Genetic Relationships of Crown Rust Resistance, Grain Yield, Test Weight, and Seed Weight in Oat

Integrating selection for agronomic performance and quantitative resistance to crown rust, caused by Puccinia coronata Corda var. avenae W.P. Fraser & Ledingham, in oat (Avena sativa L.) requires an understanding of their genetic relationships. This study was conducted to investigate the genetic relationships of crown rust resistance, grain yield, test weight, and seed weight under both inoculated and fungicide-treated conditions. A Design II mating was performed between 10 oat lines with putative partial resistance to crown rust and nine lines with superior grain yield and grain quality potential. Progenies from this mating were evaluated in both crown rust-inoculated and fungicide-treated plots in four Iowa environments to estimate genetic effects and phenotypic correlations between crown rust resistance and grain yield, seed weight, and test weight under either infection or fungicide-treated conditions. Lines from a random-mated population derived from the same parents were evaluated in three Iowa environments to estimate heritabilities of, and genetic correlations between, these traits. Resistance to crown rust, as measured by area under the disease progress curve (AUDPC), was highly heritable (H = 0.89 on an entry-mean basis), and was favorably correlated with grain yield, seed weight, and test weight measured in crown rust-inoculated plots. AUDPC was unfavorably correlated or uncorrelated with grain yield, test weight, and seed weight measured in fungicide-treated plots. To improve simultaneously crown rust resistance, grain yield, and seed weight under both lower and higher levels of crown rust infection, an optimum selection index can be developed with the genetic parameters estimated in this stud

Origin and evolution of the bread wheat D genome

Bread wheat (Triticum aestivum) is a globally dominant crop and major source of calories and proteins for the human diet. Compared with its wild ancestors, modern bread wheat shows lower genetic diversity, caused by polyploidisation, domestication and breeding bottlenecks1,2. Wild wheat relatives represent genetic reservoirs, and harbour diversity and beneficial alleles that have not been incorporated into bread wheat. Here we establish and analyse extensive genome resources for Tausch’s goatgrass (Aegilops tauschii), the donor of the bread wheat D genome. Our analysis of 46 Ae. tauschii genomes enabled us to clone a disease resistance gene and perform haplotype analysis across a complex disease resistance locus, allowing us to discern alleles from paralogous gene copies. We also reveal the complex genetic composition and history of the bread wheat D genome, which involves contributions from genetically and geographically discrete Ae. tauschii subpopulations. Together, our results reveal the complex history of the bread wheat D genome and demonstrate the potential of wild relatives in crop improvement

Molecular markers for leaf rust resistance gene Lr42 in wheat

Citation: Liu, Zhengli, Robert L. Bowden, and Guihua Bai. “Molecular Markers for Leaf Rust Resistance Gene Lr42 in Wheat.” Crop Science 53, no. 4 (2013): 1566–70. https://doi.org/10.2135/cropsci2012.09.0532.Wheat leaf rust, caused by Puccinia triticina Eriks., is an important wheat foliar disease worldwide. Growing cultivars incorporating genetic resistance is one of the most effective approaches for disease control. Leaf rust resistance gene Lr42 was identified from a wheat relative, Aegilops tauschii Coss, and has been transferred into hard winter wheat. A previous study identified two markers closely linked to the gene on the short arm of chromosome 1D (1DS) using a near isogenic population, but flanking markers for Lr42 were not found. In this study, a new mapping population was developed from a cross between ‘KS93U50’ (a Lr42 carrier) and a susceptible parent, ‘Morocco’. An F[subscript 2] population was analyzed with all simple sequence repeat (SSR) markers available from chromosome 1D and F[subscript 2] plants and F[subscript 3] families were evaluated for seedling resistance to isolate PNMR, a rust isolate avirulent to Lr42. The F[subscript 2] and F[subscript 3] rust data showed that Lr42 was recessive. Seven markers formed the linkage group on 1DS. The Lr42 region was flanked by two simple sequence repeat (SSR) markers; Xwmc432 and Xgdm33 at 17 cM apart. The results confirmed that Lr42 is positioned on the distal end of chromosome 1DS. The flanking markers for Lr42 should be useful for map-based cloning and marker-assisted pyramiding of Lr42 with other leaf rust resistance genes