Seedling and adult plant resistance to leaf rust in 46 Chinese bread wheat landraces and 39 wheat lines with known Lr genes

Wheat leaf rust,caused by Puccinia triticina(Pt),is an important foliar disease that has an important influence on wheat yield.The most economic,safe and effective way to control the disease is growing resistant cultivars.In the present study,a total of 46 wheat landraces and 34 wheat lines with known Lr(leaf rust resistance)genes were inoculated with 16Pt pathotypes for postulating seedling resistance gene(s)in the greenhouse.These cultivars and five wheat differential lines with adult plant resistance(APR)genes(Lr12,Lr22b,Lr34,Lr35 and Lr37)were also evaluated for identification of slow rusting resistance in the field trials in Baoding,Hebei Province of China in the 2014–2015 and 2015–2016 cropping seasons.Furthermore,10 functional molecular markers closely linked to 10 known Lr genes were used to detect all the wheat genotypes.Results showed that most of the landraces were susceptible to most of the Pt pathotypes at seedling stage.Nonetheless,Lr1 was detected only in Hongtangliangmai.The field experimental test of the two environments showed that 38 landraces showed slow rusting resistance.Seven cultivars possessed Lr34 but none of the landraces contained Lr37 and Lr46.Lr genes namely,Lr9,Lr19,Lr24,Lr28,Lr29,Lr47,Lr51 and Lr53 were effective at the whole plant stage.Lr18,Lr36 and Lr45 had lost resistance to part of pathotypes at the seedling stage but showed high resistance at the adult plant stage.Lr34 as a slowing rusting gene showed good resistance in the field.Four race-specific APR genes Lr12,Lr13,Lr35 and Lr37 conferred good resistance in the field experiments.Seven race-specific genes,Lr2b,Lr2c,Lr11,Lr16,Lr26,Lr33 and LrB had lost resistance.The 38 landraces showed slow rusting resistance to wheat leaf rust can be used as resistance resources for wheat resistance breeding in China.

Identification and Molecular Tagging of Leaf Rust Resistance Gene (Lr24) in Wheat

This research was aimed to develop AFLP markers co-segregated with gene Lr24 and validate the using for marker assisted selection （MAS）. An F2 population developed from the cross between the resistant line TcLr24 and the susceptible line Thatcher was tested for resistance to the Puccinia triticina races BGQQ and SHRT using for genetic analysis and molecular marker. A total of 224 AFLP primer combinations were used to test the resistant and susceptible parents, as well as the resistant bulk and the susceptible bulk. Four AFLP markers, P-AGA/M-CTT289 bp, P-AGC/M-CAC1ss bp, P-AGC/M- CAC162 bp, and P-ACG/M-CGC239 bp, were co-segregated with Lr24. The AFLP fragment from the primer combination P- ACG/M-CGC was cloned, sequenced and converted into a STS marker named as ASTS212. Thatcher backgrounded NILs and 115 varieties were examined by using this STS marker and the marker SCS13026oz developed by Gupta. 5R615, 5R616, IR13, and 1R17 were identified and validated to contain gene Lr24. The marker is dominant and may be useful in identification the resistance gene Lr24 in wheat and wheat breeding programs.

A SSR Marker for Leaf Rust Resistance Gene Lr19 in Wheat

Microsatellite was carded out in Thatcher, six near-isogenic lines and F2 progeny of TcLr19xThatcher to develop molecular markers for leaf rust resistance gene Lr19. Thirteen primer pairs were screened, of which one primer pair Xgwm44 displayed polymorphsim in the population of TcLr 19, Thatcher, and their F2 generations. One marker closed linked to Lr19 resistance trait was obtained, and was named Xgwm44139bp with the genetic distance 0.9 cM. The research shows that Lr19 has more potential in marker-assisted breeding programs in wheat and provides a step stone for mapping genetic map, physical map and the eventual cloning.

