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CROP BREEDING, GENETICS & CYTOLOGY

Chromosomal Location of the Russian Wheat Aphid Resistance Gene, Dn5

^a Dep. of Genetics, Univ. of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
^b Centraalbureau voor Schimmelcultures, P.O. Box 85167, 3508 AD Utrecht, the Netherlands
^c (retired), PANNAR, P.O. Box 17164, Bainsvlei 9338, South Africa
^d Small Grain Institute, Private Bag X29, Bethlehem 9700, South Africa

^* Corresponding author (gfm{at}sun.ac.za)

Recent reports suggested that the Russian wheat aphid (Diuraphis noxia Mordvilko, RWA) resistance gene Dn5 is located on wheat (Triticum aestivum L.) chromosome arm 7DS rather than on 7DL. A further attempt was therefore made to physically map the gene employing the same source material previously used to describe, name, and map it. It was possible to derive monotelosomic 7DL plants carrying Dn5 on the telosome. Such plants could not be developed for the short arm. The identities of the 7DS and 7DL telosomes were confirmed using mapped microsatellite a-nd endopeptidase markers and showed unequivocally that Dn5 occurs on 7DL. It appears that use of the wrong Dn5 source material could explain some of the inconsistencies in earlier genetic studies involving this gene. In an attempt to also genetically map Dn5, a doubled haploid (DH) mapping population was derived from the cross PI 294994 x ‘Chinese Spring’ (CS). A single RWA resistance gene, believed to be Dn5, segregated in the population and was mapped together with 12 microsatellite loci and the Ep-D1 locus. The Dn gene mapped near the centromere on 7DS. However, closer inspection of the data suggested that segregation distortion with opposite effect occurred within two areas of the region that was being mapped. The combined distortion effect rendered the data unreliable and it was not possible to unambiguously determine the chromosome arm on which the Dn gene resides. It appeared that the chromosome 7D proximal regions may be problematic in terms of genetic analysis based on segregation data.

Abbreviations: cM, centimorgan • DH, doubled haploid • RWA, Russian wheat aphid • CS, ‘Chinese Spring’

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