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Quantitative resistance (QR) to disease is usually more durable than qualitative resistance, but its genetic basis is not well understood. We used the barley/barley stripe rust pathosystem as a model for the characterization of the QR phenotype and associated genomic regions. As an intermediate step in the preparation of near-isogenic lines representing individual QTL alleles and combinations of QTL alleles in a homogeneous genetic background, we developed a set of QTL introgression lines. These intermediate barley near-isogenic (i-BISON) lines represent disease resistance QTL combined in one-, two-, and three-way combinations in a susceptible background. In the first described experiment, we measured four components of disease resistance on the i-BISON lines: latent period, infection efficiency, lesion size, and pustule density. The greatest differences between the target QTL introgressions and the susceptible controls were for the latter three traits. On average, however, the QTL introgressions also had longer latent periods than the susceptible parent (Baronesse). There were significant differences in the magnitudes of effects of different QTL alleles. The 4H QTL allele had the largest effect, followed by the alleles on 1H and 5H. Pyramiding multiple QTL alleles led to higher levels of resistance in terms of all components of quantitative resistance except latent period. In the second experiment, we measured the response to inoculation with the pathogen, as either infection type or percent disease severity, on the i-BISON lines at the seedling and adult plant stages, in controlled and field environments, with varying races of the pathogen, and combinations there of. The i-BISON QTL allele introgression effects are consistent across controlled and field testing environments and across the Mexico and Washington locations. Stripe rust resistance QTL alleles have consistent effects across varying races but show interactions with growth stage, mainly due to magnitude of response. The data do not conclusively support a benefit to pyramiding multiple resistance alleles; yet, the potential durability may justify their construction. |
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