Chromosomal Location of the Russian Wheat Aphid Resistance Gene, Dn5

Abstract

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 × ‘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.

Effect of segregation distortion on genetic mapping of a PI 294994-derived Russian Wheat Aphid resistance gene

“…is probably the same gene as Dn4 that is located on IDL. The result obtained confirms ;that Heyns et al (2006) were correct in questioning the validity of their genetic mapping data. However, while they suspected that the segregation distortion observed might have affected only the order of the genes being mapped on 7D, it turned out to be even worse with the genes in reality occurring on different chromosomes.…”

“…The latter authors included a further gene, presumed to be Dn5 in this cluster, bu~ as it did not derive from the Dn5 source material (Marais & du Toit, 1993), the result is unconfirmed. Du Toit, Wessels & Marais (1995) and Heyns et al (2006) physically mapped Dn5 to 7DL. Heyns et al (2006) also genetically mapped an unknown gene with preliminary label Dn?…”

“…Du Toit, Wessels & Marais (1995) and Heyns et al (2006) physically mapped Dn5 to 7DL. Heyns et al (2006) also genetically mapped an unknown gene with preliminary label Dn? to the 7DS proximal region.…”

“…doubled haploid (no 13) from the mapping population of Heyns et al (2006) was crossed as the male parent with (a) Chinese Spring ditelosomic 7DS and (b) with W1376 which is ditelosomic 7DL and has the pedigree: (87S149 = 41 + 7DS + 7DL)llndis//lnia 66/3/PI 294994/4/ Chinese Spring nullisomic 7D. Both ditelosomics were confirmed with appropriate 7D microsatellite loci in the study of Heyns et al (2006). F) monotelo disomics were selected from each cross and pollinated with the RWA susceptible line, W84-17.…”

Trends in Research using Plant Genetic Resources from Germplasm Collections: From 1996 to 2006

“…In developing countries, 69% of the institutions were universities and 27% NARCs; only seven private companies were found (4%), of which one was located in Brazil (Pinto et al, 2006), one in South Africa (Heyns et al, 2006), one in Argentina (De La Vega and Chapman 2006), one in India (Mishra et al, 2006), and three in the Czech Republic (Ř epková et al, 2006;Treuren et al, 2006;Watanabe et al, 2006) (Table 2). In developing countries, 69% of the institutions were universities and 27% NARCs; only seven private companies were found (4%), of which one was located in Brazil (Pinto et al, 2006), one in South Africa (Heyns et al, 2006), one in Argentina (De La Vega and Chapman 2006), one in India (Mishra et al, 2006), and three in the Czech Republic (Ř epková et al, 2006;Treuren et al, 2006;Watanabe et al, 2006) (Table 2).…”