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.     

The role of Lr34 in imparting durable resistance to wheat leaf rust through gene interaction

Summary The leaf rust responses of wheat lines carrying the complementary genes Lr27 and Lr31 and the same genes in a Chinese Spring background which contains Lr34, indicate that Lr34 interacts with the complementary genes to give enhanced levels of field resistance to leaf rust. Lr34, particularly in combination with other genes, is considered to be an important gene for imparting a high degree of durable resistance to leaf rust. Its similarity to Sr2, an adult plant gene for resistance to stem rust and its association with adult plant resistances to stem and stripe rusts are discussed.     

Variation of characters in near-isogenic lines of wheat with added genes for leaf rust resistance

Summary Using the cultivar Arina as the recurrent parent, six backcrosses were made with two donor lines carrying the leaf rust resistance genes Lr1 and Lr9, respectively. Selection for leaf rust resistance occurred at the seedling stage in the greenhouse; the first plants transferred to the field were BC₆F₄s. Frequency distribution of the 332 Lr1/7 × Arina and the 335 Lr9/7 × Arina lines showed continuous variation for yellow rust resistance and heading date in these leaf rust near-isogenic lines (NILs). Similar results were also obtained for plant height, for resistance to powdery mildew and glume blotch, as well as for baking quality characters in another set of more advanced NILs. The available information on the behaviour of one of the parents of cultivar Arina led to the conclusion that the expressed yellow rust resistance is quantitative and might possibly be durable.     

Allelic variation for the rust resistance gene <Emphasis Type="Italic">Lr34</Emphasis>/<Emphasis Type="Italic">Yr18</Emphasis> in Canadian wheat cultivars

The wheat (Triticum aestivum L.) gene Lr34/Yr18 conditions resistance to leaf rust, stripe rust, and stem rust, along with other diseases such as powdery mildew. This makes it one of the most important genes in wheat. In Canada, Lr34 has provided effective leaf rust resistance since it was first incorporated into the cultivar Glenlea, registered in 1972. Recently, molecular markers were discovered that are either closely linked to this locus, or contained within the gene. Canadian wheat cultivars released from 1900 to 2007, breeding lines and related parental lines, were tested for sequence based markers caSNP12, caIND11, caIND10, caSNP4, microsatellite markers wms1220, cam11, csLVMS1, swm10, csLV34, and insertion site based polymorphism marker caISBP1. Thirty different molecular marker haplotypes were found among the 375 lines tested; 5 haplotypes had the resistance allele for Lr34, and 25 haplotypes had a susceptibility allele at this locus. The numbers of lines in each haplotype group varied from 1 to 140. The largest group was represented by the leaf rust susceptible cultivar “Thatcher” and many lines derived from “Thatcher”. The 5 haplotypes that had the resistance allele for Lr34 were identical for the markers tested within the coding region of the gene but differed in the linked markers wms1220, caISBP1, cam11, and csLV34. The presence of the resistance or susceptibility allele at the Lr34 locus was tracked through the ancestries of the Canadian wheat classes, revealing that the resistance allele was present in many cultivars released since the 1970s, but not generally in the older cultivars.     

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.     

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.     

Identification of recombinants carrying stripe rust resistance gene Yr57 and adult plant stem rust resistance gene Sr2 through marker‐assisted selection

Many stem rust resistance genes have been formally named in wheat. Adult plant stem rust resistance gene Sr2 was mapped in the short‐arm of chromosome 3B. Stripe rust resistance gene Yr57, identified in Aus91463, was mapped about 5 cM away from Sr2 based on its linkage with Sr2‐linked marker gwm533. The objective of this study was to combine Sr2 and Yr57 in a single genotype. A mapping population containing 107 recombinant inbred lines was developed from a cross between Aus91463‐Yr57 and Hartog‐Sr2. This population was tested at the seedling stage in the glasshouse for variation in stripe rust response, and high temperature induced Sr2‐linked seedling chlorosis. The RIL population was screened for Sr2‐linked pseudo black chaff phenotype at the adult plant stage in field. Five recombinants carrying Sr2 and Yr57 in coupling were detected using phenotypic and marker data. Four recombinants also carried leaf rust resistance gene Lr23 from Aus91463. These recombinants are being used as triple rust resistance source in the Australian Cereal Rust Control Program.     

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.     

‘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.     

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.     

Enhanced leaf rust resistance in wheat conditioned by resistance gene pairs with Lr13

Summary Leaf rust resistance gene Lr13 is present in many North American hard red spring wheat cultivars that have shown durable resistance to leaf rust. Fifteen pair-wise combinations of Lr13 and seedling leaf rust resistance genes were developed by intercrossing near isogenic Thatcher lines. In both seedling and adult plant tests, homozygous paired combinations of specific resistance genes with Lr13 had enhanced resistance relative to either parent to rust isolates that had intermediate avirulent infection types to the additional genes. In field tests, homozygous lines were more resistant than either parent if the additional leaf rust gene conditioned an effective level of resistance when present singly.     

