Thesis (PhD (Agric)) -- Stellenbosch University, 2003. / ENGLISH ABSTRACT: Stripe (yellow) rust of wheat, caused by Puccinia striiformis f.sp. tritici, was first detected as a
single introduction into South Africa in 1996. Two additional pathotypes have since been
identified. Control of the disease may be achieved by use of genetic adult plant resistance
(APR) as is present in the local cultivar 'Kariega'. The aim of this project was to understand the
genetic basis of the APR in 'Kariega' to facilitate breeding of new varieties with genetic
resistance to stripe rust.
A partial linkage map of a 'Kariega X Avocet S' doubled haploid population covering all 21
wheat chromosomes was generated using 208 DNA markers, viz, 62 SSR, 133 AFLP, 3 RGA
and 10 SRAP markers, and 4 alternative loci. The different marker techniques detected varying
polymorphism, viz, overall SSR: 46%, AFLP: 7%, SRAP: 6% and RGA: 9%, and the markers
produced low levels of missing data (4%) and segregation distortion (5%). A significant feature
of the linkage map was the low polymorphism found in the D genome, viz, 19% of all mapped
DNA markers, 11% of all AFLP markers and 30% of the total genome map distance. A region
exhibiting significant segregation distortion was mapped to chromosome 4A and a seedling
resistance gene for stem rust (Puccinia graminis f.sp . tritici), Sr26, mapped to chromosome 6A
close to three SSR markers. The leaf tip necrosis gene, Ltn, which was also segregating in the
population, mapped to chromosome 7D. Protocols for SRAP and RGA were optimised, and
SRAP marker use in wheat genetic linkage studies is reported for the first time.
The linkage map was used together with growth chamber and replicated field disease scores for
QTL mapping. Chromosomes showing statistically significant QTL effects were then targeted
with supplementary SSR markers for higher resolution mapping. The quality of disease
resistance phenotypic data was confirmed by correlation analysis between the different scorers
for reaction type (0.799±0.023) and for transformed percentage leaf area infected
(0.942±0.007).
Major QTL were consistently identified on chromosome 7D (explaining some 25-48% of the
variation) and on chromosome 2B (21-46%) using transformed percentage leaf area infected and transformed reaction type scores (early and final) with interval mapping and modified
interval mapping techniques. Both chromosomal regions have previously been identified in
other studies and the 7D QTL is thought likely to be the previously mapped APR gene Yr 18.
Minor QTL were identified on chromosomes lA and 4A with the QTL on 4A being more
prominent at the early field scoring for both score types. A QTL evidently originating from
'Avocet S' was detected under growth chamber conditions but was not detected in the field,
suggesting genotype-environment interaction and highlighting the need for modifications of
growth chamber conditions to better simulate conditions in the field.
The genetic basis of the APR to stripe rust exhibited by 'Kariega' was established by mapping
of QTL controlling this trait. The linkage map constructed will be a valuable resource for
future genetic studies and provides a facility for mapping other polymorphic traits in the
parents of this population with a considerable saving in costs. / AFRIKAANSE OPSOMMING: Streep of geelroes van koring word veroorsaak deur Puccinia striiformis f. sp tritici, en is die
eerste keer in 1996 in Suid-Afrika na introduksie van 'n enkele patotipe waargeneem. Twee
verdere patotipes is sedertdien in Suid-Afrika gei"dentifiseer. Beheer van die siekte word veral
moontlik gemaak deur die gebruik van genetiese volwasseplantweerstand soos gei"dentifiseer in
die plaaslike kultivar 'Kariega'. Die doel van hierdie studie was om die genetiese grondslag van
die streeproesweerstand te ontrafel ten einde die teling van nuwe bestande kultivars moontlik te
maak.
'n Verdubbelde haplo1ede populasie uit die kruising 'Kariega X Avocet S' is aangewend om 'n
gedeeltelike koppelingskaart vir die volle stel van 21 koring chromosome saam te stel. Die kaart
het uit 208 DNA merkers, nl., 62 SSR, 133 AFLP, 3 RGA, 10 SRAP merkers en 4 ander lokusse
bestaan. Totale polimorfisme wat deur die verskillende merkersisteme opgespoor is, was as volg:
SSR: 46%, RGA: 9%, AFLP: 7% en SRAP: 6%. Die mate van ontbrekende data was gering
(4%) asook die mate van segregasie distorsie (5%) van 'n enkele geval wat op chromosoom 4A
gekarteer is. 'n Prominente kenmerk van die koppelingskaart is die relatiewe gebrek aan
polimorfiese merkers op die D-genoom, nl., slegs 19% van alle DNA merkers en 11% van alle
AFLP merkers wat slegs 30% van die totale genoom kaartafstand bestaan het. Die stamroes
(Puccinia graminis f. sp. tritici) saailingweerstandsgeen, Sr26, karteer op chromosoom 6A naby
drie SSR merkers. Die geen vir blaartipnekrose, Ltn, karteer op chromosoom 7D. Protokolle vir
SRAP en RGA merkers is ge-optimiseer en gebruik van SRAP merkers in koppelings-analise
word vir die eerste keer in koring gerapporteer.
Die koppelingskaart is in kombinasie met groeikamerdata en gerepliseerde veldproefdata gebruik
om die gene (QTL) vir volwasseplant streeproesweerstand te karteer. Chromosome met statisties
betekenisvolle QTL is met aanvullende SSR merkers geteiken om die resolusie van kartering
verder te verhoog. Die kwaliteit van fenotipiese data, soos in die proewe aangeteken, is bevestig
deur korrelasies te bereken tussen lesings geneem deur onafhanklike plantpataloe (0.799 ± 0.023
vir reaksietipe en 0.942 ± 0.007 vir getransformeerde persentasie blaaroppervlakte besmet).
Hoofeffek QTL vir die twee maatstawwe van weerstand is deur middel van die metodes van
interval QTL kartering en gemodifiseerde interval QTL kartering konsekwent op chromosome
7D (25-48% van variasie verklaar) en 2B (21-46% van variasie verklaar) ge"identifiseer. In
vorige studies is aangetoon dat beide chromosome 7D en 2B QTL vir volwasseplant
streeproesweerstand dra. Die 7D QTL is waarskynlik die weerstandsgeen, Yr 18. QTL met klein
effekte op weerstand is op chromosome lA en 4A ge"identifiseer. Die effek van laasgenoemde
geen was meer prominent in die velddata in die vroee datum van weerstandsbeoordeling. Een
QTL, afkomstig van 'Avocet S', is slegs onder groeikamertoestande identifiseerbaar. Dit dui op
moontlike genotipe-omgewing wisselwerking en beklemtoon die noodsaaklikheid om
aanpassings te maak in groeikamertoestande vir beter simulasie van veldproeftoestande.
Die genetiese grondslag van volwasseplantweerstand teen streeproes in die kultivar 'Kariega' is
deur QTL kartering bepaal. Die 'Kariega X Avocet S' koppelingskaart kan as 'n waardevolle basis
dien vir toekomstige genetiese ontledings van ander polimorfiese kenmerke in die populasie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53438 |
| Date | 04 1900 |
| Creators | Ramburan, Viresh Premraj |
| Contributors | Prins, R., Louw, J. H., Warnich, L., 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 | 132 p. : ill. |
| Rights | Stellenbosch University |
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