Molecular and Biochemical Diversity Among Isolates of Radopholus spp. from Different Areas of the World.

Eleven isolates of Radopholus similis from various banana-growing areas around the world and one isolate of R. bridgei from turmeric in Indonesia were compared using DNA and isoenzyme analysis. The polymerase chain reaction (PCR) was used to amplify a fragment of ribosomal DNA (rDNA), comprising the two internal transcribed spacers (ITS) and the 5.8S gene. Restriction fragment length polymorphisms (RFLPs) in this rDNA fragment were used to compare the 10 isolates. The analysis of this rDNA region revealed little variation among the isolates tested. However, data also were obtained by random amplified polymorphic DNA (RAPD) analysis of total DNA, and a hierarchical cluster analysis of these data arranged the R. similis isolates into two clusters. The first cluster consisted of isolates from Nigeria, Cameroon, Queensland, and Costa Rica; the second was comprised of isolates from Guinea, Guadeloupe, the Ivory Coast, Uganda, and Sri Lanka. The isolate of R. bridgei from turmeric in Indonesia appeared to be more divergent. This grouping was consistent with that obtained when phosphate glucose isomerase (PGI) isoenzyme patterns were used to compare the R. similis isolates. The results from both RAPD analysis and PGI isoenzyme studies indicate that two gene pools might exist within the R. similis isolates studied. No correlation could be detected between the genomic diversity as determined by RAPD analysis and either geographic distribution of the isolates or differences in their pathogenicity. The results support the hypothesis that R. similis isolates have been spread with banana-planting material.