Leaf rust and stripe rust resistance genes transferred to common wheat from Triticum dicoccoides

Linked leaf rust and stripe rust resistance genes introduced from Triticum dicoccoides protected common wheat seedlings against a range of pathotypes of the respective pathogens. The genes were chromosomally mapped using monosomic and telosomic analyses, C-banding and RFLPs. The data indicated that an introgressed region is located on wheat chromosome arm 6BS. The introgressed region did not pair with the ‘Chinese Spring’ 6BS arm during meiosis possibly as a result of reduced homology, but appeared to pair with 6BS of W84-17 (57% of pollen mother cells) and ‘Avocet S’. The introgressed region had a very strong preferential pollen transmission (0.96–0.98) whereas its transmission through egg cells (0.41–0.66) varied with the genetic background of the heterozygote. Homozygous resistant plants had a normal phenotype, were fertile and produced plump seeds. Symbols Lr53 and Yr35 are proposed to designate the respective genes.     

Transfer of rust resistance from Aegilops ovata into bread wheat (Triticum aestivum L.) and molecular characterisation of resistant derivatives

An interspecific cross was made to transfer leaf rust and stripe rust resistance from an accession of Aegilops ovata (UUMM) to susceptible Triticum aestivum (AABBDD) cv. WL711. The F₁was backcrossed to the recurrent wheat parent, and after two to three backcrosses and selfing, rust resistant progenies were selected. The C-banding study in a uniformly leaf rust and stripe rust resistant derivative showed a substitution of the 5M chromosome of Ae. ovata for 5D of wheat. Analysis of rust resistant derivatives with mapped wheat microsatellite makers confirmed the substitution of 5M for 5D. Some of these derivatives also possessed one or more of the three alien translocations involving 1BL, 2AL and 5BS wheat chromosomes which could not be detected through C-banding. A translocation involving 5DSof wheat and the substituted chromosome 5M of Ae. ovata was also observed in one of the derivatives. Susceptibility of this derivative to leaf rust showed that the leaf rust resistance gene(s) is/are located on short arm of 5M chromosome of Ae. ovata. Though the Ae. ovatasegment translocated to 1BL and 2AL did not seem to possess any rust resistance gene, the alien segment translocated to 5BS may also possess gene(s) for rust resistance. The study demonstrated the usefulness of microsatellite markers in characterisation of interspecific derivatives. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cytogenetic studies in wheat XIX. Chromosome location and linkage studies of a gene for leaf rust resistance in the Australian cultivar 'Harrier'

Monosomic analysis indicated that a seedling leaf rust resistance gene present in the Australian wheat cultivar ‘Harrier’(tentatively designated LrH) is located on chromosome 2A. LrH segregated independently of the stripe rust resistance gene Yr1 located in the long arm of that chromosome, but failed to recombine with Lr17 located in the short arm. LrH was therefore designated Lr17b and the allele formerly known as Lr17 was redesignated as Lr17a. The genes Lr17b and Lr37 showed close repulsion linkage. Tests of allelism indicated that Lr1 7b is also present in the English wheats ‘Dwarf A’(‘Hobbit Sib’), ‘Maris Fundin’ and ‘Norman’. Virulence for Lr17b occurs in Australia, and pathogenicity studies have also demonstrated virulence in many western European isolates of the leaf rust pathogen. Despite this, it is possible that the gene may be of value in some regions if used in combination with other leaf rust resistance genes.     

Monosomic analyses of stripe rust and leaf rust resistance genes in winter wheat varieties Lüquyu and Yantar

Summary A set of 21 monosomics of Novosadska Rana-1 was used to locate the rust resistance genes of Lüqiyu, a stripe rust resistant line developed by BAU and Yantar, a leaf rust resistant wheat introduced from Bulgaria. The resistance of the former to p. striiformis race C25 was conditioned by a dominant gene located on chromosome 2B, whereas that of the latter to P. recondita race CL3 was controlled by two complementary dominant genes located on chromosomes 5A and 1D, respectively. The relationship of the stripe rust resistance gene in Lüqiyu to Yr5, Yr7 or Yr _Suwon' all located on chromosome 2B is unknown. The two complementary leaf rust resistance factors in Yantar appear to be new.     

