Identification and characterization of seedling and adult plant resistance to Puccinia hordei in Chinese barley germplasm

Leaf rust of barley, caused by Puccinia hordei, occurs in all barley‐growing regions of Australia causing significant yield losses under epidemic conditions. The development and use of resistant cultivars are the most economical and environmentally sustainable method to control leaf rust which in turn relies on ongoing efforts to identify and characterize new sources of resistance. The aim of this study was to postulate known genes and/or identify new sources of resistance to P. hordei. Fifty‐two genotypes were assessed at the seedling and adult plant growth stages. On the basis of multipathotype tests, 39 genotypes lacked detectable seedling resistance, and nine were postulated to carry the genes Rph2, Rph4, Rph12 and Rph19 singly. Four genotypes carried uncharacterized seedling resistance; however, the gene(s) present in each were ineffective to at least one of the pathotypes used. Field tests at the adult plant growth stage revealed the presence of adult plant resistance (APR) in 12 genotypes. Tests of allelism and marker analysis indicated that resistance genes present in these genotypes were independent of the APR gene Rph20.     

Identification and characterization of seedling and adult plant resistance to <Emphasis Type="Italic">Puccinia hordei</Emphasis> in selected African barley germplasm

A collection of 112 African barley accessions were assessed for response to Puccinia hordei in seedling greenhouse tests using 10 pathotypes and in adult plant field tests over three successive field seasons in Australia. One of the 10 pathotypes (viz. 5457P+) used in seedling tests was also used in field tests to allow assessment of the presence of adult plant resistance (APR) in lines that were seedling susceptible to this pathotype. The seedling resistance genes Rph1, Rph2, Rph3, Rph9.am and Rph9.z were postulated in a number of accessions, singly and in various combinations, with Rph2 and Rph9.z being the most common. Twenty-six accessions carried seedling resistance that was either uncharacterized or could not be determined using the 10 P. hordei pathotypes. One accession carried high levels of APR and 11 accessions showed moderate levels of APR, all of which were susceptible to all P. hordei pathotypes at the seedling stage. All barley accessions were genotyped for the presence of marker alleles that are closely linked to the APR genes Rph20 and Rph23 (bPb-0837 and Ebmac0603, respectively). No accession was positive for bPb-0837, suggesting that Rph20 is not frequent in African germplasm. Thirteen accessions were postulated to carry Rph23 based on the presence of the marker allele Ebmac0603 found in Yerong (Rph23), and 10 out of the 11 accessions with moderate APR lacked the bPb-0837 and Ebmac0603 marker alleles, indicating that they likely carry new uncharacterized APR genes. Inheritance studies were performed using populations derived from four of the accessions that carried APR (Clho 9776, Clho 11958, Mecknes Maroc and Sinai) by crossing with the susceptible barley genotype Gus. Chi squared analysis of the phenotypic data from F₃ populations suggested that CIho9776 carried a single APR gene and CIho11958, Mecknes Maroc and Sinai each carried two genes for APR to leaf rust.     

Evaluation of seedling and adult plant resistance in European wheat cultivars to Australian isolates of <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>

A set of 105 European wheat cultivars was assessed for seedling resistance and adult plant resistance (APR) to stripe (yellow) rust in greenhouse and field tests with selected Australian isolates of Puccinia striiformis f. sp. tritici (Pst). Twelve cultivars were susceptible to all pathotypes, and among the remainder, 11 designated seedling genes (Yr1, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr27, Yr32, YrHVII and YrSP) and a range of unidentified seedling resistances were detected either singly or in combination. The identity of seedling resistance in 43 cultivars could not be determined with the available Pst pathotypes, and it is considered possible that at least some of these may carry uncharacterised seedling resistance genes. The gene Yr9 occurred with the highest frequency, present in 19 cultivars (18%), followed by Yr17, present in 10 cultivars (10%). Twenty four cultivars lacked seedling resistance that was effective against the pathotype used in field nurseries, and all but two of these displayed very high levels of APR. While the genetic identity of this APR is currently unknown, it is potentially a very useful source of resistance to Pst. Genetic studies are now needed to characterise this resistance to expedite its use in efforts to breed for resistance to stripe rust. Colin R. Wellings seconded from NSW Department of Primary Industries.     

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.     

