In September 2011, diagnostic samples were taken from ‘Tifway’ Bermudagrass (Cynodon dactylon × C. transvaalensis) tees and from ‘Emerald’ Zoysia (Zoysia japonica) roughs of a golf course in Charleston, SC. Additional samples were taken from a sod farm located near Charleston, SC from a field of ‘Empire’ Zoysia. The soil was sandy loam and the samples were taken at a depth of 10 to 15 cm from symptomatic turf. Symptoms on bermudagrass and zoysiagrass included stubby roots and lightly to severely chlorotic or dead patches of irregular sizes and shapes. Nematodes were extracted by sugar centrifugal-flotation and counted. The predominant nematode species recovered was Trichodorus obtusus Cobb, 1913: syn. T. proximus Allen, 1957, n.syn. (3). Nematode densities (per 100 cm3 of soil) were 30 to 170 (average 94, n = 5) at the sod farm, and 30 to 230 (average 107, n = 7) at the golf course. This nematode has been reported as a pathogen of bermudagrass in Florida, where it is more damaging than Paratrichodorus minor, the other stubby root nematode commonly associated with turfgrass (1). In Florida, 120 T. obtusus individuals per 100 cm3 is considered high risk (2). We have encountered several additional samples from across South Carolina with comparable densities since our first diagnosis. Infested soil (94 individuals per 100 cm3) collected from the sod farm was put into columns and planted with ‘Empire’ sod and maintained in the greenhouse. After 140 days, the population density increased to an average of 230 individuals per 100 cm3. Plants were prone to wilting and new root growth showed symptoms similar to those observed in the field. Morphologic and morphometric identification of T. obtusus was made by examining male and female specimens in temporary water mounts. Males had ventrally curved spicules with three ventral precloacal papillae, with the posterior papilla just anterior to the head of the retracted spicules, one ventromedian cervical papilla anterior to the excretory pore, and tail with non-thickened terminal cuticle. Females had a deep, barrel-shaped, pore-like vulva, and one or two postadvulvar lateral body pores on each side. Males and females had distinctly offset esophagus. Females (n = 10) were 1,100 to 1,440 (1,250) μm long, body width 40 to 53 (45) μm, onchiostyle 63 to 75 (67) μm, and V 583 to 770 (673) μm. Males (n = 10) were 1,076 to 1,353 (1,222) μm long, body width 33 to 45 (39) μm, onchiostyle 62 to 69 (65) μm, and spicule 55 to 63 (59) μm. From individuals representing the two locations, an 898-bp section of the 18S rDNA region was sequenced using primers 37F (5′-GCCGCGAAAAGCTCATTACAAC-3′) and 932R (5′-TATCTGATCGCTGTCGAACC-3′) (4). A BLASTn search revealed no similar sequences to those of our two populations (Accessions JX289834 and JX279930). As such, it appears that these are the first sequences of this portion of the 18S rDNA for T. obtusus, although a different, non-overlapping portion of 18S was found in GenBank (AY146460) under the synonym T. proximus. To our knowledge, this is the first report of T. obtusus on zoysiagrass and the first report of the species on bermudagrass in South Carolina.
References: (1) W. T. Crow and J. K. Welch. Nematropica 34:31, 2004. (2) W. T. Crow et al. Florida Nematode Management Guide. SP-54. University of Florida, Gainesville, 2003. (3) W. Decraemer. The Family Trichodoridae: Stubby Root and Virus Vector Nematodes. Kluwer Academic Publishers, Dordrecht, The Netherlands. Pp. 27-30, 1995. (4) I. Duarte et al. Nematology 12:171, 2010.