Genetics of leaf rust resistance in spring wheat cultivars alsen and norm

ABSTRACT Alsen is a recently released spring wheat cultivar that has been widely grown in the United States because it has resistance to Fusarium head blight and leaf rust caused by Puccinia triticina. Norm is a high yielding wheat cultivar that has been very resistant to leaf rust since it was released. Alsen and Norm were genetically examined to determine the number and identity of the leaf rust resistance genes present in both wheats. The two cultivars were crossed with leaf rust susceptible cv. Thatcher and F(1) plants were backcrossed to Thatcher. Eighty one and seventy three BCF(1) of Thatcher times; Alsen and Thatcher x Norm respectively, were selfed to obtain BCF(2) families. The BCF(2) families were tested as seedlings with different isolates of P. triticina that differed for virulence to specific leaf rust resistance genes. The BCF(2) families that lacked seedling resistance were also tested as adult plants in greenhouse tests and in a field rust nursery plot. Segregation of BCF(2) families indicated that Alsen had seedling genes Lr2a, Lr10, and Lr23 and adult plant genes Lr13 and Lr34. Norm was determined to have seedling genes Lr1, Lr10, Lr16, and Lr23 and adult plant genes Lr13 and Lr34. The characterization of Lr23 in the segregating populations was complicated by the presence of a suppressor gene in Thatcher and the high temperature sensitivity of resistance expression for this gene. The effective leaf rust resistance in Alsen is due to the interaction of Lr13 and Lr23, with Lr34; and the effective leaf rust resistance in Norm is due to the interaction of Lr13, Lr16, and Lr23, with Lr34.     

Molecular marker mapping of leaf rust resistance gene lr46 and its association with stripe rust resistance gene yr29 in wheat

ABSTRACT Leaf and stripe rusts, caused by Puccinia triticina and P. striiformis, respectively, are globally important fungal diseases of wheat that cause significant annual yield losses. A gene that confers slow rusting resistance to leaf rust, designated as Lr46, has recently been located on wheat chromosome 1B. The objectives of our study were to establish the precise genomic location of gene Lr46 using molecular approaches and to determine if there was an association of this locus with adult plant resistance to stripe rust. A population of 146 F(5) and F(6) lines produced from the cross of susceptible 'Avocet S' with resistant 'Pavon 76' was developed and classified for leaf rust and stripe rust severity for three seasons. Using patterns of segregation for the two diseases, we estimated that at least two genes with additive effects conferred resistance to leaf rust and three to four genes conferred resistance to stripe rust. Bulked segregant analysis and linkage mapping using amplified fragment length polymorphisms with the 'Avocet' x 'Pavon 76' population, F(3) progeny lines of a single chromosome recombinant line population from the cross 'Lalbahadur' x 'Lalbahadur (Pavon 1B)', and the International Triticeae Mapping Initiative population established the genomic location of Lr46 at the distal end of the long arm of wheat chromosome 1B. A gene that is closely linked to Lr46 and confers moderate levels of adult plant resistance to stripe rust is identified and designated as Yr29.     

Microsatellite markers for genes lr34/yr18 and other quantitative trait Loci for leaf rust and stripe rust resistance in bread wheat

ABSTRACT Leaf rust and stripe rust, caused by Puccinia triticina and P. striiformis, respectively, are important diseases of wheat in many countries. In this study we sought to identify molecular markers for adult plant resistance genes that could aid in incorporating such durable resistance into wheat. We used a doubled haploid population from a Japanese cv. Fukuho-komugi x Israeli wheat Oligoculm cross that had segregated for resistance to leaf rust and stripe rust in field trials. Joint and/or single-year analyses by composite interval mapping identified two quantitative trait loci (QTL) that reduced leaf rust severity and up to 11 and 7 QTLs that might have influenced stripe rust severity and infection type, respectively. Four common QTLs reduced stripe rust severity and infection type. Except for a QTL on chromosome 7DS, no common QTL for leaf rust and stripe rust was detected. QTL-7DS derived from 'Fukuho-komugi' had the largest effect on both leaf rust and stripe rust severities, possibly due to linked resistance genes Lr34/Yr18. The microsatellite locus Xgwm295.1, located almost at the peak of the likelihood ratio contours for both leaf and stripe rust severity, was closest to Lr34/Yr18. QTLs located on 1BL for leaf rust severity and 3BS for stripe rust infection type were derived from 'Oligoculm' and considered to be due to genes Lr46 and Yr30, respectively. Most of the remaining QTLs for stripe rust severity or infection type had smaller effects. Our results indicate there is significant diversity for genes that have minor effects on stripe rust resistance, and that successful detection of these QTLs by molecular markers should be helpful both for characterizing wheat genotypes effectively and combining such resistance genes.     

