue are evident on the taproot and lateral roots along with areas of necrosis within the root and white mycelia within the pith. Upright stromata typical of Xylaria can be observed on crop debris and emerging from infested roots in fields where taproot decline is present, but these have not been determined to contain fertile perithecia. Symptomatic plant material was collected across the known range of the disease in the southern U.S., and the causal agent was isolated from roots. Four loci, ⍺-actin (ACT), β-tubulin (TUB2), the nuclear rDNA internal transcribed spacers (nrITS), and the RNA polymerase subunit II (RPB2), were sequenced from representative isolates. Both maximum likelihood and Bayesian phylogenetic analyses showed consistent clustering of representative TRD isolates in a highly supported clade within the Xylaria arbuscula species complex in the "HY" clade of the family Xylariaceae, distinct from any previously described taxa. In order to understand the origin of this pathogen, we sequenced herbarium specimens previously determined to be "Xylaria arbuscula" based on morphology and xylariaceous endophytes collected in the southern U.S. Some historical specimens from U.S. herbaria collected in the southern region as saprophytes as well as a single specimen from Martinique clustered within the "TRD" clade in phylogenetic analyses, suggesting a possible shift in lifestyle. The remaining specimens that clustered within the family Xylariaceae, but outside of the "TRD" clade, are reported. Both morphological evidence and molecular evidence indicate that the TRD pathogen is a novel species, which is described as Xylaria necrophora.

Bermudagrass decline (BD) is a destructive root rot disease of hybrid bermudagrass putting greens in the southeastern United States. Previous studies reported a single ectotrophic root-infecting (ERI) fungus, Gaeumannomyces graminis, associated with BD. Recently, three novel ERI fungi, Gaeumannomyces sp., Magnaporthiopsis cynodontis, and Candidacolonium cynodontis, have also been associated with BD. Current diagnostic methods for identification can be inconclusive and inaccurate for distinguishing these ERI fungal species. Here, we present the development and application of novel real-time PCR assays designed to detect four selected ERI fungi associated with BD. The distribution of these ERI fungi in hybrid bermudagrass samples collected from putting greens and fairways throughout the southeastern United States was also assessed. In addition, we established a reliable and rapid protocol to simultaneously detect these selected fungi directly from bermudagrass root tissue. The limit of detection for each assay was as low as 1 pg/µl of DNA per reaction, proving the sensitivity of the method to detect low quantities of fungal DNA when present in bermudagrass roots. The presence of the selected ERI fungi was detected in 36 of 37 bermudagrass root samples, with one fungus having a wider distribution among the samples tested and two fungi with greater DNA quantities when compared with the bermudagrass roots. The novel assays provide a reliable method for accurate detection of the four selected ERI fungi. The acute sensitivity of each assay makes it a viable tool for early detection of ERI fungi in hybrid bermudagrass roots.

The genus Magnaporthiopsis of Magnaporthaceae (Magnaporthales, Sordariomycetes, Ascomycota) contains species that are predominantly necrotrophic pathogens, often producing simple hyphopodia and dark, ectotrophic runner hyphae on plant roots and stems during colonization. Fungal isolates from turfgrass roots with dark and ectotrophic runner hyphae were examined and identified based on morphological, biological, and phylogenetic analyses. Maximum likelihood and Bayesian methods were implemented to obtain phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions, and of the minichromosome maintenance complex 7 (MCM7), largest subunit of RNA polymerase II (RPB1), and translation elongation factor 1-alpha (TEF1) genes. Our isolates consistently formed a distinct and highly supported clade within Magnaporthiopsis. These findings were reinforced by common and distinctive biological and morphological characters. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass, one of its native hosts, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, Magnaporthiopsis cynodontis, which has widespread distribution in the United States.

The draft genome of Xylaria sp. isolate MSU_SB201401, causal agent of taproot decline of soybean in the southern U.S., is presented here. The genome assembly was 56.7 Mb in size with an L50 of 246. A total of 10,880 putative protein-encoding genes were predicted, including 647 genes encoding carbohydrate-active enzymes and 1053 genes encoding secreted proteins. This is the first draft genome of a plant-pathogenic Xylaria sp. associated with soybean. The draft genome of Xylaria sp. isolate MSU_SB201401 will provide an important resource for future experiments to determine the molecular basis of pathogenesis.

