Golf Course Management

AUG 2018

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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08.18 GOLF COURSE MANAGEMENT 67 Maria Tomaso-Peterson, Ph.D. Dog's footprint? We call it 'ink spot' in these parts A new foliar disease of bermudagrass and zoysiagrass golf turf has been identified in the southeastern United States. In the late 2000s, golf course superinten- dents in the greater Houston metropolitan area were seeing a foliar patch disease on ber - mudagrass and zoysiagrass greens, tee boxes and fairways. Because a primary symptom of the disease was small, dark brownish-black patches, the disease was called "ink spot." During that time, Mississippi State Uni - versity received a sample for disease diagno- sis that had been taken from a Tifgreen (also known as 328 or Tifton 328) bermudagrass putting green with a distinct chocolate-brown patch in the turf canopy. Black lesions were present on the leaves. e symptoms observed in the diseased turf sample were unlike any I had observed. Infected leaves were plated onto water agar, a nutrient-deficient medium that promotes fungal reproduction. Within 36 hours, black, robust mycelium of the patho - gen was growing out of the leaf tissue. In pure culture, the fungus was black and sterile; no reproductive structures developed that would aid in fungal identification. In that same growing season, samples of this conspicuous disease were received from bermudagrass putting greens, tee boxes, fair - ways and zoysiagrass fairways. In the ensu- ing years, turfgrass pathologists at Mississippi State University and Texas A&M University independently isolated a darkly pigmented sterile fungus from lesions associated with chocolate brown-to-black spots occurring in golf course samples from the region. Dr. Young-Ki Jo at Texas A&M and I began a col - laborative effort to characterize ink spot and the undescribed causal agent. As the samples came into the lab, our living culture collection was increasing in number. However, because the fungal pathogen is sterile, we used molec - ular methods for identification purposes. Amplification of the universal DNA bar - code gene of fungi, the internal nuclear ribo- somal transcribed spacer region (ITS), was the first step toward identification. e amplified ITS product was sequenced and uploaded in GenBank, a genetic sequence database. e initial ITS match was an undescribed fungal pathogen from Japan associated with dog's footprint disease in zoysiagrass. In the 1997 book Color Atlas of Turfgrass Diseases (1), a foliar disease of zoysiagrass in Japan showed turf symptoms identical to those of ink spot in the United States and was identified as Cur - vularia blight. Among the pathogens associ- ated with Curvularia blight is a black sterile fungus that was not fully characterized in the book. As time progressed, we received pictures and samples of ink spot from golf courses in Alabama, Mississippi, Tennessee and Hainan Province in China, broadening our under - standing of the distribution of the disease. Be- cause the sterile fungal pathogen causing ink spot was undescribed, a comprehensive phy - logenetic analysis was employed, resulting in the identification of a novel fungal species (2). The pathogen A novel species of Curvularia was identi- fied as the foliar pathogen of bermudagrass and zoysiagrass in the southeastern United States (2). Curvularia malina sp. nov. (mean - ing black, dirty, stained) refers to the myce- lium and symptoms in the turf. e black, net-like mycelium of C. malina can be ob - served under low magnification on the outer surface of infected leaves and stems (Figure 1). As indicated, the fungus is sterile and, there - fore, it develops no asexual conidia, unlike its very distant relatives, C. lunata and C. genicu - lata, which are prolific conidia producers. e optimal growing temperature of C. malina is 77 F (25 C). e fungus proliferates under ideal temperature and moisture conditions, allowing for rapid identification in culture. Symptoms and climatological conditions favorable for disease Symptoms On bermudagrass and zoysiagrass man - aged under golf course conditions, ink spot presents as conspicuous chocolate-brown-to- black spots that range in size from less than Figure 1. Robust, black mycelium of Curvularia malina may be observed colonizing infected stems and leaves of bermu- dagrass and zoysiagrass. Photo by Maria Tomaso-Peterson

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