Marker Assisted Transfer of Two Powdery Mildew Resistance Genes PmTb7A.1 and PmTb7A.2 from Triticum boeoticum (Boiss.) to Triticum aestivum (L.)

Abstract

Powdery mildew (PM), caused by Blumeria graminis f. sp. tritici, is one of the important wheat diseases, worldwide. Two PM resistance genes, designated as PmTb7A.1 and PmTb7A.2, were identified in T. boeoticum acc. pau5088 and mapped on chromosome 7AL approximately 48cM apart. Two resistance gene analogue (RGA)-STS markers Ta7AL-4556232 and 7AL-4426363 were identified to be linked to the PmTb7A.1 and PmTb7A.2, at a distance of 0.6cM and 6.0cM, respectively. In the present study, following marker assisted selection (MAS), the two genes were transferred to T. aestivum using T. durum as bridging species. As many as 12,317 florets of F1 of the cross T. durum /T. boeoticum were pollinated with T. aestivum lines PBW343-IL and PBW621 to produce 61 and 65 seeds, respectively, of three-way F1. The resulting F1s of the cross T. durum/T. boeoticum//T. aestivum were screened with marker flanking both the PM resistance genes PmTb7A.1 and PmTb7A.2 (foreground selection) and the selected plants were backcrossed to generate BC1F1. Marker assisted selection was carried both in BC1F1 and the BC2F1 generations. Introgression of alien chromatin in BC2F1 plants varied from 15.4 - 62.9 percent. Out of more than 110 BC2F1 plants showing introgression for markers linked to the two PM resistance genes, 40 agronomically desirable plants were selected for background selection for the carrier chromosome to identify the plants with minimum of the alien introgression. Cytological analysis showed that most plants have chromosome number ranging from 40-42. The BC2F2 plants homozygous for the two genes have been identified. These will be crossed to generate lines combining both the PM resistance genes but with minimal of the alien introgression. The PM resistance gene PmTb7A.1 maps in a region very close to Sr22, a stem rust resistance gene effective against the race Ug99. Analysis of selected plants with markers linked to Sr22 showed introgression of Sr22 from T. boeoticum in several BC2F1 plants. Thus, in addition to PM resistance, these progeny might also carry resistance to stem rust race Ug99.

Fine mapping of powdery mildew resistance genes PmTb7A.1 and PmTb7A.2 in Triticum boeoticum (Boiss.) using the shotgun sequence assembly of chromosome 7AL

“…The PmTb7A.2 is a potential source of resistance for PM in India and Europe and has been transferred to hexaploid wheat using linked RGA-STSmarkers identified in the present investigation (Elkot et al 2015). Not conclusively, but most evidences from mapping and phenotypic reaction support that it might be an additional allele of Pm1 but different from Pm1a already identified from T. monococcum.…”

“…Not conclusively, but most evidences from mapping and phenotypic reaction support that it might be an additional allele of Pm1 but different from Pm1a already identified from T. monococcum. SNP marker Tm_147956055_snp developed from T. monococcum and T. boeoticum sequence, and two co-located RGA-STS markers Ta7AL-4426363_rga and Ta7AL-4544237_rga (mapped as CAPS) at a distance of 5.1 and 6.4 cM, respectively, could be used for MAS (Elkot et al 2015). The PmTb7A.2 is a potential source of resistance for PM in India and Europe and has been transferred to hexaploid wheat using linked RGA-STSmarkers identified in the present investigation (Elkot et al 2015).…”

“…The nearest STS, STS-RGA or SNP markers were Xmag1759, Xmag2185, Tm_147956055_snp, Ta7AL-4426363_rga and Ta7AL_4544237_rga encompassing a 7.3 cM region. The new set of linked RGA-STS markers for both the powdery mildew resistance genes PmTb7A.1 and PmTb7A.2 have been used for marker-assisted transfer of the two PM resistance genes from Tb5088 to hexaploid wheat (Elkot et al 2015). However, we identified new markers, i.e.…”

Transfer and mapping of the heat tolerance component traits of Aegilops speltoides in tetraploid wheat Triticum durum

“…Two backcrosses with T. durum followed by selfing led to the normal chromosome number and pairing in the progenies. We have successfully used this strategy for transferring useful variability from other diploid progenitor species Chhuneja et al 2008;Elkot et al 2015) in cultivated wheat where pairing between wheat and alien chromosomes was not restricted.…”

Transferability and Polymorphism Between Group 7 Chromosome Specific Simple Sequence Repeat (SSR) Markers of Bread Wheat and Its Related Non-ProgenitorAegilopsSpecies

“…The 7S and 7U consensus map could be utilized to monitor introgressions and map genes for useful variability on respective chromosomal arms. In several reports, SSR markers have been utilized for identification and mapping of gene(s) or traits, such as powdery mildew resistance genes Pm51 (Zhan et al 2014), and PmTb7A.1 and PmTb7A.2 (Elkot et al 2015) and identification of 2S K and 7U K introgressions conferring high grain iron and zinc content in bread wheat (Tiwari et al 2010). The use of polymorphic SSR markers has been verified by identification of 7U/7S addition and substitution lines.…”