Biotype 2 Russian wheat aphid resistance among wheat germplasm accessions

The Russian wheat aphid [Diuraphis noxia (Mordvilko), RWA] is an important pest of wheat (Triticum aestivum L.) in the western Great Plains region of the United States. The recent identification of a RWA biotype (provisionally denoted as Biotype 2) that is virulent on currently deployed RWA-resistant cultivars necessitates the rapid identification of resistance to the new biotype. The objective of this study was to identify Biotype 2 RWA resistance among a collection of germplasm accessions previously determined to be resistant to the original North American biotype of RWA (provisionally denoted as Biotype 1). A collection of 761 germplasm accessions was evaluated in standard seedling screening tests with Biotype 2 RWA. 'TAM 107' (carries no RWA resistance genes) and 'Halt' (Dn4 resistance gene) were used as susceptible checks while the germplasm line 94M370 (Dn7 resistance gene) was used as a resistant check. Evaluation of accessions showing at least a moderate level of resistance in unreplicated tests was repeated with three replications in a randomized complete block design. Forty-four germplasm accessions were identified as having high to moderate levels of resistance to Biotype 2 RWA. Most of these accessions originated from areas of the world where RWA is endemic or were derived from germplasm accessions that originated from these areas. Ten accessions showed a level of resistance comparable with the 94M370 check. These accessions should prove useful in future genetic studies and for breeding for resistance to Biotype 2 RWA.