Mapping and restructuring of an Ae. kotschyi derived translocation segment in common wheat

[摘要] ENGLISH ABSTRACT: The wild relatives are an important source of new genes for the genetic improvementof wheat. At Stellenbosch University the leaf and stripe rust resistance genes Lr54 andYr37 were transferred from Aegilops kotschyi to chromosome 2DL of wheat. In anattempt to reduce the size of the whole-arm translocation on which the resistancegenes occur, homoeologous pairing was induced between the wheat andcorresponding Ae. kotschyi chromatin. The purpose of this study was to: (i) Evaluatethe testcross progeny thus obtained; identify translocation recombinants that retainedLr54/Yr37 and to characterize these using molecular markers (ii) Test for the presenceof genes for photoperiod insensitivity (Ppd) and reduced height (Rht) believed to beassociated with the translocation (iii) Develop a SCAR marker for the most usefulrecombinant that could be recovered.Ten putative translocation recombinants were identified following thescreening of 159 hemizygous testcross F1 plants with three microsatellite markersspecific for chromosome arm 2DL. The recombinants were then characterized withanother five microsatellite markers. Using the eight microsatellite markers therecombinants were ordered in two size categories with recombinant #74 being theshortest and having retained only proximal alien chromatin on 2DL. In addition tomicrosatellite markers, RAPDs, RGAs, AFLPs and SCAR markers were geneticallymapped to the translocation and further resolved the recombinants into three sizecategories. In an attempt to find suitable markers linked to the shortest recombinant(#74) a polymorphic 410 bp AFLP fragment produced with the enzyme/selectivenucleotide combination EcoRI – AAC/MseI – CAT, was converted into a dominantSCAR marker. In addition three microsatellite markers that mapped to recombinant#74 provided a useful recessive molecular marker system to detect Lr54/Yr37.Evaluation of the 10 recombinants with four 2DS-specific microsatellite markersrevealed a large deletion of this chromosome arm in recombinant #74. This deletionmay affect plant phenotypic characteristics and a strategy to replace the deleted regionin recombinant #74 is proposed.To test for the presence of a gene for photoperiod insensitivity on the translocation,translocation-carriers plus controls were subjected to long and short day treatments,and the effect on time to flowering was studied. However, no evidence was found forthe presence of such a gene. A height experiment to test for the presence of an Rhtgene on the translocation confirmed its presence. This gene (designated H) appearedto be different from Rht8 on chromosome 2DS and was mapped on 2DL. While Hdoes not occur in a chromosome region that corresponds with the location of Rht8, itdoes not rule out the possibility that they could be orthologous loci. Plant height dataobtained for recombinant #74 suggested that H was lost through recombination in thisparticular recombinant. A greenhouse experiment suggested that the full-lengthtranslocation increased 100 kernel mass but had a detrimental effect on overall plantyield. Since a much shorter recombinant (#74) has been obtained, this will also haveto be evaluated for associated effects. Such an evaluation needs to be done undercommercial growing conditions and should involve the comparison of near-isogenicbulks with and without recombinant chromosome #74.The stripe rust resistance gene (Yr37) was mapped by screening hemizygousTF2 progeny of the 10 recombinants with Puccinia striiformis pathotype 6E22A+.Recombinant #74 retained both Lr54 and Yr37 and the two genes therefore occurtowards the centromere.

[发布机构] Stellenbosch University