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Disease Note.

First Report of Necrotic Ring Spot (Leptosphaeria korrae) in Creeping Red Fescue in Maryland. P. H. Demoeden, Department of Agronomy, University of Maryland, College Park 20742. M. Zhang, and H. C. Wetzel, Department of Agronomy, University of Maryland, College Park 20742. Plant Dis. 79:966. Accepted for publication 10 July 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0966A.

Leptosphaeria korrae J. C. Walker & A. M. Sm. incites necrotic ring spot (NRS) in Kentucky bluegrass (Poa prtensis L.) (2). Beginning in May, and continuing through November 1994, symptoms resembling NRS were observed in shaded areas of a 20-year-old creeping red fescue (Festuca rubra L. subsp, rubra Smith) lawn located 40 km west of Baltimore. Diseased patches ranged from 6 to 60 cm in diameter, but most patches were 12 to 18 cm in diameter. Patches contained a few or no living plants. There were 12-cm-diameler sunken patches and one large, 60-cm-diameter ring or “frog-eye” patch. The affected zone of the ring ranged from 5 to 12 cm wide. Foliage of affected plants was reddish-brown, yellow, or tan, and leaves died back from the tips. Roots were dark brown and covered with large amounts of darkly pigmented runner hyphae and pseudoparenchymatous mats. A sterile fungus was isolated on water agar from surface-disinfested (sodium hypochlorite) roots of affected plants. Diseased root, stem, and leaf tissues were then incubated in a glass dish humidity chamber beginning on 6 September. On 24 October, pseudothecia were found on necrotic stems. Fifty, pale brown, filiform ascospores from four ascocarps were measured. Ascospores ranged from 100 to 163 ?m (average = 125 μm) long, 4 to 7 ?m (average = 5 ?m) wide, and contained 4 to 14 (average = 7) septations per asco-spore. Ascospore measurements conform to reported ranges for L. korrae (1). Single ascospore colonies appeared identical to the sterile fungus isolated from roots, and random amplified polymorphic DNA polymerase chain reaction confirmed that the isolates were L. korrae. Thirty-day-old creeping red fescue plants (cv. Flyer) were inoculated with four isolates of L. korrae: two from field-infected creeping red fescue (one from root tissue and a single ascospore isolate), and two isolates from spring dead spot-affected Cynodon dactylon L. All four isolates caused >82% mortality, produced pseudothecia on stem bases, and all were reisolated from infected roots by 8 weeks after inoculation. This is the first report of necrotic ring spot in Maryland and constitutes the southernmost known occurrence of the disease.

References: (1) J. Walker and A. M. Smith. Trans. Br. Mycol. Soc. 58:459, 1972. (2) G. L. Worf et al. Plant Dis. 70:453, 1986.