Quantitative trait loci mapping of adult‐plant resistance to leaf rust in a Fundulea 900 × ‘Thatcher’ wheat cross

Wheat leaf rust (LR), caused by the obligate biotrophic fungus Puccinia triticina (Pt), is a destructive foliar disease of common wheat (Triticum aestivum L.) worldwide. The most effective, economic means to control the disease is resistant cultivars. The Romanian wheat line Fundulea 900 showed high resistance to LR in the field. To identify the basis of resistance to LR in Fundulea 900, a population of 188 F_2:3 lines from the cross Fundulea 900/‘Thatcher’ was phenotyped for LR severity during the 2010–2011, 2011–2012 and 2012–2013 cropping seasons in the field at Baoding, Hebei Province. Bulked segregant analysis and simple sequence repeat markers were used to identify the quantitative trait loci (QTLs) for LR adult‐plant resistance in the population. Three QTLs were detected and designated as QLr.hebau‐1BL, QLr.hebau‐2DS and QLr.hebau‐7DS. Based on the chromosome positions and molecular marker tests, QLr.hebau‐1BL is Lr46, and QLr.hebau‐7DS is Lr34. QLr.hebau‐2DS was derived from ‘Thatcher’ and was close to Lr22. This result suggests that Lr22b may confer residual resistance on field nurseries when challenged with isolates virulent on Lr22b, or another gene linked to Lr22b confers this resistance from ‘Thatcher’. This study confirms the value of Lr34 and Lr46 in breeding for LR resistance in China; the contribution of the QTL to chromosome 2D needs further validation.     

Rapid phenotyping of adult plant resistance in barley (Hordeum vulgare) to leaf rust under controlled conditions

Breeding for adult plant resistance (APR) is currently impeded by the low frequency of annual field‐based testing and variable environmental conditions. We developed and implemented a greenhouse‐based methodology for the rapid phenotyping of APR to leaf rust in barley to improve the efficacy of gene discovery and cloning. We assessed the effects of temperature (18 and 23°C) and growth stage (1–5 weeks) on the expression of APR in the greenhouse using 28 barley genotypes with both known and uncharacterized APR. All lines were susceptible in week 1, while lines carrying Rph20 and several with uncharacterized resistance expressed resistance as early as week 2. In contrast, lines lacking Rph20 and carrying either Rph23 and/or Rph24 expressed resistance from week 4. Resistant phenotypes were clearest at 18°C. A subset of 16 of the 28 lines were assessed for leaf rust across multiple national and international field sites. The greenhouse screening data reported in this study were highly correlated to most of the field sites, indicating that they provide comparable data on APR phenotypes for screening purposes.     

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.     

Stripe rust resistance gene Yr18 and its suppressor gene in Chinese wheat landraces

The slow‐rusting and mildewing gene Yr18/Lr34/Pm38/Sr57 confers partial, durable resistance to multiple fungal pathogens and has its origins in China. A number of diagnostic markers were developed for this gene based on the gene sequence, but these markers do not always predict the presence of the resistant phenotype as some wheat varieties with the gene are susceptible to stripe rust in China. We hypothesized that these varieties have a suppressor of Yr18. This study was undertaken to determine the presence of Yr18, the suppressor and/or another resistance gene in 144 Chinese wheat landraces using molecular markers and stripe rust field data. Forty‐three landraces were predicted to have Yr18 based on the presence of the markers, but had final disease severities higher than 70%, indicating that this gene may be under the influence of a suppressor. Four of these landraces, ‘Sichuanyonggang 2’, ‘Baikemai’, ‘Youmai’ and ‘Zhangsihuang’, were chosen for genetic studies. Crosses were made between the lines and ‘Avocet S’, with further crosses of Sichuanyonggang 2 ×  ‘Huixianhong’ and Sichuanyonggang 2 ×  ‘Chinese Spring’. The F₁ plants of Sichuanyonggang 2/Chinese Spring was susceptible indicating the presence of a dominant suppressor gene. The results of genetic analyses of F_2:3 and BC₁F₂ families derived from these crosses indicated the presence of Yr18, a Yr18 suppressor and another additive resistance gene. The Yr18 region in Sichuanyonggang 2 was sequenced to ensure that it contained the functional allele. This is the first report of a suppressor of Yr18/Lr34/Pm38/Sr57 gene with respect to stripe rust response.     

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.     

