Clinal resistance structure and pathogen local adaptation in a serpentine flax-flax rust interaction

Because disease resistance is a hallmark signature of pathogen-mediated selection pressure on hosts, studies of resistance structure (the spatial distribution of disease resistance genes among conspecific host populations) can provide valuable insights into the influence of pathogens on host evolution and spatial variation in the magnitude of their effects. To date few studies of wild plant-pathogen interactions have characterized resistance structure by sampling across the host's biogeographic range, and only a handful have paired such investigations with studies of disease levels under natural conditions. I used a greenhouse cross-inoculation experiment to characterize genetic resistance of 16 populations of California dwarf flax (Hesperolinon californicum) to attack by multiple samples of the rust fungus Melampsora lini. I documented a latitudinal cline in resistance structure, manifest across the host's biogeographic range, which mirrored almost identically a cline in infection prevalence documented through field surveys of disease in study populations. These results provide empirical evidence for clinal patterns of antagonistic selection pressure, demonstrate that such patterns can be manifest across broad biogeographic scales, and suggest that rates of disease prevalence in wild plant populations may be tightly linked to the distribution of host resistance genes. Tests for local adaptation of the fungus revealed evidence of the phenomenon (significantly greater infection in sympatric plant-fungal pairings) as well as the potential for substantial bias to be introduced into statistical analyses by spatial patterns of host resistance structure.     

Major-gene resistance to the rust pathogen Coleosporium ipomoeae is common in natural populations of Ipomoea purpurea

The genetic basis of resistance to pathogens is well studied in crops, yet our understanding of the evolution of this trait in natural populations will be improved by determining how resistance is inherited in a wide range of plant-pathogen interactions. Here, we examined resistance to Coleosporium ipomoeae, a common fungal rust pathogen of Ipomoea purpurea. Natural populations across North Carolina, South Carolina, and Georgia (USA) were surveyed for the presence of C. ipomoeae and seeds were collected. A combination of crosses and controlled infections was then used to determine the genetic basis of qualitative resistance. In one population studied in detail, complete resistance to natural infection and a bulk collection of C. ipomoeae is conferred by a single locus (Rci1), where resistance is dominant to susceptibility. Allelic, major-gene resistance to this same bulk collection of C. ipomoeae appears to also occur in nine other natural populations. The prevalence of this resistance phenotype in natural populations suggests that the evolution of resistance to C. ipomoeae in I. purpurea may be dominated by genes of large phenotypic effect.     

Genetics of adult plant stripe rust resistance in CSP44, a selection from Australian wheat

Wheat line CSP44, a selection from an Australian bread wheat cultivar Condor, has shown resistance to stripe rust in India since the last twenty years. Seedlings and adult plants of CSP44 showed susceptible infection types against stripe rust race 46S119 but displayed average terminal disease severity of 2.67 on adult plants against this race as compared to 70.33 of susceptible Indian cultivar, WL711. This suggests the presence of nonhypersensitive adult plant stripe rust resistance in the line CSP44. The evaluation of F₁, F₂ and F₃ generations and F₆ SSD families from the cross of CSP44 with susceptible wheat cultivar WL711 for stripe rust severity indicated that the resistance in CSP44 is based on two genes showing additive effect. One of these two genes isYr18 and the second gene is not yet described.     

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.     

The genetics of rust resistance in sugar cane seedling populations

The inheritance of rust resistance was studied in sugar cane seedling populations using a factorial mating design over 1 summer and 2 winter seasons. Frequency distributions for rust infection pooled over 2 winter seasons for resistant x resistant parents were highly skewed with the majority of progenies grouped towards the resistant classes, whereas crosses between susceptible x highly susceptible parents tended to be skewed with the majority of progenies grouped towards the susceptible ones. Both categories of crosses produced transgressive segregants at either extremes. Distribution of infection within progeny of the selfed resistant parent ’R 570’ and distribution in the majority of crosses tended to support the hypothesis of a major gene with a dominant effect for resistance. However, the action of other minor genes acting in a quantitative way is also suggested. The female (F) and male (M) variance components were very important, and F×M interaction indicated the existence of non-additive genetic effects. F×S, M×S and F×M×S interaction mean squares were generally low or insignificant. Broad-sense heritability for the individual season ratings and for the combined ratings was high (0.75–0.90), whereas narrow-sense heritability was generally moderate (0.40–0.52) with the additive genetic effects accounting for 44–68% of the total genetic variation. The implications of these findings in the breeding for rust resistance in the local programme are discussed. Received: 2 June 1999 / Accepted: 22 June 1999     

