山东省12个主栽小麦品种(系)抗叶锈性分析

本研究旨在明确山东省12个小麦主栽品种(系)抗叶锈性及抗叶锈基因,为小麦品种推广与合理布局、叶锈病防治及抗病育种提供依据。利用2015年采自山东省的5个小麦叶锈菌流行小种的混合小种对这些材料进行苗期抗性鉴定,然后选用15个小麦叶锈菌生理小种对这些品种(系)进行苗期基因推导,并利用与24个小麦抗叶锈基因紧密连锁(或共分离)的30个分子标记对其进行抗叶锈基因分子检测。结果显示,山东省12个主栽小麦品种(系)苗期对该省2015年的5个小麦叶锈菌混合流行小种均表现高度感病。通过基因推导与分子检测发现,济南17含有Lr16,矮抗58和山农20含有Lr26,其余济麦系列、烟农系列、良星系列等9个品种(系)均未检测到所供试标记片段。此外,本研究还对山东省3个非主栽品种进行了检测,结果发现,中麦175含有抗叶锈基因Lr1和Lr37,含有成株抗性基因;皖麦38只检测到Lr26,济麦20未检测到所供试标记片段。综合以上结果,山东省主栽小麦品种(系)所含抗叶锈基因丰富度较低,尤其不含有对我国小麦叶锈菌流行小种有效的抗锈基因,应该引起高度重视,今后育种工作应注重引入其他抗叶锈基因,提高抗叶锈性。     

Quantitative trait loci for slow-rusting resistance in wheat to leaf rust and stripe rust identified with multi-environment analysis

Rust diseases are a major cause of yield loss in wheat worldwide, and are often controlled through the incorporation of resistance genes using conventional phenotypic selection methods. Slow-rusting resistance genes are expressed quantitatively and are typically small in genetic effect thereby requiring multiple genes to provide adequate protection against pathogens. These effects are valuable and are generally considered to confer durable resistance. Therefore an understanding of the chromosomal locations of such genes and their biological effects are important in order to ensure they are suitably deployed in elite germplasm. Attila is an important wheat grown throughout the world and is used as a slow-rusting donor in international spring wheat breeding programs. This study identified chromosomal regions associated with leaf rust and stripe rust resistances in a cross between Attila and a susceptible parent, Avocet-S, evaluated over 3 years in the field. Genotypic variation for both rusts was large and repeatable with line-mean heritabilities of 94% for leaf rust resistance and 87% for stripe rust. Three loci, including Lr46/Yr29 on chromosome 1BL, were shown to provide resistance to leaf rust whereas six loci with small effects conferred stripe rust resistance, with a seventh locus having an effect only by epistasis. Disease scoring over three different years enabled inferences to be made relating to stripe rust pathogen strains that predominated in different years.     

QTL mapping of adult-plant resistances to stripe rust and leaf rust in Chinese wheat cultivar Bainong 64

Stripe rust and leaf rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss. and P. triticina, respectively, are devastating fungal diseases of common wheat (Triticum aestivum L.). Chinese wheat cultivar Bainong 64 has maintained acceptable adult-plant resistance (APR) to stripe rust, leaf rust and powdery mildew for more than 10?years. The aim of this study was to identify quantitative trait loci/locus (QTL) for resistance to the two rusts in a population of 179 doubled haploid (DH) lines derived from Bainong 64?×?Jingshuang 16. The DH lines were planted in randomized complete blocks with three replicates at four locations. Stripe rust tests were conducted using a mixture of currently prevalent P. striiformis races, and leaf rust tests were performed with P. triticina race THTT. Leaf rust severities were scored two or three times, whereas maximum disease severities (MDS) were recorded for stripe rust. Using bulked segregant analysis (BSA) and simple sequence repeat (SSR) markers, five independent loci for APR to two rusts were detected. The QTL on chromosomes 1BL and 6BS contributed by Bainong 64 conferred resistance to both diseases. The loci identified on chromosomes 7AS and 4DL had minor effects on stripe rust response, whereas another locus, close to the centromere on chromosome 6BS, had a significant effect only on leaf rust response. The loci located on chromosomes 1BL and 4DL also had significant effects on powdery mildew response. These were located at the same positions as the Yr29/Lr46 and Yr46/Lr67 genes, respectively. The multiple disease resistance locus for APR on chromosome 6BS appears to be new. All three genes and their closely linked molecular markers could be used in breeding wheat cultivars with durable resistance to multiple diseases.     

