Relative importance of components affecting the leaf rust progress curve in wheat

Summary The relative importance of various components (latent period, uredium area, infectious period, infectibility, sporulation and weather) affecting the progress of leaf rust (Puccinia recondita) in wheat, in the field, was determined by calculating the effect of equivalent changes in the individual components. The effect was calculated in terms of the period of delay in the epidemic reaching 100 per cent severity of leaf rust. Only four components viz., latent period, infectibility, sporulation and weather were found to be important. Further, it was found that these four components were equally important and that they collectively determined the rate of progress of leaf rust in an additive manner.     

Autoinfection in wheat leaf rust epidemics

Autoinfection (within-host inoculum transmission) allows plant pathogens locally to increase their density on an infected host. Estimating autoinfection is of particular importance in understanding epidemic development in host mixtures. More generally, autoinfection influences the rate of host colonization by the pathogen, as well as pathogen evolution. Despite its importance in epidemiological models, autoinfection has not yet been directly quantified. It was measured here on wheat (Triticum aestivum) leaves infected by a pathogenic fungus (Puccinia triticina). Autoinfection was measured either on inoculated leaves or by assessing the local progeny of spontaneous infections, and was described by a model of the form y = microx(alpha), where alpha accounts for host saturation and micro represents the pathogen multiplication rate resulting from autoinfection. It was shown that autoinfection resulted in typical patterns of disease aggregation at the leaf level and influenced lesion distribution in the crop during the first epidemic stages. The parameter micro was calculated by taking overdispersion of the data and density dependence into account. It was found that a single lesion produced between 50 and 200 offspring by autoinfection, within a pathogen generation. By taking into account environmental variability, it was possible to estimate autoinfection under optimal conditions for epidemic development.     

Observed and hypothetical leaf rust progress curves of some genotypes of wheat

Summary The hypothetical leaf rust progress curves of 15 genotypes of wheat were generated by integrating the components of slow rusting resistance determined in the glasshouse. The area under the disease progress curve (AUDPC) from the hypothetical and observed leaf rust progress curves were compared. It was found that the hypothetical AUDPC values of all the genotypes studied were smaller than their respective observed AUDPC values. Possible causes for the discrepancies in the observed and hypothetical values are discussed.     

Secretome analysis of the phytopathogen Macrophomina phaseolina cultivated in liquid medium supplemented with and without soybean leaf infusion

Macrophomina phaseolina (Tassi) Goid. is a fungal pathogen that causes root and stem rot in several economically important crops. However, most of disease control strategies have shown limited effectiveness. Despite its impact on agriculture, molecular mechanisms involved in the interaction with host plant remains poorly understood. Nevertheless, it has been proven that fungal pathogens secrete a variety of proteins and metabolites to successfully infect their host plants. In this study, a proteomic analysis of proteins secreted by M. phaseolina in culture media supplemented with soybean leaf infusion was performed. A total of 250 proteins were identified with a predominance of hydrolytic enzymes. Plant cell wall degrading enzymes together peptidases were found, probably involved in the infection process. Predicted effector proteins were also found that could induce plant cell death or suppress plant immune response. Some of the putative effectors presented similarities to known fungal virulence factors. Expression analysis of ten selected protein-coding genes showed that these genes are induced during host tissue infection and suggested their participation in the infection process. The identification of secreted proteins of M. phaseolina could be used to improve the understanding of the biology and pathogenesis of this fungus. Although leaf infusion was able to induce changes at the proteome level, it is necessary to study the changes induced under conditions that mimic the natural infection process of the soil-borne pathogen M. phaseolina to identify virulence factors.     

Evaluation of inheritance to leaf rust in wheat using area under disease progress curve