二倍体及四倍体中抗叶锈病基因在双二倍体中的表达与抑制

 通过杂交将近缘植物中的抗病基因导入普通小麦是抗病育种的常用方法。在利用二倍体和四倍体杂交合成双二倍体小麦过程中, 二倍体或四倍体携带的抗叶锈病基因在双二倍体中大多数情况下可以完全表达或部分表达其固有的抗病性, 但部分抗叶锈病基因则不能表达。四倍体波斯小麦Ps5、Ps8和野生二粒小麦D s3含有相同的抗叶锈病基因LrPs (暂定名), 在双二倍体Am1、Am2、Am3、Am5和Am7中可以表达其抗病性, 但在Am4中不能表达;二倍体粗山羊草Ae37含有Lr41和未知基因, 但Lr41在双二倍体Am2中不能表达;四倍体硬粒小麦Dr147携带Lr23和未知基因, 在双二倍体Am6中不能充分表达。抑制基因的存在是导致抗病基因不能表达或部分表达的主要原因之-。抑制基因位于AB染色体组或D染色体组上, 其抑制作用对抗病基因和病菌致病类型具有专化性, 还可能受温度等环境条件和寄主遗传背景等因素的影响。遗传分析结果表明, 在常温下, 双二倍体Am1、Am2、Am3和Am5对叶锈菌致病类型DGS/HB的抗病性均由1对相同的隐性抗病基因LrPs (暂定名)控制, 与它们具有共同的四倍体亲本Ps5有关。Am4不具有苗期抗叶锈病基因, 但含有来自粗山羊草A e39的1对隐性抑制基因SuLrPs (暂定名), 可抑制Am1、Am2、Am3和Am5中隐性抗叶锈病基因的表达。对抗病抑制基因存在原因和遗传分析验证方法等进行了讨论。     

中国小麦贵州98-18中抗叶锈基因的分子定位

小麦(Triticum aestivum)品系贵州98-18对中国目前大多数叶锈菌(Puccinia triticina)生理小种表现抗性。基因推导表明,贵州98-18可能携带新的抗叶锈基因。为了有效利用这一抗源,将贵州98-18和感病小麦品种郑州5389杂交,获得F1、F2代群体,用我国叶锈菌优势小种THTT对双亲及其杂交后代进行接种鉴定。结果表明,贵州98-18对THTT的抗性由1对显性基因控制,暂命名为LrG98。采用SSR技术对贵州98-18携带的抗病基因进行分子标记,共筛选了1 274对SSR或STS引物,位于1BL染色体上的4对引物可在抗/感池和双亲中扩增出多态性DNA片段。遗传连锁分析结果表明,该抗病基因位于小麦1BL染色体上,与Xbarc582-1B和Lr26的STS标记ω-secali(Glu-B3)的遗传距离最近,均为3.8 cM。该基因与目前所有已知的抗叶锈基因不同,可能是1个新的抗病基因。     

Mapping of Aegilops umbellulata‐derived leaf rust and stripe rust resistance loci in wheat

