During late June and early July of 2005, signs of bermudagrass ergot were reported from numerous northern and eastern counties in Oklahoma. Signs were observed primarily on forage-type bermudagrass (Cynodon dactylon (L.) Pers.), as well as bermudagrass turf. During the “honeydew” stage, honeydew was frequently observed exuding from most of the ovaries of infected inflorescences. These signs of ergot have been observed previously on bermudagrass in Oklahoma and Texas (1). Sphacelia-type conidia were abundantly produced during the honeydew stage and were single-celled, hyaline, averaged 14 × 5 μm in size, and were reniform to allantoid in shape. When streaked on water agar, conidia produced terminal holoblastic secondary conidia. Single-spore cultures were isolated from the honeydew of bermudagrasses from Logan and Muskogee counties in Oklahoma and grew slowly as white mycelium on potato dextrose agar (PDA). Koch's postulates were fulfilled for these two isolates by spray inoculating four bermudagrass inflorescences at anthesis with mycelium scraped from a PDA plate and homogenized in water. Control plants' inflorescences were sprayed with a water suspension of a similar amount of sterile PDA as inoculated plants. Plants were placed inside plastic bags to maintain humidity and incubated in a growth chamber at 22°C (14-h photoperiod) and 20°C (10 h of darkness). After 9 days, honeydew exuded from the inoculated inflorescences, but not from the controls. Single-spore cultures were reisolated from the honeydew, and conidia streaked on water agar formed identical secondary conidia. The complete nuclear ribosomal internal transcribed spacer (ITS) region was amplified from DNA extracted from honeydew and single-spore cultures using the ITS4 and ITS5 primers (4) and sequenced. All sequences were identical and a search of GenBank at NCBI found these sequences were most similar to the ITS regions of Claviceps cynodontis Langdon (100%, Accession No. AJ557074) and C. maximensis Theis (99%, Accession No. AJ133396). The ITS sequence from the Logan County isolate was deposited at Gen-Bank (Accession DQ187312). The morphology, secondary conidiation, and ITS sequences identify the causal fungus as C. cynodontis (2) and differentiate it from C. purpurea (Fr.) Tul., the previously identified cause of bermudagrass ergot (1). To our knowledge, this is the first report of C. cynodontis on bermudagrass in Oklahoma and may represent a recent introduction to the United States (2; S. Pažoutová and M. Flieger, personal communication). A Claviceps sp. isolated from bermudagrass has been shown to produce ergot alkaloids possibly causing “bermudagrass tremors” in cattle (3). In regions where bermudagrass is the predominant forage for livestock, the toxicological significance of bermudagrass ergot caused by C. cynodontis is unclear and requires further research.
References: (1) K. E. Conway et al. Plant Dis. 76:1077, 1992. (2) S. Pažoutová et al. Can J. Plant Pathol. 27:541, 2005. (3) J. K. Porter et al. J. Agric. Food Chem. 22:838, 1974. (4) T. J. White et al. Pages 315--322 in: PCR Protocols: A Guide to Methods and Applications. Academic Press Inc., New York, 1990.
