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The wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), race TTKSK and related races pose a serious threat to world wheat production. Knowing the effectiveness of wheat stem rust resistance (Sr) genes against Pgt race TTKSK is fundamental in mitigating this threat through resistance breeding. Sr15 was previously identified as being ineffective against Pgt race TTKSK. Here, multirace disease phenotyping data, linkage analyses, allelism testing and haplotype analyses are presented to support the conclusion that Sr15 is effective against Pgt race TTKSK. Resistance to race TTKSK was mapped to Sr15 in a biparental population. Thirty‐two accessions with Sr15 displayed seedling resistance phenotypes against race TTKSK. However, these accessions were susceptible as seedlings at high temperatures (22–25 °C), consistent with previous reports that the interaction between avirulent Pgt isolates and Sr15 is temperature‐sensitive. Markers STS638, wri4 and KASP_IWB30995 were found to predict the presence of Sr15, suggesting the utility of these assays for marker‐assisted selection in breeding programmes. The effectiveness of Sr15 to specific Pgt races and temperatures makes it a less‐desirable TTKSK‐effective gene. Wheat lines assayed as resistant to race TTKSK at the seedling stage may possess Sr15 and breeders should be aware of the limitations of Sr15 for conferring stem rust resistance. [ABSTRACT FROM AUTHOR]

'Caldwell' is a US soft red winter wheat (Triticum aestivum L.) that has partial, adult plant resistance to the leaf rust pathogen Puccinia triticina Eriks. A line of 'Thatcher*2/Caldwell' with adult plant resistance derived from Caldwell was crossed with 'Thatcher' to develop a population of recombinant inbred lines (RILs). The parents and RIL population were evaluated for segregation of leaf rust resistance in four field tests. A genetic map of the RIL population was constructed using 90K single-nucleotide polymorphism (SNP) markers with the Illumina Infinium iSelect 90K wheat bead array. Significant effects for reduction of leaf rust severity in all four tests were found for a quantitative trait locus on chromosome 3BS. Simple sequence repeat (SSR) markers linked to the adult plant resistance gene Lr74 and kompetitive allele specific polymerase chain reaction (KASP) assay markers were added to the map on chromosome 3BS. Thatcher and the resistant Thatcher*2/Caldwell parent were negative for the presence of Sr2 on chromosome 3BS based on the tightly linked marker csSr2. The SSR marker cfb5006 linked closely to Lr74 mapped the closest to the logarithm of odds peak for leaf rust resistance on chromosome 3BS. The SNP and SSR markers on chromosome 3BS can be used to add Caldwell leaf rust resistance to wheat breeding germplasm. [ABSTRACT FROM AUTHOR]

Aegilops umbellulata, a non-progenitor diploid species, is an excellent source of resistance to various wheat diseases. Leaf rust and stripe rust resistance genes from A. umbellulata were transferred to the susceptible wheat cultivar WL711 through induced homoeologous pairing. A doubly resistant introgression line IL 393-4 was crossed with wheat cultivar PBW343 to develop a mapping population. Tests on BC2F7 RILs indicated monogenic inheritance of seedling leaf rust and stripe rust resistance in IL 393-4 and the respective co-segregating genes were tentatively named LrUmb and YrUmb. Bulked segregant analysis placed LrUmb and YrUmb in chromosome 5 DS, 7.6 cM distal to gwm190. Aegilops geniculata-derived and completely linked leaf rust and stripe rust resistance genes Lr57 and Yr40 were previously located in chromosome 5 DS. STS marker Lr57/ Yr40 MAS- CAPS16 ( Lr57/ Yr40- CAPS16), linked with Lr57/ Yr40 (T756) also co-segregated with LrUmb/ YrUmb. Seedling infection types differentiated LrUmb from Lr57. Absence of leaf rust-susceptible segregants among F3 families of the intercross ( IL 393-4/T756) indicated repulsion linkage between LrUmb and Lr57. YrUmb expressed a consistently low seedling response under greenhouse conditions, whereas Yr40 expressed a higher seedling response. Based on the origin of LrUmb/ YrUmb from the U genome and Lr57/ Yr40 from the M genome, as well as phenotypic differences, LrUmb and YrUmb were formally named Lr76 and Yr70, respectively. These genes have been transferred to Indian wheat cultivars PBW343 and PBW550, and advanced breeding lines are being tested in state and national trials. [ABSTRACT FROM AUTHOR]

A recombinant inbred line population derived from a cross between the winter wheat cultivars Arina and Forno was used to study the genetic relationship between genes Yr1 and SrAn1 in chromosome 2AL. Yr1 from Forno showed repulsion linkage (16·5 cM) with SrAn1 carried by Arina and was proximal to SrAn1. Based on the chromosomal location of SrAn1 with respect to Yr1 and its ineffectiveness against the Australian Puccinia graminis f. sp. tritici pathotype 34-1,2,7 + Sr38, it was concluded that SrAn1 is distinct from Sr21 and was designated as Sr48. An attempt was made to map more markers in the distal region of chromosome 2AL in order to determine the precise location of Sr48. Unfortunately none of the markers tested mapped between Yr1 and Sr48, with the latter being the most distal locus. However, close linkage was identified between Yr1 and the PCR-based molecular marker stm673acag. Genotyping with stm673acag amplified a 120-bp fragment in eight of nine genotypes carrying Yr1. Avocet S was the only line tested without Yr1 that also amplified the 120-bp product. A 124-bp product was amplified in 40 Australian wheat cultivars known to lack Yr1. These results suggest that stm673acag could be used for marker assisted selection of Yr1. Genotypes carrying both Yr1 and Sr48 were identified. [ABSTRACT FROM AUTHOR]