Characterization and molecular mapping of Yr52 for high-temperature adult-plant resistance to stripe rust in spring wheat germplasm PI 183527

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive diseases of wheat worldwide. Resistance is the best approach to control the disease. High-temperature adult-plant (HTAP) stripe rust resistance has proven to be race non-specific and durable. However, genes conferring high-levels of HTAP resistance are limited in number and new genes are urgently needed for breeding programs to develop cultivars with durable high-level resistance to stripe rust. Spring wheat germplasm PI 183527 showed a high-level of HTAP resistance against stripe rust in our germplasm evaluations over several years. To elucidate the genetic basis of resistance, we crossed PI 183527 and susceptible wheat line Avocet S. Adult plants of parents, F(1), F(2) and F(2:3) progeny were tested with selected races under the controlled greenhouse conditions and in fields under natural infection. PI 183527 has a single dominant gene conferring HTAP resistance. Resistance gene analog polymorphism (RGAP) and simple sequence repeat (SSR) markers in combination with bulked segregant analysis (BSA) were used to identify markers linked to the resistance gene. A linkage map consisting of 4 RGAP and 7 SSR markers was constructed for the resistance gene using data from 175 F(2) plants and their derived F(2:3) lines. Amplification of nulli-tetrasomic, ditelosomic and deletion lines of Chinese Spring with three RGAP markers mapped the gene to the distal region (0.86-1.0) of chromosome 7BL. The molecular map spanned a genetic distance of 27.3?cM, and the resistance gene was narrowed to a 2.3-cM interval flanked by markers Xbarc182 and Xwgp5258. The polymorphism rates of the flanking markers in 74 wheat lines were 74 and 30?%, respectively; and the two markers in combination could distinguish the alleles at the resistance locus in 82?% of tested genotypes. To determine the genetic relationship between this resistance gene and Yr39, a gene also on 7BL conferring HTAP resistance in Alpowa, a cross was made between PI 183527 and Alpowa. F(2) segregation indicated that the genes were 36.5?±?6.75?cM apart. The gene in PI 183527 was therefore designed as Yr52. This new gene and flanking markers should be useful in developing wheat cultivars with high-level and possible durable resistance to stripe rust.     

Identification and mapping QTL for high-temperature adult-plant resistance to stripe rust in winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivar ‘Stephens’

High-temperature adult-plant (HTAP) resistance from the winter wheat (Triticum aestivum) cultivar 'Stephens' has protected wheat crops from stripe rust caused by Puccinia striiformis f. sp. tritici for 30 years. The objectives of this study were to identify quantitative trait loci (QTL) for HTAP resistance in Stephens through genetic linkage analysis and identify DNA markers linked to the QTL for use in marker-assisted breeding. Mapping populations consisted of 101 recombinant inbred lines (RILs) through single-seed descent from 'Stephens' (resistant) x 'Michigan Amber' (susceptible). F(5), F(6) and F(7) RILs were evaluated for stripe rust resistance at Pullman, WA in 1996, 1997 and 1998, respectively, whereas F(8) RILs were evaluated at Mt Vernon, WA, USA in 2005. The 101 F(8) RILs were evaluated with 250 resistance gene analog polymorphism (RGAP), 245 simple sequence repeat (SSR) and 1 sequence tagged site (STS) markers for genetic linkage map construction. Two QTL, which explained 48-61% of the total phenotypic variation of the HTAP resistance in Stephens, were identified. QYrst.wgp-6BS.1 was within a 3.9-cM region flanked by Xbarc101 and Xbarc136. QYrst.wgp-6BS.2 was mapped in a 17.5-cM region flanked by Xgwm132 and Xgdm113. Both two QTL were physically mapped to the short arm of chromosome 6B, but in different bins. Validation and polymorphism tests of the flanking markers in 43 wheat genotypes indicated that the molecular markers associated with these QTL should be useful in marker-assisted breeding programs to efficiently incorporate HTAP resistance into new wheat cultivars.     

