Characterization of intraspecific variations of Belonolaimus longicaudatus by morphology, developmental biology, host specificity, and sequence analysis of ITS-1 rDNA

Sting nematode, Belonolaimus longicaudatus, is one of the most economically important plant-parasitic nematodes in the southeastern United States. Our objectives were to determine the intraspecific variation based on morphology, developmental biology, host specificity, and ITS-1 DNA sequence among isolates collected from different geographical locations and host crops. Five isolates that were compared by all criteria included: HA isolate from potato in Hastings, FL; GV isolate from bermudagrass in Gainesville, FL; LA isolate from citrus in Lake Alfred, FL; GA isolate from cotton in Tifton, GA; and NC isolate from corn in Scotland County, NC. Two additional isolates from corn (NB) and bermudagrass (TX) were obtained from Columbus, NB and Poteet, TX, and compared with the other five isolates with respect to ITS-1 DNA sequence. The ITS-1 DNA sequence of a South Carolina (SC) isolate was downloaded from the Gene Bank and added for sequence comparison.; Females of the LA and NC isolates were larger in body length and tail length and the LA isolate had a longer stylet length compared with the other isolates (P ≤ 0.05). The GV isolate had the shortest stylet length and body length among all isolates (P ≤ 0.05). Development from egg to adult, which was observed on excised corn root in Gamborg B-5 medium at 28°C, ranged from 18.1 days (GA isolate) to 25 days (NC isolates). The GA and LA isolates reproduced on five crop plants tested, whereas the NC and GV isolates reproduced poorly on all plants except cotton. The LA (citrus) and HA (potato) isolates reproduced better on their original hosts than on other plants tested. However, the GV (bermudagrass) isolate did not reproduce well on its original host. The length of the ITS-1 region were identical, 468 by for all isolates, excepting the TX isolate which had a length of 427 by with a deletion of 41 bp. Sequences of the ITS-1, determined in two separate PCR-generated clones for each isolate, showed some differences in a single nucleotide position. Significant patterns of heterogeneity were seen in ITS-1 sequences from different isolates. Based on three different phylogenetic analyses of ITS-1, the TX, NB, and SC isolates were closely related, but completely different from the HA, LA, GV, GA, and NC isolates.