Leaf Rust and Stripe Rust Resistance Genes Derived from Aegilops Sharonensis

Summary Linked leaf and stripe rust resistance genes introgressed into hexaploid wheat from Aegilops sharonensis provided protection in the seedling stage to a wide range of pathotypes of the two diseases. Monosomic and telosomic analyses showed that the resistance genes occur on wheat chromosome 6A. This result could be confirmed making use of mapped chromosome 6A microsatellite markers. The introgressed chromatin appeared to involve the proximal part of 6AL and the complete 6AS arm and it was thus not possible to deduce the chromosome arm harbouring the resistance genes. The resistance showed non-Mendelian transmission. The genetic background of a heterozygote interacted with the introgressed region to result in either preferential or impaired female transmission. Male transmission appeared to be affected in a different way from female transmission and was exclusive in the genetic background studied. Symbols Lr56 and Yr38 are proposed to designate the respective genes of which line 0352-4 is the appropriate source material.     

Cytogenetical studies in wheat. XVIII. Gene Yr24 for resistance to stripe rust

A new gene, Yr24, for resistance to stripe rust was transferred from a durum accession to common wheat via an amphiploid (synthetic wheat) with Aegilops tauschii. Yr24 was located in chromosome 1B by monosomic analysis. Its genetic linkage of 4 cM with Yr15 indicated its localization to the short arm.     

Cytogenetical studies in wheat XIX. Location and linkage studies on gene Yr27 for resistance to stripe (yellow) rust

The stripe (yellow) rust resistance gene Yr27 was located in wheat (Triticum aestivum L.) chromosome 2B and shown to be closely linked to the leaf (brown) rust resistance genes Lr13 and Lr23 in the proximal region of the short arm. Gene Yr27 was genetically independent of Lr16, which is distally located in the same arm. While Yr27 was often difficult to score in segregating seedling populations, it is apparently quite effective in conferring resistance to avirulent cultures under field conditions. The occurrence of Yr27 in Mexican wheat germplasm and the current over-dependence on Yr27 for crop protection in Asia are discussed.     

Resistance to leaf rust in cultivars of bread wheat and durum wheat grown in Spain

A set of bread wheat and durum wheat cultivars adapted to Spanish conditions was tested for resistance against leaf rust caused by different pathotypes of Puccinia triticina in field trials and in growth chamber studies. Lower levels of resistance were found in durum wheat than in bread wheat. The most frequent Lr genes found in bread wheat were Lr1, Lr10, Lr13, Lr20, Lr26 and Lr28. In durum wheat, additional resistance genes that differed from the known Lr genes were identified. The level of partial resistance to leaf rust was in general low, although significant levels were identified in some bread wheat and durum wheat cultivars.     

The reaction of x Tritordeum and its Triticum spp. and Hordeum chilense parents to rust diseases

Summary Hexaploid and octoploid tritordeums and their parents Hordeum chilense and Triticum spp. were screened for resistance to isolates of wheat and barley yellow and brown rusts. All H. chilense lines were highly resistant to both wheat and barley brown rust, few lines were susceptible to wheat yellow rust while susceptibility to barley yellow rust was common. In general the resistance of tritordeum is predominantly contributed by the wheat parent and apparently the genes for resistance in H. chilense are inhibited in their expression by the presence of the wheat genome.Abbreviations WYR wheat yellow rust - WBR wheat brown rust - BYR barley yellow rust - BBR barley brown rust     

Genes for wheat stem rust resistance postulated in German cultivars and their efficacy in seedling and adult‐plant field tests

