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A New Disease of Agrostis palustris Incited by an Undescribed Species of Ophiosphaerella

Creeping bentgrass (Agrostis palustris; syn. Agrostis stolonifera) is widely used on golf course putting greens. In September and October 1998, samples of diseased creeping bentgrass were received from golf courses in Maryland, Virginia, and Ohio. Disease symptoms developed in August or September 1998, and appeared initially as 1.0- to 2.0-cm-diameter, reddish brown spots that enlarged to about 8.0 cm in diameter. Leaves of plants in the center of diseased patches were tan and those on the periphery were reddish brown. Dark, ectotrophic hyphae were not observed on roots. Numerous pseudothecia were embedded in necrotic leaf and stolon tissues. A fungus was isolated from leaves, stems, and roots, and single-spore isolates were obtained from pseudothecia. Colonies of all isolates were identical in appearance and were initially rose-quartz to pinkish brown, developing a gray color as they aged. Inoculum was prepared by placing mycelium from a single-spore isolate on an autoclaved medium consisting of 50% tall fescue (Festuca arundinacea) seed, and 50% wheat (Triticum aestivum) bran (vol/vol) and grown at 28°C for 8 days. Putter and Crenshaw creeping bentgrass seedlings were grown for 14 days in 12 cm² pots containing an autoclaved topdressing mix with a mechanical analysis of 95% sand, 1% silt, and 4% clay. The inoculum (200 mg) was mixed into the upper 5 mm of the sandy soil. Pots were placed in plastic bags and incubated during the daytime on a windowsill bench (20 to 24°C), and were maintained at 25°C at night in a darkened growth chamber. After 7 days, 2.0-cm-diameter patches of blighted leaves were observed on both cultivars in nearly all pots, and pseudothecia were found on the inoculum or on blighted foliage in some pots after 20 days. Blighted leaves were covered with a pale pinkish white mycelium and newly infected leaves at the periphery of the dead spot were a pale reddish brown. Most plants were dead 20 days after inoculation. The fungus was reisolated from blighted leaves of both cultivars and all isolates produced colonies identical in appearance and growth rate to those produced by the single-spore isolate. Pseudothecia produced in vivo were sectioned with a freezing microtome and examined microscopically. Bitunicate asci were observed and contained light-brown, 6- to 15-septate, filiform ascospores that were usually spirally twisted in the ascus and measured 70 to 150 × 2.0 to 2.5 μm. Characteristics of the pseudothecia and the ascospores fit those of the genus Ophiosphaerella Speg. (1). Based on morphometric studies of 12 collections from three different states, this fungus can be distinguished from O. graminicola by the lack of periphyses and fewer septa in ascospores (i.e., 12 to 20 septa in O. graminicola). It was distinguished from O. herpotricha by characteristics of the pseudothecia neck, ascospores, and colony color. Because of these differences, we suggest that this fungus represents a new species attacking creeping bentgrass, which will be described after further morphometric and molecular analyses.

Reference: (1) J. Walker. Mycotaxon 11:1, 1980.