Preemergence herbicides generally have a negative effect on hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] establishment. However, little is known about the effect they have on root architecture and development. Research was conducted to determine the effects of commonly used preemergence herbicides on ‘Latitude 36’ hybrid bermudagrass root architecture and establishment. The experiment was conducted in a climate-controlled greenhouse maintained at 26 °C day/night temperature at Mississippi State University in Starkville, MS, from Apr. 2016 to June 2016 and repeated from July 2016 to Sept. 2016. Hybrid bermudagrass plugs (31.6 cm2) were planted in 126-cm2 pots (1120 cm3) and preemergence herbicide treatments were applied 1 d after planting at the recommended labeled rate for each herbicide. Preemergence herbicide treatments included atrazine, atrazine + S-metolachlor, dithiopyr, flumioxazin, indaziflam, liquid and granular applied oxadiazon, S-metolachlor, pendimethalin, prodiamine, and simazine. Treatments were arranged in a completely randomized design with four replications. Plugs treated with indaziflam and liquid applied oxadiazon failed to achieve 50% hybrid bermudagrass cover by the end of the experiment. Of the remaining herbicide treatments, all herbicides other than granular applied oxadiazon and atrazine increased the number of days required to reach 50% cover (Days50). In addition, all herbicide treatments reduced root mass when harvested 6 weeks after treatment (WAT) relative to the nontreated. By 10 WAT, all treatments reduced root mass in run 1, but during run 2, only prodiamine, pendimethalin, simazine, atrazine + S-metolachlor, liquid applied oxadiazon, and indaziflam reduced dry root mass compared with the nontreated. At 4 WAT, all treatments other than simazine and granular applied oxadiazon reduced root length when compared with the nontreated. By 10 WAT, only dithiopyr, S-metolachlor alone, and indaziflam reduced root length when compared with the nontreated. No differences were detected in the total amounts of nonstarch nonstructural carbohydrates (TNSC) within the roots in either run of the experiment. Results suggest that indaziflam, dithiopyr, and S-metolachlor are not safe on newly established hybrid bermudagrass and should be avoided during establishment. For all other treatments, hybrid bermudagrass roots were able to recover from initial herbicidal injury by 10 WAT; however, future research should evaluate tensile strength of treated sod.

Isolates of Cercospora sojina, causal agent of frogeye leaf spot of soybean (Glycine max), were collected across Alabama, Arkansas, Delaware, Illinois, Indiana, Iowa, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Ohio, Tennessee, and Virginia and were evaluated for quinone outside inhibitor (QoI) fungicide resistance. Collection of these isolates from these 14 states occurred between 2010 and 2017. QoI fungicide-resistant C. sojina isolates were detected in all 14 states surveyed and represent a total of 240 counties or parishes. In 2017, these 240 counties and parishes represented approximately 13% of the harvested soybean hectares in the United States. In light of this widespread occurrence of QoI fungicide-resistant C. sojina isolates, management of frogeye leaf spot should focus on integrated management practices such as planting resistant soybean cultivars, rotating with nonhost crops, and tilling to speed up decomposition of infested soybean residue. When foliar fungicide application is warranted, fungicide products that contain active ingredients from chemistry classes other than the QoI class should be applied for frogeye leaf spot management.

Shelf‐life and transplant success of sodded and sprigged turfgrasses are negatively affected by harvest and post‐harvest handling/storage conditions. Research was conducted to evaluate effects of several commercially available fungicides, a bio‐nutritional plant extract, and a commonly used plant growth regulator on sod shelf‐life and transplant success. Field studies were conducted in 2018 and 2019 on ‘Latitude 36’ hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy]. Treatments included: the experimental bio‐nutritional plant extract ACA‐3434; the fungicides fluxapyroxad + pyraclostrobin, fluopyram + trifloxystrobin, and azoxystrobin; and the plant growth regulator trinexapac‐ethyl. Sod was harvested, stacked to a height of 12 layers, and stored for 72 h; treated and untreated sod were stored at ambient field temperature (28 °C average). To evaluate storage refrigeration on sod establishment, an additional untreated check was stored at 4 °C refrigeration. Sod was installed on an adjacent prepared native soil, and the treatment effects on bermudagrass transplanting were measured visually, by spectral reflectance, and by root analysis. Research failed to simulate heating inside stored sod masses, and treatments failed to affect internal storage temperatures. Nevertheless, refrigeration and, in some cases, fluxapyroxad + pyraclostrobin application, increased plant health characteristics of transplanted sod. None of the treatments affected recovery of areas from which sod was harvested. Albeit often unrealistic, refrigeration of harvested sod may be the best practice to extend sod shelf‐life. When applied prior to harvest, fluxapyroxad + pyraclostrobin fungicides provided slight improvements in post‐installation sod health; however, little is known about the mechanism by which this occurs.

Take-all root rot has been reported as a destructive disease of St. Augustinegrass home lawns in Florida and Alabama (1). In June 1998 and 1999, St. Augustinegrass home lawns in central Mississippi developed chlorotic, thinning patches ranging from 0.5 to 4.5 m in diameter. By August of each summer, plants within affected patches were necrotic and dead. Roots of affected St. Augustinegrass were necrotic and shorter than those of unaffected plants; nodes on stolons were necrotic, and lesions developed on internodes. Ectotrophic runner hyphae and dark brown, lobed hyphopodia were visible on roots and aboveground plant parts, respectively. Symptomatic tissues collected from St. Augustinegrass home lawns were plated onto potato dextrose agar (PDA); the incitant of take-all root rot, Gaeumannomyces graminis(Sacc.) Arx & Olivier var. graminis, was isolated. Verification of G. graminis var. graminis was based on colony morphology and taxonomic identification consistent with the description by Walker (2). G. graminis var. graminis isolated from symptomatic St. Augustinegrass was grown on sterile tall fescue seed and incorporated into sterile sand/peat moss mix. Asymptomatic St. Augustinegrass sprigs were washed, and roots were removed prior to planting in infested and noninfested soil. Plants were cultured in the greenhouse for 60 days. St. Augustinegrass planted into noninfested soil was asymptomatic while plants collected from G. graminis var. graminis-infested soil were symptomatic for take-all root rot. Crowns and roots of affected plants were necrotic; leaves were chlorotic and necrotic. Both runner hyphae and lobed hyphopodia were visible. G. graminis var. graminis was reisolated from symptomatic tissues and confirmed as the incitant of take-all root rot. This is the first report of take-all root rot of St. Augustinegrass in Mississippi. References: (1) M. Elliott. Plant Dis. 77:206, 1993. (2) J. Walker. Trans. Br. Mycol. Soc. 58:427, 1972.

