Thesis (PhD (Genetics))--University of Stellenbosch, 2010. / Includes bibliography. / ENGLISH ABSTRACT: The wild relatives are an important source of new genes for the genetic improvement
of wheat. At Stellenbosch University the leaf and stripe rust resistance genes Lr54 and
Yr37 were transferred from Aegilops kotschyi to chromosome 2DL of wheat. In an
attempt to reduce the size of the whole-arm translocation on which the resistance
genes occur, homoeologous pairing was induced between the wheat and
corresponding Ae. kotschyi chromatin. The purpose of this study was to: (i) Evaluate
the testcross progeny thus obtained; identify translocation recombinants that retained
Lr54/Yr37 and to characterize these using molecular markers (ii) Test for the presence
of genes for photoperiod insensitivity (Ppd) and reduced height (Rht) believed to be
associated with the translocation (iii) Develop a SCAR marker for the most useful
recombinant that could be recovered.
Ten putative translocation recombinants were identified following the
screening of 159 hemizygous testcross F1 plants with three microsatellite markers
specific for chromosome arm 2DL. The recombinants were then characterized with
another five microsatellite markers. Using the eight microsatellite markers the
recombinants were ordered in two size categories with recombinant #74 being the
shortest and having retained only proximal alien chromatin on 2DL. In addition to
microsatellite markers, RAPDs, RGAs, AFLPs and SCAR markers were genetically
mapped to the translocation and further resolved the recombinants into three size
categories. In an attempt to find suitable markers linked to the shortest recombinant
(#74) a polymorphic 410 bp AFLP fragment produced with the enzyme/selective
nucleotide combination EcoRI – AAC/MseI – CAT, was converted into a dominant
SCAR marker. In addition three microsatellite markers that mapped to recombinant
#74 provided a useful recessive molecular marker system to detect Lr54/Yr37.
Evaluation of the 10 recombinants with four 2DS-specific microsatellite markers
revealed a large deletion of this chromosome arm in recombinant #74. This deletion
may affect plant phenotypic characteristics and a strategy to replace the deleted region
in recombinant #74 is proposed. To test for the presence of a gene for photoperiod insensitivity on the translocation,
translocation-carriers plus controls were subjected to long and short day treatments,
and the effect on time to flowering was studied. However, no evidence was found for
the presence of such a gene. A height experiment to test for the presence of an Rht
gene on the translocation confirmed its presence. This gene (designated H) appeared
to be different from Rht8 on chromosome 2DS and was mapped on 2DL. While H
does not occur in a chromosome region that corresponds with the location of Rht8, it
does not rule out the possibility that they could be orthologous loci. Plant height data
obtained for recombinant #74 suggested that H was lost through recombination in this
particular recombinant. A greenhouse experiment suggested that the full-length
translocation increased 100 kernel mass but had a detrimental effect on overall plant
yield. Since a much shorter recombinant (#74) has been obtained, this will also have
to be evaluated for associated effects. Such an evaluation needs to be done under
commercial growing conditions and should involve the comparison of near-isogenic
bulks with and without recombinant chromosome #74.
The stripe rust resistance gene (Yr37) was mapped by screening hemizygous
TF2 progeny of the 10 recombinants with Puccinia striiformis pathotype 6E22A+.
Recombinant #74 retained both Lr54 and Yr37 and the two genes therefore occur
towards the centromere. / AFRIKAANSE OPSOMMING: Wilde verwante spesies is ‘n belangrike bron van nuwe gene vir die genetiese
verbetering van koring. By die Universiteit van Stellenbosch is die blaar-roes en
streep-roes weerstandsgene Lr54 en Yr37 vanaf Aegilops kotschyi na chromosoom
2DL van koring oorgedra. ‘n Poging is vervolgens aangewend om die vol-armtranslokasie
waarop die weerstandsgene voorkom te verklein deur homoeoloë paring
tussen die koring en ooreenstemmende Ae. kotschyi chromatien te induseer. Die
doelstelling van hierdie studie was daarom as volg: (a) Evaluering van die verkreë
toetskruis-nageslag asook die identifisering en karakterisering van translokasie
rekombinante wat Lr54/Yr37 behou het. (b) Toetsing vir fotoperiode onsensitiwiteits-
(Ppd) en verkorte plant-hoogte (Rht) gene wat moontlik op die translokasie kon
voorkom. (c) Die ontwikkeling van ‘n volgorde-spesifieke polimerase kettingreaksie
(PKR) vir die mees bruikbare rekombinant.