Novel complementary genes for adult plant leaf rust resistance in a wheat stock carrying the 1BL-1RS translocation

The wheat-rye translocation (IBL-IRS) that carries the tightly linked genes Lr26/Sr31/Yr9, has been widely exploited in the development of wheat cultivars worldwide. This resistance, however, has become ineffective owing to the evolution of new pathotypes of Puccinia recondita that neutralize the resistance of Lr26. Inheritance studies on ‘Federation4′/‘Kavkaz’ revealed complementary genes derived separately from ‘Federation’ and ‘Kavkaz’ for adult plant resistance. This previously undescribed source of resistance appears to be widely effective and could therefore be used to broaden the genetic base for resistance in India. Its effectiveness in other geographical areas is unknown.     

Inheritance of seedling and adult plant resistance to leaf rust of selected Australian spring and English winter wheat varieties

Genetic studies were conducted to gain an understanding of the inheritance of adult plant resistance (APR) to leaf rust in six common wheat varieties. The Australian varieties ‘Cranbrook’ and ‘Harrier’ each carry two genes for APR to leaf rust. These genes are genetically independent of the seedling resistance genes Lr23 and Lrl7b, carried by the respective varieties. Adult plant resistance in ‘Suneca’ was conferred by at least two genes, in addition to the seedling genes Lr1 and Lrli. It is likely that the APRs in ‘Cranbrook’, ‘Harrier’ and ‘Suneca’ are conferred by uncharacterized gene(s). Tests of allelism confirmed that seedling resistances in the varieties ‘Avocet R’, ‘Hereward’, ‘Moulin’ and ‘Pastiche’ are conferred by Lrli. Adult plant resistance in the variety ‘Hereward’ was inherited monogenically, whereas varieties ‘Moulin’ and ‘Pastiche’ each carried two dominant genes. On the basis of rust specificity and pedigree analysis, it would seem likely that the APR genes in ‘Hereward’, ‘Moulin’ and ‘Pastiche’ are also currently uncharacterized.     

Seedling and adult plant resistance to yellow rust in Iranian bread wheats

In order to evaluate wheat response to yellow rust, 25 advanced, promising and commercial bread wheat cultivars were tested as seedlings in greenhouse conditions in Karaj, Iran, and as adult plants in field conditions at four locations. Five pathotypes of yellow rust, 14E176A⁺, 134E142A+, 6E210A+, 4E128A- and 64E146A+ prevailing in field test locations, were used in the seedling tests. The results showed that some of the cultivars have seedling or overall resistance to the pathotypes and some have adult plant resistance. Cultivars M-70-4 and MV17 were resistant to all pathotypes as seedlings and showed good adult plant resistance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetics of adult plant stripe rust resistance in four Australian wheats and the French cultivar 'Hybride-de-Bersée'

Long-term resistance to rust diseases depends on the identification and use of durable resistance sources or on the continuing use of new resistances and combinations of genes for specific resistance. These studies include four Australian wheats with intermediate, but inadequate levels of resistance and a French wheat ‘Hybride-de-Bersée’ (‘Bersee’), with reputed durable resistance to stripe rust. Studies of F₂ and F₃ populations from crosses with the susceptible ‘Avocet’ indicated that intermediate levels of adult plant stripe rust resistance in cultivars ‘Harrier’, ‘Flinders’ and ‘M2435’ were inherited monogenically, whereas King possessed two genes for resistance. Cultivars Harrier and M2435 possessed the same gene. Similarly, cvs. King and Flinders carried a gene in common. Like ‘Harrier’ and ‘M2435’, ‘King’ and ‘Flinders’ share common parents. The higher level of resistance in ‘Bersee’ was controlled by four genes. This conclusion was based on conventional genetic analysis, tests on F₂-derived F₇ single-seed descent lines and testcross progenies.     