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

A total of 105 European wheat cultivars were assessed for seedling and adult plant resistance (APR) to stem rust using an array of Australian isolates of Puccinia graminis f. sp. tritici. Twenty-seven cultivars were susceptible at both seedling and adult plant growth stages. Twelve catalogued seedling stem rust resistance genes (Sr7b, Sr8a, Sr8b, Sr9b, Sr9g, Sr11, Sr15, Sr17, Sr29, Sr31, Sr36 and Sr38) were detected in the remaining cultivars, and 13 cultivars carried additional seedling resistance genes that could not be postulated with the isolates used. Low levels of APR to stem rust were found in the cultivars Artaban, Forno, Mec, Mercia, Pandas and Vlada. Although the genetic identity of this APR was not determined, it was clear that the only designated stem rust APR gene Sr2 was not present in any of the cultivars tested based on the absence of the linked traits seedling chlorosis and pseudo black chaff. One of these cultivars, Forno, is believed to carry the leaf rust APR gene Lr34, previously reported to be associated with improved resistance to stem rust. A detailed genetic characterisation of the APRs in these cultivars will be needed to understand their modes of inheritance and relationships with catalogued stem rust resistance genes. Such knowledge may help in developing cultivars with effective gene combinations that confer higher levels of protection.     

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.     

Genetic Diversity for Adult Plant Resistance to Leaf Rust (Puccinia recondita) in Near-Isogenic Lines and in Indian Wheats

Variation for adult plant resistance in near-isogenic wheat lines carrying Lrl4b, Lrl4ab and Lr30 in a ‘Thatcher’ background indicated the possible presence of novel adult plant resistance genes effective against the Indian leaf rust population. Sixty-one wheats released for cultivation in India were grown in isolated nurseries. Each nursery was separately inoculated with one of four leaf rust pathotypes which had been selected to aid identification of resistance effective only in the adult plant stage. Seven distinct response groups were recognised and a minimum of six sources of adult plant resistance were postulated. In a group of 14 wheats, resistance was explained on the basis of the seedling response genes that were identified. Similar results for two years with pathotype 77-1 gave support to the reliability of field tests. Adult plant resistance (APR) sources were either race-specific or effective against all pathotypes used. Seedlings of cultivars with APR showed susceptible reactions. The possible presence of Lr34 in Indian wheats and its role in durable leaf rust resistance are discussed.     

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.     

Postulation of leaf-rust resistance genes in Czech and Slovak barley cultivars and breeding lines

Leaf‐rust resistance (Rph) genes in 61 Czech and Slovak barley cultivars and 32 breeding lines from registration trials of the Czech Republic were postulated based on their reaction to 12 isolates of Puccinia hordei with different combinations of virulence genes. Five known Rph genes (Rph2, Rph3, Rph4, Rph7, and Rph12) and one unknown Rph gene were postulated to be present in this germplasm. To corroborate this result, the pedigree of the barley accessions was analysed. Gene Rph2, as well as Rph4, originated from old European cultivars. The donor of Rph3, which has been mainly used by Czech and Slovak breeders, is ‘Ribari’ (‘Baladi 16’). Rph12 originates from barley cultivars developed in the former East Germany. Rph7 in the registered cultivar ‘Heris’ originates from ‘Forrajera’. A combination of two genes was found in 10 cultivars. Nine heterogeneous cultivars were identified; they were composed of one component with an identified Rph gene and a second component without any resistance gene. No gene for leaf rust resistance was found in 17 of the accessions tested. This study demonstrates the utility of using selected pathotypes of P. hordei for postulating Rph genes in barley.     

‘CPAN 1842’: a new source of adult plant leaf rust resistance in bread wheat

There is worldwide interest in adult plant resistance (APR) because of greater durability of APR to the cereal rusts. Peruvian bread wheat genotype ‘CPAN (Coordinated Project Accession Number) 1842’ (LM 50–53) has shown leaf rust resistance in disease screening nurseries since its introduction in 1977. However, it is susceptible at the seedling stage to several Puccinia triticina (Pt) pathotypes including the widely prevalent 77‐5 (121R63‐1) that infects bread wheat. Inheritance studies showed that CPAN 1842 carried a dominant gene for APR to pathotype 77‐5, which was different from Lr12, Lr13, Lr22a, Lr34, Lr35, Lr37, Lr46, Lr48, Lr49 and Lr68, based on the tests of allelism; and from Lr67, based on genotyping with the closely linked SSR marker cfd71. This gene should also be different from Lr22b as the latter is totally ineffective against pathotype 77‐5. CPAN 1842 therefore appears to be a new promising source of leaf rust resistance. Also having resistance to stem rust and stripe rust, this line can contribute to breeding for multiple rust resistances in wheat.     