Six varieties, Kundan (K), Galvez-87 (G), Trap (T), Chris (C), Mango (M) and PBW-348 (P) along with fast ruster, Agra Local (AL), were screened for seedling reaction and adult pant response to leaf rust. Seedlings of all six varieties were susceptible while adult plants showed lower susceptability response than Agra Local. The F1s among the varieties, and also with Agra Local, showed the values lesser than the respective mid parental values for AUDPC suggesting a polygenic mode of inheritance. ANOVA for combining ability effects indicated variation due to the GCA and SCA effects, which indicated that both additive as well as non-additive type of genetic variances, govern AUDPC. The higher values for the GCA variance over the SCA variance indicated the predominance of an additive component over the dominance component for AUDPC. Significant values for GCA effects indicated that Kundan, Galvez-87 and Trap can be used as good general combiners for AUDPC. The crosses, KxAL, GxAL and TxAL showed significant sca effects for AUDPC, which indicated the predominance of non-additive gene effects in these crosses. Additive x additive and dominance x dominance components of the 5- parameter model were highly significant and contributed maximum extent compared to the additive and dominance components in the cross KxG, while dominance and dominance x dominance components contributed maximum in the remaining crosses. Under such a situation, improvement in the character may be expected through standard selection procedure, which may first exploit the additive gene effects and simultaneously care should be taken to see that the dominance effects are not dissipated, but rather they should be concentrated.     

Inheritance of leaf rust and stem rust resistance in 'Roblin' wheat.

The Canadian common wheat (Triticum aestivum L.) cultivar 'Roblin' is resistant to both leaf rust (Puccinia recondita Rob. ex. Desm.) and stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. and E. Henn.). To study the genetics of this resistance, 'Roblin' was crossed with 'Thatcher', a leaf rust susceptible cultivar, and RL6071, a stem rust susceptible line. A set of F6 random lines was developed from each cross. The random lines and the parents were grown in a field rust nursery artificially inoculated with a mixture of P. recondita and P. graminis isolates and scored for rust reaction. The same material was tested with specific races of leaf rust and stem rust. These data indicated that 'Roblin' has Lr1, Lr10, Lr13, and Lr34 for resistance to P. recondita and Sr5, Sr9b, Sr11, and possibly Sr7a and Sr12 for resistance to P. graminis. In a 'Thatcher' background, the presence of Lr34 contributes to improve stem rust resistance, which appears also to occur in 'Roblin'.     

Association mapping of leaf rust response in durum wheat

Resistance to leaf rust (Puccinia triticina Eriks.) is a main objective for durum wheat (Triticum durum Desf.) breeding. Association mapping on germplasm collections is now being used as an additional approach for the discovery and validation of major genes/QTLs. In this study, a collection of 164 elite durum wheat accessions suitable for association mapping has been tested for leaf rust response at the seedling stage and under field conditions (adult plant stage). Seedling tests were carried out with 25 selected isolates from durum wheat, bread wheat and triticale, while field experiments were carried out in artificially inoculated plots in Italy and in Mexico. The collection has been profiled with 225 simple sequence repeat (SSR) loci of known map position and a PCR assay targeting Ppd-A1. Associations showing highly consistent experiment-wise significances across leaf rust isolates and field trials were mainly detected for the 7BL distal chromosome (chr.) region (harbouring Lr14 from cultivar Llareta INIA and QLr.ubo-7B.2 from cultivar Creso) and for two chr. regions located in chrs. 2A and 2B. Additionally, isolate-specific associations and/or associations with smaller effects in the field trials were identified in most of the chromosomes. The chr. 7BL distal region was investigated in detail through haplotyping with 15 SSR markers, revealing that the Creso and Llareta INIA alleles are identical by descent at 6 adjacent SSR loci in the most distal 7BL region spanning 8 cM. Association mapping allowed us to further refine the map location of the Lr14/QLr.ubo-7B.2 resistance gene to the most distal region of the linkage group, tagged by Xcfa2257.2, Xgwm344.2 and Xwmc10. The resistant haplotype is present in a number of accessions (ca. 15% of the accessions included in the collection) from the Italian, CIMMYT and ICARDA breeding programmes. Therefore, this chr. 7BL region can be considered as the most important source of resistance to leaf rust currently exploited by durum breeders in the Mediterranean areas. Furthermore, the field trials at the adult plant stage allowed us to identify marker associations (e.g. chrs. 2BL and 3BS, proximal regions; chr. 7BS, distal region) which suggest the presence of minor QTLs for slow-rusting resistance.     

Molecular markers for leaf rust resistance genes in wheat

Over 100 genes of resistance to rust fungi: Puccinia recondita f. sp. tritici, (47 Lr - leaf rust genes), P. striiformis (18 Yr - yellow rust genes) and P. graminis f. sp. tritici (41 Sr - stripe rust genes) have been identified in wheat (Triticum aestivum L.) and its wild relatives according to recent papers. Sixteen Lr resistance genes have been mapped using restriction fragments length polymorphism (RFLP) markers on wheat chromosomes. More than ten Lr genes can be identified in breeding materials by sequence tagged site (STS) specific markers. Gene Lrk 10, closely linked to gene Lr 10, has been cloned and its function recognized. Available markers are presented in this review. The STS, cleaved amplified polymorphic sequence (CAPS) and sequence characterized amplified regions (SCAR) markers found in the literature should be verified using Triticum spp. with different genetic background. Simple sequence repeats (SSR) markers for Lr resistance genes are now also available.     