Aegilops umbellulata, a non‐progenitor diploid species, is an excellent source of resistance to various wheat diseases. Leaf rust and stripe rust resistance genes from A. umbellulata were transferred to the susceptible wheat cultivar WL711 through induced homoeologous pairing. A doubly resistant introgression line IL 393‐4 was crossed with wheat cultivar PBW343 to develop a mapping population. Tests on BC₂F₇ RILs indicated monogenic inheritance of seedling leaf rust and stripe rust resistance in IL 393‐4 and the respective co‐segregating genes were tentatively named LrUmb and YrUmb. Bulked segregant analysis placed LrUmb and YrUmb in chromosome 5DS, 7.6 cM distal to gwm190. Aegilops geniculata‐derived and completely linked leaf rust and stripe rust resistance genes Lr57 and Yr40 were previously located in chromosome 5DS. STS marker Lr57/Yr40MAS‐CAPS16 (Lr57/Yr40‐CAPS16), linked with Lr57/Yr40 (T756) also co‐segregated with LrUmb/YrUmb. Seedling infection types differentiated LrUmb from Lr57. Absence of leaf rust‐susceptible segregants among F₃ families of the intercross (IL 393‐4/T756) indicated repulsion linkage between LrUmb and Lr57. YrUmb expressed a consistently low seedling response under greenhouse conditions, whereas Yr40 expressed a higher seedling response. Based on the origin of LrUmb/YrUmb from the U genome and Lr57/Yr40 from the M genome, as well as phenotypic differences, LrUmb and YrUmb were formally named Lr76 and Yr70, respectively. These genes have been transferred to Indian wheat cultivars PBW343 and PBW550, and advanced breeding lines are being tested in state and national trials.     

Virulence of Puccinia triticina in Turkey and leaf rust resistance in Turkish wheat cultivars

Leaf rust caused by Puccinia triticina is a common disease on wheat in the coastal regions of Turkey. Collections of P. triticina from infected wheat leaves were obtained from the main wheat production zones of Turkey in 2009 and 2010. A total of 104 single uredinial isolates were tested for virulence on 20 lines of Thatcher wheat that differ for single leaf rust resistance genes. Forty-four different virulence phenotypes were identified over both years. Four phenotypes were found in both years. Phenotype FHPTQ found in 2009, with virulence to genes Lr2c, Lr3, Lr16, Lr26, Lr3ka, Lr17a, Lr30, LrB, Lr10, Lr14a, Lr18, Lr3bg, and Lr14b, was the most common phenotype at 15.4 % of the total isolates. Forty-three winter and spring wheat cultivars from Turkey were tested as seedlings with 13 different P. triticina virulence phenotypes from Canada, the US and Turkey. The infection types on the cultivars were compared with infection types on the Thatcher near isogenic lines to postulate the presence of seedling leaf rust resistance genes in the cultivars. Resistance genes Lr1, Lr3a, Lr10, Lr14a, Lr17a, Lr20, Lr23, and Lr26 were postulated to be present in the Turkish wheat cultivars. DNA of the wheat cultivars was tested with PCR markers to determine the presence of the adult plant resistance genes Lr34 and Lr37. Marker data indicated the presence of Lr34 in 20 cultivars and Lr37 in three cultivars. Field plot evaluations of the wheat cultivars indicated that no single Lr gene conditioned highly effective leaf rust resistance. Resistant cultivars varied for combinations of seedling and adult plant resistance genes.     

Breeding cereals for rust resistance in Australia

Rust diseases have caused significant losses to Australian cereal crops, and continue to pose a serious threat. Because Australian cereal crop yields are generally low, genetic resistance remains the most economical means of rust control. Resistant cultivars also contribute significantly to reducing over-summer rust survival. A policy of releasing only rust resistant wheats in northern New South Wales and Queensland has resulted in industry-wide protection from rust in this region for the past 40 years. The Australian Cereal Rust Control Program conducts annual pathogenicity surveys for all cereal rust pathogens, undertakes genetic research to identify and characterize new sources of resistance, and provides a germplasm screening and enhancement service to all Australian cereal breeding groups. These three activities are interdependent, and are closely integrated with particular emphasis on linking pathology and genetics to ensure breeding outcomes. Recent changes in the wheat rust pathogens, including the development of virulences for Yr17 , Lr24 , Lr37 and Sr38 resistance genes, and the introduction of a new pathotype of the wheat stripe rust pathogen, have provided new and significant challenges for wheat rust resistance breeding. Similar challenges exist in breeding barley and oats for rust resistance. Examples are discussed to illustrate the ways in which rust isolates are providing information that can be used in breeding for rust resistance. In future, as more markers linked to durable rust resistance sources become available, it is likely that the use of marker-assisted selection will become more common-place in rust resistance breeding.     

