Title: Limited genetic variation within and between Russian wheat aphid (Hemiptera: Aphididae) biotypes in the United States Authors
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2008
Publication Date: February 1, 2009
Citation: Shufran, K.A., Payton, T. 2009. Limited genetic variation within and between Russian wheat aphid (Hemiptera: Aphididae) biotypes in the United States. Journal of Economic Entomology. 102(1):440-445. Interpretive Summary: The Russian wheat aphid is a pest of wheat in the US since 1986 and was managed primarily by the planting of resistant cultivars from 1996 until 2003. In 2003, a biotype capable of injuring resistant wheat was found in Colorado. The injurious biotype was named Biotype 2, and the non-injurious extant population was then referred to as Biotype 1. Using molecular genetic markers, we estimated the genetic relatedness between these two biotypes. Almost no genetic variation was found between the two biotypes. They were so closely related that genetic markers could not be used to tell them apart. The results suggest that the origin of the injurious Biotype 2 was not from another introduction into the US. Rather, Biotype 2 most likely arose from the extant population originally introduced into the US in 1986. Biotype 2 was probably present in low numbers and then selected for by the planting of resistant wheat.
Technical Abstract: Five Russian wheat aphid, Diuraphis noxia (Kurdjumov) biotypes have been described in the US and given number designations 1 through 5. Of these only Biotypes 1 and 2 (non-damaging and damaging to Dn4 resistant wheat, respectively) are common and agriculturally important. Only a single clone of Biotypes 3, 4, and 5 have been found in nature and exist in the laboratory. To understand the genetic relatedness and origin of D. noxia biotypes in the US, we used three molecular markers to assay for genetic variation within and between Biotypes 1 (n=11) and 2 (n=12), and for variation between Biotypes 1, 2, 3, 4 and 5 (total n=26). Only 2 out of 54 primers revealed any RAPD variation. In each case the polymorphism was due to the presence/absence of a single band, and was only found in 2 individuals. No DNA sequence variation in the COI mitochondrial gene was found between all 26 D. noxia clones. Likewise, all D. noxia showed no variation at 7 SSR loci. The lack of variation found within and between biotypes suggests Biotype 2 (the Dn4 virulent population) arose from the extant population, and does not represent a second introduction of a genetically divergent biotype into the US.