Development of PCR markers for the selection of wheat stem rust resistance genes Sr24 and Sr26 in diverse wheat germplasm

The use of major resistance genes is the most cost-effective strategy for preventing stem rust epidemics in Australian wheat crops. The long-term success of this strategy is dependent on combining resistance genes that are effective against all predominant races of the pathogen, a task greatly assisted by the use of molecular markers linked to individual resistance genes. The wheat stem rust resistance genes Sr24 and Sr26 (derived from Agropyron elongatum) and SrR and Sr31 (derived from rye) are available in wheat as segments of alien chromosome translocated to wheat chromosomes. Each of these genes provides resistance to all races of wheat stem rust currently found in Australia .We have developed robust PCR markers for Sr24 and Sr26 (this study) and SrR and Sr31 (previously reported) that are applicable across a wide selection of Australian wheat germplasm. Wheat lines have recently become available in which the size of the alien segments containing Sr26, SrR and Sr31 has been reduced. Newly developed PCR-markers can be used to identify the presence of the shorter alien segment in all cases. Assuming that these genes have different gene-for-gene specificities and that the wheat industry will discourage the use of varieties carrying single genes only, the newly developed PCR markers will facilitate the incorporation of two or more of the genes Sr24, Sr26, SrR and Sr31 into wheat lines and have the potential to provide durable control to stem rust in Australia and elsewhere.     

Genetic studies of leaf and stem rust resistance in six accessions of Triticum turgidum var. dicoccoides.

Six accessions of Triticum turgidum var. dicoccoides L. (4x, AABB) of diverse origin were tested with 10 races of leaf rust (Puccinia recondita f.sp. tritici Rob. ex Desm.) and 10 races of stem rust (P. graminis f.sp. tritici Eriks. &Henn.). Their infection type patterns were all different from those of lines carrying the Lr or Sr genes on the A or B genome chromosomes with the same races. The unique reaction patterns are probably controlled by genes for leaf rust or stem rust resistance that have not been previously identified. The six dicoccoides accessions were crossed with leaf rust susceptible RL6089 durum wheat and stem rust susceptible 'Kubanka' durum wheat to determine the inheritance of resistance. They were also crossed in diallel to see whether they carried common genes. Seedlings of F1, F2, and BC1F2 generations from the crosses of the dicoccoides accessions with RL6089 were tested with leaf rust race 15 and those from the crosses with 'Kubanka' were tested with stem rust race 15B-1. The F2 populations from the diallel crosses were tested with both races. The data from the crosses with the susceptible durum wheats showed that resistance to leaf rust race 15 and stem rust race 15B-1 in each of the six dicoccoides accessions is conferred by a single dominant or partially dominant gene. In the diallel crosses, the dominance of resistance appeared to be affected by different genetic backgrounds. With one exception, the accessions carry different resistance genes: CI7181 and PI 197483 carry a common gene for resistance to leaf rust race 15. Thus, wild emmer wheat has considerable genetic diversity for rust resistance and is a promising source of new rust resistance genes for cultivated wheats.     

河南省16个主栽小麦品种抗叶锈基因分析

为了明确河南省小麦品种的抗叶锈性及抗叶锈基因的分布,为小麦品种推广与合理布局、叶锈病防治及抗病育种提供依据,本研究利用2015年采自河南省的5个小麦叶锈菌流行小种混合菌株,对近几年河南省16个主栽小麦品种进行了苗期抗性鉴定,然后选用12个小麦叶锈菌生理小种对这些品种进行苗期基因推导,同时利用与24个小麦抗叶锈基因紧密连锁(或共分离)的30个分子标记对该16个品种进行了抗叶锈基因分子检测。结果显示,供试品种苗期对小麦叶锈菌混合流行小种均表现高度感病;基因推导与分子检测结果表明,供试品种可能含有Lr1、Lr16、Lr26和Lr30这4个抗叶锈基因,其中先麦8号含有Lr1和Lr26;郑麦366和郑麦9023含有Lr1;西农979和怀川916含有Lr16;中麦895、偃展4110、郑麦7698、平安8号、众麦1号、周麦16、衡观35和矮抗58含有Lr26;周麦22中含有Lr26,还可能含有Lr1和Lr30;豫麦49-198和洛麦23可能含有本研究中检测以外的其他抗叶锈基因。因此,河南省主栽小麦品种的抗叶锈基因丰富度较低,今后育种工作应注重引入其他抗叶锈性基因,提高抗叶锈性,有效控制小麦叶锈病。     