Genetics of resistance to wheat leaf rust, stem rust, and powdery mildew in Aegilops sharonensis

Aegilops sharonensis (Sharon goatgrass) is a wild relative of wheat and a rich source of genetic diversity for disease resistance. The objectives of this study were to determine the genetic basis of leaf rust, stem rust, and powdery mildew resistance in A. sharonensis and also the allelic relationships between genes controlling resistance to each disease. Progeny from crosses between resistant and susceptible accessions were evaluated for their disease reaction at the seedling and/or adult plant stage to determine the number and action of genes conferring resistance. Two different genes conferring resistance to leaf rust races THBJ and BBBB were identified in accessions 1644 and 603. For stem rust, the same single gene was found to confer resistance to race TTTT in accessions 1644 and 2229. Resistance to stem rust race TPMK was conferred by two genes in accessions 1644 and 603. A contingency test revealed no association between genes conferring resistance to leaf rust race THBJ and stem rust race TTTT or between genes conferring resistance to stem rust race TTTT and powdery mildew isolate UM06-01, indicating that the respective resistance genes are not linked. Three accessions (1644, 2229, and 1193) were found to carry a single gene for resistance to powdery mildew. Allelism tests revealed that the resistance gene in accession 1644 is different from the respective single genes present in either 2229 or 1193. The simple inheritance of leaf rust, stem rust, and powdery mildew resistance in A. sharonensis should simplify the transfer of resistance to wheat in wide crosses.     

小麦-滨麦易位系M8657-1抗条锈病基因遗传分析和分子标记

 M8657-1, one of the wheat translocation lines derived from Leymus mollis Trin. Hara, is possessed of effective resistance at all stages to Su-ll and other dominant races of Puccinia striiformis f. sp. tritici in China. Seedlings of the parents, F₁, and F₂ progeny derived from the cross of M8657-1 (resistant) Mingxian169 (susceptible) were inoculated with Su-ll in greenhouse to identify and map the probable new stripe rust resistance gene. The results suggested that the stripe rust resistance in M8657-1 was conferred by a pair of recessive genes. Simple sequence repeat (SSR) technique was used to detect molecular marker associated with the resistance gene:208 pairs of wheat SSR primers were used to screen the two parents, as well as resistant and susceptible bulks and then three SSR markers were selected for genotyping the F₂ population. The geue, temporarily designated as YrLml, was found to be located on the chromosome 7DL and flanked by three SSR markers GDM67, WMC150 and WMC671, with the genetic distance of 5.0, 9.7 and 11.8cM, respectively.     

春小麦品种沈免2063抗叶锈性遗传分析

为明确春小麦品种沈免2063所含抗叶锈病基因的对数、身份、显隐性和互作关系,以沈免2063为父本,分别与感病品种Thatcher及小麦抗叶锈病近等基因系Lr9、Lr19、Lr24、Lr25、Lr28、Lr42和Lr43的载体品系杂交,获得F1、F2和F3代群体后,分别在苗期和成株期进行抗病性测定。结果表明:沈免2063含有3对显性遗传且相互独立作用的抗叶锈病基因Lr9、Lr19和Lr25,在苗期,沈免2063对致病类型CBG/QQ的抗病性由Lr9和Lr25控制,对PHT/RP的抗病性由上述3对抗叶锈病基因控制;在成株期,沈免2063对优势致病类型PHT/RP和THT/TP等比混合菌种的抗病性由上述3对抗叶锈病基因控制。Lr9、Lr19和Lr25在育成品种中出现频率很低,目前尚很有效,但这3个基因均为典型的垂直抗病性基因,应进行基因布局、基因轮换等科学组配,才能延长其使用寿命。     

Allele sequencing of the barley stem rust resistance gene Rpg1 identifies regions relevant to disease resistance

