An EnSpm interspersed repeat identified in Triticum aestivum and implicated in resistance to Diuraphis noxia

Diuraphis noxia Kurdjumov, 1913 (Hemiptera: Aphididae), commonly known as the Russian wheat aphid, is a devastating pest of wheat and barley. Although fourteen sources of resistance (Dn genes) have been identified to date, none have been cloned. In this study a mapping population of 373 F3/4 segregating wheat plants and ‘Chinese Spring’ 7D deletion lines were screened with AFLP, SSR and EST markers. From the marker screens, a 122.8 cM genetic map was constructed placing the Dn1 resistance gene on chromosome 7DS near the centromere, in bin 7DS5-0.36-0.62 proportionally to the physical ‘Chinese Spring’ deletion 7D map. The map contains 38 new AFLP markers, one microsatellite (Xgwm111) and two EST markers. Of all the markers, AFLP E-ACT/M-CTG_0270.84 showed the closest linkage to Dn1 and were mapped at 3.5 cM, whereas EST markers RGA2-29_30 and SSH-RGA2 were mapped at 15.3 cm and 15.9 cM, respectively, from Dn1. An AFLP marker, E-ACA/M-CAG-257, located 21.4 cM from the Dn1 resistance gene, was successfully cloned and sequenced. The marker sequence was identified to belong to the interspersed repeat class of the subfamily CMC-EnSpm.