First Report of Stunt Nematode (Tylenchorhynchus annulatus) on Corn in Ohio

Stunt nematodes (Tylenchorhynchus spp.) are economically important migratory ectoparasitic nematodes that cause damage to many crops, including corn (Benson and Barker 1985; Handoo et al. 2014). Typical damage includes stunting of roots and shoots, chlorosis, and sometimes wilt and defoliation (Benson and Barker 1985). In 2017 and 2018, soil samples were collected from each of five arbitrarily selected 48 × 14-m sections of a 30-year continuous-corn field in Fulton County, Ohio, planted with corn (Zea mays) hybrid NK0142-3120. Localized stunting and wilting were observed in the field. Plant-parasitic nematodes were extracted from 100 cm³ of soil through sieving and decanting, followed by sucrose centrifugal flotation (Jenkins 1964), and initially identified to genus based on morphological traits, using a compound light microscope. Nematodes with traits typical of Tylenchorhynchus sp. were detected in all samples, with a maximum population density of 848 and 1,212/100 cm³ of soil in 2017 and 2018, respectively. Only females were present. Twenty females were picked and individually examined, measured, and identified as Tylenchorhynchus annulatus (Cassidy), based on morphological and morphometric characteristics (Handoo 2000). Females had stylets with lateral knob inclination and lip region slightly offset from body contour with two to three lip annules. The lateral field contained four incisures. The esophagus did not overlap the intestine. The tail was subcylindrical with a broadly rounded terminus. Body, stylet, and tail lengths ranges and means were 756.1 to 914.7 μm (807.1 μm), 17.7 to 21.8 μm (20.8 μm), and 41.4 to 53.6 μm (47.9 μm), respectively. Vulva position ranged from 52.2 to 57.5% (55.3%) and dorsal esophageal outlet from 2.2 to 3.4 μm (2.8 μm). Additionally, de Man’s ratios were as follows: a = 26.8 to 35.4 (29.8), b = 5.3 to 6.8 (6.0), c = 15.6 to 19.1 (16.9), and c′ = 2.2 to 3.0 (2.7). DNA was extracted from single adult females, and the D2-D3 expansion region of the 28S rRNA gene was amplified using forward primer ACAAGTACCGTGAGGGAAAGTTG and reverse primer TCGGAAGGAACCAGCTACTA (Tenente et al. 2004). The PCR product was purified and sequenced. The sequence was deposited in GenBank (MN378401.1) and compared with reference sequences by means of BLAST. The comparison revealed a sequence similarity of 99% with T. annulatus (e.g., GenBank accession no. KJ461532.1). A greenhouse bioassay was conducted to fulfill a modified version of Koch’s postulates and confirm reproduction of T. annulatus on corn. Nine pots, each containing soil naturally infested with an average of 348 T. annulatus/100 cm³ of soil were planted with two dwarf corn plants (PI 401757). Pots with soil media containing no stunt nematodes were used as controls. Pots were maintained in the greenhouse at a mean temperature of 24.4°C (22.2 to 26.7°C). After 10 weeks, nematodes were extracted and enumerated as described above, and reproduction factor (RF) was estimated as final population/initial population. All T. annulatus-infested pots had RF ranging from 1.71 to 4.49, with a mean of 3.18. T. annulatus was not recovered from control pots. According to our greenhouse bioassay, T. annulatus is capable of reproducing on corn. There was also a trend toward lower root mass in infested pots compared with check pots, but the mean difference in root weight was not statistically significant. Further research will be needed to assess the impact of this nematode on corn production. To our knowledge, this is the first report of T. annulatus in Ohio.