Over the past decade, a soybean root issue of unknown etiology has been observed across a widespread geography in the southern United States. Recently, pathologists began referring to the problem as taproot decline of soybean, based on the appearance of root symptoms. Taproot decline has been observed to cause foliar symptoms in vegetative and reproductive soybean plants ranging in maturity from V6 to R6. Symptom expression can appear similar to other notable root-associated diseases except that taproot decline exhibits a progression of symptom expression from subtle to severe interveinal chlorosis during the season. However, one distinct symptom associated with taproot decline is observed as darkened, black stroma on the taproot and, in some cases, the lateral roots of affected plants. Pathogenicity was confirmed by isolating the suspected fungus from naturally-infected soybean roots in multiple states and completing Koch’s postulates. The causal agent was identified, based on morphological characters and multilocus phylogenetic inference, as a member of the Xylaria arbuscula aggregate. At present, research projects are underway to address the role of the newly described disease and extent of the pathogen in the southern soybean production region in addition to developing integrated strategies for managing the disease.

Traditional hollow-tine (HT) aerification programs can cause substantial damage to the putting green surface resulting in prolonged recovery. Despite the growing interest in new and alternative aerification technology, there is a lack of information in the literature comparing new or alternative technology with traditional methods on ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis (Burtt-Davy)] putting greens. Therefore, the objective of this research was to determine the best combination of dry-injection (DI) cultivation technology with modified traditional HT aerification programs to achieve minimal surface disruption without a compromise in soil physical properties. Research was conducted at the Mississippi State University golf course practice putting green from 1 June to 31 Aug. 2014 and 2015. Treatments included two HT sizes (0.6 and 1.3 cm diameter), various DI cultivation frequencies applied with a DryJect 4800, and a noncultivated control. The HT 1.3 cm diameter tine size had 76% greater water infiltration (7.6 cm depth) compared with the DI + HT 0.6 cm diameter tine size treatment. However, DI + HT 0.6 cm diameter tine size had greater water infiltration at the 10.1 cm depth than the noncultivated control. Results suggest a need for an annual HT aerification event due to reduced water infiltration and increased volumetric water content (VWC) in the noncultivated control treatment. It can be concluded that DI would be best used in combination with HT 1.3 or 0.6 cm diameter tine sizes to improve soil physical properties; however, the DI + HT 0.6 cm diameter tine size treatment resulted in minimum surface disruption while still improving soil physical properties compared with the noncultivated control.

A novel species of Curvularia was identified as a foliar pathogen of Cynodon dactylon (bermudagrass) and Zoysia matrella (zoysiagrass), two important warm-season turfgrasses in the southeastern United States. Field symptoms were conspicuous chocolate brown to black spots in turf of both species on golf course putting greens and fairways. Leaves of plants within these spots exhibited prominent, black eyespot lesions from which a darkly pigmented fungus was consistently isolated. The fungus produced gray- to black-olivaceous mycelium within 10 d on potato dextrose agar at 25 C but never produced conidia despite numerous attempts to induce them. Field symptoms were reproduced in inoculated plants of both grasses, and re-isolation of the pathogen from symptomatic tissues confirmed its pathogenicity in fulfillment of Koch's postulates. A phylogenetic analysis was performed using sequence markers of internal nuclear ribosomal transcribed spacer region (ITS), glyceralde-hyde-3-phosphate dehydrogenase (GPD1) and translation elongation factor 1-α (TEF 1). The concatenated phylogenetic tree showed strong support for a new species within Curvularia that is distinctly divergent from other Curvularia spp. Therefore, the darkly pigmented pathogen of warm-season turfgrasses is described and illustrated as a new species, Curvularia malina.