Genetic analysis of durable leaf rust resistance in winter wheat

Quantitative resistance that delays the epidemic development of leaf rust in wheat is an important source for durable resistance breeding. The Swiss winter wheat variety ’Forno’ shows a high level of quantitative resistance against leaf rust. This resistance has been effective for more than 10 years and can therefore be considered to be durable. In order to map quantitative trait loci (QTL) for durable leaf rust resistance we analysed 204 F₅ recombinant inbred lines (RILs) of the cross between the winter wheat ’Forno’ and the winter spelt ’Oberkulmer’ for their level of leaf rust resistance (LR) and leaf tip necrosis (LTN) in four different environments. Both traits showed a continuous distribution and were significantly correlated (r=−0.5). Across environments we detected 8 QTL for leaf rust resistance (6 inherited from ’Forno’) and 10 QTL for the quantitative expression of LTN (6 inherited from ’Forno’). Of the 6 QTL responsible for the durable leaf rust resistance of ’Forno’, 1 major QTL coincided with a thaumatin locus on 7BL explaining 35% of the phenotypic variance. Four QTL for LR coincided with QTL for LTN. At these loci the alleles of ’Forno’ increased the level of resistance as well as the extent of LTN, indicating pleiotropy. Received: 1 July 1999 / Accepted: 30 July 1999     

Molecular mapping of stem and leaf rust resistance in wheat

Stem rust caused by Puccinia graminis f. sp. tritici Eriks and Henn and leaf rust caused by Puccinia triticina Rob. ex Desm. are major constraints to wheat production worldwide. In the present study, F₄-derived SSD population, developed from a cross between Australian cultivars ‘Schomburgk’ and ‘Yarralinka’, was used to identify molecular markers linked to rust resistance genes Lr3a and Sr22. A total of 1,330 RAPD and 100 ISSR primers and 33 SSR primer pairs selected ob the basis of chromosomal locations of these genes were used. The ISSR marker UBC 840₅₄₀ was found to be linked with Lr3a in repulsion at a distance of 6.0 cM. Markers cfa2019 and cfa2123 flanked Sr22 at a distance of 5.9 cM (distal) and 6.0 cM (proximal), respectively. The use of these markers in combination would predict the presence or absence of Sr22 in breeding populations. A previously identified PCR-based diagnostic marker STS638 linked to Lr20 was validated in this population. This marker showed a recombination value of 7.1 cM with Lr20.     

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。     

叶锈菌胁迫下的小麦基因组MSAP分析

内源DNA甲基化是真核生物表观遗传调控的重要组成部分, 在真核生物的基因表达调控中具有重要的作用。生物胁迫为植物提供一种内在的表观遗传进化动力。研究生物胁迫下DNA甲基化的变异模式, 有助于全面理解DNA甲基化的表观调控生物学功能。小麦近等基因系TcLr19、TcLr41及其感病亲本Thatcher在苗期对叶锈菌生理小种THTT、TKTJ分别表现为小种特异性抗病反应和感病反应。文章利用甲基化敏感扩增多态性(Methylation-sensitive amplified polymorphism, MSAP)技术分析了小麦的甲基化水平, 同时比较了苗期在生物胁迫前后基因组DNA胞嘧啶甲基化模式。用60对MSAP引物对接种前后的小麦DNA进行全基因组筛选, 没有直接分离得到接菌前后的甲基化模式的差异, 结果初步表明, 叶锈菌并没有诱导稳定且特异的植物基因组DNA胞嘧啶位点的甲基化模式变化, 但发现TcLr41及其感病亲本Thatcher之间存在表观遗传学差异。     

Genetic analysis of durable resistance against leaf rust in durum wheat

The Italian durum wheat cultivar Creso possesses a high level of durable resistance to leaf rust based on both hypersensitive and non-hypersensitive components. In order to investigate the genetic basis of this resistance, a segregating population composed of 123 recombinant inbred lines (RILs) derived from the cross Creso × Pedroso, was evaluated for disease severity in adult plants under field conditions. Furthermore, the resistance of parents and RILs was evaluated by assessing macroscopically the latency period and microscopically the number and type of pathogen colonies formed following artificial inoculation with a specific isolate. This experiment was performed at controlled conditions at two developmental stages. Besides some minor QTLs, one major QTL explaining both reduction of disease severity in the field and increased latency period was found on the long arm of chromosome 7B, and closely associated PCR-based and DArT markers were identified. Daniela Marone and Ana I. Del Olmo contributed equally to the work.     