Stem rust of wheat (caused by Puccinia graminis f.sp. tritici) gained high international attention in the last two decades, but does not occur regularly in Germany. Motivated by a regional epidemic in 2013, we analysed 15 spring and 82 winter wheat cultivars registered in Germany for their resistance to stem rust at the seedling stage and tested 79 of these winter wheat cultivars at the adult‐plant stage. A total of five seedling stem rust resistance genes were postulated: Sr38 occurred most frequently (n = 29), followed by Sr31 (n = 11) and Sr24 (n = 8). Sr7a and Sr8a occurred only in two spring wheat genotypes each. Four cultivars had effective seedling resistance to all races evaluated that could only be explained by postulating additional resistance genes (‘Hyland’, ‘Pilgrim PZO’, ‘Tybalt’) or unidentified gene(s) (‘Memory’). The three winter wheat cultivars (‘Hyland’ ‘Memory’ and ‘Pilgrim PZO’) were also highly resistant at the adult‐plant stage; ‘Tybalt’ was not tested. Resistance genes Sr24 and Sr31 highly protected winter wheat cultivars from stem rust at the adult‐plant stage in the field. Disease responses of cultivars carrying Sr38 varied. Mean field stem rust severity of cultivars without postulated seedling resistance genes ranged from 2.71% to 41.51%, nine of which were significantly less diseased than the most susceptible cultivar. This suggests adult‐plant resistance to stem rust may be present in German wheat cultivars.     

Identification of microsatellite markers for a leaf rust resistance gene introgressed into common wheat from Triticum timopheevii

The tetraploid wheat Triticum timopheevii Zhuk (A^tA^tGG) is known as a source of genes determining resistance to many diseases. An introgressive line 842, with durable resistance to leaf rust was established by crossing T. aestivum cv. ‘Saratovskaya29’ with T. timopheevii ssp. viticulosum and used for mapping leaf rust resistance genes. Molecular analysis of the line 842 with polymorphic microsatellite markers detected introgressions of T. timopheevii into the homoeologous group 2 chromosomes of common wheat. Transloca‐tion breakpoints of introgressed fragments were localized between the markers Xgwm95 and Xgwm817 on chromosome 2A, as well as Xgwm1128 and Xgwm1067 on chromosome 2B. Linkage analysis demonstrated the association of disease resistance at the seedling stage with chromosome 2A. The gene was found to be linked with marker Xgwm817 at a genetic distance of 1.5 cM. The alien leaf rust resistance gene was temporarily designated as lrTt1.     

Identification and molecular mapping of a leaf rust resistance gene in spelt wheat landrace Altgold

Leaf rust, caused by Puccinia triticina, is an important disease for wheat production, both in China and worldwide. In laboratory studies spelt wheat (Triticum aestivum ssp. spelta) landrace Altgold was resistant to P. triticina races THT and PHT and genetic analysis indicated that it possessed a dominant leaf rust resistance gene, temporarily designated LrAlt. F₆ recombinant inbred lines (RILs) derived from a cross with the susceptible common wheat cultivar Nongda 3338 were used to map LrAlt with SSR markers. The resistance gene was distal to SSR loci Xbarc212, Xwmc382, Xgwm636, and Xwmc407 on the short arm of chromosome 2A. The closest markers Xbarc212 and Xwmc382 which co-segregated were 1.8 cM away from LrAlt. The relationships of LrAlt and other wheat leaf rust resistance genes located on the short arm of chromosome 2A were discussed, suggesting that LrAlt might be a new leaf rust resistance gene.     

A microsatellite marker linked to leaf rust resistance transferred from Aegilops triuncialis into hexaploid wheat

Aegilops triuncialis (UUCC) is an excellent source of resistance to various wheat diseases, including leaf rust. Leaf rust‐resistant derivatives from a cross of a highly susceptible Triticum aestivum cv.‘WL711’ as the recurrent parent and Ae. triuncialis Ace.3549 as the donor and with and without a pair of acrocentric chromosomes were used for molecular tagging. The use of a set of sequence tagged microsatellite (STMS) markers already mapped to different wheat chromosomes unequivocally indicated that STMS marker gwm368 of chromosome 4BS was tightly linked to the Ae. triuncialis leaf rust resistance gene transferred to wheat. The presence of the Ae. Triuncialis‐specific STMS gwm368 homoeoallele along with the non‐polymorphic 4BS allele in the rust‐resistant derivatives with and without the acrocentric chromosome indicates that the resistance has been transferred from the acrocentric chromosome to either the A or the D genome of wheat. This alien leaf rust resistance gene has been temporarily named as LrTr.     

