Thesis (PhD (Agric)) -- Stellenbosch University, 2001. / ENGLISH ABSTRACT: Chromosome arm 7DL of common wheat carries genes for agronomically important traits such
as leaf rust, stem rust, Russian wheat aphid and eye spot resistance. Some of these genes occur
on introgressed foreign chromatin, which restricts their utility in breeding. The 7DL genetic
maps are poorly resolved, which seriously hampers attempts to manipulate the genes and
introgressed regions in breeding. This dissertation represents an attempt to improve our
knowledge of the relative map positions of three resistance genes that have significant potential
for use in local breeding programmes.
The leaf rust resistance gene, Lr19, is located on a Thinopyrum ponticum-derived translocation
which occupies a large part of the terminal end of 7DL. The translocation also carries genes for
less favourable traits such as yellow flour colour. Attempts have been made to reduce the size of
the translocation through allosyndetic pairing induction; the primary aims being to remove
deleterious genes and to minimise the amount of foreign chromatin associated with Lr19 so it can
be recombined with other useful 7DL genes. Twenty-nine 'Indis'-derived Lr 19 deletion mutants
were previously produced by gamma irradiation and a physical map was constructed. In this
study, the set of mutant lines were further analysed using 144 Sse8387I/Msei and 32 EcoRI/Msel
amplified fragment length polymorphism (AFLP) primer combinations. The previous physical
map, which was based on five restriction fragment length polymorphism (RFLP) markers and five
structural gene loci, was extended and now includes 95 novel AFLP markers (86 Sse8387I/Msei
and 9EcoRI!Msel markers), of which seven map close to Lr 19. Most of the deletions could be
ordered according to size and the improved map has already been used to characterise shortened
recombinant forms of the Lr 19 translocation. An unsuccessful attempt was made to convert one
of the seven markers closest to Lr 19 into a sequence-specific marker. However, an AFLP
marker located distally from Lr 19 was successfully converted into a sequence-specific marker in
collaboration 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 cM
and 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 homozygous
resistant 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 useful
polymorphisms (one in coupling and one in repulsion phase) were identified. Conversion of the
coupling phase marker to a sequence-specific marker was not successful.
The eyespot resistance gene, Pchl , was derived from Triticum ventricosum and is present in the
wheat VPM-1. Close association between Pchl and the endopeptidase Ep-Dlb allele has been
reported previously. Pchl/Ep-Dl was tagged by screening ten wheat genotypes (each
homozygous for the confirmed presence or absence of Pchl and/or Ep-Dl b) with 36
Sse83 87I/ Msei AFLP primer combinations. Three AFLP markers were closely associated with
Pchl I Ep-D 1, one of which was targeted for conversion into a sequence-specific marker. The
sequence-specific marker contained a microsatellite core motif and was found to be useful for
tagging Pchl!Ep-Dl. A genetic distance of 2 cM was calculated between the novel
microsatellite marker and Ep-Dl. The microsatellite marker was also polymorphic for the Lr 19
translocation 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 the
targeted regions, it was not possible to fully integrate the data obtained for the three regions. / AFRIKAANSE OPSOMMING: Chromosoom arm 7DL van broodkoring dra gene vir agronomies-belangrike kenrnerke soos
blaarroes, stamroes, Russiese koringluis en oogvlek weerstand. Sommige van hierdie gene kom
voor in blokke spesie-verhaalde chromatien wat hul bruikbaarheid in teling beperk. Die
genetiese kaarte van 7DL is swak ontwikkel en dit maak dit baie moeilik om hierdie gene en
spesie-verhaalde streke tydens teling te manipuleer. Hierdie proefskrif verteenwoordig 'n paging
om kennis van die relatiewe kaart liggings van drie weerstandsgene, met betekenisvolle
potensiaal in plaaslike tee! programme, te verbreed.
Die blaarroes weerstandsgeen, Lr 19, kom voor op 'n Thinopyrum ponticum-verhaalde
translokasie wat 'n groot terminale gedeelte van 7DL beslaan. Die translokasie dra ook gene vir
minder gewensde kenrnerke soos gee! meelkleur. Pogings is aangewend om die translokasie
deur homoeoloe parings-induksie te verkort. Die doe! was om nadelige gene te verplaas en die
hoeveelheid vreemde chromatien geassosieer met Lr 19 te minimiseer sodat dit met ander nuttige
gene op 7DL gerekombineer kan word. Nege-en-twintig 'Indis'-verhaalde Lr 19 delesie mutante
is vroeer met gamma bestraling geproduseer en gebruik om 'n fisiese kaart op te stel.
