Genetic variation and phylogenetic relationships among worldwide collections of the Russian wheat aphid, Diuraphis noxia (Mordvilko), inferred from allozyme and RAPD-PCR markers.

Genetic analyses were conducted on Diuraphis noxia (Mordvilko) populations collected from wheat, barley and other grasses from various countries throughout the world. These collections had been found to contain clones that differed in virulence from various cultivars, cuticular hydrocarbon profiles and life cycle characters. Discrete genetic markers analysed in this study included allozymes and arbitrary regions of the genome amplified by the polymerase chain reaction (RAPD-PCR). In all, 23 enzymes were evaluated; 17 of these enzymes representing 20 isozyme loci, were judged suitable for allozyme analysis. Polymorphisms were detected at three (15 per cent) loci: beta-esterase (beta-EST), phosphoglucose isomerase (PGI), and 6-phosphogluconate dehydrogenase (6-PGDH). The average expected heterozygosity amongst these loci was 4.9 per cent in the worldwide collection. Allozyme variation was absent within most populations, particularly within those countries where the species was recently introduced. Much greater genetic variation was detected when populations were analysed with RAPD-PCR. Populations were analysed with 69 polymorphic bands amplified by seven primers. All populations could be distinguished with this method. Cluster analyses indicated strong similarities between U.S.A. populations and collections from South Africa, Mexico, France and Turkey. The most variation was detected among populations from the Middle East and southern Russia.