Genetic mapping and molecular characterisation of Russian wheat aphid resistance loci in wheat

The Russian wheat aphid (RWA, Diuraphis noxia Kurdmojov) is considered as one of the most destructive pest of wheat around the world, causing significant yield loss in wheat cultivation. A continuous process of searching for novel resistance loci (Dn) to combat evolving new RWA biotypes has been successful in providing RWA resistance to breeding programs. Australia was declared as a RWA free country but Infestation of RWA was first time reported in Tarlee, South Australia in April, 2016. A novel resistance source, PI94365 with expressing resistance to several biotypes found in other countries was selected to incorporate its resistance into the Australian cultivar EGA Gregory. A double haploid (DH) population developed through the microspore technique was phenotyped in South Africa, Turkey and Morocco with respective biotypes. A genetic linkage map was constructed with 4053 molecular markers including simple sequence repeats (SSR), genome by sequencing (GBS) and Diversity array technology (DArT) molecular markers. Major QTLs to RWA resistance were mapped on 1DS, 7DS and 7BL and minor QTLs were mapped on 3BL, 4AS and 4DL. POPSEQ genetic map distances for the QTLs identified on chromosomes 1DS and 7DS were determined by comparative genomics studies with published consensus and POPSEQ maps. A large number of molecular markers have been identified in the region of RWA resistance loci for the marker assisted plant breeding. Proteomics studies in the absence of live aphids (due to quarantine restriction in Australia) were carried out in order to reveal the resistance mechanism driven by constitutive genes. Ten proteins were significantly differentially expressed between resistance and susceptible lines selected from the double haploid population that was mapped in detail through haplotype analysis. These proteins were annotated using the current wheat genome assembly and functional annotation in relation to RWA resistance. Studies identified several induced proteins with RWA infestations. Differentially expressed genes identified in these studies annotated to the wheat genome together with their genetic map location assigned some of the genes to major RWA resistance QTLs and thus this study provided some new insights into RWA resistance. Over all, the work carried out in this study delivered RWA resistant wheat lines for breeding resistance cultivars that are well characterized by a broad range of molecular markers in the regions of the RWA resistance loci. The high density of new molecular markers provides for the efficient tracking of RWA resistance loci in the pipe-line of cultivar development within the framework of quarantine restrictions