Adaptation of wheat rusts to the wheat cultivars in former Czechoslovakia

Summary In former Czechoslovakia virulence of rusts attacking wheat was studied since the sixties. Since the same time genes for resistance in the registered cultivars were identified. The role of Berberis and Thalictrum as alternate hosts for stem rust and leaf rust, respectively, was investigated as well. Determined changes of virulence in rust populations could only partially be ascribed to changes of resistance genes in the grown cultivars. Unnecessary genes for virulence had no negative effect on the fitness of the pathogen. All tested samples of aeciospores from barberries attacked rye, not wheat. None of Thalictrum species occurring in the Czech and Slovak Republics was found to host wheat leaf rust. However, the sexual stage of wheat stem rust and wheat leaf rust could be induced on Berberis vulgaris and Thalictrum speciosissimum, respectively. General epidemiological conclusions are drawn from the results and experience of the last 35 years.     

Genetic protection of wheat from rusts and development of resistant varieties in Russia and Ukraine

Leaf rust represents the major threat to wheat production in Russia and Ukraine. It has been present for many years and epidemics of the pathogen occur in different regions on both winter and spring wheat. In some regions there is evidence of more frequent epidemics, probably due to higher precipitation as a result of climate change. There is evidence that the virulence of the leaf rust population in Ukraine and European Russia and on winter wheat and spring wheat is similar. The pathogen population structure in Western Siberia is also similar to the European part, although there are some significant differences based on the genes employed in different regions. Ukrainian wheat breeders mostly rely on major resistance genes from wide crosses and have succeeded in developing resistant varieties. The North Caucasus winter wheat breeding programs apply the strategy of deploying varieties with different types of resistance and genes. This approach resulted in decreased leaf rust incidence in the region. Genes Lr23 and Lr19 deployed in spring wheat in the Volga region were rapidly overcome by the pathogen. There are continuing efforts to incorporate resistance from wild species. The first spring wheat leaf rust resistant varieties released in Western Siberia possessed gene LrTR which protected the crop for 10–15 years, but was eventually broken in 2007. Slow rusting is being utilized in several breeding programs in Russia and Ukraine, but has not become a major strategy.     

Improving wheat stripe rust resistance in Central Asia and the Caucasus

Wheat is the most important cereal in Central Asia (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan) and the Caucasus (Armenia, Azerbaijan and Georgia). Stripe rust, caused by Puccinia striiformis f. sp. tritici is considered the most important disease of wheat in Central Asia and the Caucasus (CAC). Although stripe rust has been present in the region for a long time, it has become a serious constraint to wheat production in the past 10 years. This is reflected by the occurrence of five epidemics of stripe rust in the CAC region since 1999, the most recent in 2010. Several wheat varieties occupying substantial areas are either susceptible to stripe rust or possess a low level of resistance. Information on the stripe rust pathogen in terms of prevalent races and epidemiology is not readily available. Furthermore, there is an insufficient understanding of effective stripe rust resistance genes in the region, and little is known about the resistance genes present in the commercial varieties and advanced breeding lines. The deployment of resistant varieties is further complicated by putative changes in virulence in the pathogen population in different parts of the CAC. Twenty four out of 49 improved wheat lines received through international nurseries or other exchange programs showed high levels of resistance to stripe rust to local pathogen populations in 2009. Fifteen of the 24 stripe rust resistant lines also possessed resistance to powdery mildew. It is anticipated that this germplasm will play an important role in developing stripe rust resistant wheat varieties either through direct adoption or using them as parents in breeding programs.     

Specific resistance to leaf rust expressed at the seedling stage in cultivars grown in France from 1983 to 2007

Host resistance is the most economical means to reduce yield losses caused by wheat leaf rust. Knowledge of the effective specific resistance genes is a prerequisite for analysis of the non-specific components of resistance, assumed to be more durable than specific resistance. Lr genes were inferred from seedling response phenotype of 275 wheat cultivars and 21 standard isolates of Puccinia triticina. Enough cultivars were selected for analysis so that findings would account for at least two-thirds of the French agricultural land dedicated to wheat from 1983 to 2007. In this paper, genes Lr13, Lr37, Lr10, Lr14a, Lr3, Lr26, Lr1, Lr24, Lr20 are postulated, alone or in combinations, in, respectively, 67%, 45%, 34%, 20%, 8%, 7%, 6%, 1%, and 1% of the cultivars. Forty five phenotypic arrays were found, the most frequent being (Lr10, Lr13, Lr37) and (Lr13) in 45 and 37 cultivars, respectively. Over the period, the combinations became increasingly complex. Isolates with virulence corresponding to most of the Lr gene combinations were identified in the pathogen population, except for combinations involving Lr24 and some unidentified genes. These findings will help breeders and extension service staff (Arvalis) in diversifying sources of resistance to wheat leaf rust. This information is also crucial for research programs aiming, on the one hand, to identify sources of quantitative resistance, and, on the other hand, to quantify selection pressure exerted on pathogen populations.     

