Thesis ( MScAgric) -- Stellenbosch University, 1997. / ENGLISH ABSTRACT: Stem rust is considered the most damaging of the wheat rusts causing yield losses of more than
50% in epidemic years. Similarly, Russian wheat aphids (RWA) can be regarded as one ofthe
most devastating insect pests of wheat. Yield losses due to R W A primarily result from a
reduction in plant resources (sucking plant sap). Secondary losses are incurred by viruses
transmitted during feeding. Mapping disease and insect resistance genes that are effective against
prevailing pathotypes and biotypes of South Africa will optimize their utilization in breeding
programmes.
The wheat line, 87M66-2-l, is homozygous for a single dominant stem rust resistance gene
located on chromosome lD. This stem rust resistance gene has been derived from Triticum
tauschii accession RL5289 and is here referred to as Srtau. The aim of this study was to
determine the chromosome arm involved. Following the chromosome arm allocation of Srtau,
its possible linkage with the genes Rg2, Lr 21 , Sr X and Sr 33 was studied.
A telosomic analysis has shown that Srtau is located on chromosome arm 1 DS and is linked to
the centromere with a recombination frequency of 21 ± 3 .40%. Glume blotch and a heavy
mildew infection of segregating families planted in the field in 1996 made the linkage study
between Lr 21 (leaf rust resistance) and Rg2 (glume colour) impossible. However, estimated
linkages of 9 ± 1.9 map units between Sr33 (stem rust resistance) and Srtau, ± 6 map units
between Sr X (stem rust resistance) and Sr 3 3 and ± 1 0 map units between Sr X and Srtau suggested
that SrX, Sr33 and Srtau are closely linked on I DS. Taking existing map data into consideration,
it seems that the most likely order of the genes is: centromere - Srtau - Sr 3 3 - Sr X.
A single dominant R W A resistance gene, Dn5, was identified in the T aestivum accession 'SA
463' and is located on chromosome 7D. The aim ofthis study was to determine the chromosome
arm involved. The possible linkage of Dn5 with the endopeptidase locus, Ep-D1 b. and chlorina
mutant gene, cn-D1, was then studied. Endopeptidase zymograms of 'SA 463' revealed two
unknown polymorphisms. F 2 monosomic analyses involving the chromosomes 7 A, 7B and 7D
were performed in an attempt to identify the loci associated with these polymorphisms.
Dn5 was mapped on chromosome arm 7DL. A recombination frequency of60 ± 4.53% between
Dn5 and the centromere suggested the absence of linkage. Linkage between Ep-Dl and cn-Dl
could not be calculated as a result of similar isoelectric points of the 7DL encoded endopeptidases
of the parental material studied. Recombination frequencies of32 ± 4.97% between Dn5 and EpDl
and 37 ± 6.30% between Dn5 and cn-Dl were, however, encountered. The two novel
endopeptidase alleles encountered in 'SA 463' were designated as Ep-Dle and Ep-Ald.
A RWA resistance gene was transferred from the rye accession ' Turkey 77' to wheat and in the
process the RWA resistant wheat lines 91M37-7 and 91M37-51 were derived. No rye chromatin
could be detected in these plants following C-banding. The aim of this study was to determine
(i) on which chromosome the gene(s) is located, and (ii) whether the resistance can be the result
of a small intercalary translocation of rye chromatin.
A monosomic analysis of the RWA resistance gene in 91M37-51 has shown that a single
dominant resistance gene occurs on chromosome 7D. The use of rye-specific dispersed probes
did not reveal any polymorphisms between the negative controls and RW A resistant lines 91M3 7-
7 and 91M37-51 which would suggest that it is unlikely that the resistance was derived from rye. / AFRIKAANSE OPSOMMING: Stamroes word as die mees vemietigende graanroessiekte beskou en het in epidemiese jare
oesverliese van meer as 50% tot gevolg. Russiese koringluise is eweneens een van die emstigste
insekplae van koring. Russiese koringluise veroorsaak oesverliese deurdat dit plantsap uitsuig
en die plant van voedingstowwe beroof. Dit tree egter ook as 'n virusvektor op en kan so
indirekte oesverliese veroorsaak. Kartering van siekte- en insekweerstandsgene wat effektief is
teen die Suid-Afrikaanse patotipes en biotipes, sal hulle gebruik in teelprogramme optimiseer.