Molecular cytogenetic characterization and phenotypic evaluation of new wheat–rye lines derived from hexaploid triticale ‘Certa’ × common wheat hybrids

Hexaploid triticale contains valuable genes from both tetraploid wheat and rye and plays an important role in wheat breeding programmes. In order to explore the potential of hexaploid triticale ‘Certa’ in wheat improvement, two crosses were made using ‘Certa’ as female parent, and common wheat cultivars ‘Jinmai47’ (JM47) and ‘Xinong389’ (XN389) as male parents. The karyotyping of BCF_4:5 lines from Certa/JM47//JM47 and F_5:6 lines from Certa/XN389 was investigated using sequential fluorescence in situ hybridization (FISH). One 1B(1R) substitution line and five 1BL.1RS whole‐arm translocation lines were identified, one of which was found lacking ω‐secalin locus. Many structural alterations on wheat chromosomes were detected in the progeny. Great morphologic differences resulting from genetic variations were observed, among which the photosynthetic capability was increased while grain quality was slightly improved. Compared with both parents, the stripe rust resistance at adult stage was increased in lines derived from Certa/JM47//JM47, while it was decreased in lines derived from Certa/XN389. These newly developed lines might have the potential to be utilized in wheat improvement programmes.     

Genetic analysis of adult plant leaf rust resistance in three bread wheat (Triticum aestivum L.) cultivars

Genetic basis of adult plant leaf rust resistance in three released Indian wheat cultivars viz. DWR195, RAJ3765 and HP1731 was investigated through detailed inheritance study under controlled polythene house condition at Flowerdale, India. The F₂, F_3, F₄ and F₅ generations were analyzed with the most frequent and virulent Indian leaf rust pathotype 121R63-1. Two complementary recessive genes imparted resistance in DWR195, two complementary dominant genes governed the resistance of RAJ3765 whereas two independent dominant genes were involved in the resistance of HP1731. The genes responsible for adult plant resistance in the three cultivars were not allelic. The two complementary genes of DWR195 and two independent dominant genes of HP1731 have been isolated as single gene lines. Utilization of resistance from HP1731, which carries two independent dominant genes, will be easy as compared to DWR195 and RAJ3765.     

Evaluation of seedling and adult plant resistance to leaf rust in European wheat cultivars

Summary A set of 105 European wheat cultivars, comprising 68 cultivars with known seedling resistance genes and 37 cultivars that had not been tested previously, was tested for resistance to selected Australian pathotypes of P. triticina in seedling greenhouse tests and adult plant field tests. Only 4% of the cultivars were susceptible at all growth stages. Twelve cultivars lacked detectable seedling resistance to leaf rust, and among the remaining cultivars, 10 designated genes were present either singly or in combination. Lr13 was the most frequently detected gene, present in 67 cultivars, followed by the rye-derived gene Lr26, present in 19 cultivars. Other genes present were Lr1, Lr3a, Lr3ka, Lr10, Lr14a, Lr17b, Lr20 and Lr37. There was evidence for unidentified seedling resistance in addition to known resistance genes in 11 cultivars. Field tests with known pathotypes of P. triticina demonstrated that 57% of the cultivars carried adult plant resistance (APR) to P. triticina. The genetic identity of the APR is largely unknown. Genetic studies on selected cultivars with unidentified seedling resistances as well as all of those identified to carry APR are required to determine the number and inheritance of the genes involved, to determine their relationships with previously designated rust resistance genes, and to assess their potential value in breeding for resistance to leaf rust.     

Novel gene for adult plant resistance to Puccinia recondita in the wheat cultivar'Arjun'

Inheritance of resistance in the wheat cultivar‘Arjun’(HD 2009) against leaf rust pathotype 77–1 revealed that its durable resistance is attributable to a novel dominant adult plant resistance (APR) gene. Lr13, another gene reported in the cultivar played no role. This new gene is established as different from Lr34, the only effective APR gene from Triticum aestivum known for durability.     

Chromosomal locations in common wheat of three new leaf rust resistance genes from Triticum monococcum

Monosomic analysis was conducted to determine chromosomal locations of three new leaf rust resistance genes recently transferred to common wheat (Triticum aestivum) from T. monococcum. The resistance gene in wheat germplasm line KS92WGRC23 was transferred from T. monococcum ssp. monococcum. The resistance genes found in KS93U3 and KS96WGRC34 were transferred from T. monococcum ssp. aegilopoides. Allelism tests showed that the three resistance genes were unlinked. The three lines were crossed with each of the seven A-genome Wichita monosomic lines. The leaf rust resistance genes in KS92WGRC23, KS93U3, and KS96WGRC34 were located on chromosomes 6A, 1A, and 5A, respectively, by monosomic analysis. These results demonstrate that the three new genes derived from T. monococcum are each different. They also differ from previously reported Lr genes. This information on chromosome location and the development of mapping populations will facilitate molecular tagging of the new genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Rph23: A new designated additive adult plant resistance gene to leaf rust in barley on chromosome 7H

