| Summary: | Thesis (MSc)--Stellenbosch University, 2012. === ENGLISH ABSTRACT: Plant diseases are among the major causes of food insecurity. In South Africa the wheat fungal
diseases including stem rust caused by Puccinia graminis f. sp. tritici, leaf rust caused by P.
triticina and stripe rust caused by P. striiformis f. sp. tritici are the most important. Genetic
resistance is a viable way of protecting wheat crops against the wheat rusts, especially cultivars
carrying multiple genes that confer durable resistance. In order to breed for multi-gene resistance an
effective breeding strategy that allows for selecting multiple resistance genes and other desirable
traits needs to be devised.
The aim of this study was to identify a number of genotypes with combinations of different rust
resistance genes, good grain yield and end-use quality out of an existing pre-breeding population
and thereby identify superior parents. In order to achieve the stated aim the following objectives
have been identified: identify wheat lines through marker-assisted selection (MAS) carrying the
gene complexes, Sr31/Lr26/Yr9, Lr24/Sr24, Lr37/Sr38/Yr17, Lr34/Yr18 and Sr2; to develop inbred
lines to evaluate selected lines under field trials.
From the initial subset of 64 lines, 60 were chosen and advanced to the doubled haploid (DH) phase
and seed multiplication. The 60 lines either carried one or more of the three rust resistance gene
complexes. The genes that were the most prominent were Sr31/Lr26/Yr9 and Lr24/Sr24. The
selected lines were incorporated into a DH seed multiplication phase. After 4 cycles of seed
increases and preliminary field evaluation during multiplication, 15 lines were chosen and subjected
to multi-location field trails.
The extensive multi-location field trails carried out in this study aided in identifying genotypes from
the 15 MS-MARS lines with good adaptability and stability in regards to yield and baking quality.
An important observation was that the molecular markers employed to indentify quality loci
correlated well with the genes encoding the HMW-GS 5, 10 and 12 as observed with the Agilent©
2100 Bioanalyzer.
In future studies the lines which performed the best could be re-introduced into the existing MSMARS
pre-breeding programme of the Stellenbosch University’s Plant Breeding Laboratory (SUPBL).
The frequencies of desired alleles could be increased in this manner. Since the majority of
these characteristics are influenced by quantitatively inherited alleles, using these lines as recurrent parents will increase the frequencies of these alleles in the existing SU-PBL pre-breeding
population. === AFRIKAANSE OPSOMMING: Plantsiektes is van die belangrikste oorsake van voedselonsekerheid ter wêreld. In Suid-Afrika is
die roesswamme van die belangrikste plantsiektes wat koring produksie beïnvloed. Hierdie siektes
sluit in, stamroes wat veroorsaak word deur Puccinia graminis f. sp. tritici, blaarroes wat
veroorsaak word deur P. triticina en streeproes wat veroorsaak word deur P. striiformis f. sp. tritici.
Genetiese weerstand is ‘n uitstekende manier om koring te beskerm teen hierdie swamsiektes.
Weerstand wat gebasseer is op veelvuldige weerstandsgene is veral ‘n goeie middel om genetieseweerstand
op ‘n volhoubare basis in koringteling toe te pas. Om veelvuldige weerstandsgene in
koringkultivars in te teel word ‘n effektiewe telingstrategie benodig.
Die doel van die studie was om genotipes te identifiseer met kombinasies van veelvuldige
weerstandsgene vir roes, sowel as goeie eienskappe belangrik vir graanopbrengs en bakkwaliteit.
Lyne is geïdentifiseer uit ‘n bestaande voortelingspopulasie van Stellenbosch Universiteit se
Planteteelt Laboratorium (SU-PTL) wat geteel was met spesifiek weerstand en opbrengs potensiaal
in gedagte. Om die doel van die studie te bereik is sekere doelwitte daar gestel. Hierdie doelwitte
sluit in om lyne uit die populasie te selekteer deur middel van merker bemiddelde seleksie (MBS)
vir gene naamlik Sr31/Lr26/Yr9, Lr24/Sr24, Lr37/Sr38/Yr17, Lr34/Yr18 en Sr2; om die
geselekteerde lyne suiwertelend te maak; sowel as om die suiwertelende lyne in veld proewe in te
sluit.
Van die oorspronklike stel van 64 lyne, is 60 gekies vir verdere studie. Deur middel van die
verdubbelde haploïed (VH) tegniek is die lyne suiwertelend gemaak. Die 60 lyne het een of meer
van die geselekteerde gene bevat. Die mees prominente gene was die twee geen komplekse
Sr31/Lr26/Yr9 en Lr24/Sr24. Na vier siklusse van saadvermeerdering en voorloppige seleksies is 15
lyne ingesluit by ‘n multi-omgewing veldproef.
Hierdie uitgebreide multi-omgewing veldproewe het gehelp om individue uit die 15 lyne te
identifiseer wat oor goeie aanpasbaarheid en stabiliteit beskik met betrekking tot opbrengs en bak
kwaliteit. Die molekulêre merkers gebruik om die gene verantwoordelik vir die kodering van HMGGS
5, 10 en 12 op te spoor het goed gekorreleer met die HMG-GS bande bepaal met behulp van die
Agilent© 2100 Bioanalyzer.
Toekomstige studies kan moontlik insluit die gebruik van die lyne wat geïdentifiseer was met goeie
kenmerke in die bestaande MS-MARS teelprogram van die SU-PTL. Die frekwensies van die
verlangde allele kan op hierdie manier in die populasie verhoog word.
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