PCR-based molecular markers linked to the leaf rust resistance gene Lr19 in different bread wheat cultivars

61 varieties of wheat collected in the gene fund of the Research Institute of Crop Husbandry were screened using SCAR-markers associated with the gene of resistance to brown leaf rust, Lr19. As a result of PCR analysis using SCS123 marker the 737 bp locus was detected in 48 genotypes. The expected fragment of the 688 bp was detected in 53 genotypes using the SCS253 marker. The results obtained using both markers indicate that the Lr19 gene is present on 7D chromosomes of 45 genotypes. The existence of the Lr19 gene has not been proven only for 5 from the 61 analyzed wheat genotypes.

High-resolution genetic mapping and identification of candidate genes for the wheat stem rust resistance gene Sr8155B1

Stem rust,caused by Puccinia graminis f.sp.tritici(Pgt),threatens global wheat production.Development of cultivars with increased resistance to stem rust by identification,mapping,and deployment of resistance genes is the best strategy for controlling the disease.In this study,we performed fine mapping and characterization of the all-stage stem rust resistance(Sr)gene Sr8155B1 from the durum wheat line 8155-B1.In seedling tests of biparental populations,Sr8155B1 was effective against six Chinese Pgt races tested.In a segregating population of 5060 gametes,Sr8155B1 was mapped to a 0.06-cM region flanked by markers Pku2772 and Pku43365,corresponding to 1.5-and 2.7-Mb regions in the Svevo and Chinese Spring reference genomes.Both regions include several typical nucleotide-binding leucine-rich repeat(NLR)and protein kinase genes that represent candidate genes.Among them,three NLR genes and three receptor-like protein kinases were highly polymorphic between the parental lines and their transcripts were upregulated in the homozygous resistant line TdR2 relative to its susceptible sister line TdS4.Four markers(Pku2772,Pku43365,Pku2950,and Pku3721)developed in this study,together with seedling resistance responses,correctly predicted Sr8155B1 absence or presence in 78 tetraploid wheat genotypes tested.The presence of Sr8155B1 in tetraploid wheat accessions CItr 14916,PI 197492,and PI 197493 was confirmed by mapping in three F_(2)populations.The genetic map and linked markers developed in this study may accelerate the deployment of Sr8155B1-mediated resistance in wheat breeding programs.

Molecular Markers for Leaf Rust Resistance Gene Lr45 in Wheat Based on AFLP Analysis

Amplified fragment length polymorphism （AFLP） analysis was carried out in Thatcher, near isogenic lines （NILs） canting different genes conferring resistance against wheat leaf rust, and TcLr45 × Thatcher F2 progenies were used to develop markers for Lr45 gene. Sixty AFLP primer combinations were screened and most of them provided clear amplification products, 31 primer combinations displayed polymorphism of TcLr45 in 23 NILs. Two AFLP markers closely linked to the gene Lr45 were acquired： P-AGG/M-GAG261bp, which was found closely linked to the Lr45 locus at a distance of 0.6 cM on one side, and P-ACA/M-GGT105bp, which was found at a distance of 1.3 cM on the other side. The specific hands were cloned and subsequently sequenced. The 261-bp fragment produced by P-AGG/M-GAG showed 86% similarity with the sequence of Vulgate Hort I gene; the 105-bp fragment produced by P-ACA/M-GGT showed 96% similarity with the phosphatidylserine decarboxylase gene of the Triticum monococcum. Both included an open reading frame （ORF）.

Postulation of seedling leaf rust resistance genes in 84 Chinese winter wheat cultivars

