Intraspecific variation in Radopholus similis isolates assessed with restriction fragment length polymorphism and DNA sequencing of the internal transcribed spacer region of the ribosomal RNA cistron.

Restriction fragment length polymorphism and direct sequencing of the internal transcribed spacer rDNA region of 19 isolates of Radopholus similis yielded significant diversity, both among isolates and within some individuals. Restriction fragment length polymorphism with HaeIII, AluI and Tru9I yielded two sets of patterns. Digestion with RsaI revealed one or two supernumerary bands in single nematodes from five isolates, and sequencing confirmed microheterogeneity in four of these. Phylogenetic analysis grouped most isolates closely together, except for the five isolates with additional bands for RsaI. Our data reveal more population structure than previously found and lend further support to the synonymy of R. similis and 'Radopholus citrophilus'.