Genetics and molecular mapping of genes for race-specific all-stage resistance and non-race-specific high-temperature adult-plant resistance to stripe rust in spring wheat cultivar Alpowa

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most widespread and destructive wheat diseases worldwide. Growing resistant cultivars is the preferred control of the disease. The spring wheat cultivar ‘Alpowa’ has both race-specific, all-stage resistance and non-race-specific, high-temperature adult-plant (HTAP) resistances to stripe rust. To identify genes for the stripe rust resistances, Alpowa was crossed with ‘Avocet Susceptible’ (AVS). Seedlings of the parents, and F₁, F₂ and F₃ progeny were tested with races PST-1 and PST-21 of P. striiformis f. sp. tritici under controlled greenhouse conditions. Alpowa has a single partially dominant gene, designated as YrAlp, conferring all-stage resistance. Resistance gene analog polymorphism (RGAP) and simple sequence repeat (SSR) techniques were used to identify molecular markers linked to YrAlp. A linkage group of five RGAP markers and two SSR markers was constructed for YrAlp using 136 F₃ lines. Amplification of a set of nulli-tetrasomic Chinese Spring lines with RGAP markers Xwgp47 and Xwgp48 and the two SSR markers indicated that YrAlp is located on the short arm of chromosome 1B. To map quantitative trait loci (QTLs) for the non-race-specific HTAP resistance, the parents and 136 F₃ lines were tested at two sites near Pullman and one site near Mount Vernon, Washington, under naturally infected conditions. A major HTAP QTL was consistently detected across environments and was located on chromosome 7BL. Because of its chromosomal location and the non-race-specific nature of the HTAP resistance, this gene is different from previously described genes for adult-plant resistance, and is therefore designated Yr39. The gene contributed to 64.2% of the total variation of relative area under disease progress curve (AUDPC) data and 59.1% of the total variation of infection type data recorded at the heading-flowering stages. Two RGAP markers, Xwgp36 and Xwgp45 with the highest R ² values were closely linked to Yr39, should be useful for incorporation of the non-race-specific resistance gene into new cultivars and for combining Yr39 with other genes for durable and high-level resistance.     

Molecular mapping of stripe rust resistance gene YrSN104 in Chinese wheat line Shaannong 104

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a serious yield-limiting factor for wheat production worldwide. The objective of this study was to identify and map a stripe rust resistance gene in wheat line Shaannong 104 using SSR markers. F(1) , F(2) and F(3) populations from Shaannong 104/Mingxian 169 were inoculated with Chinese Pst race CYR32 in a greenhouse. Shaannong 104 carried a single dominant gene, YrSN104. Six potential polymorphic SSR markers identified in bulk segregant analysis were used to genotype F(2) and F(3) families. YrSN104 was closely linked with all six SSR markers on chromosome 1BS with genetic distances of 2.0 cM (Xgwm18, Xgwm273, Xbarc187), 2.6 cM (Xgwm11, Xbarc137) and 5.9 cM (Xbarc240). Pedigree analysis, pathogenicity tests using 26 Pst races, haplotyping of associated markers on isogenic lines carrying known stripe rust resistance genes, and associations with markers suggested that YrSN104 was a new resistance gene or an allele at the Yr24/Yr26 locus on chromosome 1BS. Deployment of YrSN104 singly or in combination to elite genotypes could play an effective role to lessen yield losses caused by stripe rust.     

Combination of all-stage and high-temperature adult-plant resistance QTL confers high-level,durable resistance to stripe rust in winter wheat cultivar Madsen

Key message

Wheat cultivar Madsen has a new gene on the short arm of chromosome 1A and two QTL for all-stage resistance and three QTL for high-temperature adult-plant resistance that in combination confer high-level, durable resistance to stripe rust.

Abstract

Wheat cultivar Madsen has maintained a high-level resistance to stripe rust over 30 years. To map quantitative trait loci (QTL) underlying the high-level, durable resistance, 156 recombinant inbred lines (RILs) developed from cross Avocet S?×?Madsen were phenotyped with selected races of Puccinia striiformis f. sp. tritici in the greenhouse seedling tests, and in naturally infected fields during 2015–2017. The RILs were genotyped by SSR and SNP markers from genotyping by sequencing and the 90 K wheat SNP chip. Three QTL for all-stage resistance were mapped on chromosomes 1AS, 1BS and 2AS, and two QTL for high-temperature adult-plant (HTAP) resistance were mapped on 3BS and 6BS. The most effective QTL on 2AS, explaining 8.97–23.10% of the phenotypic variation in seedling tests and 8.60–71.23% in field tests, contained Yr17 for all-stage resistance and an additional gene for HTAP resistance. The 6BS QTL, detected in all field tests, was identified as Yr78. The 1AS QTL, conferring all-stage resistance, was identified as a new gene, which explained 20.45 and 30.23% of variation in resistance to races PSTv-37 and PSTv-40, respectively, and contributed significantly to field resistance at Pullman in 2015-2017, but was not detected at Mount Vernon. The interactions among QTL were mostly additive, and RILs with all five QTL had the highest level of resistance in the field, similar to Madsen. Genotyping 148 US Pacific Northwest wheat cultivars with markers for the 1AS, 2AS and 6BS QTL validated the genes and markers, and indicated their usefulness for marker-assisted selection.