Die koringlyn, 87M66-2-l , is homosigoties vir 'n dominante stamroes-weerstandsgeen wat op
chromosoom ID voorkom. Hierdie weerstandsgeen is uit die Triticum tauschii aanwins, RL5289,
afkomstig en word hiema verwys as Srtau. Daar is gepoog om te bepaal op watter chromosoomarm
Srtau voorkom, waama sy koppeling met betrekking tot die gene Rg2, Lr21 , SrX en Sr33
bepaal is.
'n Telosoomanalise het getoon dat Srtau op chromosoom-arm 1 DS voorkom en gekoppel is aan
die sentromeer met 'n rekombinasie-frekwensie van 21 ± 3.40%. Segregerende populasies wat
in 1996 in die land geplant is, is hewig deur aarvlek en poeieragtige meeldou besmet en dit het
die moontlike bepaling van koppeling tussen Lr21 (blaarroesweerstand) en Rg2 (aarkaffie kleur)
belemmer. Koppelingsafstande van 9 ± 1. 9 kaart-eenhede tussen Sr 33 (stamroesweerstand) en
Srt au, ± 6 kaart -eenhede tussen Sr X ( stamroesweerstand) en Sr 3 3 en ± 1 0 kaart -eenhede tussen
SrX en Srtau is geraam en toon dat SrX, Sr33 en Srtau nou gekoppel is. Die waarskynlikste
volgorde van die gene op lDS is: sentromeer- Srtau- Sr33- SrX.
'n Enkele dominante Russiese koringluis-weerstandsgeen, Dn5, is in dieT aestivum aanwins 'SA
463 ' ge"identifiseer en kom op chromosoom 7D voor. Die studie het ten doel gehad om te bepaal
op watter chromosoom-arm Dn5 voorkom, asook wat die koppeling van Dn5 met die
endopeptidase lokus, Ep-Dl, en die chlorina mutante geen, cn-Dl , is. Endopeptidase
simograrnme van 'SA 463' het twee onbekende polimorfismes getoon. Die gene wat kodeer vir
hierdie twee polimorfismes is met behulp van F2 monosoom-analises wat die chromosome 7 A,
7B en 7D betrek, gei:dentifiseer.
Dn5 is op chromosoom 7DL gekarteer. 'n Rekombinasie-frekwensie van 60 ± 4.53% is gevind
vir die sentromeer en Dn5 en dui op die afwesigheid van koppeling. Koppeling tussen Ep-Dl en
cn-Dl kon nie bepaal word nie omdat die endopeptidase bande geproduseer deur die ouerlike
materiaal wat in die studie gebruik is, nie met sekerheid in die nageslag onderskei kon word nie.
Rekombinasie-frekwensies van 32 ± 4.97% tussen Dn5 en Ep-Dl en 37 ± 6.30% tussen Dn5 en
cn-Dl is egter bereken. Dit word voorgestel dat daar na die twee onbekende endopeptidase-allele
wat in 'SA 463 ' voorkom, verwys word as Ep-Dle en Ep-Ald.
'n Russiese koringluis-weerstandsgeen is uit die rog-aanwins, 'Turkey 77', oorgedra na koring
en in die proses is die Russies koringluis weerstandbiedende lyne, 91M37-7 en 91M37-51 ,
geproduseer. Geen rog-chromatien kon egter met behulp van C-bande in hierdie lyne
waargeneem word nie. Die doel van die studie was om te bepaal (i) op watter chromosoom die
geen(e) voorkom, en (ii), of die Russiese koringluis weerstandsgeen die gevolg kan wees van 'n
klein interkalere translokasie van rog- chromatien.
'n Monosoom-analise van die Russiese koringluis-weerstandsgeen in 91M37-51 het getoon dat
'n enkele dominante weerstandsgeen op chromosoom 7D voorkom. Rog-spesifieke herhalende
peilers het geen polimorfismes tussen negatiewe kontroles en die Russiese koringluis
weerstandbiedende lyne 91M37-7 en 91M37-51 getoon nie. Dit is dus onwaarskynlik dat die
weerstand in die lyne uit rog verhaal is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/55580 |
| Date | 03 1900 |
| Creators | Wessels, Willem Gerhardus |
| 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 | 118 p. : ill. |
| Rights | Stellenbosch University |
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