Maria Tomaso-Peterson

Anthracnose disease of centipedegrass turf caused by Colletotrichum eremochloae, a new fungal species closely related to Colletotrichum sublineola.

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.

Fungal occurrence, disease incidence and severity, and yield of maize symptomatic for seedling disease in Mississippi

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.

Two Mutations in β-Tubulin 2 Gene Associated with Thiophanate-Methyl Resistance in Colletotrichum cereale Isolates from Creeping Bentgrass in Mississippi and Alabama

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.

Occurrence and Molecular Identification of Azoxystrobin-Resistant Colletotrichum cereale Isolates from Golf Course Putting Greens in the Southern United States

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.

Curvularia malina sp. nov. incites a new disease of warm-season turfgrasses in the southeastern United States

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.

Seasonal Variation in Frequency of Isolation of Ophiosphaerella korrae from Bermudagrass Roots in Mississippi and Pathogenicity and Optimal Growth of Selected Isolates

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°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°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.

Take-all root rot of St. Augustinegrass: first report in Mississippi.

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.

Preemergence Herbicide Effects on Hybrid Bermudagrass Root Architecture and Establishment

Determine the effects of commonly used PRE herbicides on hybrid bermudagrass root architecture and establishment. Introduction Hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) is commonly produced as sod in the southern US and other warm-season climates around the world. Preemergence herbicides are sometimes used to control annual weeds. However, these herbicides may negatively affect hybrid bermudagrass establishment from sprigs and/or sod. Preemergence Herbicide Effects on Hybrid Bermudagrass Root Architecture and Establishment Erick G. Begitschke, James D. McCurdy, Te-Ming (Paul) Tseng, T. Casey Barickman, Barry R. Stewart, Christian M. Baldwin, Michael P. Richard, and Maria Tomaso-Peterson Mississippi State University

Draft genome sequence of Xylaria sp., the causal agent of taproot decline of soybean in the southern 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.

Anthracnose of Centipedegrass Turf

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.