Wheat leaf rust（caused by Puccinia triticina） is one of the most important fungal diseases in China. There are tens of winter wheat cultivars which are approved to be released by the government at a national level and more than 100 wheat cultivars at the provincial level. But there is no information about leaf rust（Lr） genes in these cultivars, which makes it difficult for farmers and breeders to select which cultivars they should plant in their fields and use in their breeding programs. The objective of this paper was to identify the leaf rust resistant genes at seedling stage present in the 84 commercial wheat cultivars from China that have been released in the past few years. A set of 20 near isogenic lines with Thatcher background and 6 lines with known Lr genes were used to test the virulence of 12 races of P. triticina（Pt）. By comparing the infection types（ITs） produced on the 84 cultivars by the 12 Pt races with the ITs on the differential sets, the Lr genes were postulated. In addition, 8 molecular markers of Lr genes such as Lr9, Lr10, Lr19, Lr20, Lr21, Lr24, Lr26 and Lr29, which are closely linked to or co-segregated with the Lr gene, were used for further validation of the genes in the 84 Chinese winter wheat cultivars. Twelve Lr genes, including Lr1, Lr3,（Lr3bg）,（Lr3ka）, Lr11, Lr13, Lr14 a, Lr16, Lr26, Lr27, Lr30 and Lr31 were postulated to be present either singly or in combinations in these Chinese wheat cultivars. Lr3 and Lr26 were detected most often in the tested cultivars, with frequencies of 51.2 and 38.1%, respectively. No wheat Lr genes were detected in 16 cultivars, and 4 cultivars may carry unknown Lr genes other than those used in this study. Lr9, Lr20, Lr21, Lr24, Lr25 and Lr29 were not present in any of the 84 tested accessions.

Identification of AFLP Markers Linked to Leaf Rust Resistance Genes Using Near Isogenic Lines of Wheat

The present investigation was undertaken to find molecular markers linked to leaf rust resistance genes, Lr9 and Kharchia local mutant KLM4-3B. Preliminary AFLP analysis was carried out with different stocks, a survey of primer combinations with different selective nucleotide indicated that for each primer combination, the number of scorable loci ranged from 34 to 123. Only a limited primer combination used in the set of parental and near isogenic lines showed a high level of polymorphism for AFLP marker. Putative AFLP marker were found to be linked to Lr9, Lr19 and KLM4-3B. The alien genes were readily identified.

Molecular mapping of leaf rust resistance genes in the wheat line Yu 356-9

The Chinese wheat line Yu 356-9 exhibits a high level of resistance to leaf rust. In order to decipher the genetic base of resistance in Yu 356-9, gene postulation, inheritance analyses, and chromosome linkage mapping were carried out. Gene postulation completed using 15 leaf rust pathotypes and 36 isogenic lines indicated that Yu 356-9 was resistant to all pathotypes tested. F1 and F2 plants from the cross Yu 356-9 （resistant）/Zhengzhou 5389 （susceptible） were tested with leaf rust pathotype ＂FHNQ＂ in the greenhouse. Results indicated a 3：1 segregation ratio, indicative of the presence of a single dominant leaf rust resistance gene in Yu 356-9 which was temporarily designated as LrYu. Bulk segregant analysis and molecular marker assays were used to map LrYu. Five simple sequence repeat （SSR） markers on chromosome 2BS were found closely linked to LrYu. Among these markers, Xwmc770 is the most closely linked, with a genetic distance of 5.7 cM.

Advances in Localization and Molecular Markers of Wheat Leaf Rust Resistance Genes

Genetic resistance is the most economical method of reducing yield losses caused by wheat leaf rust. To identify the leaf rust resistance genes in commonly used parental germplasm and released cultivars become very important for utilizing the genetic resistance to wheat leaf rust fully. Up to date, about 90 leaf rust resistance genes have been found, of which 51 genes have been located and mapped to special chromosomes, and 56 genes have been designated officially according to the standards set forth in the Catalogue of Gene Symbols for wheat. Twenty-four wheat leaf rust resistance genes have been developed for their molecular markers. It is very important to isolate, characterize, and map leaf rust resistance genes due to the resistance losses of the genes caused by the pathogen continuously.

