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Miscanthus × giganteus is a warm-season perennial grass, native to eastern Asia. Brought into the United States as a landscape plant, it is currently being considered as a potential biomass fuel crop. In August 2009, a newly established and a 2-year-old M. × giganteus field research trial near Lexington, KY were found to have 100% incidence of severe leaf blight. Brown, mosaic-like, coalesced necrotic lesions covered leaf blades and sheaths on every stand, ultimately killing some leaves and tillers. The disease was more destructive in the newly established trial where 4- to 5-month-old M. × giganteus tillers were killed. No fruiting bodies were found immediately on diseased leaves. However, surface-disinfested diseased leaf tissue produced a sooty black mass of conidia after 1 week following incubation in a petri dish moisture chamber at 25°C in the dark. Single conidia isolations were made on half-strength potato dextrose agar (HSPDA) amended with 25 mg/liter of rifamycin and incubated at 25°C. Morphological characteristics of the fungus fit those originally described for Pithomyces chartarum (Berk. & Curt.) M.B. Ellis (2). Colonies were fast growing on HSPDA, at first hyaline, then shortly punctiform, grayish black, up to 1-mm diameter, and then became confluent, producing several dark brown multicellular conidia on small peg-like denticles on branched conidiophores. Every detached conidium had a small piece of the denticle attached to its base. The conidia were echinulate, broadly ellipsoidal, pyriform, 18 to 29 × 11 to 18 μm, with three transverse septa, and a longitudinal septum constricted at the transverse septa. The identity of the fungus was confirmed by sequence analysis of the internal transcribed spacers (ITS) region of the nuclear ribosomal DNA. The 615-bp cloned and sequenced amplicon (Accession No. GU195649) was 99% identical to sequences from multiple isolates of Leptosphaerulina chartarum (anamorph Pithomyces chartarum) in the GenBank. Five potted M. × giganteus plants (45 days old) were spray inoculated with an aqueous conidial suspension (2 × 106 conidia/ml) and incubated in one tier of a two-tiered-growth chamber at 86 to 90% relative humidity. Initial incubation was in the dark at 26°C for 48 h, and thereafter at alternating 15 h of light (320 μmol) at 25°C and 9 h of darkness at 23°C. Control plants were sprayed with sterile water and incubated in the second tier of the same growth chamber. A week after inoculation, leaf blight developed on all inoculated plants, but not the controls. P. chartarum was reisolated from infected leaves 2 weeks after inoculation. To our knowledge, this is the first report of P. chartarum causing a disease on Miscanthus (3). The fungus is cosmopolitan, usually saprophytic, but can cause diseases on a wide range of plants as well as produce mycotoxins (3). It has been reported to cause a leaf spot of smooth bromegrass (Bromus inermis) in Nebraska (1) and a leaf blight of wheat (Triticum aestivum) in Hungary (4). The observed disease severity suggests P. chartarum could potentially limit M. × giganteus production as an ethanol feedstock. References: (1) C. Eken et al. Plant Dis. 90:108, 2006. (2) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey, England, 1971. (3) D. F. Farr et al. Fungal Databases, Systematic Mycology and Microbiology Laboratory. Online publication. ARS, USDA, 2010. (4) B. Tóth et al. J. Plant Pathol. 89:405, 2007.

Ascochyta blight (AB) of pulse crops (chickpea, field pea, and lentils) causes yield loss in Montana, where 1.2 million acres was planted to pulses in 2016. Pyraclostrobin and azoxystrobin, quinone outside inhibitor (QoI) fungicides, have been the choice of farmers for the management of AB in pulses. However, a G143A mutation in the cytochrome b gene has been reported to confer resistance to QoI fungicides. A total of 990 isolates of AB-causing fungi were isolated and screened for QoI resistance. Out of these, 10% were isolated from chickpea, 81% were isolated from field peas, and 9% isolated from lentil. These were from a survey of grower’s fields and seed lots (chickpea = 17, field pea = 131, and lentil = 21) from 23 counties in Montana sent to the Regional Pulse Crop Diagnostic Laboratory, Bozeman, MT, United States for testing. Fungicide-resistant Didymella rabiei isolates were found in one chickpea seed lot each sent from Daniels, McCone and Valley Counties, MT, from seed produced in 2015 and 2016. Multiple alignment analysis of amino acid sequences showed a missense mutation that replaced the codon for amino acid 143 from GGT to GCT, introducing an amino acid change from glycine to alanine (G143A), which is reported to be associated with QoI resistance. Under greenhouse conditions, disease severity was significantly higher on pyraclostrobin-treated chickpea plants inoculated with QoI-resistant isolates of D. rabiei than sensitive isolates (p-value = 0.001). This indicates that where resistant isolates are located, fungicide failures may be observed in the field. D. rabiei-specific polymerase chain reaction primer sets and hydrolysis probes were developed to efficiently discriminate QoI- sensitive and - resistant isolates.

A macroarray was developed for the detection of 11 potato viruses and Potato spindle tuber viroid. The 11 viruses detected included those commonly found or tested for in North American potato seed certification programs: Alfalfa mosaic virus, Cucumber mosaic virus, Potato mop top virus, Potato leafroll virus, Potato latent virus, Potato virus A, Potato virus M, Potato virus S, Potato virus X, Potato virus Y, and Tobacco rattle virus. These viruses were detected using oligonucleotide 70-mer probes and labeled targets prepared by a random primed amplification procedure. Potato plants analyzed included those infected with 12 reference virus stocks and 36 field isolates. Results from the macroarray were entirely consistent with those obtained using a standard serological assay (enzyme-linked immunosorbent assay). Four isolates of Potato spindle tuber viroid, in mixed infection with one or more viruses, also were detected in the array, although strong hybridization signals required amplification with viroid-specific primers in combination with anchored-random primers. In individual plants, up to four viruses, or a viroid plus two viruses, were detected, with no apparent competition or inhibition. Macroarrays are a cost-effective approach to the simultaneous diagnostic detection of multiple pathogens from infected plants.