Kikuyugrass (Pennisetum clandestinum) is a C4 grass and invasive weed adopted for use as a primary turf species in some golf course fairways and roughs in southern California. In September 2008, a new Rhizoctonia-like fungus was isolated from a diseased kikuyugrass sample received from a golf course fairway in Oceanside, CA. The kikuyugrass was from a mature stand (>20 years old) that was maintained at a height of approximately 1.25 cm. Symptoms on kikyuygrass developed initially as irregular, blighted, chlorotic patches, several centimeters to one meter, which occurred during a period of warm, humid weather (27 to 29°C maximum daytime temperature, 75 to 85% average relative humidity) on a small part of one fairway. Affected areas became brown and necrotic as the disease progressed. Leaf chlorosis and stem rot were observed on affected plants. The organism was isolated by placing symptomatic leaves on acidified one-quarter-strength potato dextrose agar (PDA) (600 μl of 85% lactic acid per liter of medium) in a petri dish (1). A colony of a Rhizoctonia-like fungus with yellow aerial hyphae, multinucleate hyphal cells, and irregularly shaped, golden brown sclerotia (4 to 7 mm) developed within 30 days at 28°C. The rDNA internal transcribed spacer (ITS) sequence was obtained (GenBank Accession No. HQ850254) using PCR amplification with primers ITS1F and ITS4 (1,2), and a BLAST search showed 100% similarity with Waitea circinata var. prodigus (GenBank Accession No. HM597145), which had recently been described as the cause of basal leaf blight of seashore paspalum (Paspalum vaginatum), another C4 grass (3), in Florida. Colony morphology and other physical characteristics were similar but not completely identical to those from Florida, reflecting the reported morphological variation inherent in the pathogen (3). Koch's postulates were performed by growing this isolate on PDA in a petri dish for 7 days, homogenizing the culture with 100 ml of sterilized water, filtering the suspension through two layers of cheesecloth, and pipetting 10 ml of the mycelial suspension onto the foliage and stems of 4-week-old AZ-1 kikuyugrass plants grown in UC-soilless-mix in 7.5-cm-diameter pots (4). Control plants were treated with a homogenized and filtered dish of PDA only. There were three replicate pots for inoculated and noninoculated treatments and the experiment was repeated independently three times. All of the pots were incubated in a moist chamber with a 12-h light period at 28°C. Yellow lesions were observed on leaves and stems of inoculated plants 4 days postinoculation and necrosis developed 8 days later in all experiments. The same organism was isolated from symptomatic plants. The control plants did not exhibit any symptoms. To our knowledge, this is the first report of basal leaf blight caused by W. circinata var. prodigus on kikuyugrass in California and the first report of this pathogen affecting turfgrass in the western United States.
References: (1) C. M. Chen et al. Plant Dis. 93:906, 2009 (2) K. de la Cerda et al. Plant Dis. 91:791, 2007. (3) S. J. Kammerer et al. Plant Dis. 95:515, 2011. (4) T. Toda et al. J. Gen. Plant Pathol. 73:379, 2007.
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