Race non-specific resistance to rust diseases in CIMMYT spring wheats

Rust diseases continue to cause significant losses to wheat production worldwide. Although the life of effective race-specific resistance genes can be prolonged by using gene combinations, an alternative approach is to deploy varieties that posses adult plant resistance (APR) based on combinations of minor, slow rusting genes. When present alone, APR genes do not confer adequate resistance especially under high disease pressure; however, combinations of 4?C5 such genes usually result in ??near-immunity?? or a high level of resistance. Although high diversity for APR occurs for all three rusts in improved germplasm, relatively few genes are characterized in detail. Breeding for APR to leaf rust and stripe rust in CIMMYT spring wheats was initiated in the early 1970s by crossing slow rusting parents that lacked effective race-specific resistance genes to prevalent pathogen populations and selecting plants in segregating populations under high disease pressure in field nurseries. Consequently most of the wheat germplasm distributed worldwide now possesses near-immunity or adequate levels of resistance. Some semidwarf wheats such as Kingbird, Pavon 76, Kiritati and Parula show high levels of APR to stem rust race Ug99 and its derivatives based on the Sr2-complex, or a combination of Sr2 with other uncharacterized slow rusting genes. These parents are being utilized in our crossing program and a Mexico-Kenya shuttle breeding scheme is used for selecting resistance to Ug99. High frequencies of lines with near-immunity to moderate levels of resistance are now emerging from these activities. After further yield trials and quality assessments these lines will be distributed internationally through the CIMMYT nursery system.     

A new source of resistance against coffee leaf rust from New-Caledonian natural interspecific hybrids between Coffea arabica and Coffea canephora

The development of cultivars resistant to coffee leaf rust caused by the fungal pathogen Hemileia vastatrix is a priority in coffee breeding. However, only very few descendants of interspecific hybrids between Coffea arabica and diploid relative species have been used as resistance source. Identification of new sources of resistance appeared therefore particularly worthwhile. Hybrid plants derived from interspecific hybridization between C. arabica and Coffea canephora and found in neo‐natural coffee tree populations of New Caledonia were therefore investigated. Amplified Fragment Length Polymorphism and microsatellites amplification were used to evaluate the genetic diversity of 14 hybrid plants, and rust resistance was evaluated by inoculation with a panel of rust races representing a large variability in virulence. An important genetic diversity was characterized in hybrid plants originating from introgressions into C. arabica from various C. canephora progenitors. On the 14 plants tested for leaf rust resistance, eight appeared resistant to all races investigated. Such plant material should represent a highly valuable resource for C. arabica breeding against coffee leaf rust.     

Resistance spectra of wheat genotypes and virulence patterns of <Emphasis Type="Italic">Mycosphaerella graminicola</Emphasis> isolates in Iran

Co-evolution of wheat and its devastating pathogen Mycosphaerella graminicola (anamorph Septoria tritici), the causal agent of septoria tritici blotch, a foliar disease of wheat, is suggested to occur in Fertile Crescent as their center of origin and, thus, interaction between pathogen virulence and host resistance is important subject to be addressed. We have investigated resistance spectra of 54 wheat genotypes including a set of differentials carrying known resistance genes and virulence patterns of 14 M. graminicola isolates at seedling stage under controlled environmental conditions. The isolates were collected in Iran from five provinces. Diversity in virulence and aggressiveness was observed among the isolates from four provinces. Isolates collected from Golestan province were virulent to all wheat genotypes from germplasm of Iran, while specific resistances were identified to the isolates from other provinces. Among wheat genotypes, cvs. Chamran, Morvarid and Hirmand had the greatest number of specific resistances as well as partial resistance. Wheat genotypes of the differential set also differed in their reactions to the isolates. Arina, Flame and TE 9111 were specifically resistant to the greatest number of isolates from different provinces. Most isolates were virulent to the other differentials such as cvs. Shafir, Estanzuela federal and Courtot indicating that extensive adaption of virulence to most of the known resistance genes (Stb) has occurred in these regions. The new sources of resistance to highly virulent isolates from Iran may also be utilized in wheat breeding programs to develop resistant cultivars against pathogen populations in other countries.     

