Variation in the ribosomal RNA cistron among host-adapted races of an aphid (Schizaphis graminum).

The greenbug, Schizaphis graminum, is an aphid species that consists of races that can be separated based on morphology, life histories, cytogenetics, mitochondrial DNA RFLPs and virulence to plant cultivars. Variation in the greenbug rDNA multigene family was studied to determine the extent to which rDNA cistrons have diverged among and within races. A restriction map of the rDNA cistron was constructed. Probing DNA from different races with subclones from rDNA coding regions and internal spacers identified little variation. However, probing with subclones of the intergenic spacer (IGS) identified continuous length variation within and among races. Race specific patterns were identified. Within a race, almost continuous variation in total IGS length was detected and asexual lineages possessed distinct patterns useful in genetic fingerprinting studies.