Abstract
Resistance to the Australian pea aphid (PA; Acyrthosiphon pisum) biotype in cultivar Jester of the model legume Medicago truncatula is mediated by a single dominant gene and is phloem-mediated. The genetic map position for this resistance gene, APR (Acyrthosiphon pisum resistance), is provided and shows that APR maps 39 centiMorgans (cM) distal of the A. kondoi resistance (AKR) locus, which mediates resistance to a closely related species of the same genus bluegreen aphid (A. kondoi). The APR region on chromosome 3 is dense in classical nucleotide binding site leucine-rich repeats (NLRs) and overlaps with the region harbouring the RAP1 gene which confers resistance to a European PA biotype in the accession Jemalong A17. Further screening of a core collection of M. truncatula accessions identified seven lines with strong resistance to PA. Allelism experiments showed that the single dominant resistance to PA in M. truncatula accessions SA10481 and SA1516 are allelic to SA10733, the donor of the APR locus in cultivar Jester. While it remains unclear whether there are multiple PA resistance genes in an R-gene cluster or the resistance loci identified in the other M. truncatula accessions are allelic to APR, the introgression of APR into current M. truncatula cultivars will provide more durable resistance to PA.
Highlights
Sap-sucking insects such as aphids, psyllids, scales and whiteflies cause significant damage in agricultural crops throughout the world
The biology of the resistance to both aphid species in this cultivar shared similarities with resistances occurring at the phloem level and requires an intact plant and involves a combination of antibiosis, antixenosis and plant tolerance [14,24]
The donor for bluegreen aphid resistance was a different donor than that of pea aphid (PA) resistance, resistance to both aphids are controlled by distinct single dominant resistance genes with the PA resistance locus tentatively named APR [19]
Summary
Sap-sucking insects such as aphids, psyllids, scales and whiteflies cause significant damage in agricultural crops throughout the world. In the model legume Medicago truncatula, single dominant resistance genes to other aphid species including bluegreen aphid (BGA; Acyrthosiphon kondoi), spotted alfalfa aphid (Therioaphis trifolii) and pea aphid (PA; Acyrthosiphon pisum) map to regions dense in these NLR encoding genes [14,15,16,17]. Thirty-five accessions of the South Australian Research and Development Institute (SARDI) M. truncatula core collection, which represent the major clades in the phylogenetic tree of the SARDI core accessions [31] were selected to evaluate PA resistance performance These included accessions A20, Cyprus and Borung, previously identified as being highly susceptible to PA, A17 which is moderately resistant, as well as Jester and Caliph which are highly resistant to PA [32]. A17 SA3919 SA24968 SA3054 SA8618 SA11734 SA9357 SA22323 SA7749 SA9710 SA9712 Cyprus Borung
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