The inheritance of stem rust and leaf rust resistance in some Ethiopian wheat collections

Summary Common and durum wheat populations obtained from Sweden and originally collected in Ethiopia were screened for resistance to steum rust and leaf rust. Resistant selections of common wheat were crossed and backcrossed with either stem rust susceptible RL6071, or leaf rust susceptible Thatcher. Genetic studies, based largely on tests of backcross F₂ families, showed that four of the selections had in common a recessive gene SrA. Plants with this gene were resistant (1⁺ infection type) to all stem rust races tested. This gene was neither Sr26 nor Sr29. The resistance of other selections, based on tests with an array of rust isolates, was due to various combinations of Sr6, 8a, 9a, 9d, 9c, 11, 13, 30, and 36. One of the selections had linked genes, Lr19/Sr25. Another selection had a dominant gene for resistance (;1 infection type) to all the races of leaf rust. With the possible exception of this gene for leaf rust resistance and SrA, no obviously new resistance was found.     

Effect of partial resistance to barley leaf rust, <Emphasis Type="Italic">Puccinia hordei</Emphasis>, on the yield of three barley cultivars

Three barley cultivars, Shyri, Clipper and Terán, with different levels of partial resistance to barley leaf rust, caused by Puccinia hordei, were exposed to six levels of the pathogen. These levels were obtained by 5, 4, 3, 2, 1 and 0 fungicide (Propiconazol) applications respectively and occurred every 15 days starting at 66 days after sowing. No application served as the control treatment. There were three replicates. The six-row plots were surrounded by a row of a highly susceptible barley cultivar in which the barley leaf rust arrived naturally in a fairly early plant stage. The disease severity was assessed five times with 15 days intervals starting at 66 days after sowing. The yields were determined by harvesting the inner four rows of the plots. An analysis of variance was carried out on the area under the disease progress curve (AUDPC) data and on the yield data. ‘Shyri’ was the least susceptible cultivar, ‘Terán’ the most. The percentage yield losses varied with the six levels of pathogen from 0 to 31.5% (‘Shyri’), from 0 to 46% (‘Clipper’) and from 0 to 63.5% (‘Terán’). The yield losses correlated strongly with the AUDPC, the linear correlation coefficient being 0.97. The yield losses indicate the importance of the pathogen in Ecuador. It also means that high levels of partial resistance are needed to prevent significant yield damage.     

山西省小麦品种与不同生态区叶锈菌相互作用的研究

1991年在河北农业大学温室用1989年从山西省南部中熟冬麦区、中部晚熟冬麦区、北部春麦区的13个县(市)的不同生态区采集的181个叶锈菌菌株与山西省的33个生产品种、后备品种及亲本材料研究二者之间的相互作用.结果表明,不同生态区叶锈菌群体具有不同的毒性.例如丰抗13在各生态区表现的抗、感反应不一致,即使在表现抗病的地区,其抗性也不一致.     

Race-specific aspects of partial resistance in wheat to wheat leaf rust,Puccinia recondita f.sp. tritici

Summary Partial resistance (PR) in wheat to wheat leaf rust (Puccinia recondita f.sp. tritici) is characterized by a slow epidemic build-up despite a susceptible infection type. Two greenhouse tests and two field tests, in which 11 spring wheat cultivars were exposed to five wheat leaf rust races, revealed some indication for race-specificity of PR.In the greenhouse, the expression of PR was highly dependent on the environment. Significant cultivar-race interactions in the first experiment were lost in the second experiment probably due to cultivar-environment and cultivar-race-environment interactions.In the polycyclic field tests several factors played a role in explaining the inconsistency of the cultivar-race interactions, such as differences in initial inoculum, genotypic differences in earliness, interplot interference or environmental conditions.One cultivar-race combination showed a significant but small interaction towards susceptibility in both field experiments. The interaction was probably too small to detect in the monocyclic greenhouse tests. The results do not conflict with the idea that a gene-for-gene relationship could exist between PR-genes in the host and genes in the pathogen.Some problems with regard to the selection of PR in wheat to wheat leaf rust are discussed.     

