J. M. LeBoldus, North Dakota State University, Department of Plant Pathology, Fargo 58108;
Q. Zhang, North Dakota State University, Department of Plant Science, Fargo 58108; and
K. Kinzer, North Dakota State University, Department of Plant Pathology, Fargo 58108
Dollar spot disease is a major concern for golf courses nationwide, resulting in poor turf quality and significant damage to playing surfaces. To manage this disease effectively, fungicides need to be applied regularly. This management strategy represents a significant cost to turfgrass managers and may impact the economics of the industry in North Dakota. In the summer of 2011, small, circular, sunken brown patches of dead turf approximately 5 cm in diameter and resembling dollar spot disease were observed on a creeping bentgrass (Agrostis stolonifera L.) variety trial at the North Dakota State University Agricultural Experiment Station in Fargo, ND. Fresh individual leaf specimens with distinct lesions having straw colored centers and reddish brown margins were collected. Leaves were surface disinfected in a 0.05% sodium chloride solution for 60 s, rinsed three times in sterile distilled water, then placed onto potato dextrose agar (PDA). Three isolates were obtained from the disease infested leaves with similar morphology to that described for Sclerotinia homoeocarpa F.T. Bennett (1). Fungal colonies were initially colorless followed by the development of sparse white columnar aerial mycelia with cinnamon colored bases. Hyphae were 5 to 8 μm wide and thin walled with dense granular contents and septations at irregular intervals. Fourteen days after culturing, dark brown to black mycelial stroma developed. A single representative isolate was selected to conduct inoculations. Inoculum was produced by placing six 5-mm-diameter plugs of PDA with actively growing mycelium into an Erlenmeyer flask with 40 g of sterile millet seed. The inoculum was incubated for 14 days at ambient temperature (20 to 25°C). Three creeping bentgrass cultivars, Crenshaw, Declaration, and L-93, were inoculated (two pots per cultivar). Following inoculation, the pots were misted with water, sealed in separate plastic bags, and placed in the dark for 48 h. For the next 5 days, plants were placed for 8 h outside of bags on a bench with full spectrum fluorescent bulbs, followed by 16 h in plastic bags in the dark. Finally, pots were placed on a bench for 48 h. Signs and symptoms of S. homoeocarpa developed on all pots, whereas the controls remained asymptomatic. The same fungus was reisolated from grass leaves, satisfying Koch's postulates. To confirm the identity of the fungus, the internal transcribed spacer was amplified using the ITS4 and ITS5 primers (2). The amplicon was sequenced, generating a 549-bp sequence (Accession No. JQ735942) with 100% similarity to sequences of S. homoeocarpa in GenBank (Accession Nos. GQ924924.1, GQ924923.1, and EU123801.1). To our knowledge, this is the first confirmed report of dollar spot in North Dakota.
References: (1) F. T. Bennett. Ann. Appl. Biol. 24:236, 1937. (2) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press Inc., New York, 1990.