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First Report of Tawny Blotch Caused by Parastagonospora caricis on Phalaris arundinacea in New York

Fulcher, M. R., Winans, J. B., Bergstrom, G. C.
Plant disease 2018 v.102 no.8 pp. 1659
Carex, DNA, DNA-directed RNA polymerase, Parastagonospora, Phalaris arundinacea, Stagonospora, antibiotics, canopy, color, conidia, culture media, forage, fungi, genes, grasses, greenhouses, herbaria, hosts, internal transcribed spacers, leaf spot, leaves, mists, mycelium, pathogens, photoperiod, plant tissues, plastic bags, pycnidia, pycniospores, ribosomal RNA, runoff, sodium hypochlorite, species identification, summer, tubulin, wheat, Maryland, Netherlands, New York
Leaf spots were observed on reed canarygrass (Phalaris arundinacea L.) growing in a commercial wheat field in Seneca County, NY, during summer 2016. Lesions were elliptical to cigar shaped, brown-red, and ringed by a light tan band with an irregular margin. Mature lesions contained single erumpent points of white tissue in their center. Damage was most severe in the lower canopy, where spots had coalesced to cover entire leaves. Symptomatic leaf tissue was surface sterilized in 1.65% sodium hypochlorite, rinsed with sterile distilled water, and placed on potato dextrose agar (PDA) amended with antibiotics. Cultures kept at 22°C under a 12-h photoperiod consistently yielded slow growing, cottony mycelium with a pale pink pigment and abundant pycnidia. Pycniospores produced by monosporic isolates grown on PDA amended with sterilized leaves of reed canarygrass were narrow, roughly cylindrical with equally blunt ends. They contained three to eight septa and measured 27.1 to 49.2 μm (mean, 37.7 μm) × 2.5 to 7.4 μm (mean, 5.4 μm) (n = 55). Morphology, symptomology, and host were characteristic of tawny blotch caused by Stagonospora foliicola (Bres.) Bubák (Sprague 1950). Two isolates were sequenced for species identification using the internal transcribed spacer region of rRNA, RNA polymerase subunit II gene, and β-tubulin gene. Sequences (GenBank KY604740, MF593838, and MF593839, respectively) had a 99 to 100% identity match to the type culture of Parastagonospora caricis deposited in GenBank and did not show homology to the type isolate of S. foliicola from Maryland. Although colony color of the New York isolates did not match that described for P. caricis, pycniospores produced on PDA without plant tissue amendments measured 61.2 × 6.3 µm, consistent with those recorded from the type culture of P. caricis (Quaedvlieg et al. 2013). A specimen was deposited at the Cornell herbarium (CUP-068300), and a representative culture was stored at CBS-KNAW (CBS 144011). Using one New York isolate, Koch’s postulates were completed in a greenhouse with 2-month-old, potted reed canarygrass. A conidial suspension of 1 × 10³ spores/ml in sterile water was washed from 2-week-old cultures grown on PDA amended with reed canarygrass leaves. Three pots were treated with the fungus, and three pots received a sterile water control treatment. Plants were spray inoculated with a fine mist until runoff and incubated under plastic bags for 24 h. After 2 weeks, inoculated plants showed symptoms typical of those seen in the field, and the pathogen was reisolated from multiple lesions. Control plants showed no signs of disease, and no fungi were isolated from their leaves. Tawny blotch is one of the most important diseases of reed canarygrass worldwide (Braverman et. al. 1986), and the damage can be significant under humid or moist conditions (Zeiders 1975). This disease may impact the quality and quantity of forage. P. caricis was first identified on Carex acutiformis in the Netherlands and has not been recorded from other hosts or locations. To the authors’ knowledge, this is the first report of P. caricis infecting reed canarygrass. It is possible that other North American reports of S. foliicola lacking DNA sequence data could be misidentifications of P. caricis, and both organisms should be considered in future studies of tawny blotch on associated grasses.