Geographic Distribution and Genetic Diversity of <i>Bakernema inaequale</i>

Plant-parasitic nematodes of the family Criconematidae (ring nematodes) are distributed worldwide. Although several species are significant pathogens of turf and fruit crops, they reach their greatest diversity in natural systems. Ring nematodes are an important component of various soil habitats, and several criconematid species often are present in a soil sample. One of the most distinctive ring nematodes is the heavily fringed Bakernema inaequale, endemic to eastern North America. This nematode has been found as far north as Ontario, Canada, and up to the present, as far south as Grundy County, Tennessee. This research focused on determining the geographic boundaries and plant host associations of B. inaequale, as well as analyzing molecular data to detect any genetic variability among populations. Soil samples were collected from diverse habitats of non-agricultural land east of the Mississippi River, from the Gulf coast to New England, focusing primarily on both sides of the Appalachian chain. At each collection site, photographs were taken, GPS coordinates and elevation noted, and surrounding vegetation and general soil type documented. Soil samples remained refrigerated until processing. After extraction, at least five living specimens from a sample were viewed individually on a differential interference (DIC) microscope, given an identification number unique to the nematode, imaged, measured, and ruptured with a micropipette tip to release DNA. Each nematode was then frozen in a PCR tube, and samples were shipped to the University of Nebraska, Lincoln, for DNA amplification using the cytochrome oxidase subunit 1 (COI) gene sequence. Molecular analysis indicated very little genetic diversity among B. inaequale, with only two specimens collected in Tuskegee National Forest differing significantly from the remaining twenty-five specimens. Some morphological differences were noted, primarily relating to annule scale size and shape, head region, and tail. However, morphological differences were not correlated with molecular differences. This survey expanded the known southern boundary of B. inaequale to Tuskegee National Forest in southeast Alabama.