Two independent resistance genes in the Medicago truncatulacultivar Jester confer resistance to two different aphid species of the genus Acyrthosiphon

In recent years the biology of resistance to aphids and other sap-sucking insects has been studied in detail, whereas the genetic basis underlying this resistance is still poorly understood. Genetic resistance to Acyrthosiphon kondoiShinji (bluegreen aphid; BGA) has been identified in Medicago truncatulaGaertn and backcrossed into susceptible cultivars. One of these M. truncatula cultivars named Jester also has good resistance to an Australian biotype of pea aphid (PA; A. pisumHarris). Until now it has been unclear whether resistance to each aphid species of the genus Acyrthosiphonis conferred by distinct genes or the same gene termed AKRfor A. kondoiresistance. Infestation of the progenitors of the cultivar Jester with both aphid species revealed that resistance to BGA came from a different donor than resistance to PA, demonstrating that resistance to these aphid species is mediated by different resistance genes. However, an interaction between these genes for resistance to Acyrthosiphonspecies remains a possibility, given that PA resistance was not one of the parameters selected for in the creation of Jester. The identification of resistance to the model aphid, PA, and a closely related aphid BGA in the same genetic background of the model legume M. truncatulamakes this system an attractive model for the study of plant-aphid interactions, as well as R gene specificity and evolution.