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

[摘要] ENGLISH ABSTRACT:Stem rust is considered the most damaging of the wheat rusts causing yield losses of more than50% in epidemic years. Similarly, Russian wheat aphids (RWA) can be regarded as one ofthemost devastating insect pests of wheat. Yield losses due to R W A primarily result from areduction in plant resources (sucking plant sap). Secondary losses are incurred by virusestransmitted during feeding. Mapping disease and insect resistance genes that are effective againstprevailing pathotypes and biotypes of South Africa will optimize their utilization in breedingprogrammes.The wheat line, 87M66-2-l, is homozygous for a single dominant stem rust resistance genelocated on chromosome lD. This stem rust resistance gene has been derived from Triticumtauschii accession RL5289 and is here referred to as Srtau. The aim of this study was todetermine 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 tothe centromere with a recombination frequency of 21 ± 3 .40%. Glume blotch and a heavymildew infection of segregating families planted in the field in 1996 made the linkage studybetween Lr 21 (leaf rust resistance) and Rg2 (glume colour) impossible. However, estimatedlinkages of 9 ± 1.9 map units between Sr33 (stem rust resistance) and Srtau, ± 6 map unitsbetween Sr X (stem rust resistance) and Sr 3 3 and ± 1 0 map units between Sr X and Srtau suggestedthat 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 'SA463' and is located on chromosome 7D. The aim ofthis study was to determine the chromosomearm involved. The possible linkage of Dn5 with the endopeptidase locus, Ep-D1 b. and chlorinamutant gene, cn-D1, was then studied. Endopeptidase zymograms of 'SA 463' revealed twounknown polymorphisms. F 2 monosomic analyses involving the chromosomes 7 A, 7B and 7Dwere 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% betweenDn5 and the centromere suggested the absence of linkage. Linkage between Ep-Dl and cn-Dlcould not be calculated as a result of similar isoelectric points of the 7DL encoded endopeptidasesof the parental material studied. Recombination frequencies of32 ± 4.97% between Dn5 and EpDland 37 ± 6.30% between Dn5 and cn-Dl were, however, encountered. The two novelendopeptidase 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 theprocess the RWA resistant wheat lines 91M37-7 and 91M37-51 were derived. No rye chromatincould 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 resultof a small intercalary translocation of rye chromatin.A monosomic analysis of the RWA resistance gene in 91M37-51 has shown that a singledominant resistance gene occurs on chromosome 7D. The use of rye-specific dispersed probesdid 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.

[发布机构] Stellenbosch University