Belonolaimus longicaudatus has been reported as a complex species because of its variations in morphology and pathogenicity among different isolates. However there is no information about genetic characteristics of B. longicaudatus among different populations coupled with detailed morphological characteristics. Our objectives were to determine the intraspecific variation based on morphology and ITS1 DNA sequence among isolates collected from different geographical locations and host crops. Five isolates compared by all criteria were HA-potato, Hastings, FL; GV-bermudagrass, Gainesville, FL; LA-citrus, Lake Alfred, FL; GA-cotton, Tifton, GA; and NC-corn, Scotland County, NC. Two additional isolates compared with these five isolates with respect to ITS1 DNA sequence were NE-corn, Columbus, NE, and TX-bermudagrass, Poteet, TX. The ITS1 DNA sequence previously reported for South Carolina (SC) isolate (GenBank accession #U89696) was included for sequence comparison. Females of the LA and NC isolates were longer in body length and the LA isolate had a longer stylet compared with the other isolates (P = 0.05). The stylet knobs of the NC and LA isolates were typically teardrop or kidney-shaped, whereas the GA isolate was typically oval. The vaginal pieces of the LA isolate were the most prominent and clearly recognized among all isolates, but that of NC isolate was weakly developed and not clearly recognized. The lengths of the ITS1 region were similar, 468 bp for all isolates, excepting the TX isolate which had a length of 428 bp. For phylogenetic analysis, maximum parsimony, neighbor-joining, and maximum likelihood methods were used and phylogenetic trees were constructed. All three trees supported that the NE, SC, and TX isolates were clearly different from the FL (GV, HA, LA), GA, and NC isolates. The TX isolate seemed to have diverged from the group of FL, GA, and NC isolates, which was supported by a 100 bootstrap value.