Characterization of wheat monogenic lines with known Sr genes and wheat cultivars for resistance to three new races of Puccinia graminis f. sp. tritici in China

Wheat stem rust, caused by Puccinia graminis f. sp. tritici(Pgt), is a potentially devastating fungal disease of wheat worldwide. The present study was to evaluate the resistance of 42 wheat monogenic lines with known stem rust resistance(Sr) genes and 69 wheat cultivars to three new Pgt races(34C0MRGQM, 34C3MKGQM, and 34C6MTGSM)identified from aeciospores at the seedling and adult-plant stages. The phenotyping results revealed that monogenic lines harboring resistance genes Sr9e, Sr17, Sr21, Sr22, Sr26, Sr30, Sr31, Sr33, Sr35, Sr36, Sr37, Sr38, Sr47, SrTmp,and SrTt3 were effectively resistant to all three Pgt races at the seedling and adult-plant stages. In contrast, monogenic lines containing Sr5, Sr6, Sr7b, Sr9a, Sr9d, Sr9f, Sr9g, Sr9b, Sr16, Sr24, Sr28, and Sr39 were highly susceptible to these races at both seedling and adult-plant stages. The other lines with Sr8a, Sr10, Sr11, Sr13, Sr14, Sr15, Sr18, Sr20,Sr19, Sr23, Sr25, Sr27, Sr29, Sr32, and Sr34, displayed variable levels of resistance to one or two of the tested races.Seedling infection types(ITs) and adult-plant infection responses(IRs) indicated that 41(59.4%) of the wheat cultivars showed high resistance to all the three races. Molecular marker analysis showed that four wheat culitvars likely carried Sr2, 20 wheat culitvars likely carried Sr31, 9 wheat culitvars likely carried Sr38, and none of the cultivars carried Sr24,Sr25, and Sr26. Our results provide a scientific basis for rational utilization of the tested Sr genes and wheat cultivars against these novel Pgt races.

Postulation of Seedlings Resistance Genes to Yellow Rust in Commercial Wheat Cultivars from Yunnan Province in China

The objective of this study was to characterize yellow （stripe） rust resistance gene（s） in 52 commercial wheat cultivars from Yunnan Province in China, and to provide information for their rational deployment in field. Seedlings of wheat cultivars were inoculated with 25 differential isolates ofPuccinia striiformis from foreign and home to postulate resistance genes to yellow rust, and then validated by pedigree. There were 10 probable resistance genes characterized in these cultivars, in which, Yr9 was most commonly postulated to be present in thirteen cultivars. Yr21, the second, was present in four cultivars. Yr8, the third, were present in three cultivars. Yr6, Yrl 7 and Yr26, the fourth, was present in two cultivars respectively. The other gene（s） such as, Yr2＋YrA, Yr7 and Yr27, were only present in single cultivar（s）; unknown gene（s） or gene（s） combination（s） were present in 22 cultivars. One cultivar （Yunmai 42） had no resistance gene tested in this study. Cultivars such as Yunmai 52, Mian 1971-98, Kunmai 4, and Yunmai 56 carried effective genes and can be popularized mainly; Yr9 should be planted with other Yr genes. In the meantime other effective genes should be introduced to realize gene diversity for controlling wheat yellow rust. Yunmai 42 should be reduced to avoid rust breakout. Unknown gene cultivars should be utilized and be researched deeply.

Isolation and Characterization of NBS-LRR Class Resistance Homologous Gene from Wheat

One resistance gene analog fragment named RGA-CIN14 was isolated from TcLr19 wheat,which contains kinase-2,kinase-3a,and the GLPL motif of the NBS-spanning region,using degenerated primers according to the nucleotide binding site （NBS） conserved domain.Based on the RGA-CIN14,a full-length cDNA,CIN14,which was 2 987 bp encoding 880 amino acids,was obtained by using the method of the rapid amplification cDNA ends （RACE）.Bioinformatics analysis showed that the deduced amino acids of CIN14 protein consisted of a NB-ARC conserved domain and many leucine-rich repeats （LRR） domains.The phylogenetic tree analysis indicated a considerable identity of the protein encoded by CIN14 with that of wheat leaf rust resistance gene Lr1,but a lower similarity with Lr21.The expression profile of the CIN14 gene detected by semi-quantitative RT-PCR showed that the CIN14 gene was not induced by Puccinia triticina and it was a constitutive gene with low abundance in the wheat leaf tissue.The resistance homology sequence was successfully obtained,which provides the shortcut for cloning of the resistance gene in TcLr19 wheat.