     

Molecular Detection of Stripe Rust Resistance Gene(s) in 115 Wheat Cultivars (lines) from the Yellow and Huai River Valley Wheat Region

Stripe rust (yellow rust), caused by Puccinia striiformis f.sp. tritici (Pst), is a serious disease of wheat worldwide, including China. Growing resistant cultivars is the most cost‐effective and environmentally friendly approach to control the disease. To assess the stripe rust resistance in commercial wheat cultivars and advanced lines in the Yellow and Huai River Valley Wheat Region, 115 wheat cultivars (lines) collected from 13 provinces in this region were evaluated with the most prevalent Chinese Pst races CYR32, CYR33 and the new race V26 at seedling stage. In addition, these wheat entries were inoculated with the mixed races of CYR32 and CYR33 at the adult‐plant stage in the field. The results indicated that 53 (46.1%) cultivars (lines) had all‐stage resistance to all the three races, and 16 (13.9%) cultivars (lines) showed adult‐plant resistance. The possible stripe rust resistance genes in these entries were postulated by the closely linked markers of all‐stage resistance genes Yr5, Yr9, Yr10, Yr15 and Yr26 and adult‐plant resistance gene Yr18. Molecular analysis indicated that resistance genes Yr5, Yr9, Yr10, Yr18 and Yr26 were found in 5 (4.3%), 38 (33.0%), 1 (0.9%), 2 (1.7%) and 8 (7.0%) entries, respectively. No entry was found to carry the Yr15 gene. In future breeding programs, Yr5, Yr15 and Yr18 should be used to pyramid with other effective genes to develop wheat cultivars with high‐level and durable resistance to stripe rust, whereas Yr9, Yr10 and Yr26 should not be used or used in a limited way due to the virulent races present in China.     

Mapping novel sources of leaf rust and stripe rust resistance introgressed from Triticum dicoccoides in cultivated tetraploid wheat background

Wild emmer wheat, Triticum dicoccoides, the progenitor of modern tetraploid and hexaploid wheats, is an important resource for new variability for disease resistance genes. T. dicoccoides accession pau4656 showed resistance against prevailing leaf rust and stripe rust races in India and was used for developing stable introgression lines (IL) in T. durum cv Bijaga yellow and named as IL pau16068. F₅ Recombinant inbred lines (F₅ RILs) were developed by crossing IL pau16068 with T. durum cultivar PBW114 and RIL population was screened against highly virulent Pt and Pst pathotypes at the seedling and adult plant stages. Inheritance analyses revealed that population segregated for two genes for all stage resistance (ASR) against leaf rust, one ASR gene against stripe rust and three adult plant resistance (APR) genes for stripe rust resistance. For mapping these genes a set of 483 SSR marker was used for bulked segregant analysis. The markers showing diagnostic polymorphism in the resistant and susceptible bulks were amplified on all RILs. Single marker analysis placed all stage leaf rust resistance genes on chromosome 6A and 2A linked to the SSR markers Xwmc256 and Wpaus268, respectively. Likewise one all stage stripe rust resistance gene were mapped on long arm of chromosome 6A linked to markers 6AL-5833645 and 6AL-5824654 and two APR genes mapped on chromosomes 2A and 2B close to the SSR marker Wpaus268 and Xbarc70, respectively. The current study identified valuable leaf rust and stripe rust resistance genes effective against multiple rust races for deployment in the wheat breeding programme.

