Insect resistance. Russian Wheat Aphid (RWA)
References
1. Genetic mapping of Russian wheat aphid resistance genes Dn2 and Dn4 in wheat. Ma, Z.Q.; Saidi, A.; Quick, J.S.; Lapitan, N.L.V. In:Crop Science, 2001. 41: 1584-1589
To obtain markers for marker-assisted breeding of Russian wheat aphid resistance in wheat (Triticum aestivum L.), resistance genes Dn2 and Dn4 were mapped with restriction fragment length polymorphism (RFLP) markers, using populations derived from PI 62660 x ‘Carson’ and PI 372129 x ‘Yuma’. PI 262660 and PI 372129 are the donor parents of Dn2 and Dn4, respectively. A locus detected by marker KsuA1 was linked to Dn2 at a distance of 9.8 cM on the long arm of chromosome 7D, and a locus detected by marker ABC156 was 11.6 cM away from Dn4 on the short arm of chromosome 1D.
2. A microsatellite marker for tagging Dn2, a wheat gene conferring resistance to the Russian wheat aphid. Miller C. A.; Altinkut, A.; Lapitan N. L. V. In: Journal of Phytopathology, 2001, 149(11-12):641-648.
The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is an economically important pest of wheat (Triticum aestivum L.). An effective means to control the RWA is through the use of resistant cultivars. While a phenotype-based selection has been useful for selection of resistant plants, it has inherent limitations. Screening can only be done during cool months of the year, and symptom expression is influenced by the environment. Pyramiding of two or more RWA resistance genes is also difficult because of the presence of only one aphid biotype in the USA at present. This study was conducted to develop a DNA marker that is tightly linked to Dn2, and to test the effectiveness of the marker as a tag for Dn2 among a limited number of cultivars tested. We report mapping of five microsatellite markers linked to Dn2. The closest marker was Xgwm437 at 2.8 cM, and it distinguished lines containing Dn2 from eight susceptible cultivars and seven resistant cultivars carrying other RWA resistance genes. Xgwm437 should be effective for marker-assisted selection of Dn2-containing plants and for combining Dn2 with other resistance genes in a gene pyramiding program.
3. Development of RAPD and SCAR markers linked to the Russian wheat aphid resistance gene Dn2 in wheat. Myburg, A.A.; Cawood, M.; Wingfield, B.D.; Botha, A.M. In:Theoretical and Applied Genetics, 1998, 96: 1162-1169
RAPD (random amplified polymorphic DNA) analysis was used to identify molecular markers linked to the Dn2 gene conferring resistance to the Russian wheat aphid (Diuraphis noxia Mordvilko). A set of near-isogenic lines (NILs) was screened with 300 RAPD primers for polymorphisms linked to the Dn2 gene. A total of 2700 RAPD loci were screened for linkage to the resistance locus. Four polymorphic RAPD fragments, two in coupling phase and two in repulsion phase, were identified as putative RAPD markers for the Dn2 gene. Segregation analysis of these markers in an F2 population segregating for the resistance gene revealed that all four markers were closely linked to the Dn2 locus. Linkage distances ranged from 3.3 cM to 4.4 cM. Southern analysis of the RAPD products using the cloned RAPD markers as probes confirmed the homology of the RAPD amplification products. The coupling-phase marker OPB10880c and the repulsion-phase marker OPN1400r were converted to sequence characterized amplified region (SCAR) markers. SCAR analysis of the F2 population and other resistant and susceptible South African wheat cultivars corroborated the observed linkage of the RAPD markers to the Dn2 resistance locus. These markers will be useful for marker-assisted selection of the Dn2 gene for resistance breeding and gene pyramiding.
4. Microsatellite markers linked to six Russian wheat aphid resistance genes in wheat. Liu, X.M.; Smith, C.M.; Gill, B.S.; Tolmay, V.In: Theoretical and Applied Genetics, 2000, 102: 504-510
The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is a serious economic pest of wheat and barley in North America, South America, and South Africa. Using aphid-resistant cultivars has proven to be a viable tactic for RWA management. Several dominant resistance genes have been identified in wheat, Triticum aestivum, including Dn1 in PI 137739, Dn2 in PI 262660, and at least three resistance genes (Dn5+) in PI 294994. The identification of RWA-resistant genes and the development of resistant cultivars may be accelerated through the use of molecular markers. DNA of wheat from near-isogenic lines and segregating F2 populations was amplified with microsatellite primers via PCR. Results revealed that the locus for wheat microsatellite GWM111 (Xgwm111), located on wheat chromosome 7DS (short arm), is tightly linked to Dn1, Dn2 and Dn5, as well as Dnx in PI 220127. Segregation data indicate RWA resistance in wheat PI 220127 is also conferred by a single dominant resistance gene (Dnx). These results confirm that Dn1, Dn2 and Dn5 are tightly linked to each other, and provide new information about their location, being 7DS, near the centromere, instead of as previously reported on 7DL. Xgwm635 (near the distal end of 7DS) clearly marked the location of the previously suggested resistance gene in PI 294994, here designated as Dn8. Xgwm642 (located on 1DL) marked and identified another new gene Dn9, which is located in a defense gene-rich region of wheat chromosome 1DL. The locations of markers and the linked genes were confirmed by di-telosomic and nulli-tetrasomic analyses. Genetic linkage maps of the above RWA resistance genes and markers have been constructed for wheat chromosomes 1D and 7D. These markers will be useful in marker-assisted breeding for RWA-resistant wheat.
5. Identification of microsatellite markers linked to Russian wheat aphid resistance genes Dn4 and Dn6.. Liu, X. M.; Smith, C. M.; Gill, B. S. In:Theoretical and Applied Genetics, 2002, 104: 1042-1048.
The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a serious economic pest of wheat worldwide. Host plant resistance is the preferred method to control RWA infestations. The identification and mapping of RWA-resistant genes and the development of resistant wheat cultivars can be facilitated through the use of molecular markers. In the present study, microsatellite (SSR) markers linked to the RWA-resistant genes Dn4 and Dn6 were identified using several F2 mapping populations derived from crosses of susceptible wheat cultivars and resistant sources. Two flanking microsatellite markers Xgwm106 and Xgwm337 are linked in coupling phase with Dn4 on the short arm of wheat chromosome 1D at 7.4 cM and 12.9 cM, respectively. Two other microsatellite markers Xgwm44 and Xgwm111 are linked to Dn6 in coupling phase near the centromere on the short arm of chromosome 7D at 14.6 cM and 3.0 cM, respectively. This is the first report on the chromosomal location of Dn6, which proved to be either allelic or tightly linked to Dn1, Dn2 and Dn5. This result of Dn6 location contradicts previous reports that Dn6 was independent of Dn1, Dn2 and Dn5. The linked markers can be conveniently used for marker-assisted selection in wheat breeding programs for the identification and/or pyramiding of Dn4 and Dn6 genes.