Transcript abundance of resistance- and susceptibility-related genes in a barley breeding pedigree with partial resistance to the bird cherry-oat aphid (Rhopalosiphum padi L.)

Aphids such as the bird cherry-oat aphid (Rhopalosiphum padi L.) are serious pests in agriculture worldwide. Partially resistant barley genotypes have been produced in a breeding program for resistance to R. padi. The resistance is manifested as smaller aphids after a certain period of nymphal growth on the test plants. A large number of doubled haploid breeding lines thereby characterized as partially resistant or susceptible to R. padi are available from this breeding program. In the present study a selection of these lines, spanning four generations and 23 genotypes, was used for the evaluation of the constitutive transcript abundance of gene sequences in young barley plants. The genes were selected from an earlier microarray study where they had been identified as being up-regulated by aphids in all four barley genotypes studied or differentially up-regulated or constitutively expressed in the two resistant as compared to the two susceptible barley genotypes. The prediction for constitutive transcript abundance across the selection of genotypes was here confirmed for five out of eight investigated genes. Two of these were, as predicted, expressed at equal levels in all genotypes. Two gene sequences exhibited higher transcript abundance in resistant than in susceptible offspring; one coding for a thionin and another for a proteinase inhibitor. A lipoxygenase gene had higher transcript abundance in the susceptible lines. The study thus gives further support for putative constitutive roles of three genes previously identified as significant in the barley–R. padi interaction.