Genetic basis of seedling-resistance to leaf rust in bread wheat 'Thatcher'

The bread wheat cultivar ‘Thatcher’ is documented to carry the gene Lr22b for adult‐plant resistance to leaf rust. Seedling‐resistance to leaf rust caused by Puccinia triticina in the bread wheat cultivar ‘Thatcher’, the background parent of the near‐isogenic lines for leaf rust resistance genes in wheat, is rare and no published information could be found on its genetic basis. The F₂ and F₃ analysis of the cross ‘Agra Local’ (susceptible) × ‘Thatcher’ showed that an apparently incompletely dominant gene conditioned seedling‐resistance in ‘Thatcher’ to the three ‘Thatcher’‐avirulent Indian leaf rust pathotypes – 0R8, 0R8‐1 and 0R9. Test of allelism revealed that this gene (temporarily designated LrKr1) was derived from ‘Kanred’, one of the parents of ‘Thatcher’. Absence of any susceptible F₂ segregants in a ‘Thatcher’ × ‘Marquis’ cross confirmed that an additional gene (temporarily designated LrMq1) derived from ‘Marquis’, another parent of ‘Thatcher’, was effective against pathotype 0R9 alone. These two genes as well as a second gene in ‘Kanred’ (temporarily designated LrKr2), which was effective against all the three pathotypes, but has not been inherited by ‘Thatcher’, seem to be novel, undocumented leaf rust resistance genes.     

The inheritance of stem rust and leaf rust resistance in some Ethiopian wheat collections

Summary Common and durum wheat populations obtained from Sweden and originally collected in Ethiopia were screened for resistance to steum rust and leaf rust. Resistant selections of common wheat were crossed and backcrossed with either stem rust susceptible RL6071, or leaf rust susceptible Thatcher. Genetic studies, based largely on tests of backcross F₂ families, showed that four of the selections had in common a recessive gene SrA. Plants with this gene were resistant (1⁺ infection type) to all stem rust races tested. This gene was neither Sr26 nor Sr29. The resistance of other selections, based on tests with an array of rust isolates, was due to various combinations of Sr6, 8a, 9a, 9d, 9c, 11, 13, 30, and 36. One of the selections had linked genes, Lr19/Sr25. Another selection had a dominant gene for resistance (;1 infection type) to all the races of leaf rust. With the possible exception of this gene for leaf rust resistance and SrA, no obviously new resistance was found.     

Detection of molecular markers linked to the durable adult plant stripe rust resistance gene Yr18 in bread wheat (Triticum aestivum L.)

Stripe rust of wheat caused by Puccinia striiformis West. f. sp. tritici presents a serious problem for wheat production worldwide, and identification and deployment of resistance sources to it are key objectives for many wheat breeders. Here we report the detection of simple sequence repeat (SSR) markers linked to the durable adult plant resistance of cv. ‘Otane’, which has conferred this resistance since its release in New Zealand in 1984. A double haploid population from a cross between ‘Otane’ and the susceptible cv. Tiritea’ was visually assessed for adult plant infection types (IT) in the glasshouse and field, and for final disease severity in the field against stripe rust pathotype 106E139A⁺. At least three resistance loci controlled adult plant resistance to stripe rust in this population. Quantitative trait loci (QTL) mapping results revealed that two of these, one on chromosome 7DS corresponds to the durable adult plant resistance gene Yr18 and other on chromosome 5DL were contributed from ‘Otane’; while the remaining one on chromosome 7BL, was contributed from the susceptible ‘Tiritea’. Interval mapping placed the ‘Otane’‐resistant segment near the centromere of chromosome 7DS at a distance of 7 cM from the SSR marker gwm44. The stability of QTL in the two environments is discussed. SSR gwm44 is potentially a candidate marker for identifying the durable resistance gene Yr18 in breeding programmes.     

Genetics of leaf rust resistance in three Americano landrace-derived wheat cultivars from Uruguay

A genetic analysis of the landrace‐derived wheat accessions Americano 25e, Americano 26n, and Americano 44d, from Uruguay was conducted to identify the leaf rust resistance genes present in these early wheat cultivars. The three cultivars were crossed with the leaf rust susceptible cultivar ‘Thatcher’ and approximately 80 backcross (BC1) F₂ families were derived for each cross. The BC1F₂ families and selected BC1F₄ lines were tested for seedling and adult plant leaf rust resistance with selected isolates of leaf rust, Puccinia triticina. The segregation and infection type data indicated that Americano 25e had seedling resistance genes Lr3, Lr16, an additional unidentified seedling gene, and one adult plant resistance gene that was neither Lr12 nor Lr13, and did not phenotypically resemble Lr34. Americano 26n was postulated to have genes Lr11, Lr12, Lr13, and Lr14a. Americano 44d appeared to have two possibly unique adult plant leaf rust resistance genes.     

