Verkorting van die Ae. peregrina-verhaalde Lr59-translokasie van koring

[摘要] The aim of this study was to analyse testcross-material that was generated during ahomoeologous pairing-induction experiment. Absence of the homoeologous pairingsuppressor gene, Ph1, was employed to induce meiotic pairing between the Lr59translocation (Aegilops peregrina) and 1AL of normal wheat. The study aimed tocharacterize the test-cross plants derived from this experiment and to identify recombinantswhich retained the least amount of species chromatin but which still contained the Lr59gene. The test-cross F1 population, 07M5 (total 635 plants), was screened for Lr59resistance by inoculating seedlings with the leaf rust pathotype, UVPrt8. The 168 resistantplants were characterized with molecular markers in order to identify recombinants. Thedata were used to construct a physical map which showed the relative sizes of therecombinants and which could be used to identify those recombinants which contained theleast amount of residual species chromatin.Microsatellite (Xcfa2219, Xbarc83 and Xgwm164) and SCAR (S15T3)analysis was used for the initial identification of recombinants. The results showed that 152of the 168 resistant plants were recombinants for the four loci; that eight of the remaining16 plants represented non-recombinant, wild species-types and that the last eight plantsrepresented the wheat parental-types which were resistant (and thus, also recombinants).This extremely high recombination frequency can largely be attributed to strongsegregation distortion that was evident in the cross. It is also possible that the translocationsegment could derive from the S genome rather than the U genome of Ae. peregrina. The Sgenome is closer related to the wheat genomes than the U genome and may be more proneto recombination.With the use of the microsatellite and SCAR data, a physical map was constructed whichshowed the relative location of the Lr59 gene on the translocation. It appeared that the eightshortest recombinants retained terminal species chromatin. In an attempt to characterize theeight recombinants, additional marker loci had to be identified within that region. RAPD, ivAFLP and DArT markers were investigated for this purpose. RAPD analyses did notproduce any useful markers. AFLP and DArT analyses did identify useful markers withwhich the eight recombinants could be screened. The data showed which recombinantsprobably retained the least amount of species chromatin. Seeing that AFLP and DArTmarkers are anonymous and that the distances between marker loci are unknown, it is notpossible to say which recombinant is the shortest and consequently it will be nessecary toalso evaluate the group of eight recombinants agronomically in order to identify the mostuseful ones. The results showed that multiple cross-overs apparently occured on both sidesof Lr59. Multiple cross-overs are higly unlikely in material of this nature, therefore it wasspeculated that the observation resulted from incomplete synteny between the telomericareas of the translocation and 1AL. A structural difference between the two chromosomeregions might have given rise to abnormal meiotic pairing structures and thus unexpectedgamete genotypes.Each of the eight recombinants did express one or more of the Ae. peregrina derived AFLPloci which can in future be verified for use as a marker for marker assisted selection.The study succeeded in identifying a number of potentially useful recombinants whichcontain the Lr59 resistance. It would, however, be risky to select only one of the shortestrecombinants for further development on the basis of the present knowledge as somerecombinants may contain genetic abnormalities which resulted from reduced synteny inthe Lr59 region. It would therefore be wise to further evaluate all eight recombinants beforethe best one is selected for agronomic use.

[发布机构] Stellenbosch University