Prehaustorial resistance to the wheat leaf rust fungus, Puccinia triticina, in Triticum monococcum (s.s.)

Diploid wheat, Triticum monococcum s.l., is a host for the wheat leaf rust fungus, Puccinia triticina. Some accessions have been reported to show a high degree of prehaustorial resistance. This is non-hypersensitivity resistance, which acts before the formation of haustoria by the pathogen. To assess the frequency of prehaustorial resistance 598 accessions of diploid wheat were inoculated with the wheat leaf rust isolate Felix. Most T. monococcum s.s. accessions (84%) were resistant whereas all T. urartu and all but three T. boeoticumaccessions were susceptible. Histological components analysis revealed that a high percentage of prehaustorial resistance to P. triticina was found in only three T. monococcum accessions. No haustoria were observed in such infection units confirming the prehaustorial nature of the resistance. Prehaustorial abortion of certain infection units in an accession always coincided with posthaustorial abortion of the other infection units. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rust-proofing wheat for a changing climate

This paper offers projections of potential effects of climate change on rusts of wheat and how we should factor in a changing climate when planning for the future management of these diseases. Even though the rusts of wheat have been extensively studied internationally, there is a paucity of information on the likely effects of a changing climate on the rusts and their influence on wheat production. Due to the lack of published empirical research we relied on the few published studies of other plant diseases, our own unpublished work and relevant information from the vast literature on rusts of wheat to prepare this overview. Three broad areas of potential risks from a changing climate were described: increased loss from wheat rusts, new rust pathotypes evolving faster and the reduced effectiveness of rust resistances. Increased biomass of wheat crops grown in the presence of elevated CO₂ concentrations and higher temperatures will increase the leaf area available for attack by the pathogen leading to increased inoculum production. If changed weather conditions were to accelerate the life cycle of a pathogen, the increased inoculum can lead to severe rust epidemics in many environments. Likewise should the effects of climate change result in more conducive conditions for rust development there will also be a corresponding increase in the rate of evolution of new pathotypes which could increase the rate of appearance of new virulences. The effectiveness of some rust resistance genes is influenced by temperature and crop development stage. Climate change may directly or indirectly influence the effectiveness of some resistance genes but this can not be ascertained due to a complete lack of knowledge. Since disease resistance breeding is a long term strategy it is important to determine if any of the important genes may become less effective due to climate change. Studies must be made to acquire new information on the rust disease triangle to increase the adaptive capacity of wheat under climate change. Leadership within the Borlaug Global Rust Initiative (BGRI) is needed to broker research on rust evolution and the durability of resistance under climate change.     

Attempts to remove gametocidal genes co-transferred to common wheat with rust resistance from <Emphasis Type="Italic">Aegilops speltoides</Emphasis>

Rust resistance genes (introgressions S24 and S13) transferred to hexaploid wheat from two Aegilops speltoides accessions could not be used commercially due to associated gametocidal (Gc) genes. Crosses to wheat followed by rigorous selection for increased fertility were employed in an attempt to separate the unmapped S24 stem rust resistance from the Gc gene(s). However, improved fertility of the better selections could not be maintained in subsequent generations. Since the S13 introgression (leaf, stripe and stem rust resistances) mapped to chromosome 3A, allosyndetic pairing induction was used in an attempt to remove the Gc gene(s). This produced putative primary recombinants with improved fertility and plant type, the best of which had exchanged a small region of Ae. speltoides chromatin, yet was still associated with (reduced) Gc effects. This selection (04M127-3, which appears to have the Su1-Ph1 suppressor) was then crossed with wheat. Surprisingly, the 04M127-3 gametocidal effect differed drastically from that of the original introgression allowing the recovery of 35 recombinant, leaf rust resistant progeny. Microsatellite and DArT markers showed that each secondary recombinant had exchanged most of the Ae. speltoides chromatin. Although the data suggested that a complex multigenic interaction may govern the gametocidal response, preliminary indications are that the Gc effect had largely been removed and it now seems possible to completely separate the gametocidal genes from the S13 leaf rust resistance gene (here designated Lr66). The associated (S13) stripe rust and stem rust resistance genes were lost during recombination.     

