First Report of Marasmiellus mesosporus Causing Marasmiellus Blight on Seashore Paspalum.

Seashore paspalum (Paspalum vaginatum Sw.) is a newly cultivated C4 turfgrass that has exceptional salinity tolerance and is highly suited for use on golf courses in coastal areas. In October 2008 and June 2009, circular patches of blighted seashore paspalum ranging from 30 cm to >3 m in diameter were observed in fairways, tees, and roughs established with 'Supreme' seashore paspalum at Roco Ki Golf Club in Macao, Dominican Republic. Affected patches were initially chlorotic followed by reddish brown necrosis of leaves and leaf sheaths. Reddish brown-to-gray lesions were also observed on leaf sheaths during the early stages of necrosis. During periods of wet or humid weather from June through October, basidiocarps were produced on necrotic plant tissue and identified as Marasmiellus mesosporus Singer (2). Three isolates were obtained by plating symptomatic leaf sheaths that were surface sterilized with a 0.5% NaOCl solution on potato dextrose agar amended with 50 ppm each of streptomycin, chloramphenicol, and tetracycline (PDA+++). Sequences of the internal transcribed spacer (ITS) region of rDNA, obtained from these three isolates and three stipes of basidiocarps, were identical to each other and 99% similar to a M. mesosporus sequence deposited in the NCBI database (Accession No. AB517375). To confirm pathogenicity, a M. mesosporus isolate obtained from symptomatic plant tissue was inoculated onto 6-week-old P. vaginatum ('Seaspray') planted (0.5 mg seed/cm²) in 10-cm-diameter pots containing a mixture of 80% sand and 20% reed sedge peat. Two weeks prior to inoculation, the isolate was grown on a sterilized mixture of 100 cm³ of rye grain, 4.9 ml of CaCO₃, and 100 ml of water. Infested grains were placed 0.5 cm below the soil surface for inoculation. Pots were inoculated with five infested grains or five sterilized, uninfested grains with three replications of each treatment. After inoculation, pots were placed in a growth chamber with a 12-h photoperiod set to 30°C during the day and 26°C at night. Approximately 20% of plants in inoculated pots were necrotic 7 days postinoculation and this increased to 75% by 21 days postinoculation. Diseased plants in inoculated pots exhibited symptoms similar to those observed in the field. Leaves were initially chlorotic with brown lesions on lower leaf sheaths and eventually turned necrotic, reddish brown, and collapsed. Pots receiving uninfested grains were healthy and showed no symptoms on all rating dates. At 21 days postinoculation, basidiocarps were observed emerging from three colonized plants at the base of the oldest leaf sheath near the crown. Three reisolations were made on PDA+++ from stem lesions surface sterilized with a 0.5% NaOCl solution. All reisolations were confirmed as M. mesosporus by culture morphology and ITS sequence data. M. mesosporus was previously reported causing disease on American beachgrass (Ammophila breviligulata Fernald) in North Carolina (1) and recently in Japan (3). The pathogen was initially placed in the genus Marasmius and reported as the cause of the disease Marasmius blight (1). Subsequent morphological observation found that the pathogen belonged in the genus Marasmiellus (2). To our knowledge, this is the first report of M. mesosporus causing Marasmiellus blight on seashore paspalum, a high-amenity turfgrass. References: (1) L. Lucas et al. Plant Dis. Rep. 55:582, 1971. (2) R. Singer et al. Mycologia 65:468, 1973. (3) S. Takehashi et al. Mycoscience 48:407, 2007.