Golf Course Management

MAY 2014

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

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05.14 GOLF COURSE MANAGEMENT 83 Clypei. Light and electron microscope ob- servations conclusively showed that the le- sion on the paspalum plants was made up of a shield-like structure called the clypeus (plural clypei) (4,7,10,12). The clypei are oval in shape with a slightly raised center and seem to push through the epidermis of the plant tissue, dra - matically changing the structure and anatomy of the plant epidermis. The size of clypei ranges from 170 micrometers × 152 micrometers to 203 micrometers × 495 micrometers. Ascocarps and asci. An ascocarp is a nest-like or spherical structure that contains the asci (plural of ascus), bean-pod-shaped structures that are the sexual spore-bearing cells pro - duced by ascomycete fungi (12) (Figure 3). When seen under an electron microscope, the asci are cylindrical and arranged in a palisade formation with vegetative tissue dispersed throughout the ascocarp. The asci range from 7 to 8 micrometers in width × 48 to 51 mi - crometers in length. Ascospores. An individual ascus containing eight ascospores (fungal spores) is shown in a light microscope photo (Figure 4). The asco - spores are uniseriate, that is, they are arranged one by one in a single row (12). The ascospores also have a smooth surface and are devoid of any ornamentation (Figure 5). Their shape is ellipsoidal, and many of them have a slightly conical or parabolic end. No division, separa - tion or any other structure was observed. As- cospore size ranges from 5.7 to 7 micrometers in width × 10 to 11 micrometers in length. In an electron microscope photo, masses of asco - spores are shown oozing through small rup- tures or holes in the clypei; ascospore release appears to be limited to the inter-vein sections of the leaf (Figure 6). Infection tests The fungal organism can only grow on liv- ing tissue. After evaluating several methods of infecting the turfgrass and determining the environmental conditions conducive to in - fection, we collected grass clippings from the infected source (initial infection was observed in the cultivar SeaIsle 2000). Infected grass clippings were placed on healthy seashore pas - palum turfgrass grown in plastic pots in the greenhouse. Greenhouse temperatures were kept at 77 F-80 F (25 C-27 C) and high rela - tive humidity. The process was replicated at least four times. Healthy plants of the cultivars SeaIsle 2000, Aloha, SeaIsle Supreme and an experi - mental line (106L-1) were successfully in- fected with tar spot. All the inoculated pots were infected, but the incidence of the infec - tion was rather low (mean of 5%). Conclusions A careful visual evaluation of physical symptoms was conducted. Plants were in - spected for size, shape, color, appearance, distribution, quantity and location of le - Figure 2. Some of the tar spots coalesced to form a continuous strip on the grass blade. Figure 3. An electron microscope photo shows an ascocarp, which forms a nest-like or spherical supportive structure for asci, the bean-pod-like structures that contain the ascospores by which the tar spot fungus reproduces. Figure 4. A light compound microscope photo shows an ascus containing eight ascospores arranged in a single row. Figure 5. An electron microscope photo with a close-up of ascospores, the fungal spores from the tar spot fungus. Asci Ascocarp Plant tissue 076-087_May14_TechwellCuttingEdge.indd 83 4/16/14 2:53 PM

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