Cytogenetic studies in wheat XIX. Chromosome location and linkage studies of a gene for leaf rust resistance in the Australian cultivar 'Harrier'

Monosomic analysis indicated that a seedling leaf rust resistance gene present in the Australian wheat cultivar ‘Harrier’(tentatively designated LrH) is located on chromosome 2A. LrH segregated independently of the stripe rust resistance gene Yr1 located in the long arm of that chromosome, but failed to recombine with Lr17 located in the short arm. LrH was therefore designated Lr17b and the allele formerly known as Lr17 was redesignated as Lr17a. The genes Lr17b and Lr37 showed close repulsion linkage. Tests of allelism indicated that Lr1 7b is also present in the English wheats ‘Dwarf A’(‘Hobbit Sib’), ‘Maris Fundin’ and ‘Norman’. Virulence for Lr17b occurs in Australia, and pathogenicity studies have also demonstrated virulence in many western European isolates of the leaf rust pathogen. Despite this, it is possible that the gene may be of value in some regions if used in combination with other leaf rust resistance genes.     

Alleles on the two dwarfing loci on 4B and 4D are main drivers of FHB‐related traits in the Canadian winter wheat population “Vienna” × “25R47”

Fusarium head blight (FHB), leaf rust and stem rust are among the most destructive wheat diseases. High‐yielding, native disease resistance sources are available in North America. The objective of this study was to map loci associated with FHB traits, leaf rust, stem rust and plant height in a “Vienna”/”25R47” population. DArT markers were used to generate a genetic map, and quantitative trait loci (QTL) analysis was performed by evaluating 113 doubled haploid lines across three environments in Ontario, Canada. FHB resistance QTL were identified on chromosomes 4D, 4B, 2D and 7A, while a QTL for leaf and stem rust resistance was identified on chromosome 1B. The dwarfing alleles of both Rht‐B1 and Rht‐D1 were associated with increased FHB index and DON content.     

叶锈菌诱导的小麦叶片cDNA文库的构建及其质量评价

由小麦叶锈菌(Puccinia triticina)引起的小麦叶锈病在世界各地产麦区均有发生,利用抗病品种是防治该病害最经济、安全、有效的方法.小麦抗叶锈基因Lr19是一个十分有效的抗叶锈基因,自1966年首次将该基因从长穗偃麦草转到普通小麦中,至今仍是一个应用潜力很大的抗病基因.本研究以小麦抗叶锈病近等基因系TcLr19和叶锈菌04-15-8①(生理小种类型THTS)为材料,构建叶锈病菌诱导的小麦叶片cDNA文库.研究结果表明文库的克隆数为4.1×106,插入片段大小在0.5～3.0kb,平均插入片段大小1.0 kb.因此该文库可用于基因克隆与分析,为研究小麦抗叶锈病相关基因提供条件.     

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

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

Molecular tagging of a stripe rust resistance gene in <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most important diseases of common wheat (Triticum aestivum L.). China has the largest stripe rust epidemic areas in the world and yield losses can be large. Aegilops tauschii Coss, the D-genome progenitor of common wheat, includes two subspecies, tauschii and strangulata (Eig) Tzvel. The ssp. strangulata accession AS2388 is highly resistant to the prevailing physiological races of PST in China, and possesses a single dominant gene for stripe rust resistance. In order to tag this gene, AS2388 was crossed with the highly susceptible ssp. tauschii accession AS87. The parents, F₂ plants, and F_2:3 families were tested at adult plant stage in field trials with six currently prevailing races. Simple sequence repeat (SSR) primers were used to identify molecular markers linked to the resistance gene. SSR markers Xwmc285 and Xwmc617 were linked to the resistance gene on chromosome arm 4DS flanking it at 1.7 and 34.6 cM, respectively. Based on the chromosomal location, this gene temporarily designated as YrAS2388 is probably novel. The resistance in Ae. tauschii AS2388 was partially expressed in two newly developed synthetic hexaploid backgrounds.     

山西省不同生态区小麦叶锈菌毒性研究

利用已知抗叶锈病基因的小麦近等基因系 (或单基因系 )作鉴别寄主 ,监测来自山西省 3个不同小麦生态区 11个县 (市 )的 92份叶锈标样。在发现的 2 7个致病类型 (毒性基因组合 )中 ,TRK ,TRT ,PHT ,THT出现频率分别为 19 6% ,9 8% ,6 5 % ,6 5 % ,为优势致病类型。对叶锈菌群体毒性基因频率分析结果表明 ,毒性基因V19,V2 4 ,V38的出现频率较低 ,分别为5 4 % ,16 5 %和 0 ,其对应的抗性基因可视为山西省小麦叶锈菌的有效抗病基因