Lack of a synergistic interaction between ozone and wheat leaf rust in wheat swards

Ozone is an air pollutant regulated in the USA under the Clean Air Act. Increasingly, concerns have been raised regarding the interactions between ozone and pests, pathogens, and plant competition. This study was conducted to improve our understanding of plant responses to ozone in the presence of pathogens, and specifically to determine the effect that wheat leaf rust and ozone exposure had on wheat productivity. The study was conducted in open-top ozone exposure chambers in Corvallis, OR, using two cultivars of spring wheat (Twin and Yecora Rojo). Twin was grown at two densities. Two levels of ozone and three levels of disease were applied in all combinations, for a total of six treatments. The treatments were replicated twice and repeated over 2 years. Disease severity readings were taken three or four times during each growing season. At the completion of grain-fill, the plants were removed from the chambers and harvested. Wheat height and above-ground biomass generally decreased with ozone exposure and with increasing disease severity in both years, while total grain weight decreased significantly only with disease in 1997. There was no interaction between ozone and disease, regardless of cultivar, density, or the plant response variable measured. There was little evidence that ozone exposure affected the severity of wheat leaf rust.     

Resistance of spring wheat cultivars and lines to leaf rust

Spring wheat nursery accessions, including 18 spring wheat lines derived in CIMMYT, Mexico, and 12 spring wheat cultivars bred in Poland, along with cultivars Frontana and Sumai 3 as resistant controls, were examined for resistance to leaf rust under field conditions. Multipathotype tests with 16 different pathogen isolates were performed for postulation of Lr genes in Polish cultivars. Besides, STS markers for resistance genes Lr1, Lr9, Lr10, Lr24, Lr28, Lr37 were analysed in the studied cultivars and lines with Thatcher near-isogenic lines as positive controls. All Polish cultivars appeared to be susceptible to leaf rust. Ten of the CIMMYT nursery lines (IPG-SW: #7, 11, 14, 21, 22, 23, 27, 29, 30, 32) and cv. Frontana were resistant in the same environment and can be sources of resistance genes. Marker for the Lr10 gene was identified in 6 accessions (IPG-SW #14, 22, 23, 29, 30, 32) exhibiting resistance to leaf rust, whereas markers for Lr1 and Lr28 genes were observed in all the examined accessions. STS markers for Lr9, Lr24 and Lr37 genes were not identified in the investigated accessions.     

PstIAFLP based markers for leaf rust resistance genes in common wheat

The aim of the present study was to detect candidate DNA markers for selected leaf rust resistance genes. A total number of 286 loci in the 'Thatcher' near-isogenic lines carrying resistance gene Lr1, Lr9, Lr10, Lr13, Lr19, Lr21, Lr24, Lr26, Lr28, Lr35, and Lr37 were screened for DNA polymorphism by the PstIAFLP method. A survey with 33 selective primers yielded 16 candidate markers. Further validation studies on cultivars characterized for the presence and absence of selected resistance genes confirmed specificity of markers for Lr24, Lr26 and Lr37. The AFLP-based marker P42-530 was successfully converted into an STS marker. The new marker was linked with the Lr37-specific marker (CslVrga13) at the distance of 1.7 cM. The PstIAFLP method was found to be effective in the identification of DNA changes induced in hexaploid wheat by translocations from Agropyron elongatum, Secale cereale and Aegilops ventricosa.     

