Thesis (PhD)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Gray leaf spot (GLS) of maize, caused by the fungus Cercospora zeae-maydis,
can reduce grain yields by up to 60% and it is now recognized as one of the most
significant yield-limiting diseases of maize in many parts of the world. The most
sustainable and long-term management strategy for GLS will rely heavily on the
development of high-yielding, locally adapted GLS resistant hybrids.
Molecular markers could be useful to plant breeders to indirectly select for genes
affecting GLS resistance and to identify resistance genes without inoculation and
at an early stage of plant development. Only two studies in the USA have
examined quantitative trait loci (QTL) association with GLS resistance.
The aim of this study was to map GLS resistance genes in a resistant Seed Co
LTD, Zimbabwean inbred line. Molecular markers linked to the GLS resistance
QTL were identified by using the amplified fragment length polymorphism (AFLP)
technique together with bulked segregant analysis. Eleven polymorphic AFLP
fragments were identified and converted to sequence-specific PCR (polymerase
chain reaction) markers. Eight of the 11 converted AFLP markers were added to
the maize marker database of the University of Stellenbosch.
Five of the 8 converted AFLP markers were polymorphic between the resistant
and the susceptible parent. They were amplified on the DNA of 230 plants of a
segregating F2 population and linkage analysis was performed with
MAPMAKER/EXP. Two linkage groups consisting of two markers each, with a
linkage distance of 10.4 cM (LOD 22.83) and 8.2 cM (LOD 55.41) between the
two markers, were identified. QTL mapping with MAPMAKER/QTL confirmed the
presence of QTL in both linkage groups. Two publicly available recombinant inbred families (Burr et a/., 1988) were used
to localize the converted AFLP markers on the genetic map of maize. The QTL,
which were identified with the AFLP markers, were mapped to chromosomes 1
and 5. Another AFLP marker was mapped to chromosome 2 and a further to
chromosome 3.
To obtain more precise localizations of the QTL on chromosomes 1 and 5,
sequence-tagged site markers and microsatellite markers were used. The
markers were amplified on the DNA of the 230 plants of the F2 population and
linkage analysis was performed with MAPMAKER/EXP. The order of the markers
was in agreement with the UMC map of the Maize Genome Database. Interval
mapping using MAPMAKERlQTL and composite interval mapping using QTL
Cartographer were performed. The QTL on chromosome 1 had a LOD score of
21 and was localized in bin 1.05/06. A variance of 37% was explained by the
QTL. Two peaks were visible for the QTL on chromosome 5, one was localized in
bin 5.03/04 and the other in bin 5.05/06. Both peaks had a LOD score of 5 and
11% of the variance was explained by the QTL.
To test the consistency of the detected QTL, the markers flanking each QTL
were amplified on selected plants of two F2 populations planted in consecutive
years and regression analysis was performed. Both the QTL on chromosome 1
and the QTL on chromosome 5 were detected in these populations. Furthermore,
the presence of a QTL on chromosome 3 was confirmed with these populations.
A variance of 8 -10% was explained by the QTL on chromosome 3.
In this study, a major GLS resistance QTL was thus mapped on chromosomes 1
and two minor GLS resistance QTL were mapped on chromosomes 3 and 5
using a resistant Seed Co LTD, Zimbabwean inbred line. Markers were identified
which could be used in a marker-assisted selection program to select for the GLS
resistance QTL. / AFRIKAANSE OPSOMMING: Grys blaarvlek (GBV) van mielies, veroorsaak deur die swam Cercospora zeaemaydis,
kan graanopbrengs met tot 60% verlaag en word beskou as een van die
vernaamste opbrengs-beperkende siektes wêreldwyd. Die toepaslikste
langtermyn stragtegie vir GBV beheer sal wees om plaaslike mieliebasters met
hoë opbrengs en GBV weerstand te ontwikkel.
Molekulêre merkers kan nuttig deur plantetelers gebruik word om
weerstandsgene te selekteer. Seleksie is moontlik in die afwesigheid van
inokolum en op 'n vroeë stadium van plant ontwikkeling. Slegs twee vorige
studies (in die VSA) het kwantitatiewe-kenmerk-Iokusse (KKL), vir GBVweerstand
ondersoek.
