Genetic Variation Within and Between Russian wheat aphid, Diuraphis noxia (Kurdjumov), Biotypes Found in the United States

Abstract

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), is a pest on wheat and barley in the Western United States. Management is achieved primarily by resistant varieties. In 2003, the Russian wheat aphid caused damage to wheat with the Dn4 resistance gene in Southeastern Colorado. The damaging biotype was designated RWA-2 and the extant population RWA-1. Plant response experiments showed variation within RWA-2 clones based on chlorosis, plant height, and shoot dry weight to wheat with the Dn4 resistance gene. Phenotypic variation found within RWA-2 argues against the hypothesis that RWA-2 populations consist of a single, genetically identical clone. I conducted studies to observe variation between and within Russian wheat aphid biotypes using 12 clones of RWA-1 and RWA-2 biotype, and a single clone of: RWA-3; RWA-4; and RWA-5 biotypes, determined according to plant response to Dn genes. Using RAPD-PCR, three single band polymorphisms were detected distinguishing RWA-5 and clone 7 (RWA-2) after screening all Russian wheat aphids with 58 primers. I found no sequence variation within or between biotypes in a 436 bp fragment of the COI gene in the mtDNA. Seven microsatellite DNA markers were used to evaluate clonal diversity, but no variation was found. In addition, cuticular hydrocarbon analysis was performed on multiple aphids belonging to a single clone of RWA-1, RWA-2, RWA-3, RWA-4, and RWA-5. This method showed RWA-1 and RWA-2 had unique hydrocarbon mixtures, based on principal component analysis. Ultimately all five biotypes could be separated according to canonical variables. Using genotypic markers, Russian wheat aphid biotypes are homogenous, and consist of a single introduction into the United States. Using phenotypic markers, RWA-1 and RWA-2 are more distinctive of the five Russian wheat aphid biotypes. Lack of genotypic variation could have resulted from a founder effect upon introduction into North America, followed by bottlenecking of populations in the United States.