     

Virulence variation of Puccinia striiformis Westend. f. sp. tritici in Pakistan

Yellow rust populations of Pakistan were characterised for their virulence pathotypes/races and pathogenetic variation using seedling evaluation of differential genotypes under glasshouse conditions in Murree (6000 feet above sea level). Differential genotypes comprised a world set, an European set, near isogenic lines and the universally susceptible bread wheat cultivar “Morocco”. Over the two-year study a total of 18 race groups were identified. Out of these 18 race groups, several (68E0, 64E0, 66E0, 70E0, 6E0, 71E0, 6E0, 2E0, 67E0, and 68E16) were found previously. The new race group 70E32 found probably evolved because of mutation from the previously existing 70E16. Virulence frequencies of yellow rust (Yr) resistance genes were also determined on near isogenic lines. The highest virulence frequencies (%) were found for Yr7 (88%), Yr9 (57%), Yr18 (70%), and Yr24 (69%). Virulence frequencies were low for Yr 1 (4%), Yr5 (7%), Yr10 (10%) and Yr15 (4%). Our studies indicated that virulence existed for almost all yr genes, necessitating regular monitoring of the yellow rust populations and intensifying efforts to identify new sources of resistance to this pathogen.     

Reaction of some wheat cultivars and breeding lines to Puccinia striiformis f. sp. tritici hot races in Iran

Many physiological races of Puccinia striiformis f. sp. tritici which cause stripe rust in wheat can be determined in different parts of the world. The emergence of new races with different pathogenicity which happens very quickly breaks cultivars resistant and cause disease. Therefore, breeding cultivar for resistance to different pathogenic races should be continued. In this research, pathogenicity of two isolates collected from two regions of Iran were determined by using wheat yellow rust differential lines, which indicated race 70E50A+ and 6E18A+ The responses of 30 wheat genotypes were separately evaluated in the forms of randomized complete block design with three replicates in the seedling stage under greenhouse condition. The components of resistance including latent period and infection type were recorded. Results indicated genotypes were evaluated in terms of both traits and were significant at 1% level. Also, the results from pathogenicity study indicated of effective gene/s included Yr1, Yr2+, Yr3, Yr4, Yr5, Yr10, Yr15, Yr24, Yr26, YrSP, YrND, YrSD and YrSU. From the genotypes studied in the greenhouse condition, 39% of the genotypes showed complete resistance to both races. Probably, resistance genes, Yr32 and YrCV, or the other unknown genes which are types of seedling resistance are either alone or in combination of one another cause strength in resistant genotypes.     

Evaluation of Pakistan wheat germplasms for stripe rust resistance using molecular markers

Wheat production in Pakistan is seriously constrained due to rust diseases and stripe rust (yellow) caused by Puccinia striiformis f. sp. tritici, which could limit yields. Thus development and cultivation of genetically diverse and resistant varieties is the most sustainable solution to overcome these diseases. The first objective of the present study was to evaluate 100 Pakistan wheat cultivars that have been grown over the past 60 years. These cultivars were inoculated at the seedling stage with two virulent stripe rust isolates from the United States and two from Pakistan. None of the wheat cultivars were resistant to all tested stripe rust isolates, and 16% of cultivars were susceptible to the four isolates at the seedling stage. The data indicated that none of the Pakistan wheat cultivars contained either Yr5 or Yr15 genes that were considered to be effective against most P. striiformis f. sp. tritici isolates from around the world. Several Pakistan wheat cultivars may have gene Yr10, which is effective against isolate PST-127 but ineffective against PST-116. It is also possible that these cultivars may have other previously unidentified genes or gene combinations. The second objective was to evaluate the 100 Pakistan wheat cultivars for stripe rust resistance during natural epidemics in Pakistan and Washington State, USA. It was found that a higher frequency of resistance was present under field conditions compared with greenhouse conditions. Thirty genotypes (30% of germplasms) were found to have a potentially high temperature adult plant (HTAP) resistance. The third objective was to determine the genetic diversity in Pakistan wheat germplasms using molecular markers. This study was based on DNA fingerprinting using resistance gene analog polymorphism (RGAP) marker analysis. The highest polymorphism detected with RGAP primer pairs was 40%, 50% and 57% with a mean polymorphism of 36%. A total of 22 RGAP markers were obtained in this study. RGAP, simple sequence repeat (SSR) and sequence tagged site (STS) markers were used to determine the presence and absence of some important stripe rust resistance genes, such as Yr5, Yr8, Yr9, Yr15 and Yr18. Of the 60 cultivars analyzed, 17% of cultivars showed a RGAP marker band for Yr9 and 12% of cultivars exhibited the Yr18 marker band. No marker band was detected for Yr5, Yr8 and Yr15, indicating a likely absence of these genes in the tested Pakistan wheat cultivars. Cluster analysis based on molecular and stripe rust reaction data is useful in identifying considerable genetic diversity among Pakistan wheat cultivars. The resistant germplasms identified with 22 RGAP markers and from the resistance evaluations should be useful in developing new wheat cultivars with stripe rust resistance.     