We report on a new adult plant resistance (APR) gene Rph23 conferring resistance to leaf rust in barley. The gene was identified and characterized from a doubled haploid population derived from an intercross between the Australian barley varieties Yerong (Y) and Franklin (F). Genetic analysis of adult plant field leaf rust scores of the Y/F population collected over three successive years indicated involvement of two highly additive genes controlling APR, one of which was named Rph23. The gene was mapped to chromosome 7HS positioned at a genetic distance 36.6 cM. Rph23 is closely linked to marker Ebmac0603, which is flanked by markers bPb‐8660 and bPb‐9601 with linkage distances of 0.8 and 5.1 cM, respectively. A PCR‐based marker was optimized for marker‐assisted selection of Rph23, and on the basis of this marker, the gene was postulated as being common in Australian and global barley germplasm. Pedigree and molecular marker analyses indicated that the six‐rowed black Russian landrace ‘LV‐Taganrog’ is the likely origin of Rph23.     

Components of adult plant resistance to leaf rust in wheat

Summary Winter wheat genotypes were tested for resistance in the field by assessing the percentage sporulating leaf area after infection with wheat leaf rust. The disease level in the first field trial was too low for selection. In the second field trial a low sporulating leaf area was found on several genotypes showing a susceptible infection type. These genotypes possibly have partial resistance. Six genotypes possibly possess adult plant resistance, as they showed a resistant infection type and a low sporulating leaf area.The latency period, infection frequency and uredosorus size of sixteen genotypes were determined in the greenhouse after infection with two races of leaf rust at two temperature regimes. The temperature × genotype interaction, found for latency period and infection frequency, was mostly influenced by the cultivars Cerco, Tundra and Miller. Adult plant resistance was postulated for four genotypes whereas another four appeared to have partial resistance.Only one of the sixteen genotypes (Apexal) possessed adult plant resistance and two genotypes (Arminda and Cappelle Desprez) showed partial resistance in the field as well as in the greenhouse.     

Double dose efficiency of the yellow rust resistance gene Yr17 in bread wheat lines

Yellow rust, caused by Puccinia striiformis f. sp. tritici, is one of the most severe wheat disease worldwide. Crop losses have ranged from 10% to 70% and up to 100% in extreme conditions. Eighty-two resistance genes, designated Yr, have been identified. Among them, Yr17 derived from Aegilops ventricosa and located on chromosome 2A has been widely used in wheat breeding. However, it had been overcome already. Through recombination of the Ae. ventricosa Yr17-carrying 6N^v chromosome with 2D of wheat, we introduced Yr17 onto chromosome 2D. Then, lines carrying Yr17 on both 2A and 2D were generated. Seedlings of the latter, as well as those carrying a single dose of Yr17 either on 2A or on 2D, were inoculated with virulent or avirulent strains on wheat seedlings. The different genotypes were fully susceptible for the two pathotypes that are virulent on Yr17. In the case of avirulent pathotypes, the Yr17 double dose lines were fully resistant, while those with the Yr17 gene only on either 2A or 2D had intermediate resistance reactions towards one or the other or both pathotypes.     

Genes Lr48 and Lr49 for hypersensitive adult plant leaf rust resistance in wheat (Triticum aestivum L.)

The genetic bases of leaf rust resistance in wheat (Triticum aestivum L.) line CSP44, selected from the Australian cultivar Condor, and Indian cultivar VL404, were studied. The reaction patterns of CSP44 and VL404 against Indian races 12, 77, 77-1, 77-2, 77-3, 77-4, 77-5 and 108 were different from reaction patterns shown by near-isogenic lines with known adult plant resistance (APR) genes, viz. Lr12, Lr13, Lr22b and Lr34. Although the reaction patterns of CSP44 and VL404 were similar to the near-isogenic line Tc+Lr22a, tests of allelism indicated absence of Lr22a in both CSP44 and VL404. On the basis of genetic studies, their resistances in field tests against race 77-5, the most virulent race from the Indian sub-continent, were each ascribed to two genes. One of the two genes in each wheat was identified to be the non-hypersensitive APR gene Lr34. The second APR genes in CSP44 and VL404 gave hypersensitive reaction types and were recessive and dominant, respectively. The gene in CSP44 was designated Lr48and the gene in VL404, Lr49. This revised version was published online in August 2006 with corrections to the Cover Date.