Analysis of leaf and stripe rust severities reveals pathotype changes and multiple minor QTLs associated with resistance in an Avocet?×?Pastor wheat population

Leaf rust and stripe rust are important diseases of wheat world-wide and deployment of cultivars with genetic resistance is an effective and environmentally sound control method. The use of minor, additive genes conferring adult plant resistance (APR) has been shown to provide resistance that is durable. The wheat cultivar ‘Pastor’ originated from the CIMMYT breeding program that focuses on minor gene-based APR to both diseases by selecting and advancing generations alternately under leaf rust and stripe rust pressures. As a consequence, Pastor has good resistance to both rusts and was used as the resistant parent to develop a mapping population by crossing with the susceptible ‘Avocet’. All 148 F₅ recombinant inbred lines were evaluated under artificially inoculated epidemic environments for leaf rust (3 environments) and stripe rust (4 environments, 2 of which represent two evaluation dates in final year due to the late build-up of a new race virulent to Yr31) in Mexico. Map construction and QTL analysis were completed with 223 polymorphic markers on 84 randomly selected lines in the population. Pastor contributed Yr31, a moderately effective race-specific gene for stripe rust resistance, which was overcome during this study, and this was clearly shown in the statistical analysis. Linked or pleiotropic chromosomal regions contributing to resistance against both pathogens included Lr46/Yr29 on 1BL, the Yr31 region on 2BS, and additional minor genes on 5A, 6B and 7BL. Other minor genes for leaf rust resistance were located on 1B, 2A and 2D and for stripe rust on 1AL, 1B, 3A, 3B, 4D, 6A, 7AS and 7AL. The 1AL, 1BS and 7AL QTLs are in regions that were not identified previously as having QTLs for stripe rust resistance. The development of uniform and severe epidemics facilitated excellent phenotyping, and when combined with multi-environment analysis, resulted in the relatively large number of QTLs identified in this study.     

Mapping novel sources of leaf rust and stripe rust resistance introgressed from Triticum dicoccoides in cultivated tetraploid wheat background

Wild emmer wheat, Triticum dicoccoides, the progenitor of modern tetraploid and hexaploid wheats, is an important resource for new variability for disease resistance genes. T. dicoccoides accession pau4656 showed resistance against prevailing leaf rust and stripe rust races in India and was used for developing stable introgression lines (IL) in T. durum cv Bijaga yellow and named as IL pau16068. F₅ Recombinant inbred lines (F₅ RILs) were developed by crossing IL pau16068 with T. durum cultivar PBW114 and RIL population was screened against highly virulent Pt and Pst pathotypes at the seedling and adult plant stages. Inheritance analyses revealed that population segregated for two genes for all stage resistance (ASR) against leaf rust, one ASR gene against stripe rust and three adult plant resistance (APR) genes for stripe rust resistance. For mapping these genes a set of 483 SSR marker was used for bulked segregant analysis. The markers showing diagnostic polymorphism in the resistant and susceptible bulks were amplified on all RILs. Single marker analysis placed all stage leaf rust resistance genes on chromosome 6A and 2A linked to the SSR markers Xwmc256 and Wpaus268, respectively. Likewise one all stage stripe rust resistance gene were mapped on long arm of chromosome 6A linked to markers 6AL-5833645 and 6AL-5824654 and two APR genes mapped on chromosomes 2A and 2B close to the SSR marker Wpaus268 and Xbarc70, respectively. The current study identified valuable leaf rust and stripe rust resistance genes effective against multiple rust races for deployment in the wheat breeding programme.

     

Rust resistance in Triticum cylindricum Ces. (4x, CCDD) and its transfer into durum and hexaploid wheats.