Tomaso-Peterson, M., and Trevathan, L. E. 2007. Characterization of Rhizoctonia-like fungi isolated from agronomic crops and turfgrasses in Mississippi. Plant Dis. 91:260-265. Twenty-three isolates of Rhizoctonia spp. from agronomic crops and turfgrasses were characterized by cytological and pathological methods in order to establish the identity, pathogenicity, and virulence of Rhizoctonia spp. and anastomosis groups that occur on these hosts in Mississippi. Twelve isolates were identified as R. solani, including the five anastomosis groups (AGs) AG-1IB, AG-2-2, AG-4, AG-5, and AG-13. Rhizoctonia zeae, R. oryzae, and eight binucleate Rhizoctonia sp., including R. cerealis, also were identified. R. solani AG-4 isolates were consistently the most virulent isolates on all hosts in pathogenicity evaluations. Pathogenicity of AG-2-2 and AG-5 isolates, binucleate Rhizoctonia spp., and R. oryzae varied between hosts. Two AG-2-2 isolates from bermudagrass or wheat were determined to be clonal isolates, with numerous selfanastomosis reactions. R. solani (AG-1-IB) was pathogenic on all graminaceous hosts. R. cerealis produced sharp eyespot symptoms on wheat and corn and minimal symptoms on cotton and soybean. This is a first report of R. cerealis as a pathogen of corn. R. zeae isolates were pathogenic on all hosts, including cotton and soybean. These results indicate that a diverse group of Rhizoctonia spp. occurs as pathogens on a wide variety of agronomic crops and turfgrasses in Mississippi.

Spring dead spot (SDS) is the most destructive disease of bermudagrass (Cynodon dactylon (L.) Pers.). Symptoms of SDS appear in the spring when bermudagrass transitions out of winter dormancy. These symptoms include depressed, straw-colored patches that range from several centimeters to a meter in diameter. Infected roots and rhizomes are black, brittle, and necrotic. The disease is caused by three species of fungi: Ophiosphaerella herpotricha (Fr:Fr) J. Walker; O. korrae (J. Walker & A.M. Smith) Shoemaker & C.E. Babcock; or O. narmari (J. Walker & A.M. Smith) Wetzel, Hubert & Tisserat. However, O. korrae is the most prevalent causal organism of SDS in the southeastern United States and was the only species reported in Mississippi (1). In April of 2006, root samples were collected from a bermudagrass putting green in Booneville, MS with a high level of SDS incidence and severity. Symptomatic roots were collected and surface disinfested in 0.6% NaOCl and plated on one-quarter-strength potato dextrose agar (PDA) amended with streptomycin sulfate and chloramphenicol. Hyphae growing from the roots were transferred to full-strength PDA after 5 to 7 days. Mycelium from five pure-culture colonies plus an O. herpotricha control was harvested after 4 weeks of growth and the genomic DNA was extracted. The genomic DNA of the Booneville isolates and the O. herpotricha control were amplified by PCR using species-specific primers OHITS1 and OHITS2 for O. herpotricha (2). Amplification of a 454-bp fragment of DNA confirmed one of the five unknown isolates as O. herpotricha. The other four isolates were not identified. ‘Sahara’ bermudagrass (4 weeks old in 3.8 × 20 cm Cone-tainers containing a sand and soil mixture) was inoculated with the Booneville-O. herpotricha isolate and the O. herpotricha control. One gram of oat seed infested with O. herpotricha isolates was inserted 2 cm below the crowns in the root zone of bermudagrass plugs. The inoculated bermudagrass plants were incubated for 4 weeks in the greenhouse. A control consisting of noninfested sterile oats was included. Following incubation, black, necrotic roots were observed on the plants inoculated with both O. herpotricha isolates. No symptoms were observed on roots of noninfested plants. Symptomatic roots were disinfested and plated on one-quarter-strength PDA. Koch's postulates were completed after O. herpotricha was reisolated from roots of plants inoculated with both O. herpotricha isolates and confirmed by PCR as mentioned above. The identification of O. herpotricha as a causal organism of SDS in Mississippi clarifies the involvement of multiple causal agents in this state and broadens the geographic distribution of this root-rot species. References: (1) F. B. Iriarte et al. Plant Dis. 88:1341, 2004. (2) N. A. Tisserat et al. Phytopathology 84:478, 1994.

