Tagging and mapping of prominent structural genes on chromosome arm 7DL of common wheat

[摘要] ENGLISH ABSTRACT:Chromosome arm 7DL of common wheat carries genes for agronomically important traits suchas leaf rust, stem rust, Russian wheat aphid and eye spot resistance. Some of these genes occuron introgressed foreign chromatin, which restricts their utility in breeding. The 7DL geneticmaps are poorly resolved, which seriously hampers attempts to manipulate the genes andintrogressed regions in breeding. This dissertation represents an attempt to improve ourknowledge of the relative map positions of three resistance genes that have significant potentialfor use in local breeding programmes.The leaf rust resistance gene, Lr19, is located on a Thinopyrum ponticum-derived translocationwhich occupies a large part of the terminal end of 7DL. The translocation also carries genes forless favourable traits such as yellow flour colour. Attempts have been made to reduce the size ofthe translocation through allosyndetic pairing induction; the primary aims being to removedeleterious genes and to minimise the amount of foreign chromatin associated with Lr19 so it canbe recombined with other useful 7DL genes. Twenty-nine 'Indis'-derived Lr 19 deletion mutantswere previously produced by gamma irradiation and a physical map was constructed. In thisstudy, the set of mutant lines were further analysed using 144 Sse8387I/Msei and 32 EcoRI/Mselamplified fragment length polymorphism (AFLP) primer combinations. The previous physicalmap, which was based on five restriction fragment length polymorphism (RFLP) markers and fivestructural gene loci, was extended and now includes 95 novel AFLP markers (86 Sse8387I/Mseiand 9EcoRI!Msel markers), of which seven map close to Lr 19. Most of the deletions could beordered according to size and the improved map has already been used to characterise shortenedrecombinant forms of the Lr 19 translocation. An unsuccessful attempt was made to convert oneof the seven markers closest to Lr 19 into a sequence-specific marker. However, an AFLPmarker located distally from Lr 19 was successfully converted into a sequence-specific marker incollaboration with other researchers.An attempt was also made to map and tag the Russian wheat aphid (RWA) resistance gene, Dn5.A doubled haploid mapping population consisting of 94 lines was created and typed for Dn5,four microsatellite loci and the endopeptidase locus, Ep-Dl. The Dn5 locus mapped 25.4 cMand 28.6 cM distally from Xg.vm111 and Xg.vm437, respectively, but was not linked to Xgwm428, Xgwm3 7 or Ep-Dl. Tagging of Dn5 was attempted by screening twelve homozygousresistant and seven homozygous susceptible F2 lines from a cross between 'Chinese Spring' and'PI 294994' with 70 Sse8387IIi\1sei AFLP primer combinations. Only two potentially usefulpolymorphisms (one in coupling and one in repulsion phase) were identified. Conversion of thecoupling phase marker to a sequence-specific marker was not successful.The eyespot resistance gene, Pchl , was derived from Triticum ventricosum and is present in thewheat VPM-1. Close association between Pchl and the endopeptidase Ep-Dlb allele has beenreported previously. Pchl/Ep-Dl was tagged by screening ten wheat genotypes (eachhomozygous for the confirmed presence or absence of Pchl and/or Ep-Dl b) with 36Sse83 87I/ Msei AFLP primer combinations. Three AFLP markers were closely associated withPchl I Ep-D 1, one of which was targeted for conversion into a sequence-specific marker. Thesequence-specific marker contained a microsatellite core motif and was found to be useful fortagging Pchl!Ep-Dl. A genetic distance of 2 cM was calculated between the novelmicrosatellite marker and Ep-Dl. The microsatellite marker was also polymorphic for the Lr 19translocation and it was possible to map it between the Wsp-Dl and Sr25 loci.In this dissertation, mapping and/or tagging of three important resistance genes were achieved.Due to the fact that all markers used in these studies were not polymorphic between all of thetargeted regions, it was not possible to fully integrate the data obtained for the three regions.

[发布机构] Stellenbosch University