In order to counteract the effects of the mutant genes in races of leaf rust (Puccinia recondita f.sp. tritici Rob. ex Desm.) and stem rust (P. graminis f.sp. tritici Eriks. &Henn.) in wheat, exploration of new resistance genes in wheat relatives is necessary. Three accessions of Triticum cylindricum Ces. (4x, CCDD), Acy1, Acy9, and Acy11, were tested with 10 races each of leaf rust and stem rust. They were resistant to all races tested. Viable F1 plants were produced from the crosses of the T. cylindricum accessions as males with susceptible MP and Chinese Spring ph1b hexaploid wheats (T. aestivum, 6x, AABBDD), but not with susceptible Kubanka durum wheat (T. turgidum var. durum, 4x, AABB), even with embryo rescue. In these crosses the D genome of hexaploid wheat may play a critical role in eliminating the barriers for species isolation during hybrid seed development. The T. cylindricum rust resistance was expressed in the F1 hybrids with hexaploid wheat. However, only the cross MP/Acy1 was successfully backcrossed to another susceptible hexaploid wheat, LMPG-6. In the BC2F2 of the cross MP/Acy1//LMPG-6/3/MP, monosomic or disomic addition lines with resistance to either leaf rust race 15 (infection types (IT) 1=, 1, or 1+; addition line 1) or stem rust race 15B-1 (IT 1 or 1+; addition line 2) were selected. Rust tests and examination of chromosome pairing of the F1 hybrids and the progeny of the disomic addition lines confirmed that the genes for rust resistance were located on the added T. cylindricum C-genome chromosomes rather than on the D-genome chromosomes. The T. cylindricum chromosome in addition line 2 was determined to be chromosome 4C through the detection of RFLPs among the genomes using a set of homoeologous group-specific wheat cDNA probes. Addition line 1 was resistant to the 10 races of leaf rust and addition line 2 was resistant to the 10 races of stem rust, as was the T. cylindricum parent. The added C-genome chromosomes occasionally paired with hexaploid wheat chromosomes. Translocation lines with rust resistance (2n = 21 II) may be obtained in the self-pollinated progeny of the addition lines through spontaneous recombination of the C-genome chromosomes and wheat chromosomes. Such translocation lines with resistance against a wide spectrum of rust races should be potentially valuable in breeding wheat for rust resistance.     

Genetic mapping of the stem rust (Puccinia graminis f. sp. tritici Eriks. & E. Henn) resistance gene Sr13 in wheat (Triticum aestivum L.)

Puccinia graminis f. sp. tritici, the causative agent of stem rust in wheat, is known for its high virulence variability and ability to evolve new virulence to resistance genes. Thus, pyramiding of several resistance genes in a single line is the best strategy for a sustainable control of wheat stem rust. Sr13 is one of the few resistance genes that are effective against wide ranging P. graminis f. sp. tritici races, including the pestilent race Ug99. Its effectiveness to Ug99 makes it a valuable source for resistance to stem rust. Molecular markers play a pivotal role in the genetic characterization of the new sources of resistance as well as in stacking two or more resistance genes in a single line. Therefore, the aim of this study was to develop molecular markers for Sr13 facilitating efficient pyramiding of Sr genes. Based on the 158 F₂ individuals derived from a cross of Khapstein/9*LMPG × Morocco and SSR analyses, the Sr13 locus was mapped on chromosome 6A of wheat, and a genetic map comprising about 90 cM was constructed with the closest marker barc37 being located 4.0 cM distally of Sr13. Of the nine mapped markers, barc37 amplified an allele specific for the presence of Sr13 as shown by testing different cultivars and breeding lines. These newly developed markers will increase the efficiency of incorporating Sr13 into cultivars that are widely adopted, but susceptible to hazardous Ug99 and/or assist for the development of new elite lines that are resistant to Ug99.     

QTL mapping of resistance to race Ug99 of Puccinia graminis f. sp. tritici in durum wheat (Triticum durum Desf.)

Stem rust caused by Puccinia graminis f. sp. tritici was historically one of the most destructive diseases of wheat worldwide. The evolution and rapid migration of race TTKSK (Ug99) and derivatives, first detected in Uganda in 1999, are of international concern due to the virulence of these races to widely used stem rust resistance genes. In attempts to identify quantitative trait loci (QTL) linked with resistance to stem rust race Ug99, 95 recombinant inbred lines that were developed from a cross between two durum wheat varieties, Kristal and Sebatel, were evaluated for reaction to stem rust. Seven field trials at two locations were carried out in main and off seasons. In addition to the natural infection, the nursery was also artificially inoculated with urediniospores of stem rust race Ug99 and a mixture of locally collected stem rust urediniospores. A genetic map was constructed based on 207 simple sequence repeat (SSR) and two sequence tagged site loci. Using composite interval mapping, nine QTL for resistance to stem rust were identified on chromosomes 1AL, 2AS, 3BS, 4BL, 5BL, 6AL 7A, 7AL and 7BL. These results suggest that durum wheat resistance to stem rust is oligogenic and that there is potential to identify previously uncharacterized resistance genes with minor effects. The SSR markers that are closely linked to the QTL can be used for marker-assisted selection for stem rust resistance in durum wheat.     

Locating the broad-spectrum wheat leaf rust resistance gene Lr52 (LrW) to chromosome 5B by a new cytogenetic method

This study was conducted to genetically map a potentially new wheat leaf rust resistance gene (LrW) using a novel genetic method and to test its effectiveness against current races of leaf rust (Puccinia triticina Eriks.) in Canada. Undoubled haploids of a near-isogenic line of Thatcher carrying the resistance gene (RL6107) were pollinated with a contrasting susceptible cultivar to generate an array of hybrids with random deficiencies arising from irregular meiosis of the haploid. Genetic analysis of the deficiencies in such populations can be used to locate qualitative traits by which the two parents differ through a process that we have called haploid deficiency mapping. In the present case, 5/417 hybrids were both susceptible to leaf rust (i.e. lacked the resistance gene) and also lacked several polymorphic microsatellite alleles from RL6107 that are specific to chromosome 5B. This correlated failed transmission of the resistance gene and deficiency for chromosome 5B. Analysis of an F₂ population showed that the factor conditioning resistance was located on the short arm of 5B, 16.5 cM distal to the locus of the microsatellite Xgwm443. Since no other leaf rust resistance genes have been mapped to this region, LrW was re-designated Lr52. RL6107 was tested with 29 isolates of P. triticina, encompassing a diversity of virulence found in North America, with none showing virulence. The effectiveness and novelty of Lr52 make it a promising source of resistance for North American wheat cultivars.     

Molecular mapping of genes for race-specific overall resistance to stripe rust in wheat cultivar Express

‘Express’, a hard red spring wheat cultivar that has been widely grown in the western United States, is used to differentiate races of Puccinia striiformis f. sp. tritici, the causal fungal pathogen of wheat stripe rust. To identify genes conferring race-specific, overall resistance to stripe rust, Express was crossed with ‘Avocet S’. The parents and F₁, F₂, F₃ and F₅ populations were tested with races PST-1, PST-21, PST-43, and PST-45 of P. striiformis f. sp. tritici in the seedling stage under controlled greenhouse conditions. Two dominant genes for resistance to stripe rust were identified, one conferring resistance to PST-1 and PST-21, and the other conferring resistance to all four races. Linkage groups were constructed for the resistance genes using 146 F₅ lines to establish resistance gene analog and chromosome-specific simple sequence repeat marker polymorphisms. The gene for resistance to races PST-1 and PST-21 was mapped on the long arm of chromosome 1B, and that conferring resistance to all four races was mapped on the long arm of chromosome 5B. We temporarily designate the gene on 1BL as YrExp1 and the gene on 5BL as YrExp2. Polymorphism of at least one of the two markers flanking YrExp2 was detected in 91% of the 44 tested wheat genotypes, suggesting that they would be useful in marker-assisted selection for combining the gene with other resistance genes into many other wheat cultivars. Knowledge of these genes will be useful to understand recent virulence changes in the pathogen populations.     

Characterization of genetic loci conferring adult plant resistance to leaf rust and stripe rust in spring wheat.

Leaf (brown) and stripe (yellow) rusts, caused by Puccinia triticina and Puccinia striiformis, respectively, are fungal diseases of wheat (Triticum aestivum) that cause significant yield losses annually in many wheat-growing regions of the world. The objectives of our study were to characterize genetic loci associated with resistance to leaf and stripe rusts using molecular markers in a population derived from a cross between the rust-susceptible cultivar 'Avocet S' and the resistant cultivar 'Pavon76'. Using bulked segregant analysis and partial linkage mapping with AFLPs, SSRs and RFLPs, we identified 6 independent loci that contributed to slow rusting or adult plant resistance (APR) to the 2 rust diseases. Using marker information available from existing linkage maps, we have identified additional markers associated with resistance to these 2 diseases and established several linkage groups in the 'Avocet S' x 'Pavon76' population. The putative loci identified on chromosomes 1BL, 4BL, and 6AL influenced resistance to both stripe and leaf rust. The loci on chromosomes 3BS and 6BL had significant effects only on stripe rust, whereas another locus, characterized by AFLP markers, had minor effects on leaf rust only. Data derived from Interval mapping indicated that the loci identified explained 53% of the total phenotypic variation (R2) for stripe rust and 57% for leaf rust averaged across 3 sets of field data. A single chromosome recombinant line population segregating for chromosome 1B was used to map Lr46/Yr29 as a single Mendelian locus. Characterization of slow-rusting genes for leaf and stripe rust in improved wheat germplasm would enable wheat breeders to combine these additional loci with known slow-rusting loci to generate wheat cultivars with higher levels of slow-rusting resistance.     

A mutagenesis-derived broad-spectrum disease resistance locus in wheat

Wheat leaf rust, stem rust, stripe rust, and powdery mildew caused by the fungal pathogens Puccinia triticina, P. graminis f. sp. tritici, P. striiformis f. sp. tritici, and Blumeria graminis f. sp. tritici, respectively, are destructive diseases of wheat worldwide. Breeding durable disease resistance cultivars rely largely on continually introgressing new resistance genes, especially the genes with different defense mechanisms, into adapted varieties. Here, we describe a new resistance gene obtained by mutagenesis. The mutant, MNR220 (mutagenesis-derived new resistance), enhances resistance to three rusts and powdery mildew, with the characteristics of delayed disease development at the seedling stage and completed resistance at the adult plant stage. Genetic analysis demonstrated that the resistance in MNR220 is conferred by a single semidominant gene mapped on the short arm of chromosome 2B. Gene expression profiling of several pathogenesis-related genes indicated that MNR220 has an elevated and rapid pathogen-induced response. In addition to its potential use in breeding for resistance to multiple diseases, high-resolution mapping and cloning of the disease resistance locus in MNR220 may lead to a better understanding of the regulation of defense responses in wheat.     

Development of resistance gene analog polymorphism markers for the Yr9 gene resistance to wheat stripe rust.

The Yr9 gene, which confers resistance to stripe rust caused by Puccinia striiformis f.sp. tritici (P. s. tritici) and originated from rye, is present in many wheat cultivars. To develop molecular markers for Yr9, a Yr9 near-isogenic line, near-isogenic lines with nine other Yr genes, and the recurrent wheat parent 'Avocet Susceptible' were evaluated for resistance in the seedling stage to North American P s. tritici races under controlled temperature in the greenhouse. The resistance gene analog polymorphism (RGAP) technique was used to identify molecular markers for Yr9. The BC7:F, and BC7:F3 progeny, which were developed by backcrossing the Yr9 donor wheat cultivar Clement with 'Avocet Susceptible', were evaluated for resistance to stripe rust races. Genomic DNA was extracted from 203 BC7:F2 plants and used for cosegregation analysis. Of 16 RGAP markers confirmed by cosegregation analysis, 4 were coincident with Yr9 and 12 were closely linked to Yr9 with a genetic distance ranging from 1 to 18 cM. Analyses of nullitetrasomic 'Chinese Spring' lines with the codominant RGAP marker Xwgp13 confirmed that the markers and Yr9 were located on chromosome 1B. Six wheat cultivars reported to have 1B/1R wheat-rye translocations and, presumably, Yr9, and two rye cultivars were inoculated with four races of P. s. tritici and tested with 9 of the 16 RGAP markers. Results of these tests indicate that 'Clement', 'Aurora', 'Lovrin 10', 'Lovrin 13', and 'Riebesel 47/51' have Yr9 and that 'Weique' does not have Yr9. The genetic information and molecular markers obtained from this study should be useful in cloning Yr9, in identifying germplasm that may have Yr9, and in using marker-assisted selection for combining Yr9 with other stripe rust resistance genes.     