Teenswoordig is die stel mutante verder ontleed met behulp van 144 Sse8387I!Msei en 32
EcoRII Msel amplifikasie-fragment-lengte-polimorfisme (AFLP) inleier kombinasies. Die
bestaande fisiese kaart, wat gebaseer was op vyf restriksie-fragment-lengte-polimorfisme
(RFLP) merkers en vyf strukturele geen loki, is uitgebrei en sluit nou 95 unieke AFLP merkers
(86 Sse8387I/Msel en 9EcoRI/Msel merkers) in, waarvan sewe naby aan Lr19 karteer. Die
meeste van die delesies kon op grond van hulle grootte gegroepeer word en die verbeterde
fisiese kaart is alreeds gebruik om verkorte rekombinante vorms van die Lr 19 translokasie te
karakteriseer. 'n Onsuksesvolle paging is aangewend om een van die sewe merkers naaste aan
Lr 19 om te skakel na 'n volgorde-spesifieke merker. 'n AFLP merker wat distaal van Lr 19
karteer is egter wel suksesvol in samewerking met ander navorsers omgeskakel na 'n volgordespesifieke
merker.
'n Paging is ook aangewend om die Russiese koringluis (RKL) weerstandsgeen, Dn5, te karteer
en merkers gekoppel aan die geen te identifiseer. 'n Verdubbelde-haplo!ede karteringspopulasie
van 94 lyne is geskep en getipeer vir Dn5, vier mikrosatelliet loki en die endopeptidase lokus,
Ep-D1. Die Dn5 lokus karteer 25.4 cM en 28.6 cM distaal van Xgwml11 en Xgwm437, respektiewelik, maar was me gekoppel met Xgwm428, Xgwm37 of Ep-D1 me. Twaalf
homosigoties weerstandbiedende en sewe homosigoties vatbare F2 lyne uit die kruising:
'Chinese Spring' I 'PI 294994' is met 70 Sse8387VMsel AFLP inleier kombinasies getoets in 'n
poging om merkers vir Dn5 te identifiseer. Slegs twee moontlik bruikbare polimorfismes (een
in koppelings- en een in repulsie fase ), is ge'identifiseer. Omskakeling van die koppelingsfase
merker na 'n volgorde-spesifieke merker was onsuksesvol.
Die oogvlek weerstandsgeen, Pch1, is uit Triticum ventricosum oorgedra en kom voor in die
koringlyn, VPM-1. Noue koppeling van Pch1 en die endopeptidase alleel, Ep-D1 b, is vantevore
gerapporteer. Merkers is vir P chl I Ep-D 1 gevind deur tien koring genoti pes ( elkeen
homosigoties vir die bevestigde teenwoordigheid of afwesigheid van Pch1 en/of Ep-D1 b) te
toets met 36 Sse83871/kfsel AFLP inleier kombinasies. Drie AFLP merkers is gevind wat nou
koppel met Pchl!Ep-D1 , waarvan een gekies is vir omskakeling na 'n volgorde-spesifieke
merker. Die volgorde-spesifieke merker het 'n mikrosatelliet kernmotief bevat en was nuttig as
merker vir Pch1/Ep-D1. 'n Genetiese afstand van 2 cM is tussen die unieke mikrosatelliet
merker en Ep-D1 bereken. Die mikrosatelliet merker was ook polimorfies vir die Lr 19
translokasie en dit is tussen die Wsp-D1 en Sr25 loki gekarteer.
Kartering en/of identifikasie van merkers vir drie belangrike weerstandsgene was suksesvol in
hierdie studie. Omdat al die merkers wat gebruik is, nie polimorf was tussen al die streke van
belang nie, was dit nie moontlik om die data vir elk van die drie streke ten volle te integreer nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52474 |
| Date | 12 1900 |
| Creators | Groenewald, Johannes Zacharias |
| Contributors | Marais, G. F., Stellenbosch University. Faculty of AgricSciences. Dept. of Genetics & IPB. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 206 p. : ill. |
| Rights | Stellenbosch University |
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