Phenotypic and genetic diversity of leaf rust resistance in wheat wild relatives

Puccinia triticina (Pt), the causal agent of leaf rust evolves through forming new pathotypes that adversely affect the growth and yield of wheat cultivars. Therefore, continued production of resistant varieties through exploring novel sources of resistance in wild relatives which are abundantly found in Iran and the neighbouring regions is a major task in wheat breeding programs. The aim of the present study was to explore 60 wild wheat genotypes selected from the species Triticum monococcum, Aegilops tauschii, Ae. neglecta, Ae. cylindrica, Ae. triuncialis, Ae. umbellulata, Ae. speltoides, Ae. columnaris, Ae. crassa and Ae. ventricosa for resistance to leaf rust. The cultivar ‘Boolani’ and Thatcher near-isogenic lines were used as controls. Two-week-old seedlings were inoculated using 10 Pt pathotypes, and the infection types were recorded. The genotypes were also analysed for polymorphism using six sequence-tagged sites (STS) and sequence characterized amplified region (SCAR) markers. Forty-eight genotypes produced high infection types (3⁺) for two pathotypes, but the remaining genotypes produced low infection types of ‘0; ^=’ to ‘1⁺CN’ to all pathotypes. The latter included three accessions of Ae. tauschii, two accessions of each Ae. umbellulata, Ae. columnaris and Triticum monococcum, and one accession from each Ae. triuncialis, Ae. ventricosa and Ae. neglecta. Analysis for STS and SCAR markers suggested several genotypes could carry the genes Lr9, Lr10, Lr19, Lr24, Lr26 and Lr37 or their potential orthologs in addition to unknown resistance genes. In conclusion, the identified resistant genotypes could be further characterized and used in wheat breeding programs for leaf rust resistance.     

Molecular markers for wheat leaf rust resistance gene Lr41

Leaf rust, caused by Puccinia triticina Eriks., is an important foliar disease of common wheat (Triticum aestivum L.) worldwide. Pyramiding several major rust-resistance genes into one adapted cultivar is one strategy for obtaining more durable resistance. Molecular markers linked to these genes are essential tools for gene pyramiding. The rust-resistance gene Lr41 from T. tauschii has been introgressed into chromosome 2D of several wheat cultivars that are currently under commercial production. To discover molecular markers closely linked to Lr41, a set of near-isogenic lines (NILs) of the hard winter wheat cultivar Century were developed through backcrossing. A population of 95 BC₃F_2:6 NILs were evaluated for leaf rust resistance at both seedling and adult plant stages and analyzed with simple sequence repeat (SSR) markers using bulked segregant analysis. Four markers closely linked to Lr41 were identified on chromosome 2DS; the closest marker, Xbarc124, was about 1 cM from Lr41. Physical mapping using Chinese Spring nullitetrasomic and ditelosomic genetic stocks confirmed that markers linked to Lr41 were on chromosome arm 2DS. Marker analysis in a diverse set of wheat germplasm indicated that primers BARC124, GWM210, and GDM35 amplified polymorphic bands between most resistant and susceptible accessions and can be used for marker-assisted selection in breeding programs.     

Rab GTPases as regulators of transport through endosomes

Summary Early endocytic compartments are a highly dynamic, heterogeneous class of prelysosomal organelles that receive internalized proteins from the plasma membrane and sort these to various intracellular destinations. Several monomeric Rab GTPases are associated with the cytoplasmic surface of endosomes and regulate the dynamics of this endomembrane system. We discuss the endosomal Rab proteins and their effector proteins and how they might control vesicular transport through the endocytic pathway.     

Expression of puroindoline a enhances leaf rust resistance in transgenic tetraploid wheat

The purouindoline gene (pin) coding for puroindoline proteins (PINs) is located on chromosome 5D, controls grain hardness, and the PINs have in vitro antimicrobial activity against gram-positive (G+) bacteria, gram-negative (G-) bacteria and fungi. Wheat leaf rust caused by Puccinia triticina is one of the most important fungal diseases for common wheat with AABBDD genomes. Tetraploid wheat (AABB genome) varieties Luna and Venusia were transformed with the purouindoline a (pinA) gene by bombardment, express PINA consititutively. Transgenic plants showed enhanced response to leaf rust in greenhouse and field. Comparative study of harvesting parameters showed significant differences between transgenic and control plants. These indexes were significantly lower (P < 0.05) in control plants than that in transgenic plants, which suggests that they are significantly affected by pinA gene and that the puroindoline a protein (PINA) can effectively inhibit in vivo the growth of fungal, and the transgenic tetraploid wheat can grow well in Hubei Province, Central China, where the tetraploid wheat varieties Luna and Venusia have poor yield due to their disease-sensitivity.