Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Soil salinity is a major limiting factor of plant and crop growth, because the absorption of
water and nutrients is such a complex process while low and moderate salinity are
omnipresent. Plant growth is affected negatively if a specific ion concentration exceeds its
threshold and becomes toxic. The detrimental effect of soil affected by salt on crop
production is increasing worldwide (Tanji, 1990). The level to which plants can tolerate
high salinity levels is genetically controlled with several physiological and genetic
mechanisms contributing to salt tolerance (Epstein & Rains, 1987). The most effective way
of addressing the limitations of crop productivity in saline areas, is the development of salt
tolerant varieties. Understanding the genetics of salt tolerance is, therefore, necessary for
the development of an effective breeding strategy for salt tolerance.
The department of Genetics (US) conducts a wide crosses research programme aiming to
transfer genes for salt tolerance to wheat and triticale. The donor species, Thinopyrum
disticum, an indigenous coastal wheat grass, adapted to high concentrations of salt, was
crossed with cultivated rye (Secale cereale) in an attempt to study the genetics of salt
tolerance (Marais et al., 1998).
The primary goal of this study was to find molecular markers (RAPD and AFLP) which
associate with chromosomes promoting salt tolerance for later attempts to transfer the
genes to triticale. Seventy clones of secondary hybrids (Th disticum /4x-rye 1/2x-rye) were
tested for salt tolerance and showed different levels of salt tolerance. RAPD-marker
analyses were used to identify polymorphisms between salt tolerant and salt sensitive
plants. Twelve RAPD primers produced clear, analyzable and repetitive polymorphic
. fragments that can be used as useful markers. Different AFLP-primer combinations were
tested against the genotypes of 15 clones (Marais & Marais 2001, unpublished data) and
produced approximately 2000 clearly distinguishable AFLP fragments, of which 54 (3%)
were polymorphic fragments. Two RAPD fragments and 4 AFLP fragments that can be
used as possible markers for the presence of chromosomes that contribute to salt
tolerance were identified.
The interpretation of the markers was complicated by heterogeneity among plants with
regard to the origin of their chromosomes and the genetic diversity of the rye genome. It is also possible that chromosome re-arrangement took place during backcrossing, which
could have complicated the data. / AFRIKAANSE OPSOMMING: Versouting is een van die groot beperkende faktore op plant- en gewasgroei, omdat die
opname van water en voedingstowwe so In ingewikkelde proses is en die effek van lae of
matige versouting so alomteenwoordig is. Plantgroei word nadelig geaffekteer as 'n
spesifieke ioonkonsentrasie sy drempelwaarde oorskry en toksies word. Die nadelige effek
van soutgeaffekteerde grond op gewasproduksie, is wêreldwyd aan die toeneem (Tanji,
1990). Die vlak waartoe plante hoë konsentrasies sout kan hanteer is onder genetiese
beheer met verskeie fisiologiese en genetiese meganismes wat 'n bydrae maak tot
soutverdraagsaamheid (Epstein & Rains, 1987). Die mees effektiewe manier om die
beperkinge op gewas produktiwiteit in versoute gebiede te oorkom, is die ontwikkeling van
soutverdraagsame variëteite. Begrip van die genetika van soutverdraagsaamheid is dus
noodsaaklik vir die ontwikkeling van In effektiewe telingsstrategie.
Die departement Genetika (US) bedryf tans 'n wye-kruisings navorsingsprogram waarmee
gepoog word om gene vir soutverdraagsaamheid na korog en koring oor te dra. Die
skenkerspesie, Thinopyrum disticum, In inheemse strandkoringgras wat aangepas is by
hoë konsentrasies sout, is gekruis met verboude rog (Secale cereale) in 'n poging om die
oorerwing van soutverdraagsaamheid te bestudeer (Marais et al., 1998).
Die hoofdoel van hierdie studie was om molekulêre merkers (RAPD en AFLP) te vind,
wat assosieer met chromosome wat soutverdraagsaamheid bevorder en om nuttige
merkers daar te stel vir latere pogings om die gene na korog en koring oor te dra.
Ongeveer 70 klone van sekondêre hibriede (Th distichum I 4x-rog /I 2x-rog) is onderwerp
aan souttoetse en het verskillende grade van soutverdraagsaamheid getoon. RAPDmerker
analise is gebruik om polimorfismes te identifiseer tussen soutverdraagsame en
soutsensitiewe plante. Twaalf RAPD inleiers het duidelike, ontleedbare en herhalende
polimorfiese fragmente opgelewer en moontlike nuttige merkers uitgewys. Verskillende
AFLP-inleier kombinasies, wat getoets is teen die genotipes van 15 klone (Marais &
Marais, 2001 ongepubliseerde data) het ongeveer 2000 duidelik onderskeibare AFLP
fragmente geproduseer, waarvan 54 (3%) polimorfiese fragmente was. Twee RAPD
fragmente en 4 AFLP fragmente is geïdentifiseer wat as moontlike kandidaat merkers
gebruik kan word vir die identifisering van chromosome wat bydra tot
soutverdraagsaamheid . Die interpretasie van die merkers is bemoeilik deur heterogeniteit tussen die plante wat
betref die agtergrond van chromosome wat hulle besit en die genetiese diversiteit van die
rog genoom. Dit is ook moontlik dat chromosoom herrangskikking plaasgevind het tydens
terugkruising, wat die data verder kon kompliseer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52904 |
| Date | 03 1900 |
| Creators | Jacobs, Johan Adolf |
| Contributors | Marais, G. F., Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | af_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 99 p. : ill. |
| Rights | Stellenbosch University |
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