Genetic Analysis and Molecular Tagging a Novel Yellow Rust Resistance Gene Derived from Synthetic Hexaploid Wheat Germplasm M08

Yellow rust of wheat （caused by Puccinia striiformis Westend. f. sp. tritici Eriks.） has been periodically epidemic and severely damaged wheat production in China. The development of resistant cultivars could be an effective way to reduce yield losses of wheat caused by yellow rust. Rust reaction tests and genetic analysis indicated that M08, the synthetic hexaploid wheat derived from hybridization between Triticum durum （2n = 6X = 28; genome AABB） and Aegilops tauschii （2n = 2X = 14; genome DD）, showed resistance to current prevailing yellow rust races at seedling stage, which was controlled by a single dominant gene, designated as YrAm. Bulked segregant analysis was used to identify microsatellite markers linked to gene YrAm in an F2 population derived from cross M08 （resistant） × Jinan 17 （susceptible）. Three microsatellite marker loci Xgwm77, Xgwm285, and Xgwml31 located on chromosome 3B were mapped to the YrAm locus. Xgwml31 was the closest marker locus and showed a linkage distance of 7.8 cM to the resistance locus. Thus, it is assumed that YrAm for resistance to yellow rust may be derived from Triticum durum and is located on the long arm of chromosome 3B.

Status and strategies in breeding for rust resistance in wheat

Wheat along with rice and maize is fulfilling half of the calories demands of the world. Global Wheat production has increased tremendously since green revolution in 1960’s and helped in minimizing hunger and malnutrition. Developing countries, which consume 60% of the global wheat production, have shown a higher yield increase than the developed countries in the past [1]. It was driven by the hunger prevalence in these countries and was attributable to the introduction of high yielding and rusted resistant semi dwarf varieties developed under the collaborative efforts of International and National research systems during the last 50 years. Whereas, climate change and the emergence of new pests and diseases are threatening the food sustainability. The evolution of new races of disease pathogens like stem rust (Ug 99) is of serious concern. In order to feed the ever increasing population we have to increase wheat production at the rate 1.6% which can be achieved by developing high yielding varieties having a good tolerance level for biotic and abiotic stresses.

Yield Evaluation of a Wheat Line with Combined Resistance to Russian Wheat Aphid and Stem Rust Race “Ug99” in Kenya

InKenya, Russian wheat aphid (RWA) and stem rust race TTKS (“Ug99”) are the most devastating pests of wheat. Severe infestations by RWA result in yield losses of up to 90% while epidemics of “Ug99”can cause up to 100% loss. The two pests combined have seriously affected farmer incomes forcing them to rely heavily on pesticides and increasing the cost of production. This study sought to evaluate a wheat line that has been developed to be resistant to both RWA and “Ug99”by pyramiding two major resistance genes. Three varieties were used in this study: “Kwale”, a Kenyan high yielding commercial variety but susceptible to both RWA and “Ug99”;“Cook”, an Australian variety carrying stem rust resistance gene Sr36 conferring immunity to “Ug99”;and “KRWA9”, a Kenyan line resistant to RWA but with poor agronomic attributes. The F1 of the double cross (DC F1) was obtained by crossing the F1 of “Kwale × Cook” and the F1 of “Kwale × KRWA9”. The DC F1 population was subjected to sequential screening for both RWA and “Ug99”resistance. The surviving DC F1 progenies were left to self pollinate in the field to obtain the DC F2. The DC F2 progenies were sequentially screened against RWA and “Ug99”to obtain a resistant population to both RWA and “Ug99”. The yield and yield components of the new resistant line were compared with the three parents. Results showed that the DC F2:3 had higher yields than the three parents based on 1000 kernel weight, weight of kernel per spike, and the actual yield in tons/ha, indicating that the genes were successfully introgressed. It is concluded that though races with virulence for Sr36 have been reported, the gene provides immunity to race “Ug99”and can be used as a component for “Ug99”resistance breeding together with other Sr genes.

