Identification and characterization of resistance to cowpea aphid (Aphis craccivora Koch) in Medicago truncatula

In this study, we screened a subset of the Medicago truncatula core collection of the South Australian Research and Development Institute (SARDI) and identified strong resistance to CPA in a M. truncatula accession SA30199, compared to all other M. truncatula accessions tested. The biology of resistance to CPA in SA30199 plants was characterised compared to the highly susceptible accession Borung and showed that resistance occurred at the level of the phloem, required an intact plant and involved a combination of antixenosis and antibiosis. Quantitative trait loci (QTL) analysis using a F2 population (n？=？150) from a cross between SA30199 and Borung revealed that resistance to CPA is controlled in part by a major quantitative trait locus (QTL) on chromosome 2, explaining 39% of the antibiosis resistance.The identification of strong CPA resistance in M. truncatula allows for the identification of key regulators and genes important in this model legume to give effective CPA resistance that may have relevance for other legume crops. The identified locus will also facilitate marker assisted breeding of M. truncatula for increased resistance to CPA and potentially other closely related Medicago species such as alfalfa.Phloem-feeding aphids are a common pest of important crops world-wide. In temperate regions, approximately a quarter of all plant species are colonized by at least one aphid species [1]. In many cases, the highly specialized mode of aphid feeding causes little apparent, but nevertheless significant damage to the plant and it appears that aphids are able to evade plant defenses while moving their stylets intercellularly, as well as manipulate their host through secretion of saliva into the phloem sieve elements [2,3]. Sap-sucking insects cause damage in susceptible cultivars, directly by modifying plant metabolism and ingesting plant nutrients and in many cases indirectly, for example, through the transmission of plant-pathogenic viruses [4].Studies using th