Colletotrichum cereale Manns, formerly C. graminicola (Ces.) G.W. Wils., is the causal agent of anthracnose foliar blight (AFB) of creeping bentgrass (Agrostis stolonifera L.) and other grass species (1). AFB is most prevalent on creeping bentgrass during summer heat stress (2). Symptoms of AFB progress from older to younger leaves with leaf tips becoming chlorotic and eventually developing complete leaf necrosis. Symptoms in turf stands appear as yellow-to-bronze, irregularly shaped patches often associated with a loss of turf density (2). When C. cereale is actively infecting the foliar tissue, appressoria can be observed microscopically in the leaf sheaths of creeping bentgrass. C. cereale colonizes the foliar tissue, producing abundant acervuli, where conidia and setae develop. Creeping bentgrass samples exhibiting symptoms of AFB were collected from West Point, MS and Birmingham, AL in July 2006. Symptomatic plants with signs of C. cereale were surface disinfested and plated onto one-quarter-strength potato dextrose agar (PDA). Monoconidial C. cereale isolates were grown on full-strength PDA for 21 days at 25°C under fluorescent lights. Single-celled conidia were mostly falcate, ranged from 13.1 to 25.6 μm long × 3.6 to 6.3 μm wide, and averaged 22.2 × 4.7 μm. Hyphal appressoria were irregularly shaped and heavily lobed, ranging from 5.6 to 16.1 μm long × 4 to 10.6 μm wide, and averaged 12.1 × 7.9 μm. In culture, setae were acicular, five to seven septate, thick walled, ranged from 74 to 213.5 μm long, and averaged 151.3 μm. The morphological characteristics of 44 AFB isolates were similar to those of C. cereale reported by Crouch et al. (1). Nucleotide sequences were generated for the internal transcribed spacer rDNA for isolates OO7-T42, OW15-H32, and 04-111 (GenBank Accession Nos. EU859957, EU859958, and EU859959). Maximum likelihood-based phylogenetic analyses of these sequences with authentic isolates of Colletotrichum species from grass hosts (2) indicated that all three isolates were C. cereale. ‘Penn A-1’ creeping bentgrass seedlings (10.16-cm pots) were inoculated with the C. cereale isolates OO7-T42, OW15-H32, or 04-111 by spraying a conidial suspension (1.5 × 105 conidia/ml) on plants until water droplets were evident within the canopy. An uninoculated control sprayed with distilled water only was used for comparison. Three replicates per C. cereale isolate were included simultaneously when performing Koch's postulates. The inoculated creeping bentgrass seedlings were placed in covered plastic boxes to maintain humidity and incubated under 12 h of fluorescent light with day/night temperatures at 35/28°C. After 4 days, the covers were removed and creeping bentgrass was maintained an additional 14 days until symptoms and signs were observed on the foliage. C. cereale was reisolated from inoculated creeping bentgrass exhibiting symptoms of AFB for all three isolates used. No acervuli, setae, or conidial masses were observed on uninoculated control plants. To our knowledge, this is the first report of C. cereale causing AFB on creeping bentgrass in Mississippi and Alabama.
References: (1) J. A. Crouch et al. Phytopathology 96:46, 2006. (2) R. W. Smiley et al. Compendium of Turfgrass Diseases. The American Phytopathological Society, St. Paul, MN, 2005.