Molecular Mapping of Two Novel Stripe Rust Resistant Genes YrTp1 and YrTp2 in A-3 Derived from Triticum aestivum × Thinopyrum ponticum

Loss of variety resistance to stripe rust （Puccinia striiformis Westend f. sp.tritici） is an important factor causing massive periodical epidemic of rust in wheat production. Creation and development of new races of rust pathogen have led to serious crisis of resistance loss in widely planted varieties. This has quickened the search for new resistance resources. Molecular marker could facilitate the identification of the location of novel genes. A line A-3 with high resistance （immune） to currently epidemic yellow rust races （CY29, 31, 32） was screened out in offspring of Triticum aestivura x Thinopyrum ponticum. Segregation in F2 and BC1 populations indicated that the resistance was controlled by two independent genes： one dominant and one recessive. SSR markers were employed to map the two resistant genes in the F2 and BC1 populations. A marker WMC477-167bp located on 2BS was linked to the dominant gene with genetic distance of 0.4 cM. Another marker WMC364-2os bp located on 7BS was linked to the recessive-resistant gene with genetic distance of 5.8 cM. The two genes identified in this paper might be two novel stripe rust resistant genes, which were temporarily designated as YrTpl and YrTp2, respectively. The tightly linking markers facilitate transfer of the two resistant genes into the new varieties to control epidemic of yellow rust.

小麦慢叶锈QTL位点QLr.hebau-3DS的SSR标记开发

小麦叶锈病是小麦中分布最广的主要病害之一。挖掘抗病基因、选育抗病品种是防治小麦叶锈病最经济、安全、有效的方法。本课题组前期研究中发现农家品种‘平原50’表现出优良的慢叶锈性,利用平原50/铭贤169 DH群体,在‘平原50’中定位了位于3DS染色体上的QLr.hebau-3DS基因,该基因能在多个环境中稳定检测到,表现出优良的抗叶锈性。本试验通过成株期对平原50/铭贤169 DH群体进行抗叶锈鉴定,并利用小麦参考基因组序列开发SSR分子标记,研究结果表明平原50/铭贤169 DH群体在田间表现出连续性分布,其抗性由多个微效基因控制;开发了5对在‘平原50’和‘铭贤169’中表现多态性的SSR分子标记,其中2对分子标记SSR126和SSR208与QLr.hebau-3DS紧密连锁。本研究为下一步QLr.hebau-3DS的图位克隆和慢锈抗病品种的培育奠定了基础。

周8425B抗叶锈病基因LrZH84和LrZH22/Lr13在其衍生品种中的遗传解析

【目的】分析小麦骨干亲本周8425B的207份衍生品种中叶锈病抗性基因LrZH84和LrZH22/Lr13的分布及遗传效应。【方法】对小麦骨干亲本周8425B及其207份衍生品种开展叶锈病苗期抗性接种鉴定,同时利用叶锈病抗性基因LrZH84和LrZH22/Lr13的连锁标记或功能标记进行基因型检测。【结果】207份衍生品种对目前叶锈菌中强毒力优势生理小种KKSQ、TKTS、TKGQ均表现中抗及其以上水平的材料有42份,所占比例为20.3%;31份衍生品种仅携带LrZH84基因,其中对鉴定的3个生理小种表现中抗水平的分别有8、10、8份,所占比例分别为25.8%、32.3%、25.8%;46份衍生品种仅携带LrZH22/Lr13基因,其中对鉴定的3个生理小种表现中抗水平的分别有21、31、25份,所占比例分别为45.7%、67.4%、54.3%;14份衍生品种同时携带LrZH84和LrZH22/Lr13抗病基因,其中对鉴定的3个生理小种表现中抗水平的分别有9、11、11份,所占比例分别为64.2%、78.6%、78.6%;116份衍生品种均不携带LrZH84和LrZH22/Lr13抗病基因,其中对鉴定的3个生理小种表现中抗水平的分别有19、21、20份,所占比例分别为16.4%、18.1%、17.2%。【结论】叶锈病抗性基因LrZH22/Lr13的苗期抗性效应优于LrZH84,聚合两个叶锈病抗性基因的苗期抗性效应优于单个基因;需加强不同抗性基因的聚合,培育新的具有持久抗性的小麦新品种从而有效控制小麦叶锈病的流行。