Calamagrostis × acutifolia ‘Karl Foerster’ (feather reed grass) is a cool-season grass grown extensively as an ornamental plant throughout the United States. In July 2005, severe foliar damage was observed in feather reed grasses in a residential garden in Barrington, NJ. Symptoms were observed as small, yellowish brown, oval to irregularly shaped spots on the blades, with spread and coalescence of spots leading to eventual necrosis and plant death. Numerous acervuli with black setae diagnostic of fungi in the genus Colletotrichum were present on necrotic lesions. Two distinct fungi were isolated from diseased tissue by plating small sections of infested leaf tissue on potato dextrose agar (PDA) supplemented with 40 μg/liter each of penicillin, ampicillin, gentomycin, and streptomycin. The first fungus was identified as Colletotrichum gloeosporioides based on morphological, cultural (2), and molecular characteristics. Variable colonies of gray-white mycelia with masses of pink-to-salmon hued conidia formed at 25°C on PDA under constant light. Conidia were hyaline, aseptate, straight, and cylindrical with rounded apices (11.0 to 18.5 × 2.5 to 5.0 μm). Sequencing of the internal transcribed spacer (ITS) rDNA region showed the fungus to be most similar to C. gloeosporioides (GenBank Accession No. EU979125). The second fungus was identified as C. cereale based on morphological, cultural, and molecular characteristics (1). Variable colonies of gray-tan-white mycelia formed at 25°C on PDA under constant light and salmon-colored conidial masses surrounded numerous setae. Conidia were hyaline, aseptate, falcate, fusiform, and guttulate (15.0 to 21.5 × 2.5 to 4.5 μm). Hyphal appressoria were ovoid, sometimes lobate or multilobate (10.5 to 13.5 × 7.5 to 10.0 μm). Maximum likelihood phylogenetic analysis of the ITS sequence (GenBank Accession No. DQ126193) and fungal mating type idiomorph Mat1-2 HMG box (GenBank Accession No. DQ131962) identified the fungus as C. cereale (1). Pathogenicity was determined by inoculating healthy feather reed grasses (11.4-liter pots) established 61 cm off-center in a mulched bed. Three replicate plants per treatment were sprayed with a 20-ml conidial solution (5 × 104 conidia/ml in 0.1 potato dextrose broth) of either C. cereale or C. gloeosporioides and an uninoculated control. Temperatures ranged from 19 to 36°C and humidity varied between 31 and 79%. No symptoms were observed in uninoculated controls or plants inoculated with C. gloeosporioides. Plants inoculated with C. cereale developed disease symptoms within 21 days; the fungus was subsequently reisolated from symptomatic leaves and confirmed as C. cereale. To our knowledge, this is the first report of anthracnose of feather reed grass caused by C. cereale (formerly known as C. graminicola). Although C. cereale is known to inhabit numerous cool-season grass hosts, this is the first description of this fungus as a pathogen of an ornamental grass. Given the recent emergence of anthracnose epidemics caused by C. cereale on golf course turfgrass, the identification of this fungus as a pathogen of Calamagrostis × acutifolia highlights the need for nurseries and regulatory personnel to screen ornamental grasses such as feather reed grass for the presence of C. cereale so that the disease does not become problematic.
References: (1) J. A. Crouch et al. Phytopathology 96:46, 2006. (2) B. C. Sutton. The genus Glomerella and its anamorph Colletotrichum in: Colletotrichum: Biology, Pathology and Control. J. A. Bailey and M. J. Jeger, eds. CAB International, Wallingford, UK, 1992.