The lance nematode Hoplolaimus magnistylus Robbins 1982 (3) was found for the first time in Tennessee in a cotton (Gossypium hirsutum L.) field (35°19.550′ N, 89°24.535′ W) in Fayette County in May 2011. In June of the same year, the species was also found in soil samples collected from a corn (Zea mays L.) field (36°15.736′ N, 88°51.121′ W) and a soybean (Glycine max L.) field (36°15.616′ N, 88°51.118′ W) in Weakley County, TN. Nematodes were extracted from the soil with a semi-automatic elutriator and further processed by sugar flotation-centrifugation. Population densities were between 30 and 50 individuals per 100 cm3 of soil in areas with noticeable stunting. Helicotylenchus sp. and Pratylenchus sp. were also present at less than 10 individuals per 100 cm3 of soil. Ten soybean seeds, cv. Hutcheson, were planted and inoculated with 50 H. magnistylus per 100 cm3 in steam-sterilized soil, and were maintained in a greenhouse. Forty-five days later, soybean plants exhibited at least one of the following symptoms: stunting and chlorosis, reduced root growth, and localized root lesions. Individual nematodes were handpicked and identified under a compound light microscope as H. magnistylus based on morphological and morphometric characteristics. The main diagnostic character for this species is the size of the stylet. In the populations collected, females had stylets ranging from 49 to 58 μm (mean 56 μm). Males and females were observed with head distinctly set off and massive cephalic framework, stylet long and robust and stylet knobs pointed anteriorly. The lateral field was areolated and had four incisures most of the body length, the excretory pore was prominent and located 190 μm (175 to 200 μm) from anterior end, hemizonid was large and located one or two annules posterior to the excretory pore, phasmids were large, conspicuous, and variable in position, and vulva was prominent and near midbody. This species is most similar to the more commonly reported H. galeatus, but differs from it in the longer stylet. Total DNA was extracted from single adults from each soil sample and the species-specific primers Hoc-1f (5′-AACCTGCTGCTGGATCATTA-3′) and HM-3r (5′-AGACTGGACGGCCAAAGTT-3′) designed by Bae et al. (1) were used to confirm the identification by amplification of a distinct 340-bp amplicon that differentiates this species from H. columbus, H. galeatus, H. concaudajuvencus, and H. stephanus. H. magnistylus was first described from soil samples taken from a corn and soybean field in Marianna, AR (3), and has been reported in association with soybean and corn in Louisiana and Mississippi (4). Robbins (4) reported that H. magnistylus was not a serious pest of irrigated cotton in Arkansas, but there are no other pathogenicity studies published for soybean, corn, or non-irrigated cotton. Other lance species, mainly H. galeatus and H. columbus, have been reported to cause serious damage to cotton in the Carolinas and Georgia (3). Previously, H. galeatus was reported in Tennessee by Bernard (2). Lance nematodes feed as migratory endo- and ectoparasites and injure the growing points of roots, causing stunting of plants. Because so little is known about the pathogenicity of this nematode, it becomes relevant to add our records of its known distribution in field crops in the United States. To our knowledge, this is the first report of H. magnistylus in Tennessee.
References: (1) C. H. Bae et al. Nematology 11:471, 2009. (2) E. C. Bernard. University of Tennessee Bulletin 594, 1980. (3) R. T. Robbins. J. Nematol. 14:500, 1982. (4) R. T. Robbins. J. Nematol. 30(4S):590, 1998.