The stem rust resistance gene Rpg1 has protected North American barley cultivars from significant yield losses for over 65 years. The remarkable durability of this gene warrants further study as to its possible origin and allelic variation. Eight Swiss barley (Hordeum vulgare) landraces and eight wild barley (H. vulgare subsp. spontaneum) accessions from diverse geographic regions were analyzed to uncover new alleles of Rpg1 and learn about its possible origin. The two germplasm groups included accessions that were resistant and susceptible to Puccinia graminis f. sp. tritici pathotype MCCF. Allele-specific primers were utilized to amplify 1 kbp overlapping fragments spanning the Rpg1 gene and sequenced if a polymerase chain reaction (PCR) fragment was generated. Variation among the PCR products revealed significant polymorphisms among these Hordeum accessions. Landraces and wild barley accessions susceptible to pathotype MCCF exhibited the highest degree of Rpg1 polymorphism. One resistant landrace (Hv672) and one resistant wild barley accession (WBDC040) yielded all seven Rpg1-specific PCR fragments, but only landrace Hv672 coded for an apparently functional Rpg1 as determined by comparison to previously characterized resistant and susceptible alleles and also resistance to HKHJ, a stem rust pathotype that can specifically detect Rpg1 in the presence of other resistance genes. Accessions resistant to stem rust pathotype MCCF, but completely lacking Rpg1-specific PCR amplification and hybridization with an Rpg1-specific probe, suggested the presence of stem rust resistant gene(s) different from Rpg1 in the Hordeum germplasm pool. Some Rpg1 alleles that retained the ability to autophosphorylate did not confer resistance to Puccinia graminis f. sp. tritici pathotype MCCF, confirming our previous observations that autophosphorylation is essential, but not sufficient for disease resistance. Thus, the RPG1 protein plays a complex role in the stem rust disease resistance-signaling pathway.     

Tagging and validation of a major quantitative trait locus for leaf rust resistance and leaf tip necrosis in winter wheat cultivar forno

ABSTRACT A major leaf rust (Puccinia triticina) resistance quantitative trait locus (QTL) (QLrP.sfr-7DS) previously has been described on chromosome 7DS in the winter wheat (Triticum aestivum) cv. Forno. It was detected in a population of single-seed descent (SSD) lines derived from the cross Arina x Forno. QLrP.sfr-7DS conferred a durable and slow-rusting resistance phenotype, co-segregated with a QTL for leaf tip necrosis (LTN) and was mapped close to Xgwm295 at a very similar location as the adult plant leaf rust resistance gene Lr34 found in some spring wheat lines. Here, we describe the validation of this QTL by mapping it to the same chromosomal region close to Xgwm295 on chromosome 7DS in a population of SSD lines from the winter wheat x spelt (T. spelta) cross Forno x Oberkulmer. In both populations, the log of the likelihood ratio curves for leaf rust resistance and LTN peaked at identical or very similar locations, indicating that both traits are due to the same gene. We have improved the genetic map in the target region of QLrP.sfr-7DS using microsatellite and expressed sequence tag (EST) markers. Two EST loci (Xsfr.BF473324 and Xsfr.BE493812) define a genetic interval of 7.6 centimorgans containing QLrP.sfr-7DS, a considerably more precise genetic location for this QTL than previously described both in spring and winter wheat. The identified genetic interval is physically located in the distal 39% of chromosome 7DS. Single-marker analysis identified Xsfr.BF473324 and Xgwm1220 as the most informative loci for QLrP.sfr-7DS and QLtn.sfr-7DS. In the rice genome, the two ESTs flanking the QLrP.sfr-7DS/QLtn.sfr-7DS chromosomal segment in wheat are conserved on chromosome 6S in a region colinear with wheat chromosome 7DS. There, they define a physical region of three rice bacterial artificial chromosomes spanning approximately 300 kb.     

黑龙江省83份小麦品种抗秆锈病基因的分子检测

 为了明确黑龙江省小麦品种(系)对中国秆锈菌的抗性水平和了解抗秆锈病基因在该区域的分布情况,本研究选用中国小麦秆锈菌流行小种21C3CTHQM、34MKGQM和34C3RTGQM对从该区域征集到的83份主要小麦品种(系)进行了苗期抗秆锈病的评价,并利用与抗秆锈病基因Sr2、Sr24、Sr25、Sr26、Sr31和Sr38紧密连锁的分子标记分别进行了分子检测,结合苗期表型及系谱,推测这些品种(系)可能含有的抗病基因。结果表明,83份小麦品种(系)对供试秆锈菌小种均表现抗性,对21C3CTHQM、34MKGQM和34C3RTGQM表现免疫或近免疫的分别为57、53和60份,各占供试材料数量的68.68%、63.85%和72.29%,其他剩余材料对3个供试秆锈菌小种表现中抗或高抗。分子标记分析表明,83份主要小麦品种(系)中有12份可能含有Sr2;克旱3号可能含有Sr25;6份小麦品种可能含有Sr31;19份小麦品种可能含有Sr38;没有检测出含有Sr24和Sr26的品种。因此,黑龙江省小麦品种对中国小麦秆锈病抗性水平相对较高,含有抗秆锈病基因Sr2以及对我国小麦秆锈病表现良好抗性的基因Sr31和Sr38,可能含有其他未知抗秆锈病基因,这些优良抗源材料可作为未来小麦生产育种的种质资源。     