Identifying QTL for high-temperature adult-plant resistance to stripe rust (<Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>) in the spring wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivar ‘Louise’

Over time, many single, all-stage resistance genes to stripe rust (Puccinia striiformis f. sp. tritici) in wheat (Triticum aestivum L.) are circumvented by race changes in the pathogen. In contrast, high-temperature, adult-plant resistance (HTAP), which only is expressed during the adult-plant stage and when air temperatures are warm, provides durable protection against stripe rust. Our objective was to identify major quantitative trait loci (QTL) for HTAP resistance to stripe rust in the spring wheat cultivar ‘Louise’. The mapping population consisted of 188 recombinant inbred lines (RIL) from a Louise (resistant) by ‘Penawawa’ (susceptible) cross. F_5:6 lines were evaluated for stripe rust reaction under natural infection in replicated field trials at five locations in the US Pacific Northwest in 2007 and 2008. Infection type (IT) and disease severity were recorded for each RIL 2–4 times per location. In all environments, Penawawa, the susceptible parent, was rated with an IT ranging from 6 to 8 at all growth stages evaluated. In contrast, Louise, the resistant parent, was rated with an IT of 2 or 3 across growth stages. Distribution of IT values was bimodal, indicating a single major gene was affecting the trait. The parents and RIL population were evaluated with 295 polymorphic simple sequence repeat and one single nucleotide polymorphism markers. One major QTL, designated QYrlo.wpg-2BS, associated with HTAP resistance in Louise, was detected on chromosome 2BS (LOD scores ranging from 5.5 to 62.3 across locations and years) within a 16.9 cM region flanked by Xwmc474 and Xgwm148. SSR markers associated with QYrlo.wpg-2BS are currently being used in marker-based forward breeding strategies to transfer the target region into adapted germplasm to improve the durability of resistance in resulting cultivars.     

Development of an STS marker tightly linked to <Emphasis Type="Italic">Yr26</Emphasis> against wheat stripe rust using the resistance gene-analog polymorphism (RGAP) technique

The gene Yr26 confers resistance to all races of Puccinia striiformis f. sp. tritici (PST), the casual pathogen of wheat stripe rust in China. Here, we report development of a molecular marker closely linked to Yr26 using a resistance gene-analog polymorphism (RGAP) technique. A total of 787 F₂ plants and 165 F₃ lines derived from the cross Chuanmai 42/Taichung 29 were used for linkage analysis. Eighteen near-isogenic lines (NILs) and 18 Chinese wheat cultivars and advanced lines with different genes for stripe rust resistance were employed for the validation of STS markers. A total of 1,711 RGAP primer combinations were used to test the parents and resistant and susceptible bulks. Five polymorphic RGAP markers were used for genotyping all F₂ plants. Linkage analysis showed that the five RGAP markers were closely linked to Yr26 with genetic distances ranging from 0.5 to 2.9 cM. These markers were then converted into STS markers, one, CYS-5, of which was located 0.5 cM to Yr26 and was closely associated with the resistance gene when validated over 18 NILs and 18 Chinese wheat cultivars and lines. The results indicated that CYS-5 can be used in marker-assisted selection targeted at pyramiding Yr26 and other genes for stripe rust resistance.     

Molecular mapping of stripe rust resistance gene YrCH42 in Chinese wheat cultivar Chuanmai 42 and its allelism with Yr24 and Yr26

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most devastating diseases in common wheat (Triticum aestivum L.) worldwide. The objectives of this study were to map a stripe rust resistance gene in Chinese wheat cultivar Chuanmai 42 using molecular markers and to investigate its allelism with Yr24 and Yr26. A total of 787 F₂ plants and 186 F₃ lines derived from a cross between resistant cultivar Chuanmai 42 and susceptible line Taichung 29 were used for resistance gene tagging. Also 197 F₂ plants from the cross Chuanmai 42×Yr24/3*Avocet S and 726 F₂ plants from Chuanmai 42×Yr26/3*Avocet S were employed for allelic test of the resistance genes. In all, 819 pairs of wheat SSR primers were used to test the two parents, as well as resistant and susceptible bulks. Subsequently, nine polymorphic markers were employed for genotyping the F₂ and F₃ populations. Results indicated that the stripe rust resistance in Chuanmai 42 was conferred by a single dominant gene, temporarily designated YrCH42, located close to the centromere of chromosome 1B and flanked by nine SSR markers Xwmc626, Xgwm273, Xgwm11, Xgwm18, Xbarc137, Xbarc187, Xgwm498, Xbarc240 and Xwmc216. The resistance gene was closely linked to Xgwm498 and Xbarc187 with genetic distances of 1.6 and 2.3 cM, respectively. The seedling tests with 26 PST isolates and allelic tests indicated that YrCH42, Yr24 and Yr26 are likely to be the same gene.G.Q. Li and Z.F. Li contributed equally to the work.     

