Mapping genes for stem rust and Russian wheat aphid resistance in bread wheat (Triticum aestivum)

Wessels, Willem Gerhardus (1997-03)

Thesis ( MScAgric) -- Stellenbosch University, 1997.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/55580
This item appears in the following collections: