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.

Investigation of Aegilops umbellulata for stripe rust resistance,heading date,and the contents of iron,zinc,and gluten protein

Aegilops umbellulata(UU)is a wheat wild relative that has potential use in the genetic improvement of wheat.In this study,46 Ae.umbellulata accessions were investigated for stripe rust resistance,heading date(HD),and the contents of iron(Fe),zinc(Zn),and seed gluten proteins.Forty-two of the accessions were classified as resistant to stripe rust,while the other four accessions were classified as susceptible to stripe rust in four environments.The average HD of Ae.umbellulata was significantly longer than that of three common wheat cultivars(180.9 d vs.137.0 d),with the exception of PI226500(138.9 d).The Ae.umbellulata accessions also showed high variability in Fe(69.74-348.09 mg kg^(-1))and Zn(49.83-101.65 mg kg^(-1))contents.Three accessions(viz.,PI542362,PI542363,and PI554399)showed relatively higher Fe(230.96-348.09 mg kg^(-1))and Zn(92.46-101.65 mg kg^(-1))contents than the others.The Fe content of Ae.umbellulata was similar to those of Ae.comosa and Ae.markgrafii but higher than those of Ae.tauschii and common wheat.Aegilops umbellulata showed a higher Zn content than Ae.tauschii,Ae.comosa,and common wheat,but a lower content than Ae.markgrafii.Furthermore,Ae.umbellulata had the highest proportion of γ-gliadin among all the species investigated(Ae.umbellulata vs.other species=mean 72.11%vs.49.37%;range:55.33-86.99%vs.29.60-67.91%).These results demonstrated that Ae.umbellulata exhibits great diversity in the investigated traits,so it can provide a potential gene pool for the genetic improvement of these traits in 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.

Release of Stem Rust Resistant Wheat Varieties for Commercial Production in Kenya

Detection in 1999 of a new stem rust （Puccinia graminis f. sp. tritici） race Ug99 in Uganda with broad virulence including the virulence for Sr31 and its migration to Kenya and Ethiopia has been recognized as a significant threat to local and world wheat production. All the Current Kenyan commercial varieties are susceptible to this race. This study was aimed at identifying suitable wheat varieties with resistance to Ug99 and replacing the susceptible commercial varieties through multi-locational testing and variety release. Thirty three lines were identified from a prescreen population of 104 lines and tested in 3 wheat growing regions in Kenya for two seasons in 2006 and 2007. The resulting four superior lines were evaluated under the National Performance Trial （NPT） where two lines which out-performed the best check variety were released as for commercial production. ＇Robin＇ was the best line and out yielded the commercial variety by 27%. ＂Eaglel0＂ was the second best and was better significantly than the check variety. These two lines which combined both adult plant resistant gene Sr2 complex and other major genes are expected to have some durable resistance and may be used to replace the current susceptible commercial varieties grown in Kenya.

Evaluation of Wheat Stripe Rust Resistance in Sichuan Province

Wheat stripe rust,caused by Puccinia striiformis Westend. f. sp. tritici Erikss.（ Pst）,is one of the most destructive diseases of wheat（ Triticum aestivum L.） worldwide. Sichuan province plays an important role in stripe rust epidemic in China. To identify and evaluate wheat stripe rust resistance in Sichuan Province,134 wheat cultivars（ lines） were inoculated with seven Pst races at seedling stage and adult stage. The results indicated that the resistance frequencies of wheat cultivars（ lines） against seven races CYR31,Su11-7,CYR29,Su11-4,CYR32,CYR33 and V26 were 92. 4%,92. 5%,89. 3%,89. 4%,87. 3%,85. 0% and 82. 8%,respectively. Among 134 materials,76（ 56. 0%） performed resistance against all tested races both in seedling and adult stages. The virulence of new pathogenic type V26 of Pst on wheat cultivars（ lines） was stronger than the dominant races CYR32 and CYR33. All wheat cultivars（ lines） were classified into three types according to analysis of resistance spectrum; 66. 4% of cultivars（ lines） showed all-stage resistance,17. 9% were adult-plant resistance,and 15. 7% were susceptible. This indicated that although the overall resistance level of wheat cultivars（ lines） in Sichuan Province was very high,the resistance type was simple. Therefore,it is important to identify new resistance genes and enhance resistance gene diversity. Meanwhile,pyramiding breeding of all-stage resistance gene and adult-plant resistance gene could be gradually developed,to achieve durable resistance of wheat cultivars（lines） against stripe rust in Sichuan Province.

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.

Applying Molecular Breeding to Improve Soybean Rust Resistance in Vietnamese Elite Soybean

Soybean production in Vietnam has recently been threatened by the widespread dissemination of soybean rust (SBR) caused by the fungus Phakopsora pachyrhizi. Application of molecular breeding is considered as a feasible method to improve soybean rust resistance and minimize the adverse effects from overuse fungicides in this country. In this study, we have successfully applied molecular markers in a backcross breeding program to introgress the Rpp5 gene of SBR resistance into HL203, an elite Vietnamese soybean variety, from two donor lines of DT2000 and Stuart 99084B-28. The plants in BC4F1 generation had maximum contribution from the recurrent parents and retained SBR resistance gene.

Molecular mapping of stripe rust resistance gene YrH9017 in wheat-Psathyrostachys huashanica introgression line H9017-14-16-5-3

Several new stripe rust pathogen races emerged in the wheat growing regions of China in recent years.These races were virulent to most of the designated wheat seedling resistance genes.Thus,it is necessary and worthwhile to identify new valuable resistant materials for the sake of diversifying resistant sources,pyramiding different resistance genes and achieving durable resistance.Here,we identified the resistance gene,temporarily designated as YrH9017,in wheat-Psathyrostachys huashanica introgression line H9017-14-16-5-3.A total of 146 F2 plants and their derived F2:3 families in a cross of Mingxian 169 and H9017-14-16-5-3 were used to evaluate seedling stripe rust response and as a mapping population.Finally,we constructed a genetic map including eight simple sequence repeat(SSR) markers and expressed sequence tag(EST) markers.YrH9017 was located on the long arm of chromosome 2A and closely linked with two EST-sequence tagged site(EST-STS) markers BG604577 and BE471201 at 1.3 and 1.8 cM distance,respectively.The two closest markers could be used for marker-assisted selection of YrH9017 in breeding.

Comparative FISH and molecular identification of new stripe rust resistant wheat-Thinopyrum intermedium ssp. trichophorum introgression lines

Thinopyrum intermedium(2 n = 6 x = 42, JJJ^sJ^sStSt) has been hybridized extensively with common wheat and has proven to be a valuable germplasm source for improving disease resistance, quality attributes, and yield potential in wheat. We characterized new disease resistant wheat-Th. intermedium derivatives A1082 and A5-5 using sequential multi-color fluorescence in situ hybridization(mc-FISH), genomic in situ hybridization(GISH), PCRbased landmark unique gene(PLUG) and intron targeting(IT) markers. A1082 was identified as a wheat-Th. intermedium 3J disomic addition line, and A5-5 was a T4BS·5J^sL homozygous Robertsonian translocation line. Seventy-one and 106 pairs of primers amplified Th.intermedium-specific bands allowing chromosomes 3J and 5J^s to be tracked, respectively. A new oligonucleotide probe, Oligo-6 H-2-100, was developed for FISH labeling of the subterminal region of the long arm of chromosome 5J^s. Both lines were highly resistant to stripe rust pathogen races prevalent in Chinese field screening nurseries. A5-5 also displayed a significant increase in tiller number compared to its wheat parent. The new lines can be exploited as useful germplasms for wheat improvement.

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.

Research Progresses of Sugarcane Brown Rust Resistance Gene and Molecular Markers

Brown rust is a main sugarcane disease in China, affecting stable development of sugarcane industry. Resistance breeding is an effective measure to control sugarcane rust, and looking for diverse sugarcane rust resistance alternative resources is another important way to improve rust resistance level. This article reviewed from the aspects of construction of sugarcane genetic map, research progress of rust resistance gene, development of rust resistance molecular markers, and research strategies of rust resistance gene, in order to provide scientific guidance and reference for rust resistance breeding.

Characterization of novel wheat-Thinopyrum ponticum introgression lines derived from partial amphiploid AUS6770 for resistance to stripe rust

The wild decaploid species Thinopyrum ponticum(Podp.)Barkworth&D.R.Dewey is an important source of genes against biotic and abiotic stresses affecting wheat.The wheat–Th.ponticum partial amphiploid AUS6770 shows resistance to multiple diseases,including stripe rust,stem rust,and powdery mildew.Mitotic chromosomes of AUS6770 were characterized by non-denaturing-fluorescence in situ hybridization(ND-FISH),and the individual Th.ponticum chromosomes 1Ae to 7Ae were karyotypically distinguished by Oligo-FISH painting using bulked oligo pools based on wheat-barley collinear regions.A novel stripe rust resistant line A155,derived from AUS6770,was found to have 44 chromosomes,including a pair of 2Ae chromosomes and a pair of 6B-6Ae translocations.To detect plants with transfer of resistance genes from A155 to wheat chromosomes,1770 plants were developed from F2–F5 progenies of A155 crossed with the susceptible wheat cultivar MY11 and characterized with ND-FISH using multiple probes.A high frequency of transmission of chromosome 2Ae was observed,and 31 types of 2Ae chromosomal aberrations were identified using ND-FISH.Ten chromosomal bins on the 2Ae chromosome were determined from the deletion and translocation lines based on genome-based PCR markers.In combination with the evaluation of disease resistance,the gene(s)for stripe rust resistance was located on the FL0.79–1.00 of 2AeS and covers the corresponding region of 0–58.26 Mb in the reference genome of Th.elongatum.The newly identified wheat-Th.ponticum 2Ae translocation lines can be exploited as potential germplasm in wheat breeding for stripe rust resistance.

The Stripe Rust Resistance Gene Yr10 Encodes an Evolutionary-Conserved and Unique CC-NBS-LRR Sequence in Wheat

The first seedling or all-stage resistance （R） R gene against stripe rust isolated from Moro wheat （Triticum aes- tivum L.） using a map-based cloning approach was identified as Yr10. Clone 4B of this gene encodes a highly evolutionary- conserved and unique CC-NBS-LRR sequence. Clone 4E, a homolog of Yr10, but lacking transcription start site （TSS） and putative TATA-box and CAAT-box, is likely a non-expressed pseudogene. Clones 4B and 4E are 84% identical and divergent in the intron and the LRR domain. Gene silencing and transgenesis were used in conjunction with inoculation with differen- tially avirulent and virulent stripe rust strains to demonstrate Yr10 functionality. The Yr10 CC-NBS-LRR sequence is unique among known CC-NBS-LRR R genes in wheat but highly conserved homologs （E = 0.0） were identified in Aegilops tauschii and other monocots including Hordeum vulgare and Brachypodium distachyon. Related sequences were also identified in genomic databases of maize, rice, and in sorghum. This is the first report of a CC-NBS-LRR resistance gene in plants with limited homologies in its native host, but with numerous homologous R genes in related monocots that are either host or non-hosts for stripe rust. These results represent a unique example of gene evolution and dispersion across species.

Variation in Chromosome Constitution of the Xiaoyan Series Partial Amphiploids and Its Relationship to Stripe Rust and Stem Rust Resistance

The wild relatives of wheat （Triticum aestivum L.） contain tremendous amounts of potentially useful genes and represent a promising source of genetic diversity for wheat improvement （Bommineni and Jauhar, 1997）. Thinopyrum ponticum （Popd.） Barkworth and D. R. Dewey [syn. Agropyron elongatum （Host） P. Beauv., Elytrigia pontica （Podp.） Holub, Lophopy- rum ponticum （Podp.） A. L6ve] （2n = 10x = 70）, has high crossability with various Triticum species. Numerous studies have shown that Th. ponticum carries many potentially valu- able resistance genes against biotic and abiotic stresses （Shannon, 1978; Cox, 1991; Zheng et al., 2014a,b）. Transferring the useful genes from Th. ponticum to common wheat through chromosome engineering had been a successful way to enhance the resistance of wheat to pests and diseases （Sharma et al., 1989; McIntosh, 1991）.

Screening of Wheat Cultivars for High Temperature Resistance to Stripe Rust from Wheat Resources in Huanghuai Growth Area

[Objective] The study aimed to screen wheat cultivars with high temperature resistance to stripe rust from the wheat resources in Huanghuai growth area. [Method] Seedlings of 165 wheat cultivars from Huanghuai growth area were identified by wheat stripe rust under high temperature; then the wheat cultivars showing stripe rust at seedling stage were further used to identify the same resistance in field. [Results] 13 cultivars were proved to be stripe rust resistant under high temperature, and the expression stages of stripe rust in the 13 cultivars were revealed. The field identification results confirmed the identification results at seedling stage via inoculation of mixed stripe rust of physiological races. The stripe resistances of wheat cultivars were also proved to be non-race-specific. [Conclusion] Wheat resources in Huanghuai growth area are abundant in wheat cultivars with high temperature resistance to stripe rust.

Combined linkage and association mapping reveals two major QTL for stripe rust adult plant resistance in Shaanmai 155 and their haplotype variation in common wheat germplasm

The development and deployment of diverse resistance sources in new wheat cultivars underpin the durable control of stripe rust.In the present study,two loci for adult plant resistance(APR),QYr SM155.1 and QYr SM155.2,were identified in the Chinese wheat breeding line Shaanmai 155.QYr SM155.1 was mapped to a 3.0-c M interval between the single-nucleotide polymorphism(SNP)markers AX-109583610 and AX-110907562 on chromosome arm 2 BL.QYr SM155.2 was mapped to a 2.1-c M interval flanked by the SNP markers AX-110378556 and AX-86173526 on chromosome arm 7 AS.A genome-wide association study was used to identify markers associated with APR in a panel of 411 spring wheat lines.Thirteen and 11 SNPs were significantly associated with QYr SM155.1 and QYr SM155.2,respectively,corresponding to physical intervals of 653.75–655.52 Mb on 2 BL and 81.63–83.93 Mb on7 AS.To characterize the haplotype variation and the distribution of these QTL,haplotype analysis was performed based on these SNPs in an independent panel of 1101 worldwide wheat accessions.Three major haplotypes(2 B_h1,2 B_h2,and 2 B_h3)for QYr SM155.1 and four major haplotypes(7 A_h1,7 A_h2,7 A_h3,and 7 A_h4)for QYr SM155.2 were identified.Accessions individually harboring QYr SM155.1_h1 and QYr SM155.2_h1 haplotypes and their combination displayed resistance.Additional assays of 1306 current Chinese cultivars and breeding lines using markers flanking QYr SM155.1 and QYr SM155.2 indicated that the resistance haplotypes of the two QTL were present in respectively 1.45%and 14.16%of lines.Increasing resistance haplotype frequencies at these two loci using marker-assisted selection should benefit wheat production in China.

Identification of an AFLP marker linked to the stripe rust resistance gene Yr10 in wheat

AFLP analysis of near-isogenic lines of the stripe rust resistance gene Yr10 was carried out with 6 Pst I -primers and 10 Taq I -primers with the donor parent of Yr1O gene as the check. A total of about 4200 distinguishable bands were amplified, of which 5 were stable. The genetic linkage of the 5 polymorphic DNA fragments with the target gene were tested preliminarily on a segregating F2 population derived from a cross between the gene donor parent 'Moro' and susceptible cultivar 'Mingxian 169'. The DNA fragment PT0502 was found closely linked to the Yr10 gene and cloned and sequenced. Based on the sequence specific primers for PCR were designed and synthesized. Genetic linkage analysis with 195 segregating F2 plants indicated that the genetic distance was 0.5 cM between the main product SC200 fragment produced by PCR with the primers and the Yr10 gene. The primers can be used to detect the Yr10 gene quickly, effectively and exactly.

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.

QTL Mapping for Partial Resistance to Southern Corn Rust Using RILs of Tropical Sweet Corn

Southern corn rust is one of destructive diseases in maize caused by Puccinia polysora Undrew. A mapping population of tropical sweet corn recombinant inbred lines (RILs) derived from a cross between hA9104 and hA9035 inbred lines were set up to detect quantitative trait loci (QTLs) involved in partial resistance to southern corn rust. Eighty nine RILs were used to evaluate resistance levels using nine-point relative scale (1-9) at Sweet Seeds, Suwan Farm, Thailand include combined analysis. A genetic linkage map was constructed with 157 SSR markers, with a total length of 2123.1 cM, covering 10 chromosomes. Broad-sense heritability of individual location ranged from 0.76 and 0.82 and combined across locations was 0.87. Multiple QTL mapping (MQM) was applied for the identification of the QTLs. Fifteen QTLs were detected on chromosome 1, 2, 5, 6, 9 and 10 in both locations and combined across locations. QTLs on chromosome 1, 5 and 6 were contributed by alleles of resistant parent hA9104 while others were contributed by alleles from the susceptible parent, hA9035. Phenotypic variance of each QTL explained ranged from 6.1% to 41.8% with a total of 69.8% - 81.9%. QTL on chromosome 1, 6 and 10 were stable QTLs detected in both locations.