Characterization and molecular mapping of stripe rust resistance gene Yr61 in winter wheat cultivar Pindong 34

Key message

We report a new stripe rust resistance gene on chromosome 7AS in wheat and molecular markers useful for transferring it to other wheat genotypes.

Abstract

Several new races of the stripe rust pathogen have established throughout the wheat growing regions of China in recent years. These new races are virulent to most of the designated seedling resistance genes limiting the resistance sources. It is necessary to identify new genes for diversification and for pyramiding different resistance genes in order to achieve more durable resistance. We report here the identification of a new resistance gene, designated as Yr61, in Chinese wheat cultivar Pindong 34. A mapping population of 208 F₂ plants and 128 derived F_2:3 lines in a cross between Mingxian 169 and Pindong 34 was evaluated for seedling stripe rust response. A genetic map consisting of eight resistance gene analog polymorphism (RGAP), two sequence-tagged site (STS) and four simple sequence repeat (SSR) markers was constructed. Yr61 was located on the short arm of chromosome 7A and flanked by RGAP markers Xwgp5467 and Xwgp5765 about 1.9 and 3.9 cM in distance, which were successfully converted into STS markers STS5467 and STS5765b, respectively. The flanking STS markers could be used for marker-assisted selection of Yr61 in breeding programs.     

<Emphasis Type="Italic">Yr32</Emphasis> for resistance to stripe (yellow) rust present in the wheat cultivar Carstens V

Stripe or yellow rust of wheat, caused by Puccinia striiformis f. sp. tritici, is an important disease in many wheat-growing regions of the world. A number of major genes providing resistance to stripe rust have been used in breeding, including one gene that is present in the differential tester Carstens V. The objective of this study was to locate and map a stripe rust resistance gene transferred from Carstens V to Avocet S and to use molecular tools to locate a number of genes segregating in the cross Savannah/Senat. One of the genes present in Senat was predicted to be a gene that is present in Carstens V. For this latter purpose, stripe rust response data from both seedling and field tests on a doubled haploid population consisting of 77 lines were compared to an available molecular map for the same lines using a non-parametric quantitative trait loci (QTL) analysis. Results obtained in Denmark suggested that a strong component of resistance with the specificity of Carstens V was located in chromosome arm 2AL, and this was consistent with chromosome location work undertaken in Australia. Since this gene segregated independently of Yr1, the only other stripe rust resistance gene known to be located in this chromosome arm, it was designated Yr32. Further QTLs originating from Senat were located in chromosomes 1BL, 4D, and 7DS and from Savannah on 5B, but it was not possible to characterize them as unique resistance genes in any definitive way. Yr32 was detected in several wheats, including the North American differential tester Tres.An erratum to this article can be found at Communicated by G. Wenzel     

New slow-rusting leaf rust and stripe rust resistance genes <Emphasis Type="Italic">Lr67</Emphasis> and <Emphasis Type="Italic">Yr46</Emphasis> in wheat are pleiotropic or closely linked