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.     

Adult plant leaf rust resistance from 111 wheat (Triticum aestivum L.) cultivars

Adult plant resistance against Indian leaf rust race 77 and five of its highly virulent variants have been identified from 111 bread wheat cultivars originating from 12 countries. The adult plant resistance of only 16 of these cultivars is due to hypersensitive seedling or adult plant resistance genes. All others expressed nonhypersensitive type of resistance characteristic of the genes Lr34 and Lr46.Forty five of the 111 cultivars showed tip necrosis on flag leaves, a trait linked to the gene Lr34. Therefore, the nonhypersensilive type of resistance of these 45 cultivars is attributed to Lr34. The nonhypersensitive resistance of the remaining cultivars is likely to be due to the gene(s) different than Lr34. The reaction pattern of these 111 cultivars to six races suggests the presence of at least six to seven new hypersensitive adult plant resistance genes and at least three new hypersensitive seedling resistance genes. The known genes Lr10, Lr23 and Lr26 were detected frequently but these genes did not contribute towards the adult plant resistance of any of the 111 cultivars. Based on the presence of new genes for hypersensitive and nonhypersensitive type of resistance, the 111 cultivars have been classified into 31 diverse resistance groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Molecular genetics of race non-specific rust resistance in wheat

Over 150 resistance genes that confer resistance to either leaf rust, stripe rust or stem rust have been catalogued in wheat or introgressed into wheat from related species. A few of these genes from the ‘slow-rusting’ adult plant resistance (APR) class confer partial resistance in a race non-specific manner to one or multiple rust diseases. The recent cloning of two of these genes, Lr34/Yr18, a dual APR for leaf rust and stripe rust, and Yr36, a stripe rust APR gene, showed that they differ from other classes of plant resistance genes. Currently, seven Lr34/Yr18 haplotypes have been identified from sequencing the encoding ATP Binding Cassette transporter gene from diverse wheat germplasm of which one haplotype is commonly associated with the resistance phenotype. The paucity of well characterised APR genes, particularly for stem rust, calls for a focused effort in developing critical genetic stocks to delineate quantitative trait loci, construct specific BAC libraries for targeted APR genes to facilitate robust marker development for breeding applications, and the eventual cloning of the encoding genes.     

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.     

Use of a synthetic hexaploid Triticum miguschovae for transfer of leaf rust resistance to common wheat

Summary Triticum miguschovae, a genome addition synthetic, was used as a source for transfer of leaf rust (Puccinia recondita tritici) resistance to common wheat. This synthetic, developed from two wild species Triticum militinae and Aegilops squarrosa, proves a valuable donor of the genes for leaf rust resistance. Leaf rust resistance was transferred from T. miguschovae by both dominant and recessive genes. Stable lines phenotypically similar to their recurrent parents Kavkaz and Bezostaya 1 but differing from them in a high level of leaf rust resistance were obtained. The genes for resistance in 3 selected lines differed from each other and from the known effective genes Lr9, Lr19, and Lr24. The resistance of one of them (line 1229) is controlled by two complementary interacting genes located on chromosome 7B and 1D was revealed by monosomic analysis.     

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.     

28个小麦微核心种质抗叶锈性分析

选取在成株期表现高、中、低抗叶锈的28个小麦微核心种质,利用39个以Thatcher为背景的近等基因系(或单基因系)作为已知基因的鉴别寄主,接种8个小麦叶锈菌致病型进行苗期抗叶锈基因推导,结合成株期抗病鉴定,初步明确了这些品种(系)的抗性和可能携带的抗病基因。利用19个与Lr基因紧密连锁或共分离的分子标记,对28个微核心种质进行抗叶锈病基因的进一步鉴定,推测新克旱9号可能含有Lr17、Lr2b、Lr14a和Lr33;兴义4号可能含有Lr26、Lr36和Lr37;紫皮可能含有Lr2b和Lr34;大白皮含有Lr1;毕红穗含有Lr1、Lr10和Lr34;中优9507含有Lr10;小白麦、红粒当年老、老麦、蝉不吱、苏麦3号和车锏子含有Lr1和Lr34;红花早可能含有Lr1、Lr34、Lr14a和Lr2b;江西早、泡子麦、三月黄、有芒扫谷旦、阜阳红、成都光头和酱麦可能含有Lr34;敦化春麦和甘肃96可能含有Lr28;欧柔可能含有Lr34、Lr16、Lr11、Lr3bg和Lr33;此外,新克旱9号、兴义4号、红花早、红粒当年老、欧柔、有芒扫谷旦、成都光头、甘肃96、小红皮、定兴寨、中优9507和红冬麦中可能含有未知抗病基因;在这28份种质中,不含Lr9、Lr19、Lr20、Lr21、Lr24、Lr29、Lr35、Lr38和Lr47基因。研究结果表明,测试的微核心种质中含有比较丰富的抗叶锈病基因,可为育种提供丰富的抗源。     

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.