Lr46: a gene conferring slow-rusting resistance to leaf rust in wheat

ABSTRACT Wheat (Triticum aestivum) cultivar Pavon 76 carries slow-rusting resistance to leaf rust that has remained effective in Mexico since its release in 1976. 'Pavon 76' was crossed with two leaf rust-susceptible wheat cultivars, Jupateco 73S and Avocet S, and between 118 and 148 individual F(2) plant-derived F(3) and F(5) lines were evaluated for adult-plant leaf rust resistance at two field sites in Mexico during different seasons. Evaluation of F(1) plants and parents indicated that the slow-rusting resistance was partially dominant. Segregation in the F(3) and F(5) indicated that the resistance was based on two genes with additive effects. Monosomic analysis was carried out to determine the chromosomal locations of the resistance genes. For this purpose, two or three backcross-derived cytogenetic populations were developed by crossing 'Pavon 76' with a monosomic series of adult-plant leaf rust-susceptible cultivar Lal-bahadur. Evaluation of such BC(2)F(3) and BC(3)F(3) lines from 16 confirmed 'Lalbahadur' monosomics indicated that one slow-rusting gene was located in chromosome 1B of 'Pavon 76'. This gene, designated as Lr46, is the second named gene involved in slow-rusting resistance to leaf rust in wheat.     

Genetics of Stem Rust Resistance in Wheat Cvs. Pasqua and AC Taber

ABSTRACT Canadian wheat cvs. Pasqua and AC Taber were examined genetically to determine the number and identity of stem rust resistance genes in both. The two cultivars were crossed with stem rust susceptible line RL6071, and sets of random F(6) lines were developed from each cross. The F(6) lines, parents, and tester lines with single stem rust resistance genes were grown in a field rust nursery, inoculated with a mixture of stem and leaf rust races, and evaluated for rust resistance. The same wheat lines were tested by inoculation with specific stem rust races in seedling tests to postulate which Sr genes were segregating in the F6 lines. Segregation of F(6) lines indicated that Pasqua had three genes that conditioned field resistance to stem rust and had seedling genes Sr5, Sr6, Sr7a, Sr9b, and Sr12. Leaf rust resistance gene Lr34, which is in Pasqua, was associated with adult-plant stem rust resistance in the segregating F(6) lines. Adult-plant gene Sr2 was postulated to condition field resistance in AC Taber, and seedling genes Sr9b, Sr11, and Sr12 also were postulated to be in AC Taber.     

Pavon76苗期抗小麦叶锈性基因的推导

 选用19个具不同毒性基因组合的小麦叶锈菌致病类型对墨西哥品种Pavon76进行了抗叶锈性基因的推导。通过与48个抗叶锈单/双基因系的反应型比较,鉴定出该品种中可能含有Lr1、Lr3、L410、L413、Lr14a、Lr34和LrB抗性基因。     

116个小麦品种（系）抗叶锈基因Lr9-Lr26、Lr19-Lr20的复合PCR检测

[目的]建立简单、快速、有效的小麦抗叶锈基因复合PCR体系,从而提高分子标记辅助选择效率。[方法]以28个‘Thatcher’为背景的近等基因系和16个已知基因载体品系作为试材,测试了小麦抗叶锈病基因Lr9、Lr26、Lr19和Lr20的STS标记特异性,通过优化PCR反应体系和循环条件,构建了抗叶锈基因Lr9-Lr26和Lr19-Lr20的复合PCR检测体系。对116个小麦品种(系)所含有的抗叶锈病基因进行了分子检测。[结果]供试品种均不含有Lr9和Lr20,47个品种含有Lr26(基因频率为40.5%),‘中梁22’含有Lr19。经反复验证,Lr9-Lr26和Lr19-Lr20复合PCR技术检测结果可靠,且与上述单个分子标记检测结果一致。[结论]建立的Lr9-Lr26和Lr19-Lr20的复合PCR检测体系可以准确、稳定、高效地检测小麦抗叶锈基因Lr9、Lr26、Lr19和Lr20。