Pathogen race determines the type of resistance response in the stripe rust –Triticum dicoccoides pathosystem

Wild relatives of crop plants may serve as a promising source for screening for new disease resistance genes that can be utilized in breeding programs. Triticum dicoccoides, the wild progenitor of most cultivated wheats, was shown to harbor many resistance genes against the major diseases attacking cultivated wheat. Stripe rust is a devastating fungal disease that attacks wheat in many regions of the world. New races of Puccinia striiformis Westend. f. sp. tritici, the causative agent of stripe rust, have overcome most of the known Yr resistance genes in wheat. Therefore, there is a need to search for new resistance genes in the T. dicoccoides gene pool. A set of 120 T. dicoccoides accessions, collected from 13 populations representing different habitats in Israel and vicinity, was tested for resistance to three prevalent stripe rust races (38E134, 6E16 and 6E0). Of these 120 accessions, 14, 8 and 12% were resistant to races 38E134, 6E16 and 6E0, respectively, while 57, 2 and 4% were moderately resistant to these races, respectively. A unique resistance was found in the population of Mt Hermon where >80% of the accessions showed resistance to all races. Distribution of infection types (ITs) of race 38E134 showed a normal distribution that can fit a quantitative pattern of response, while the distributions of ITs of races 6E16 and 6E0 had excess of extreme values and therefore showing a qualitative pattern of response. anova testing the main factor effects and interaction showed significant effects of population, race and their interaction on IT. Significant positive correlations were obtained between the resistance to races 6E16 and 6E0 and humidity variables of the collections sites, while resistance to race 38E134 was positively correlated with temperature variables. These results show that the pathogen race can determine the type of resistance response, qualitative or quantitative, in the stripe rust—T. dicoccoides pathosystem. The obtained results also reveal that the distribution of resistance to different pathogen races can be affected by different climatic factors.     

Effective and ineffective resistance genes to wheat yellow rust during six years monitoring in Ardabil

Stripe (yellow) rust caused by Puccinia striiformis f. sp. tritici is the most devastating disease of bread wheat (Triticum aestivum) in the cool winter areas. This rust disease represents a constant threat to wheat production in several countries in Central and Western Asia. A wide range of virulent yellow rust pathotypes is evolving in this region causing the breakdown of widely utilised sources of resistance in wheat. Hence, the knowledge of effective resistance genes in the region will enable breeders to target those useful genes in their breeding programmes. From 2006 to 2012, in order to determine of effective resistance genes in Ardabil, north-west of Iran, virulence patterns of wheat yellow rust were studied under the field conditions by planting of differential sets and isogenic lines. The results showed that yellow rust resistance genes Yr1,Yr2⁺ , Yr3V, Yr3a, Yr4a, Yr4, Yr5, Yr7⁺ , Yr10, Yr15,Yr16, YrCV, YrSD and YrND were effective and race-nonspecific resistance genes YrA3, YrA4, Yr18 and Yr29 were partially effective during study periods. Genes Yr2, Yr6, Yr7, Yr9, Yr17, Yr20, Yr21,Yr22, Yr23, Yr24, Yr25, Yr26, Yr27, YrSU, YrSP and YrA were found ineffective. The Genes found effective against yellow rust under natural conditions may be deployed singly or in combinations with durable resistance genes to develop high yielding resistant wheat cultivars in wheat-growing areas in where yellow rust races have the same virulence profile to the prevalent race/s of Ardabil.     

An overview of stripe rust of wheat (Puccinia striiformis f. sp. tritici) in Pakistan

Stripe rust (yellow rust) caused by Puccinia striiformis f. sp. tritici has been an important disease of wheat in the Indian subcontinent since 1786. Currently, it prevails across all the wheat growing areas from north to south in the country. Due to the favourable weather conditions, the northern uplands have been historically hit by the severe disease epidemics. These epidemics caused significant losses to national wheat production. Acquisition of broader virulence pattern by the pathogen poses a serious threat to national agriculture. Although the deployed national wheat varieties have adequate resistance, these are developed around few major genes and are vulnerable to the new evolving strains of the pathogen. Utilisation of race non-specific durable resistance and seedling resistance via gene pyramiding, based on the current virulence scenario of the pathogen should provide sustainable control. This review focuses on the national milestones that recognise the economic significance of the disease and current status of stripe rust and its management in Pakistan.