Tien translokasie rekombinante is geïdentifiseer nadat 159 hemisigotiese
toetskruis F1-plante met drie mikrosatelliet-merkers, spesifiek vir chromosoom-arm
2DL, ge-evalueer is. Die rekombinante is hierna met vyf verdere mikrosatellietmerkers
getoets. Die data van die agt mikrosatelliet-loci het die rekombinante in twee
grootte-kategorieë geplaas waarvan rekombinant #74 die kortste was met slegs die
proksimale gedeelte van 2DL wat uit vreemde chromatien bestaan. Behalwe
mikrosatellite-merkers is toevallig-geamplifiseerde polimorfiese DNS (RAPD),
weerstandsgeen-analoog (RGA), geamplifiseerde volgordelengte polimorfisme
(AFLP) en volgorde-gekarakteriseerde geamplifiseerde-streke (SCAR) merkers ook
geneties op die translokasie gekarteer. Data van die addisionele merkers het dit
moontlik gemaak om die rekombinante in drie grootte-kategorieë te skei. Pogings om
‘n merker vir die kortse rekombinant (#74) te vind, het gelei tot die omskakeling van
‘n 410 bp polimorfiese AFLP-fragment (geproduseer met die ensiem/selektiewenukleotied
kombinasie EcoRI - AAC/MseI - CAT), na ‘n dominante, volgordespesifieke
PKR-merker. Hierbenewens kan drie mikrosatelliet-merkers wat op
rekombinant #74 karteer as resessiewe merkers vir die identifisering van Lr54/Yr37
gebruik word. Die evaluering van die 10 rekombinante met vier chromosoom 2DSspesifieke
mikrosatelliet-merkers het ‘n groot delesie van chromosoom-arm 2DS in rekombinant #74 uitgewys. Die delesie mag plant fenotipiese kenmerke beïnvloed en
daarom is ‘n strategie vir die vervanging daarvan in rekombinant #74 voorgestel.
Ten einde te toets of ‘n geen vir fotoperiode-onsensitiwiteit op die translokaie
voorkom is translokasie-draers en kontroles aan lang- en kortdag-behandelings
onderwerp en is die effek hiervan op dae-tot-blom gemeet. Geen bewyse vir so ‘n
geen kon gevind word nie. ‘n Hoogte-eksperiment om te toets vir die teenwoordigheid
van ‘n Rht-geen op die translokasie, het bevestig dat so ‘n geen wel voorkom. Die
geen (voorgestelde simbool H) is gekarteer op 2DL en verskil oënskynlik van Rht8 op
chromosoom 2DS. Die verskillende chromosoom-ligging van H en Rht8 skakel egter
nie die moontlikheid dat hulle ortoloë loci mag wees uit nie. Plant-hoogte data vir
rekombinant #74 het daarop gedui dat H nie meer in hierdie rekombinant voorkom
nie. Data van ‘n glashuis-eksperiment het daarop gedui dat die vollengte-translokasie
100-korrel-massa verhoog maar dat dit plant-opbrengs verlaag. Aangesien ‘n
aansienlike korter rekombinant (#74) verkry is, sal dit ook vir gekoppelde effekte
getoets moet word. So ‘n evaluering moet egter onder kommersiële toestande gedoen
word met gebruik van naby isogeniese-lyne met en sonder rekombinante chromosoom
#74.
Die streep-roes weerstandgeen (Yr37) is gekarteer deur hemisigotiese TF2-
nageslag van die 10 rekombinante te toets vir weerstand teen Puccinia striiformis
patotipe 6E22A+. Rekombinant #74 het beide Lr54 en Yr37 behou en die twee gene
karteer dus naby die sentromeer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5172 |
| Date | 12 1900 |
| Creators | Heyns, I.C. |
| Contributors | Marais, G. F., University of Stellenbosch. Faculty of Agrisciences. Dept. of Genetics. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 205 p. : ill. |
| Rights | University of Stellenbosch |
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