Mapping a gene on wheat chromosome 4BL involved in a complementary interaction with adult plant leaf rust resistance gene LrSV2

Abstract

A complementary gene to LrSV2 for specific adult plant leaf rust resistance in wheat was mapped on chromosome 4BL, tightly linked to Lr12 / 31. LrSV2 is a race-specific adult plant leaf rust (Puccinia triticina) resistance gene on subdistal chromosome 3BS detected in the cross of the traditional Argentinean wheat (Triticum aestivum) variety Sinvalocho MA and the experimental line Gama6. The analysis of the cross of R46 [recombinant inbred line (RIL) derived from Sinvalocho MA carrying LrSV2 gene and the complementary gene Lrc-SV2 identified in the current paper] and the commercial variety Relmo Siriri (not carrying neither of these two genes) allowed the detection of the unlinked complementary gene Lrc-SV2 because the presence of one dominant allele of both is necessary to express the LrSV2-specific adult plant resistance. Lrc-SV2 was mapped within a 1-cM interval on chromosome 4BL using 100 RILs from the cross Sinvalocho MA × Purple Straw. This genetic system resembles the Lr27+31 seedling resistance reported in the Australian varieties Gatcher and Timgalen where interacting genes map at similar chromosomal positions. However, in high-resolution maps, Lr27 and LrSV2 were already mapped to adjacent intervals on 3BS and Lrc-SV2 map position on 4BL is distal to the reported Lr12/31-flanking microsatellites.

Characterization and Use in Wheat Breeding of Leaf Rust Resistance Genes from Durable Varieties

“…For LrcSV2, a stepwise approach was used. The first 584 F2s from the cross SV × P were genotyped with the flanking markers gpw4388 and FSs34 [26] and 9 recombinants were detected. At the same time, 44 additional markers within this interval were developed: 8 using the wheat 4B contigs spanning the target region identified as described in Diéguez et al [26] and 36 using the sequence of the CS homologous region ( https://wheat-urgi.versailles.inra.fr/Seq-Repository/Assemblies (accessed on 16 August 2021)).…”

“…The first 584 F2s from the cross SV × P were genotyped with the flanking markers gpw4388 and FSs34 [26] and 9 recombinants were detected. At the same time, 44 additional markers within this interval were developed: 8 using the wheat 4B contigs spanning the target region identified as described in Diéguez et al [26] and 36 using the sequence of the CS homologous region ( https://wheat-urgi.versailles.inra.fr/Seq-Repository/Assemblies (accessed on 16 August 2021)). A total of 35 of them amplified a defined product of the expected size and 21 were polymorphic and associated with the gene by Bulk Segregant Analysis (Supplementary Table S2).…”

“…Chromosome 3B is the largest chromosome of wheat and its DNA sequence was the first published in a series that later included all wheat chromosomes [34,35]. This information encouraged our group to initiate fine mapping of two of the APR genes identified in Sinvalocho MA located on chromosomes 3B and 4B [17,26,36].…”

“…Three genes were identified and associated with resistance in field testing to the pathogen's natural populations in SV × G6, allowing the evaluation of different gene combinations and their individual contribution to the observed resistance: APR genes LrSV1 and LrSV2 and the ASR gene LrG6 [17]. In SV × P, the APR gene LrcSV2, complementary to LrSV2, was detected [26]. In Buck Manantial (BM), genes Lr3, Lr16 and Lr17 were previously identified by Dyck et al [21], who also suggested the presence of the adult plant resistance gene Lr13.…”

“…In each BC cycle, LrG6 was selected using the corresponding rust race; LrSV1 and LrSV2 were selected by the associated molecular markers gwm261 or P31/M42 and gwm533 or P31/M37, respectively, and LrcSV2 was tested in selfed BC2 by its associated marker gwm149 (Tables 6 and 7). Noteworthy, the complementary effect of LrcSV2 on LrSV2 was only discovered after the introgressions were started [26]. However, the availability of a closely linked marker allowed the selection of lines harbouring this gene on selfed BC2s.…”