Colletotrichum cereale Manns, formerly C. graminicola (Ces.) G.W. Wils., is the causal agent of anthracnose foliar blight (AFB) of creeping bentgrass (Agrostis stolonifera L.) and other grass species (1). AFB is most prevalent on creeping bentgrass during summer heat stress (2). Symptoms of AFB progress from older to younger leaves with leaf tips becoming chlorotic and eventually developing complete leaf necrosis. Symptoms in turf stands appear as yellow-to-bronze, irregularly shaped patches often associated with a loss of turf density (2). When C. cereale is actively infecting the foliar tissue, appressoria can be observed microscopically in the leaf sheaths of creeping bentgrass. C. cereale colonizes the foliar tissue, producing abundant acervuli, where conidia and setae develop. Creeping bentgrass samples exhibiting symptoms of AFB were collected from West Point, MS and Birmingham, AL in July 2006. Symptomatic plants with signs of C. cereale were surface disinfested and plated onto one-quarter-strength potato dextrose agar (PDA). Monoconidial C. cereale isolates were grown on full-strength PDA for 21 days at 25°C under fluorescent lights. Single-celled conidia were mostly falcate, ranged from 13.1 to 25.6 μm long × 3.6 to 6.3 μm wide, and averaged 22.2 × 4.7 μm. Hyphal appressoria were irregularly shaped and heavily lobed, ranging from 5.6 to 16.1 μm long × 4 to 10.6 μm wide, and averaged 12.1 × 7.9 μm. In culture, setae were acicular, five to seven septate, thick walled, ranged from 74 to 213.5 μm long, and averaged 151.3 μm. The morphological characteristics of 44 AFB isolates were similar to those of C. cereale reported by Crouch et al. (1). Nucleotide sequences were generated for the internal transcribed spacer rDNA for isolates OO7-T42, OW15-H32, and 04-111 (GenBank Accession Nos. EU859957, EU859958, and EU859959). Maximum likelihood-based phylogenetic analyses of these sequences with authentic isolates of Colletotrichum species from grass hosts (2) indicated that all three isolates were C. cereale. ‘Penn A-1’ creeping bentgrass seedlings (10.16-cm pots) were inoculated with the C. cereale isolates OO7-T42, OW15-H32, or 04-111 by spraying a conidial suspension (1.5 × 105 conidia/ml) on plants until water droplets were evident within the canopy. An uninoculated control sprayed with distilled water only was used for comparison. Three replicates per C. cereale isolate were included simultaneously when performing Koch's postulates. The inoculated creeping bentgrass seedlings were placed in covered plastic boxes to maintain humidity and incubated under 12 h of fluorescent light with day/night temperatures at 35/28°C. After 4 days, the covers were removed and creeping bentgrass was maintained an additional 14 days until symptoms and signs were observed on the foliage. C. cereale was reisolated from inoculated creeping bentgrass exhibiting symptoms of AFB for all three isolates used. No acervuli, setae, or conidial masses were observed on uninoculated control plants. To our knowledge, this is the first report of C. cereale causing AFB on creeping bentgrass in Mississippi and Alabama. References: (1) J. A. Crouch et al. Phytopathology 96:46, 2006. (2) R. W. Smiley et al. Compendium of Turfgrass Diseases. The American Phytopathological Society, St. Paul, MN, 2005.

Turfgrass anthracnose, caused by Colletotrichum cereale (≡C. graminicola), has become a common disease of creeping bentgrass putting greens during the summer in Mississippi and Alabama over the last 15 years. Thiophanate-methyl is a single-site mode-of-action fungicide applied to control C. cereale. In vitro bioassays were performed to evaluate the sensitivity of 103 isolates to thiophanate-methyl concentrations ranging from 0.039 to 10 μg/ml. Eighty-three isolates were collected from creeping bentgrass in Mississippi and Alabama that had been exposed to thiophanate-methyl. An additional 20 isolates were included from nonexposed turfgrasses. Radial colony growth in amended media was relative to nonamended media for all in vitro bioassays. With thiophanate-methyl at 10 μg/ml, relative growth of exposed isolates ranged from 77.5 to 130.7% with a mean of 99.3% compared with nonexposed, baseline isolates that ranged from 0.0 to 48.7% with a mean of 20.4%. A representative sample of thiophanate-methyl-exposed and nonexposed isolates was used to determine the mechanism of resistance by comparing amino acid sequences of the β-tubulin 2 protein. All of the thiophanate-methyl-exposed isolates that were sequenced had a point mutation resulting in substitutions from glutamic acid to alanine at position 198 or from phenylalanine to tyrosine at position 200 of the β-tubulin 2 protein. These amino acid substitutions in C. cereale isolates from Mississippi and Alabama appear to confer resistance to thiophanate-methyl and differ from those reported previously for this pathogen.

‘Alamo’ switchgrass (Panicum virgatum L.) seedlings growing in a soilless mix exhibiting dark brown, irregular-shaped foliar lesions with black borders were submitted to the Mississippi State University Plant Disease Diagnostic Laboratory in the summer of 2009 from a local forest products company. Symptomatic tissues were plated onto water agar (WA) and incubated for 21 days on a laboratory bench top with a 12-h photoperiod at 22°C. An asexual, sporulating, dematiaceous hyphomycete identified as Bipolaris oryzae (Breda de Haan) Shoemaker was observed. Conidiophores were single, mostly straight, multiseptate, brown, and ranging from 138 to 306 × 7.7 to 15.3 μm and averaged 221.6 × 10.7 μm. Conidia were golden brown, multiseptate, ranging from 3 to 10 septa, straight to slightly curved to fusoid, wider midway, and tapering toward the terminal cells. Conidia measured 40.8 to 109.7 × 10.2 to 20.4 μm and averaged 75.8 × 13.8 μm. Morphological characteristics of B. oryzae were similar to those described by Drechsler (1) and Sivanesan (3). The internal transcribed spacer (ITS) region of ribosomal DNA from four pure culture colonies derived from single conidia was amplified by PCR using ITS1 and ITS4 primers. The resultant 572 bp was sequenced for isolates 86 through 89 (GenBank Accession Nos. GU222690–93). The sequences were 99% similar to the sequence of B. oryzae strain ATCC-MYA 3330 (GenBank No. FJ746665) isolated from P. virgatum. Pathogenicity of isolates 86 and 88 was confirmed by inoculating sterile potting mix with a fungal slurry. Sterile Alamo switchgrass seeds were sown into the infested soil in Magenta boxes and incubated for 6 weeks in a growth chamber with a 14-h photoperiod at 30°C. Leaf lesions and leaf blight were observed in seedling stands growing in B. oryzae-infested soil. Lesions were excised and plated onto WA. Sporulation of B. oryzae was observed on symptomatic tissue. In the interim, 300 nonsterilized Alamo switchgrass seeds of the same seed lot as the original symptomatic seedlings and originating from Oklahoma were plated onto WA (10 seed per plate). The seeds were incubated on the bench top as previously described. The experiment was repeated and B. oryzae colonized 1.4% of the total switchgrass seeds evaluated, indicating seed transmission and subsequent seedling infection as previously observed in the original seedlings. Leaf spot, caused by B. oryzae, was first reported as a new disease of switchgrass in North Dakota (2). In the summer of 2009, the authors observed leaf spot in four cultivars of switchgrass, including Alamo, growing in research plots in Webster County, MS. Twenty-two isolates of B. oryzae were recovered from diseased leaves of these switchgrass cultivars. To our knowledge, this is the first report of B. oryzae causing leaf spot of switchgrass in Mississippi, which broadens the natural distribution of this disease. References: (1) C. Drechlser. J. Agric. Res. 24:641, 1923. (2) J. M. Krupinsky et al. Can. J. Plant Pathol. 26:371, 2004. (3) A. Sivanesan. Mycol. Pap. 158:201, 1987.