Inheritance and QTL mapping of leaf rust resistance in the European winter wheat cultivar ‘Beaver’

Genetic studies were conducted on an European winter wheat cultivar, Beaver, to determine the mode of inheritance of leaf rust resistance at seedling and adult plant growth stages using a recombinant doubled haploid population, Beaver/Soissons. Greenhouse studies indicated the involvement of genes Lr13 and Lr26 in governing leaf rust resistance at seedling growth stages, whereas, adult plant resistance (APR) in the field with pathotypes carrying virulence individually for Lr13 and Lr26 showed trigenic inheritance for the population. Marker regression analysis of adult plant field data indicated the involvement of six significant QTLs (chromosomes 1B, 3B, 3D, 4B, 4D and 5A) in year 2005, four QTLs (1B, 3B, 4B and 5A) in 2006, and six QTLs (1A, 1B, 3B, 4A, 4B and 5A) in 2007 for reducing leaf rust severity. QTLs on chromosomes 1B, 4B and 5A were considered the most important because of their detection across years, whereas QTLs on chromosomes 1A, 3B, 3D and 4A were either inconsistent or non-significant and unexplained. Based on an association of closely linked markers with phenotypic data, putative single gene stocks were identified for each consistent QTL and crossing was initiated to develop populations segregating for each to permit fine mapping of the identified regions.     

Genes conferring low seedling reaction to Mexican pathotypes of Puccinia recondita f. sp. tritici,and adult-plant responses of recent wheat cultivars from the former USSR

Fifty-five spring bread wheat (Triticum aestivum L.) cultivars, mostly released between 1975 and 1991 in eight leaf rust-prone spring wheat growing regions of the former USSR, were tested in the seedling growth stage for reaction to 15 Mexican pathotypes of Puccinia recondita f. sp. tritici. In total, seven known and at least two unknown genes were identified, either singly or in combinations: Lr3 (7 cultivars), Lr10 (14), Lr13 (5), Lr14a (1), Lr16 (1), Lr23 (3); the unknown genes were identified in 14 cultivars. The first unknown gene could be either Lr9, Lr19, or Lr25; however, the second unknown gene in 9 cultivars was different from any named gene. Twelve of the 15 pathotypes are virulent for this gene, hence its use in breeding for resistance will be limited. The cultivars were also evaluated at two field locations in Mexico with two pathotypes in separate experiments. The area under the disease progress curve and the final disease rating of the cultivars indicated genetic diversity for genes conferring adult plant resistance. based on the symptoms of the leaf tip necrosis in adult plants, resistance gene Lr34 could be present in at least 20 cultivars. More than half of the cultivars carry high to moderate levels of adult plant resistance and were distributed in each region.     

Comparison of the resistance and susceptibility to downy mildew [<Emphasis Type="Italic">Hyaloperonospora parasitica</Emphasis>, constant. (Pers. Ex Fr)] of nine <Emphasis Type="Italic">Brassica olearacea</Emphasis> accessions in laboratory,seedbed, and field screens

The relationship between resistance in seedlings, young and adult plants is studied for the pathosystem Brassica oleracea–Hyaloperonospora parasitica. Genotypes identified in the laboratory as resistant or susceptible or exhibiting a differential reaction to a selection of H. parasitica isolates were tested in 1997–1999 in seedbeds and fields under natural infestation. Isolates tested in the laboratory were grouped in five pathotypes, of which four were presented by isolates from Brittany, France. Genotypes susceptible to all pathotypes in the laboratory were also susceptible in the seedbed and field tests, while genotypes expressing a differential response to pathotypes were either resistant or susceptible. Accessions Everest, DEGC, ESPG and RS1105 exhibiting resistance to all pathotypes except I, were resistant in all environments and remained resistant in 2000–2002. Pathotype I was not prevailing in the field and results support the hypothesis that accessions resistant under laboratory conditions will be resistant under field conditions, provided the same pathotypes are present under the laboratory and field conditions.     

Postulation of leaf (brown) rust resistance genes in 70 wheat cultivars grown in the United Kingdom

Multi-pathotype tests on 70 U.K. wheat cultivars permitted postulation of eight known seedling genes for resistance to Puccinia recondita f. sp.tritici either singly or in combinations. The most commonly detected gene was Lr13 (present in approximately 57% of cultivars), followed by Lr26 (22%), Lr37 (20%), Lr10 (17%), Lr17b (LrH) (10%), Lr1 (7%), Lr3a (6%) and Lr20(4%). This information permitted assessments of adult plant resistance (APR) in some cultivars, in field nurseries inoculated with pathotypes of P. recondita f. sp. tritici of known pathogenicities for characterized seedling resistance genes. APR was identified in eleven cultivars, including Avalon and Maris Ranger, which lacked detectable seedling resistance genes. The results provided a better understanding of specific resistances in the cultivars tested than was available from previous reports. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance and characterization of the new and rare gene Rph25 conferring seedling resistance in Hordeum vulgare against Puccinia hordei

