First Report of Sclerotinia homoeocarpa from the Sedge Trichophorum cespitosum in Eastern Canada, Which Causes Dollar Spot Disease on Lolium perenne and Poa pratensis but not on Agrostis stolonifera.

Sclerotinia homoeocarpa is a fungal pathogen that causes dollar spot disease on more than 40 plant species, mostly in the family Poaceae (1), and is considered the most widespread pathogen of golf course turfgrasses in the St. Lawrence River Region. In June 2011, lesions were observed on tufted bulrush, Trichophorum cespitosum (Poales, Cyperaceae), on the sea shore near Peggys Cove, Nova Scotia, Canada. Single bunches had up to 40% of the leaves affected. The foliar symptoms resembled large hourglass lesions, up to 5 cm long, with a straw colored portion capped at two ends by dark zone lines on surrounding green foliar tissue. Leaf segments were taken, surface sterilized, and placed on potato dextrose agar (PDA). After 3 days of incubation at room temperature, white fluffy mycelia covered the entire petri dish. Brown columnar structures formed in the colony centers after 7 days and cultures became cinnamon colored after 14 days. Dark brown or black substratal stroma were formed on or in the agar, and cultures appeared dark brown from the bottom. DNA was extracted and amplified using primers ITS1 and ITS4 (2), and the amplicon sequenced (GenBank Accession No. KF447776). The sequence showed a top match of 522/524 bp identity with the ITS of an isolate of S. homoeocarpa, with the next 40 top matches also identified as S. homoeocarpa. Two-week-old seedlings of Agrostis stolonifera cv. Penncross, Poa pratensis cv. Touchdown, and Lolium perenne cv. Express were inoculated by placing 5-mm-diameter mycelial plugs from 5-day-old PDA cultures onto the leaves of plants grown in small containers, and incubating under enclosed humid conditions throughout the test. White aerial hyphae on the leaves and straw-colored leaf lesions were observed by 7 days after inoculation on P. pratensis and L. perenne, but no lesions or hyphal growth were observed on A. stolonifera. No signs or symptoms were observed on leaves where sterile agar plugs were used as inoculum. These tests were repeated three times with the same results, and a positive control was included by using an S. homoeocarpa isolate known to be pathogenic to A. stolonifera under the same test conditions. Disease was observed on A. stolonifera with the control isolate. S. homoeocarpa was re-isolated from the lesions on P. pratensis and L. perenne to satisfy Koch's postulates. To the best of our knowledge, this is the first report of S. homoeocarpa on T. cespitosum worldwide, an isolate that was found to cause disease on P. pratensis and L. perenne, but was not pathogenic to A. stolonifera in vitro. The original host was not used in pathogenicity tests because it is considered an endangered species in many locations. References: (1) B. Walsh et al. HortScience 34:13, 1999. (2) T. J. White et al. PCR protocols, a guide to methods and applications 18:315, 1990.