Frogeye leaf spot, caused by Cercospora sojina Hara, is a foliar disease affecting soybean (Glycine max (L.) Merr.), often managed by applications of quinone outside inhibitor (QoI) fungicides. In 2013 and 2014, 634 C. sojina monoconidial isolates were collected from soybean fields throughout Mississippi. Initially, in vitro bioassays were performed to evaluate the sensitivity of 14 of 634 isolates plus a baseline. Resistant and sensitive isolates were characterized by determining the effective fungicide concentrations at which 50% of conidial germination was inhibited (EC50). The molecular mechanism of resistance was determined for all 634 isolates, using a PCR-RFLP method and comparing nucleotide sequences of the cytochrome b gene. The state of Mississippi was divided into five distinct geographical regions (the Hills, Delta, Pines, Capital, and Coast) based on estimates of total soybean hectares. The greatest proportion (16.7%) of QoI-sensitive isolates was collected in the Hills while the Coast had no QoI-sensitive isolates. QoI-sensitive isolates from the Pines, Capital, and Delta ranged from 1.6 to 7.0%. Results of this study determined that more than 93% of C. sojina isolates collected in Mississippi carried the G143A amino acid substitution, indicating a shift to a QoI-resistant population throughout Mississippi soybean fields.

The draft genome of Xylaria sp. isolate MSU_SB201401, causal agent of taproot decline of soybean in the southern U.S., is presented here. The genome assembly was 56.7 Mb in size with an L50 of 246. A total of 10,880 putative protein-encoding genes were predicted, including 647 genes encoding carbohydrate-active enzymes and 1053 genes encoding secreted proteins. This is the first draft genome of a plant-pathogenic Xylaria sp. associated with soybean. The draft genome of Xylaria sp. isolate MSU_SB201401 will provide an important resource for future experiments to determine the molecular basis of pathogenesis.

Dollar spot is one of the most common diseases of golf course turfgrass and numerous fungicide applications are often required to provide adequate control. Weather-based disease warning systems have been developed to more accurately time fungicide applications; however, they tend to be ineffective and are not currently in widespread use. The primary objective of this research was to develop a new weather-based disease warning system to more accurately advise fungicide applications to control dollar spot activity across a broad geographic and climactic range. The new dollar spot warning system was developed from data collected at field sites in Madison, WI and Stillwater, OK in 2008 and warning system validation sites were established in Madison, WI, Stillwater, OK, Knoxville, TN, State College, PA, Starkville, MS, and Storrs, CT between 2011 and 2016. A meta-analysis of all site-years was conducted and the most effective warning system for dollar spot development consisted of a five-day moving average of relative humidity and average daily temperature. Using this model the highest effective probability that provided dollar spot control similar to that of a calendar-based program across the numerous sites and years was 20%. Additional analysis found that the 20% spray threshold provided comparable control to the calendar-based program while reducing fungicide usage by up to 30%, though further refinement may be needed as practitioners implement this warning system in a range of environments not tested here. The weather-based dollar spot warning system presented here will likely become an important tool for implementing precision disease management strategies for future turfgrass managers, especially as financial and regulatory pressures increase the need to reduce pesticide usage on golf course turfgrass.

