First Report of the Spiral Nematode Scutellonema brachyurum on Lilyturf in the United States

Abstract

Lilyturf (Liriope muscari (Decne.) L.H. Bailey), an herbaceous plant, is commonly used in landscaping including borders (along sidewalks, driveways, and trees) and mass plantings as groundcover in the southeastern United States. In December of 2009, a soil sample was submitted to our lab for diagnosis of plant-parasitic nematodes from an area planted with lilyturf located on the Clemson University main campus. A high population density (1,220 individuals/100 cm3 of soil) of spiral nematodes (Scutellonema brachyurum (Steiner, 1938) Andrássy, 1958) was found by routine extraction by sugar centrifugal flotation (3). Other plant-parasitic nematodes, mainly ring nematodes (10 individuals/100 cm3) and stubby root nematodes (10 individuals/100 cm3), were present. To verify if high numbers of spiral nematodes were consistently associated with lilyturf, 20 additional soil and root samples were collected from different places on the campus. In all cases, S. brachyurum was found in densities ranging from 680 to 1,600 individuals/100 cm3 of soil (average of 1,210 individuals/100 cm3). The species was identified by morphological characters of females, including well developed stylet (26 to 30 μm long), no spermatheca, no sperm in uterus, tail broadly rounded with 8 to 12 annules between anus and tail, and scutella at anus level. As is commonly the case for this species, no males were found in any of the samples collected. Examination of the roots revealed numerous, small, reddish brown, necrotic lesions, apparently caused by the feeding and penetration of S. brachyurum. Host plant suitability and pathogenicity of the nematode were tested in the greenhouse. Ten nematode-free lilyturf plants grown individually in 15-cm-diameter plastic pots with pasteurized soil were inoculated with 1,000 spiral nematodes each. Ten uninoculated plants were kept under identical conditions as controls. Three months after inoculation, soil population densities were measured and reproduction factors were calculated to be between 2.8 and 5.4 (final population density divided by initial population density) for the 10 plants. Characteristic lesions previously described were observed in the roots of all inoculated plants, along with slight chlorosis of foliage. These symptoms were not observed on control plants. Spiral nematodes may attack the roots and stolons of lilyturf as ectoparasites or they may enter them and feed in the cortex as endoparasites. Although root lesions were common on affected plants, root injury in general was not severe and generalized root decay was not observed on either the collected plants or those from the greenhouse study. Reports on the pathogenicity of S. brachyurum are variable. Moderate damage was recorded on amaryllis and other ornamentals (4), while measurable damage was observed on tobacco (2), with approximately 100 individuals/100 cm3 of soil, and severe damage on Aloe vera ((L.) Burm. f.), with approximately 500 individuals/100 cm3 (1). To our knowledge, this is the first report of S. brachyurum causing visible symptoms on lilyturf. As the interstate and international movement of perennial plants continues to grow, awareness of the host status of potentially harmful nematodes becomes essential information. References: (1) R. P. Esser et al. Nematropica 16:65, 1986. (2) T. W. Graham. Phytopathology (Abstr.) 45:347, 1955. (3) W. R. Jenkins. Plant Dis. Rep. 48:692, 1964. (4) L. Nong and G. F. Weber. (Abstr.) Phytopathology 54:902, 1964.