The common wheat genotype ‘RL6077’ was believed to carry the gene Lr34/Yr18 that confers slow-rusting adult plant resistance (APR) to leaf rust and stripe rust but located to a different chromosome through inter-chromosomal reciprocal translocation. However, haplotyping using the cloned Lr34/Yr18 diagnostic marker and the complete sequencing of the gene indicated Lr34/Yr18 is absent in RL6077. We crossed RL6077 with the susceptible parent ‘Avocet’ and developed F₃, F₄ and F₆ populations from photoperiod-insensitive F₃ lines that were segregating for resistance to leaf rust and stripe rust. The populations were characterized for leaf rust resistance at two Mexican sites, Cd. Obregon during the 2008–2009 and 2009–2010 crop seasons, and El Batan during 2009, and for stripe rust resistance at Toluca, a third Mexican site, during 2009. The F₃ population was also evaluated for stripe rust resistance at Cobbitty, Australia, during 2009. Most lines had correlated responses to leaf rust and stripe rust, indicating that either the same gene, or closely linked genes, confers resistance to both diseases. Molecular mapping using microsatellites led to the identification of five markers (Xgwm165, Xgwm192, Xcfd71, Xbarc98 and Xcfd23) on chromosome 4DL that are associated with this gene(s), with the closest markers being located at 0.4 cM. In a parallel study in Canada using a Thatcher × RL6077 F₃ population, the same leaf rust resistance gene was designated as Lr67 and mapped to the same chromosomal region. The pleiotropic, or closely linked, gene derived from RL6077 that conferred stripe rust resistance in this study was designated as Yr46. The slow-rusting gene(s) Lr67/Yr46 can be utilized in combination with other slow-rusting genes to develop high levels of durable APR to leaf rust and stripe rust in wheat.     

Identification and characterization of stripe rust resistance gene Yr34 in common wheat

An uncharacterized source of seedling resistance to Puccinia striiformis f.sp. tritici was identified in an advanced wheat breeding line WAWHT2046. Genetic analysis based on a WAWHT2046/Carnamah-derived double haploid (DH) population demonstrated monogenic inheritance of seedling stripe rust resistance in WAWHT2046. The gene controlling stripe rust resistance in line WAWHT2046 was tentatively designated YrWA. The chromosome 5AL located awn inhibitor gene B1, possessed by WAWHT2046, also showed monogenic inheritance when the DH population was scored for the presence and absence of awns. Joint segregation analysis at the B1 and YrWA loci indicated genetic linkage between the two loci. A recombination value of 12.2 cM was computed using Mapmanager. This association located YrWA in the chromosome arm 5AL. Molecular mapping using microsatellite markers placed YrWA distal to B1. All molecular markers mapped proximal to the awn inhibitor locus B1. As no other stripe rust resistance gene is reported to be located in the chromosome arm 5AL, YrWA was permanently designated as Yr34. Yr34 produced an intermediate (23C) seedling infection type and expressed very low stripe rust response (10R-MR) on adult plants in the field, similar to the resistance gene Yr17. In addition to Yr34, this mapping population segregated for three genetically independent adult plant stripe rust resistance genes. The detection of DH lines with completely susceptible response, higher than that shown by the Yr34-lacking parent Carnamah, suggested that both parents contributed adult plant resistance. The use of WAWHT2046 as a parent in breeding programs would also contribute APR in addition to Yr34.     

Dr. Heinz rogoll‐70 Jahre

The wheat crop remains vulnerable to all three rust diseases (leaf rust, stem rust and yellow rust) caused by Puccinia spp. according to the prevalence of the pathogen in different wheat-growing areas worldwide. Stripe rust or yellow rust caused by Puccinia striiformis f. sp. tritici is the most significant rust pathogen which prefers cool, moist areas and highlands. The pathogen is recognised as responsible for huge production losses in wheat. Genetic variation in pathogen makes its control difficult. Therefore, resistance against all the races of the pathogen known as durable or race-non-specific resistance is preferred. The present study was carried out to identify durable resistance against stripe rust in selected wheat cultivars from Pakistan through seedling testing, field evaluation at adult stage, morphological marker studies and marker-assisted selection. Results revealed that 4% of the cultivars were resistant at the seedling stage while the rest were susceptible or intermediate. To confirm their field resistance, the same cultivars were evaluated under field conditions at Cereal Crops Research Institute Pirsabak (located in Khyber Pakhtunkhwa, KP) a hot spot of stripe rust in Pakistan. Observations exhibited that at the adult stage 4% of the cultivars were resistant, 70% intermediate or moderately resistant while the others were highly susceptible. Leaf tip necrosis was observed in 30% of the cultivars. Wheat cultivars showing susceptibility at the seedling stage were highly to moderately resistant at adult stage showing durable resistance. For further validation, morphological markers were also observed in cultivars indicating the presence of Yr18/Lr34 gene. Eleven cultivars (C-518, Mexipak, Kohinoor-83, Faisalabad-83, Zardana-93, Shahkar-95, Moomal-2002, Wattan-94, Pasban-90, Kiran-95, and Haider-2000) were identified, having durable or race non-specific resistance against stripe rust. These cultivars can further be utilised in wheat breeding programmes for deploying durable resistance to attain long lasting control against stripe rust.