Regalia®, a commercial extract of giant knotweed [Fallopia sachalinensis F. Schmidt (synonyms: Reynoutria sachalinensis (F. Schmidt) Nakai, Polygonum sachalinense F. Schmidt, Tiniaria sachalinesis (F. Schmidt) Janch.)], was evaluated for its potential to enhance drought tolerance of container-grown impatiens (Impatiens walleriana Hook. f. ‘Super Elfin XP White’). In two separate experiments, Regalia® was foliar-applied once a week for 4 weeks at four different rates (0, 5, 10, or 15 mL·L−1). In Expt. 1, Regalia® was applied to impatiens grown under three target substrate volumetric water contents (TVWCs): 85%, 55%, or 25%. In Expt. 2, Regalia® was applied to impatiens watered with 1, 3, or 6 days between waterings (DBW). In Expt. 1, root dry weight (RDW) of impatiens receiving applications of Regalia® at the 0.5× rate was greater compared with the 0.0× rate across all TVWCs. Additionally, soluble protein content was greater after Regalia® application at the 0.5×, 1.0×, or 1.5× rates compared with the 0.0× rate for plants grown at 55% TVWC. In Expt. 2, leaf greenness (SPAD) and leaf net photosynthetic rate (Pn) were greater with Regalia® applied at the 0.5× and 1.0× rates compared with the 0.0× rate, respectively. Soluble protein content was greater in impatiens treated with Regalia® at the 1.5× rate and 1 DBW and the 0.5× rate with 3 DBW compared with the 0.0× rate with 1 or 3 DBW. However, there was no indication that impatiens grown under different moisture levels had increased drought tolerance after application of Regalia®.

Taxonomy Eukaryota; Fungi; Dikarya; Ascomycota; Pezizomycotina; Sordariomycetes; Hypocreomycetidae; Glomerellales; Glomerellaceae; Mitosporic Glomerellaceae; Colletotrichum; Colletotrichum eremochloae J.A. Crouch & Tomaso-Peterson. C. eremochloae was recently described based on DNA sequence data of modern cultures and archival fungarium specimens. The identification of C. eremochloae sp. nov., a pathogen of centipedegrass, was made based on phylogenetic evidence from four sequence markers, Apn2, Apn2/Mat1, Sod2, and ITS (1). C. eremochloae is closely related to C. sublineola, the pathogen of sorghum [Sorghum halapense (L.) Pers] and johnsongrass (S. vulgaris Pers.), but genealogical concordance supported their distinction as phylogenetic species (1). Currently, centipedegrass is the only host from which C. eremochloae has been isolated and confirmed as a pathogen. No teleomorph of C. eremochloae has been identified.

Turfgrass anthracnose, caused by Colletotrichum cereale (≡C. graminicola), has become a common disease of creeping bentgrass and annual bluegrass putting greens throughout the southern United States. Strobilurin (QoI) fungicides such as azoxystrobin are single-site mode-of-action fungicides applied to control C. cereale. In vitro bioassays with azoxystrobin at 0.031 and 8 μg/ml incorporated into agar were performed to evaluate the sensitivity of 175 isolates collected from symptomatic turfgrasses in Alabama, Mississippi, North Carolina, Tennessee, and Virginia. Three sensitivity levels were identified among C. cereale isolates. Resistant, intermediately resistant, and sensitive isolates were characterized by percent relative growth based on the controls with means of 81, 23, and 4%, respectively, on media containing azoxystrobin at 8 μg/ml. The molecular mechanism of resistance was determined by comparing amino acid sequences of the cytochrome b protein. Compared with sensitive isolates, C. cereale isolates exhibiting QoI resistance had a G143A substitution, whereas isolates expressing intermediate resistance had a F129L substitution. C. cereale isolates displaying azoxystrobin resistance in vitro were not controlled by QoI fungicides in a field evaluation. The dominance of QoI-resistant C. cereale isolates identified in this study indicates a shift to resistant populations on highly managed golf course putting greens.

Isolation frequency of Ophiosphaerella korrae (spring dead spot pathogen) from Cynodon dactylon (bermudagrass) roots at a golf course near West Point, Mississippi, was monitored over a 3-year investigation. Laboratory and greenhouse experiments were conducted to determine optimal temperatures for the growth of selected O. korrae isolates collected from the field study and to evaluate those isolates for pathogenicity potential. Isolation frequencies of the pathogen from naturally infested root samples were significantly higher in the winter and spring and lowest in the fall regardless of cultural, nutrient, and chemical treatments. Annual soil temperatures ranged between 8 and 29 degrees C, and no correlation was observed between temperature and percent isolation of O. korrae. Optimal in vitro growth of selected O. korrae isolates ranged from 21 to 25 degrees C. Root discoloration was significantly greater in the presence of O. korrae compared to non-inoculated roots in greenhouse studies. Results of this study confirm and are the first to document that O. korrae naturally infests roots throughout the bermudagrass growth cycle, but factors other than temperature and management practices may influence O. korrae in situ.