In this study, we characterized and mapped a new and rare resistance gene (RphFT) in the Chinese barley variety ‘Fong Tien’. RphFT, a dominant gene, was mapped to chromosome 5HL at a genetic position of 142.1 cM using DArT‐seq markers. The gene was also confirmed to be present in Australian cultivar ‘Yagan’ based on allelic tests, and likely ‘Lockyer’ based on multipathotype tests. The genetic studies also confirmed the presence of Rph12 in Australian cultivar ‘Baudin’. Rph12 is also located on chromosome 5HL close to RphFT, and the two loci were confirmed to be independent. Gene RphFT is of limited breeding value because it is effective to only one pathotype of P. hordei, 220P+ +Rph13 in Australia; nevertheless, it may play a role in controlling leaf rust if used in combination with other Rph genes. The locus symbol Rph25 is recommended for RphFT in accordance with the rules and numbering system of barley gene nomenclature.     

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.     

Quantitative resistance and its components in 16 barley cultivars to yellow rust, <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">hordei</Emphasis>

Sixteen barley cultivars with a susceptible infection type (IT = 7–8) in the seedling stage to an isolate of race 24 of Puccinia striiformis f. sp. hordei were planted at two locations in México. Disease severity (DS) parameters were assessed for the flag leaf and for the upper three leaves. The cultivars represented at least five levels of quantitative resistance ranging from very susceptible to quite resistant. “Granado”, “Gloria/Copal” and “Calicuchima-92” represented the most resistant group and had an IT of 7 or 8. The cultivar × environment interaction variance, although significant, was very small compared with the cultivar variance. The disease severity parameters were highly correlated. The monocyclic parameter DS_m, measured when the most susceptible cultivar had reached its maximum DS, was very highly correlated with the area under the disease progress curve (AUDPC), r being 0.98. Components of quantitative resistance were evaluated in two plant stages. In the seedling stage small cultivar effects for the latency period were observed, which were not correlated with the quantitative resistance measured in the field. In the adult plant stage the latency period (LP), infection frequency (IF) and colonization rate (CR) were measured in the upper two leaves. The LP was much longer than in the seedling stage and differed strongly between cultivars. The differences in IF were too large, those in CR varied much less. The components showed association with one another. The LP and IF were well correlated with the AUDPC (r = 0.7–0.8). †Deceased     

Level of partial resistance to leaf rust,Puccinia hordei,in West-European barley and how to select for it

Summary The partial resistance to leaf rust (Puccinia hordei) of 40 West-European spring barley cultivars was measured in plots isolated from one another to reduce inter plot interference. The leaf area affected by leaf rust was also measured in small plots of 0.5 m² adjacent to each other, and on individual plants. The latent period was measured in the seedling stage and the adult plant stage, the infection frequency in the seedling stage only. The cultivars varied widely for partial resistance, many cultivars carrying a considerable level. Both the small adjacent plots and the single plants showed a marked inter plot interference strongly reducing the difference between cultivars. H wever, the ranking order of the cultivars was hardly, if at all, affected. Both latent period and the infection frequency showed large differences between cultivars, the latent period in the adult plant stage being highly correlated (r=0.82) with partial resistance, infection frequency in the seedling stage only rather weakly (r=–0.33).Selection for partial resistance appeared very effective in all stages tested; the seedling, the single adult plant, and the small plot stage. Selection in the small plot stage was the most effective followed by selection in the seedling stage. Selection for partial resistance therefore appears very well possible at all stages of the selection program.     

Identification of molecular markers linked to adult plant leaf rust resistance gene <Emphasis Type="Italic">Lr48</Emphasis> in wheat and detection of <Emphasis Type="Italic">Lr48</Emphasis> in the Thatcher near-isogenic line with gene <Emphasis Type="Italic">Lr25</Emphasis>

The recessive adult plant resistance (APR) gene Lr48 in wheat was tagged with flanking random amplified polymorphic DNA (RAPD) markers. Markers S336₇₇₅ in coupling and S3₄₅₀ in repulsion with Lr48 were identified in wheat line CSP44. Tests of these markers on available Thatcher near-isogenic lines (NILs) detected the likely presence of Lr48 in TcLr25. A test of allelism of APR involving the cross TcLr25 × CSP44 indicated that Lr48 was present in both lines. A separate experiment on inheritance of resistance in an F₂ population of TcLr25 × Agra Local confirmed the presence of a dominant seedling resistance gene (Lr25) and a recessive APR gene (Lr48) in TcLr25. This study demonstrated the value of molecular markers in identifying the presence of masked genes in genetic stocks where direct phenotyping failed to detect their presence.     

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.