During the summer of 2017, corn (Zea mays L.) in production areas throughout Louisiana exhibited symptoms similar to eyespot, caused by Kabatiella zeae (Narita & Y. Hirats). Symptoms included round to oval, light tan to light brown lesions (0.5 to 2.0-mm diameter) with reddish-brown margins often with chlorotic halos in the mid to upper canopy of corn at the brown silk stage. The disease was not severe enough to warrant management; however, it was a concern to corn producers. Symptomatic leaves were obtained from diseased corn, lesion margins were disinfested, and the suspected pathogen was isolated and tentatively identified as Curvularia lunata. Koch’s postulates were completed by inoculating V4 to V5 stage corn plants with a spore suspension and subjecting plants to a 16-h dew period at 25°C, observing symptomology, reisolating the pathogen, and identification via molecular analysis. To our knowledge this is the first report of the disease in Louisiana and the United States.

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Soybean (Glycine max) is a major economic crop in Tennessee. In August 2017, foliar interveinal chlorosis progressing to necrosis and root necrosis symptoms consistent with taproot decline, caused by Xylaria sp. (Allen et al., 2017), were observed in a production field of ‘Croplan 4886’ soybean cultivar (WinField Solutions, LLC) in Hardeman County, Tennessee. Characteristic stromata were observed in the field at the base of infected plants, with some produced on cotton debris from the previous season. Infected roots of 13 plants were collected, surface sterilized in the laboratory by rinsing in tap water for 10 minutes, immersed in 10% NaOCl for 1 minute, rinsed twice in sterile distilled water, split longitudinally, and plated on potato dextrose agar amended with 0.125 g/L streptomycin sulfate salt and 0.075 g/L chloramphenicol (PDA-CS) (Allen et al., 2017). Plates were incubated at 22°C on a 12-hr fluorescent light:dark cycle for 1-2 weeks. Based on colony morphology, two isolates were selected for subsequent analyses (DMCC2477 and DMCC2478). In order to fulfill Koch’s postulates, both isolates were used to inoculate the soybean cultivar Asgrow 4632 (Monsanto Co., St. Louis, MO). Inoculum was grown on sterilized soybean stems for one month prior to inoculation. Three treatment groups (non-treated check, sterilized soybean stems, and inoculated soybean stems) were included with four replicates each, where three plants per pot was a replicate. Six seeds were initially planted in 15-cm pots in potting mix (Pro-Mix BX, Premier Horticulture Inc., Canada) and weeded thinned to 3 plants after emergence. Plants were watered every 1-2 days, supplemented with fertilizer, and grown under supplemental lighting with a 16-hr light:8-hr dark cycle with temperatures ranging from 25-35°C in a greenhouse. Foliar symptoms including wilting and interveinal chlorosis followed by necrosis were observed 3-4 weeks after inoculation on the majority of inoculated plants. No symptoms were observed on plants treated with sterilized soybean stems or non-treated plants. This experiment was repeated twice. DNA from original isolates, DMCC2477 and DMCC2478 was amplified with PCR using universal primers targeting four loci, ⍺-actin (ACT), nuclear ribosomal internal transcribed spacer (nrITS), RNA polymerase subunit II (RPB2), and β-tubulin (TUB2). DNA sequences were obtained with Sanger sequencing and deposited in GenBank (nrITS: MH046898, MH046900; ACT: MH113624, MH113625; RPB2: MH113626, MH113627; TUB2: MH113628, MH113629). Roots from symptomatic inoculated plants that had mycelial growth in the pith after 3-4 weeks were used to obtain pure cultures as described above and these were sequenced for the nrITS region to confirm presence of the fungus (GenBank accession numbers: MH046899, MH046901). Alignment of sequences of each loci with published sequences of taxa in the family Xylariaceae (Hsieh et al., 2010; U’ren et al., 2016) revealed both isolates DMCC2477 and DMCC2478 (and re-isolations) were in the Xylaria arbuscula aggregate and were conspecific with the first isolate identified as the causal pathogen of taproot decline, MSU_SB201401 (Allen et al., 2017) (Figure 1). To our knowledge, this is the first report of taproot decline in Tennessee, an emerging disease previously reported in Alabama, Arkansas, Louisiana, Mississippi, and Missouri (Allen et al., 2017). This disease has been shown to be economically significant to soybean production, threatening the ~1.64 M acres planted annually in Tennessee (USDA, 2015-2019). Education and monitoring efforts should be provided to Tennessee producers regarding the detection of this disease and management options.

Taproot decline (TRD) of soybean [Glycine max (L) Merr.] is an emerging disease caused by Xylaria necrophora, and currently observed in the southern United States. X. necrophora infects soybean roots, causing necrosis and foliar interveinal chlorosis followed by necrosis. The most recent estimates of yield losses associated with this disease (0.57 - 1.18 million bushels) highlight its potential to become a major problem for producers in the region. The mechanism by which X. necrophora affects soybean remains unknown, but a plausible explanation is that phytotoxic secondary metabolites (SMs) are produced by X. necrophora in the roots. To test this hypothesis, cell-free culture filtrates (CFCFs) from three X. necrophora strains and one putative Colletotrichum siamense were used to challenge soybean stem cuttings to determine if foliar symptoms of TRD are caused by SMs, tolerance to SMs among potentially resistant soybean cultivars identified in greenhouse and field experiments, and specificity of SMs across plant species (cotton, peanut, tomato, and soybean). Measurements of chlorophyll content and root length were obtained at 7 and 14 days of exposure (DOE). Lower chlorophyll content and shorter roots were observed on all soybean cultivars treated with CFCFs of pathogenic isolates and no effects on other plant species were observed, suggesting X. necrophora produces SMs that are detrimental to soybean exclusively and resistance upon direct exposure to SMs does not exist. These results suggest soybean-specific SMs are produced by X. necrophora in the roots causing the interveinal chlorosis and subsequent necrosis observed on plants affected by TRD.

Mammaliicoccus sciuri (previously Staphylococcus sciuri ) is a frequent colonizer of mammals. We report the draft genomes of a methicillin-resistant strain (2254A) isolated from an armadillo and a methicillin-susceptible strain (6942A) from a cow. Genomes were sequenced using long-read Nanopore sequencing.