Divergence between bread wheat and Triticum militinae in the powdery mildew resistance QPm.tut-4A locus and its implications for cloning of the resistance gene

Abstract

A segment of Triticum militinae chromosome 7G harbors a gene(s) conferring powdery mildew resistance which is effective at both the seedling and the adult plant stages when transferred into bread wheat ( T. aestivum ). The introgressed segment replaces a piece of wheat chromosome arm 4AL. An analysis of segregating materials generated to positionally clone the gene highlighted that in a plant heterozygous for the introgression segment, only limited recombination occurs between the introgressed region and bread wheat 4A. Nevertheless, 75 genetic markers were successfully placed within the region, thereby confining the gene to a 0.012 cM window along the 4AL arm. In a background lacking the Ph1 locus, the localized rate of recombination was raised 33-fold, enabling the reduction in the length of the region containing the resistance gene to a 480 kbp stretch harboring 12 predicted genes. The substituted segment in the reference sequence of bread wheat cv. Chinese Spring is longer (640 kbp) and harbors 16 genes. A comparison of the segments’ sequences revealed a high degree of divergence with respect to both their gene content and nucleotide sequence. Of the 12 T. militinae genes, only four have a homolog in cv. Chinese Spring. Possible candidate genes for the resistance have been identified based on function predicted from their sequence. Electronic supplementary material The online version of this article (10.1007/s00122-018-3259-3) contains supplementary material, which is available to authorized users.

Development of SNP, KASP, and SSR Markers by BSR-Seq Technology for Saturation of Genetic Linkage Map and Efficient Detection of Wheat Powdery Mildew Resistance Gene Pm61

“…et Migusch. [37] were mapped on chromosome arm 4AL. Two MlIW30 -linked markers, XB1g2020.2 and XB1g2070.1 , were linked to Pm61 using the mapping population of XXSYH × Mingxian 169 [35].…”

“…However, only XB1g2070.1 was linked to Pm61 with genetic distance of 1.43 cM in the mapping population of XXSYH × Zhongzuo 9504. Polymorphism of 73 markers linked to QPm.tut - 4A [37] were examined against the parents and the contrasting DNA bulks of the XXSYH × Zhongzuo 9504 cross, resulting in 5 polymorphic markers owm73 , owm98 , owm104 , owm158 , and owm204 that were linked to Pm61 . The closest QPm.tut - 4A –linked marker owm158 to Pm61 was 0.95 cM from Pm61 .…”

“…Based on the genomic sequences of the Chinese Spring reference genome that flanked the Pm61 locus, six SSR markers were linked to the target gene. Using these molecular markers, together with previously developed gene-linked markers [35,37], a new saturated genetic linkage map was established, which placed Pm61 in a 0.71 cM genetic interval corresponding to a 0.61 Mb physical interval (718,257,529–718,866,730) on the terminal region of chromosome 4AL. The closest flanking markers of Pm61 were Xicscx497/Xicscx543/owm73/owm98/owm104 and Xicsn4 with genetic distances of 0.47 and 0.24 cM, respectively.…”

“…MlIW30 and QPm.tut-4A were transferred into common wheat from the wild emmer ( T. turgidum ssp. dicoccoides ) and T. militinae , respectively [36,37]. Pm61 is derived from a Chinese landrace and is located in a 0.61 Mb (718,257,529–718,866,730) genomic interval between MlIW30 and QPm.uga-4A .…”

“…The Pm61 -linked markers, including previously developed SSR markers and the SNP markers, KASP markers, and SSR markers developed in present studies [35,37], were used to construct the high-density genetic linkage map of Pm61 using the software Mapdraw v.2.1 (Huazhong Agricultural Sciences, Wuhan, China) [47]. The genetic distance was measured by the Kosambi function.…”