Mapping stripe rust resistance gene YrZH22 in Chinese wheat cultivar Zhoumai 22 by bulked segregant RNA-Seq (BSR-Seq) and comparative genomics analyses

A stripe rust resistance gene YrZH22 was mapped by combined BSR-Seq and comparative genomics analyses to a 5.92 centimorgan (cM) genetic interval spanning a 4 Mb physical genomic region on wheat chromosome 4BL1. Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most destructive diseases of wheat and severely threatens wheat production worldwide. The widely grown Chinese wheat cultivar Zhoumai 22 is highly resistant to the current prevailing PST race CYR34 (V26). Genetic analysis of F_5:6 and F_6:7 recombinant inbred line (RIL) populations indicated that adult-plant stripe rust resistance in Zhoumai 22 is controlled by a single gene, temporarily designated YrZH22. By applying bulked segregant RNA-Seq (BSR-Seq), 7 SNP markers were developed and SNP mapping showed that YrZH22 is located between markers WGGB105 and WGGB112 on chromosome arm 4BL. The corresponding genomic regions of the Chinese Spring 4BL genome assembly and physical map of Aegilops tauschii 4DL were selected for comparative genomics analyses to develop nine new polymorphic markers that were used to construct a high-resolution genetic linkage map of YrZH22. YrZH22 was delimited in a 5.92 cM genetic interval between markers WGGB133 and WGGB146, corresponding to 4.1 Mb genomic interval in Chinese Spring 4BL and a 2.2 Mb orthologous genomic region in Ae. tauschii 4DL. The genetic linkage map of YrZH22 will be valuable for fine mapping and positional cloning of YrZH22, and can be used for marker-assisted selection in wheat breeding.

Genetic mapping of a putative Thinopyrum intermedium-derived stripe rust resistance gene on wheat chromosome 1B

Stripe rust resistance transferred from Thinopyrum intermedium into common wheat was controlled by a single dominant gene, which mapped to chromosome 1B near Yr26 and was designated YrL693. Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a highly destructive disease of wheat (Triticum aestivum). Stripe rust resistance was transferred from Thinopyrum intermedium to common wheat, and the resulting introgression line (L693) exhibited all-stage resistance to the widely virulent and predominant Chinese pathotypes CYR32 and CYR33 and to the new virulent pathotype V26. There was no cytological evidence that L693 had alien chromosomal segments from Th. intermedium. Genetic analysis of stripe rust resistance was performed by crossing L693 with the susceptible line L661. F(1), F(2), and F(2:3) populations from reciprocal crosses showed that resistance was controlled by a single dominant gene. A total 479 F(2:3) lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to six publicly available and three recently developed wheat genomic SSR markers. The linked markers were localized to wheat chromosome 1B using Chinese Spring nulli-tetrasomic lines, and the resistance gene was localized to chromosome 1B based on SSR and wheat genomic information. A high-density genetic map was also produced. The pedigree, molecular marker data, and resistance response indicated that the stripe rust resistance gene in L693 is a novel gene, which was temporarily designated YrL693. The SSR markers that co-segregate with this gene (Xbarc187-1B, Xbarc187-1B-1, Xgwm18-1B, and Xgwm11-1B) have potential application in marker-assisted breeding of wheat, and YrL693 will be useful for broadening the genetic basis of stripe rust resistance in wheat.