Genetics of stem rust resistance in the spring wheat cultivar Thatcher and the enhancement of stem rust resistance by <Emphasis Type="Italic">Lr34</Emphasis>

Three recombinant inbred line populations from the crosses RL6071/Thatcher, RL6071/RL6058 (Thatcher Lr34), and Thatcher/RL6058, were used to study the genetics of stem rust resistance in Thatcher and TcLr34. Segregation of stem rust response in each population was used to determine the number of genes conferring resistance, as well as the effect of the leaf rust resistance gene Lr34 on stem rust resistance. The relationship between resistance in seedling and adult plants was also examined, and an attempt was made to identify microsatellite markers linked to genes that were effective in adult plants. In field plot tests at least three additive resistance genes segregated in the RL6071/RL6058 population, whereas two resistance genes segregated in the RL6071/Thatcher population. The presence of the gene Lr34 permitted the expression of additional stem rust resistance in Thatcher-derived lines both at the seedling and adult plant stages. Seedling resistance to races TPMK and RKQQ was significantly associated with resistance in adult plants, whereas seedling resistance to races QCCD and QCCB may have made a minor contribution. The seedling resistance genes Sr16 and Sr12 may have contributed to resistance in adult plants. A molecular marker linked to resistance in adult plants was identified on chromosome 2BL.     

Wheat leaf rust resistance gene Lr59 derived from Aegilops peregrina

An Aegilops peregrina (Hackel in J. Fraser) Maire & Weiller accession that showed resistance to mixed leaf rust ( Puccinia triticina Eriks.) inoculum was crossed with, and backcrossed to, hexaploid wheat ( Triticum aestivum L.). During backcrossing a chromosome segment containing a leaf rust resistance gene (here designated Lr59 ) was spontaneously translocated to wheat chromosome 1A. Meiotic, monosomic and microsatellite analyses suggested that the translocated segment replaced most of, or the complete, 1AL arm, and probably resulted from centromeric breaks and fusion. The translocation, of which hexaploid wheat line 0306 is the appropriate source material, provided seedling leaf rust resistance against a wide range of South African and Canadian pathotypes.     

QTL mapping of adult‐plant resistance to stripe rust in a ‘Lumai 21 × Jingshuang 16’ wheat population

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a devastating fungal disease in common wheat (Triticum aestivum L.) worldwide. Chinese wheat cultivars ‘Lumai 21’ and ‘Jingshuang 16’ show moderate levels of adult‐plant resistance (APR) to stripe rust in the field, and they showed a mean maximum disease severity (MDS) ranging from 24 to 56.7% and 26 to 59%, respectively, across different environments. The aim of this study was to identify quantitative trait loci (QTL) for resistance to stripe rust in an F₃ population of 199 lines derived from ‘Lumai 21’ × ‘Jingshuang 16’. The F₃ lines were evaluated for MDS in Qingshui, Gansu province, and Chengdu, Sichuan province, in the 2009–2010 and 2010–2011 cropping seasons. Five QTL for APR were detected on chromosomes 2B (2 QTL), 2DS, 4DL and 5DS based on mean MDS in each environment and averaged values from all three environments. These QTL were designated QYr.caas‐2BS.2, QYr.caas‐2BL.2, QYr.caas‐2DS.2, QYr.caas‐4DL.2 and QYr.caas‐5DS, respectively. QYr.caas‐2DS.2 and QYr.caas‐5DS were detected in all three environments, explaining 2.3–18.2% and 5.1–18.0% of the phenotypic variance, respectively. In addition, QYr.caas‐2BS.2 and QYr.caas‐2BL.2 colocated with QTL for powdery mildew resistance reported in a previous study. These APR genes and their linked molecular markers are potentially useful for improving stripe rust and powdery mildew resistances in wheat breeding.