Aphid feeding response and microsatellite-based genetic diversity among diploid Brachypodium distachyon (L.) Beauv accessions
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abstract
False brome grass, Brachypodium distachyon (L.) Beauv, has been proposed as a new model species to bridge rice and temperate cereal crops for genomics research. However, much basic information for this species is still lacking. In this study, six diploid B. distachyon (2n=2x=10) accessions (Bd1-1, Bd2-3, Bd3-1, Bd18-1, Bd21 and BD29) were evaluated for their response to infestation by two cereal aphid pests of common wheat (Triticum aestivum L.): the greenbug, Schizaphis graminum Rondani, and the Russian wheat aphid (RWA), Diuraphis noxia Mordvilko. Through database mining of B. distachyon expressed sequence tag (EST) and genomic DNA sequences, 160 EST- and 21 genomic microsatellite markers were developed and used to evaluate genetic diversity among the B. distachyon accessions. All six accessions were resistant to RWA biotype RWA1 but showed distinct responses to feeding by greenbug biotypes C and E, as well as RWA2 RWAs. Although microsatellite-based genetic diversity among different accessions was generally low, Bd1-1 and BD29 were the most diverged from the other four lines. The genetic divergence was correlated with geographical distances between the Brachypodium accessions. Comparison of simple sequence repeat polymorphisms in three inbred lines (Bd2-3, Bd3-1 and Bd18-1) with their respective original parental lines revealed no effect of inbreeding on genetic diversity. Phylogenetic analysis suggested that Aegilops tauschii (Coss.) Schmal., the D genome donor of common wheat, was closer to B. distachyon than to rice. The greenbug-B. distachyon system seems to be a model of choice for plantaphid interaction studies in the grass genome.
