Verkorting van die Ae. peregrina-verhaalde Lr59-translokasie van koring
Date
2009-03
Authors
Kotze, Luigia
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Abstract
The aim of this study was to analyse testcross-material that was generated during a
homoeologous pairing-induction experiment. Absence of the homoeologous pairing
suppressor gene, Ph1, was employed to induce meiotic pairing between the Lr59
translocation (Aegilops peregrina) and 1AL of normal wheat. The study aimed to
characterize the test-cross plants derived from this experiment and to identify recombinants
which retained the least amount of species chromatin but which still contained the Lr59
gene. The test-cross F1 population, 07M5 (total 635 plants), was screened for Lr59
resistance by inoculating seedlings with the leaf rust pathotype, UVPrt8. The 168 resistant
plants were characterized with molecular markers in order to identify recombinants. The
data were used to construct a physical map which showed the relative sizes of the
recombinants and which could be used to identify those recombinants which contained the
least 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 152
of the 168 resistant plants were recombinants for the four loci; that eight of the remaining
16 plants represented non-recombinant, wild species-types and that the last eight plants
represented the wheat parental-types which were resistant (and thus, also recombinants).
This extremely high recombination frequency can largely be attributed to strong
segregation distortion that was evident in the cross. It is also possible that the translocation
segment could derive from the S genome rather than the U genome of Ae. peregrina. The S
genome is closer related to the wheat genomes than the U genome and may be more prone
to recombination.
With the use of the microsatellite and SCAR data, a physical map was constructed which
showed the relative location of the Lr59 gene on the translocation. It appeared that the eight
shortest recombinants retained terminal species chromatin. In an attempt to characterize the
eight recombinants, additional marker loci had to be identified within that region. RAPD,
iv
AFLP and DArT markers were investigated for this purpose. RAPD analyses did not
produce any useful markers. AFLP and DArT analyses did identify useful markers with
which the eight recombinants could be screened. The data showed which recombinants
probably retained the least amount of species chromatin. Seeing that AFLP and DArT
markers are anonymous and that the distances between marker loci are unknown, it is not
possible to say which recombinant is the shortest and consequently it will be nessecary to
also evaluate the group of eight recombinants agronomically in order to identify the most
useful ones. The results showed that multiple cross-overs apparently occured on both sides
of Lr59. Multiple cross-overs are higly unlikely in material of this nature, therefore it was
speculated that the observation resulted from incomplete synteny between the telomeric
areas of the translocation and 1AL. A structural difference between the two chromosome
regions might have given rise to abnormal meiotic pairing structures and thus unexpected
gamete genotypes.
Each of the eight recombinants did express one or more of the Ae. peregrina derived AFLP
loci 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 which
contain the Lr59 resistance. It would, however, be risky to select only one of the shortest
recombinants for further development on the basis of the present knowledge as some
recombinants may contain genetic abnormalities which resulted from reduced synteny in
the Lr59 region. It would therefore be wise to further evaluate all eight recombinants before
the best one is selected for agronomic use.
Description
Keywords
Aegilops peregrina, Dissertations -- Genetics, Theses -- Genetics, Translocation (Genetics), Wheat -- Cytogenetics, Molecular markers, Wheat -- Diseases and pests -- Genetic aspects, Leaf rust in wheat