Die doel van hierdie studie was om die GBV weerstandsgene in 'n
weerstandbiedende ingeteelde lyn (Seed Co BPK, Zimbabwe) te karteer.
Molekulêre merkers gekoppel aan die GBV weerstands KKL is geïdentifiseer
deur gebruik te maak van die geamplifiseerde-fragmentlengte-polimorfisme-
(AFLP-) tegniek en gebulkte-segregaat-analise. Elf polimorfiese merkers is
geïdentifiseer en omgeskakel na volgorde-spesifieke PKR (polimerase
kettingreaksie) merkers. Agt van die elf omgeskakelde AFLP-merkers is by die
mieliemerker databasis van die Universiteit van Stellenbosch gevoeg.
Vyf van die 8 omgeskakelde AFLP-merkers was polimorfies tussen die bestande
en vatbare ouers. Hulle is geamplifiseer op die DNA van 230 plante van 'n
segregerende F2-populasie en is gebruik in 'n koppelingstudie met
MAPMAKER/EXP. Twee koppelingsgroepe, elk bestaande uit twee merkers, met
onderskeidelik koppelingsafstande van 10.4 eM (LOD 22.83) en 8.2 eM (LOD
55.41) tussen die merkers, is geïdentifiseer. KKL-kartering het getoon dat KKL in
albei koppelingsgroepe aanwesig is. Twee kommersieël beskikbare, rekombinant-ingeteelde families (Burr et aI.,
1988) is gebruik om die omgeskakelde AFLP-merkers op die mielie genetiese
kaart te plaas. Die KKL wat met die AFLP-merkers geïdentifiseer is, is gekarteer
op chromosome 1 en 5. 'n Verdere AFLP-merker is op chromosoom 2 gekarteer
en 'n ander op chromosoom 3.
Ten einde die KKL op chromosome 1 en 5 meer akkuraat te karteer, is volgordege-
etikeerde en mikrosatelliet merkers gebruik. Die merkers is geamplifiseer op
die DNA van die 230 plante van die F2-populasie en koppelings-analises is
uitgevoer. Die volgorde van die merkers was dieselfde as die van die UMC-kaart
in die Mielie Genoom Databasis. Interval kartering met MAPMAKER/QTL en
komposiet interval kartering met QTL Cartographer is uitgevoer. Die KKL op
chromosoom 1 het 'n LOD-telling van 21 gehad en is in bin 1.05/06 geplaas. Die
KKL was verantwoordelik vir 37% van die variansie. Twee pieke was
onderskeibaar vir die KKL op chromosoom 5, een in bin 5.03/04 geleë en die
ander in bin 5.05/06. Elke piek het 'n LOD-telling van 5 gehad en die twee KKL
was verantwoordelik vir 11% van die variansie.
Om die herhaalbaarheid van die effek van die KKL te toets is die merkers naaste
aan elke KKL geamplifiseer op geselekteerde plante van twee F2-populasies wat
in opeenvolgende jare geplant is. Regressie analise is op die data gedoen. Beide
die KKL op chromosoom 1 en die KKL op chromosoom 5 kon in hierdie
populasies geïdentifiseer word. Verder kon die aanwesigheid van 'n verdere KKL
op chromosoom 3 in hierdie populasies bevestig word. Laasgenoemde KKL was
verantwoordelik vir 8-10% van die totale variansie.
In hierdie studie is daar dus 'n hoof GBV-weerstands KKL gekarteer op
chromosoom 1 en twee kleiner GBV-weerstands KKL gekarteer op chromosome
3 en 5. Merkers is geïdentifiseer wat moontlik in merker-gebaseerdetelingsprogramme
gebruik kan word om plante te selekteer wat die GBVweerstands
KKL het.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51776 |
| Date | 12 1900 |
| Creators | Lehmensiek, Anke |
| Contributors | Retief, A. E., Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 168 pages : illustrations |
| Rights | Stellenbosch University |
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