A study was conducted in Mississippi from 1995 to 1997 comparing soil rhizosphere fungi isolated from Pioneer 3167 hybrid maize (Zea mays L.) planted on Brooksville silty clay and Memphis silt loam soils. Maize seedlings were collected over four sampling dates from conventional and no-tillage plots. Eleven fungal genera consisting of nineteen species were isolated from these plants; Trichoderma spp. were most frequently isolated, followed by Fusarium spp. The highest disease incidence occurred in tilled plots of the latest planting date on Brooksville silty clay when samples were collected 17 days after planting. Root disease was most severe in 1996 from seedlings planted on the last planting date in tilled plots sampled 17 days after planting. Yields were significantly (P ≤ 0.05) higher on Brooksville silty clay soil than on Memphis silt loam in both 1995 and 1996. Yields were highest from no-tillage plots and from maize planted on the earliest date. There was a significant correlation between incidence of root infection and disease severity. There was no correlation between the incidence of root infection and yield or between disease severity and yield at either location.

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a popular southern turfgrass with poor cold tolerance. The objective of this study was to evaluate the inheritance of cold tolerance in St. Augustinegrass. Eight diploid genotypes were chosen as parents for a complete diallel mating with reciprocals. Three replications of each single cross and the parents were planted in a field trial at Mississippi State, MS, and winter survival was evaluated from 1994 to 1996. Differential thermal analysis was used to predict lethal low temperatures for parents and single cross progenies. Lethal temperatures of parental genotypes ranged from -3.65 to -5.25°C. Combining ability analysis revealed that general combining ability was the largest source of variation for lethal temperature and winter survival. Specific combining ability was significant only for winter survival in 1996. Redprocal effects were significant for winter survival each year. Estimated narrow sense heritability was 0.58 for lethal temperature and ranged from 0.70 to 0.98 for winter survival. Lethal temperatures were significantly correlated to winter survival of each year.

Colletotrichum is a cosmopolitan, anamorphic fungal genus responsible for anthracnose disease in hundreds of plant species worldwide, including members of the Poaceae. Anthracnose disease of the widely planted, non-native, warm-season lawn grass, Eremochloae ophiuroides (centipedegrass), is commonly encountered in the southern United States, but the causal agent has never been identified. We use DNA sequence data from modern cultures and archival fungarium specimens in this study to determine the identity of the fungus responsible for centipedegrass anthracnose disease and provide experimental confirmation of pathogenicity. C. eremochloae sp. nov., a pathogen of centipedegrass, is proposed based on phylogenetic evidence from four sequence markers (Apn2, Apn2/ Mat1, Sod2, ITS). C. eremochloae isolates from centipedegrass shared common morphology and phenotype with C. sublineola, a destructive pathogen of cultivated sorghum and Johnsongrass weeds (Sorghum halepense, S. vulgaris). Molecular phylogenetic analysis identified C. eremochloae and C. sublineola as closely related sister taxa, but genealogical concordance supported their distinction as unique phylogenetic species. Fixed nucleotide differences between C. eremochloae and C. sublineola were observed from collections of these fungi spanning 105 y, including the 1904 lectotype specimen of C. sublineola. C. eremochloae was identified from a fungarium specimen of centipedegrass intercepted at a USA port from a 1923 Chinese shipment; the multilocus sequence from this specimen was identical to modern samples of the fungus. Thus, it appears that the fungus might have migrated to the USA around the same time that centipedegrass first was introduced to the USA in 1916 from China, where the grass is indigenous. The new species C. eremochloae is described and illustrated, along with a description and discussion of C. sublineola based on the lectotype and newly designated epitype.

Nine new tetranorditerpenoid dilactones (2-10), together with two previously reported norditerpenoids dilactones (1, 11), and two known putative biosynthetic intermediates, oidiolactone-E (12) and 13, were isolated from an ethyl acetate extract of a culture medium of Sclerotinia homoeocarpa. Structures and absolute configurations of these compounds were determined by spectroscopic methods and confirmed by X-ray crystallographic analysis of representative compounds. Compounds were evaluated for herbicidal, antiplasmodial, and cytotoxic activities. Compounds 1, 2, 6, 7, and 11 were more active as growth inhibitors in a duckweed bioassay (I(50) values of 0.39-0.95 microM) than more than half of 26 commercial herbicides previously evaluated using the same bioassay. Some of these compounds exhibited strong antiplasmodial activities as well, but they also had cytotoxic activity, thus precluding them as potential antimalarial agents.

Spring dead spot is a destructive disease of bermudagrass turf in climates where the host is exposed to freezing temperatures during winter dormancy. The disease is the result of a complex interaction between a dormant host plant, fungal pathogens in the genus Ophiosphaerella, and environmental conditions. Although progress has been made in our understanding of the individual factors that determine spring dead spot development, we must begin to understand how factors interact to influence the disease. This knowledge will facilitate the development of effective and integrated management plans for spring dead spot in bermudagrass turf. Accepted for publication 8 May 2009. Published 10 July 2009.

(...) This study evaluated a new in vitro cell selection technique [Host-Pathogen Interaction System (HPIS)] that exposes calli to a pathogen without physical contact between the organisms. The material components that make up the HPIS are a double-sided petri dish (Lutri-plate ® ), a polycarbonate Nucleopore ® membrane, caulking cord, and the appropriate agar media. Callus of «Penncross» creeping bentgrass (Agrostis palustris Huds.) and two isolates of Rhizoctonia solani Kuhn. (RVPI and RATCC) were used in evaluating the HPIS (...)