Identification of QTLs for partial resistance to leaf rust (Puccinia hordei) in barley

 The partial resistance to leaf rust in barley is a quantitative resistance that is not based on hypersensitivity. To map the quantitative trait loci (QTLs) for partial resistance to leaf rust, we obtained 103 recombinant inbred lines (RILs) by single-seed descent from a cross between the susceptible parent L94 and the partially resistant parent Vada. These RILs were evaluated at the seedling and adult plant stages in the greenhouse for the latent period (LP) of the rust fungus, and in the field for the level of infection, measured as area under the disease progress curve (AUDPC). A dense genetic map based on 561 AFLP markers had been generated previously for this set of RILs. QTLs for partial resistance to leaf rust were mapped using the “Multiple Interval Mapping” method with the putative QTL markers as cofactors. Six QTLs for partial resistance were identified in this population. Three QTLs, Rphq1, Rphq2 and Rphq3, were effective at the seedling stage and contributed approximately 55% to the phenotypic variance. Five QTLs, Rph2, Rphq3, Rphq4, Rphq5, and/or Rphq6 contributed approximtely. 60% of the phenotypic variance and were effective at the adult plant stage. Therefore, only the QTLs Rphq2 and Rhpq3 were not plant-stage dependent. The identified QTLs showed mainly additive effects and only one significant interaction was detected, i.e. between Rphq1 and Rphq2. The map positions of these QTLs did not coincide with those of the race-specific resistance genes, suggesting that genes for partial resistance and genes for hypersensitive resistance represent entirely different gene families. Also, three QTLs for days to heading, of which two were also involved in plant height, were identified in the present recombinant inbred population. These QTLs had been mapped previously on the same positions in different populations. The perspectives of these results for breeding for durable resistance to leaf rust are discussed. Received: 15 July 1997 / Accepted: 30 December 1997     

Inheritance of resistance to southern corn rust in tropical-by-corn-belt maize populations

 The inheritance of resistance to southern rust (caused by Puccinia polysora Underw.) was investigated in two F_2:3 populations derived from crossing two temperate-adapted, 100% tropical maize (Zea mays L.) inbred lines (1416-1 and 1497-2) to a susceptible Corn Belt Dent hybrid, B73Ht×Mo17Ht. The inbred lines possess high levels of resistance to southern rust and may be unique sources of resistance genes. Heritability for resistance was estimated as 30% and 50% in the two populations from regression of F_2:3 family mean scores on F₂ parent scores, and as 65% and 75% from variances among F_2:3 families on a single-plot basis. RFLP loci on three chromosomal regions previously known to possess genes for resistance to either southern rust or common rust (P. sorghi Schw.) were used to localize genes affecting resistance to southern rust in selected genotypes of both populations, and to estimate their genetic effects. A single locus on 10S, bnl3.04, was associated with 82–83% of the variation among field resistance scores of selected F_2:3 families in the two populations. Loci on chromosomes 3 (umc26) and 4 (umc31) were significantly associated with resistance in the 1497-2 population, each accounting for 13–15% of the phenotypic variation for F_2:3 field scores. Multiple-marker locus models, including loci from chromosomes 3, 4, and 10 and their epistatic interactions, accounted for 96–99% of the variation in F_2:3 field scores. Similar results were obtained for resistance measured by counting pustules on juvenile plants in the greenhouse. An attempt was made to determine if the major gene for resistance from 1416-1 was allelic to Rpp9, which is also located on 10S. Testcross families from the cross (1416-1×B37Rpp9)×B14AHt were evaluated for resistance to southern rust in Mexico. Neither source of resistance was completely effective in this environment, preventing determination of allelism of the two genes; however, both sources of resistance had better partial resistance to southern rust than did B14AHt. Received: 6 May 1997/Accepted: 19 September 1997     

中国柄锈菌属—新变种和—新记录种（英文）

报道了中国柄锈菌属1新变种和1新记录种。大油芒Spodiopogon sibiricus上的三吉柄锈菌大油芒变种Puccinia miyoshiana var.spodiopogonis为新变种;田葛缕子Carum buriaticum上的密堆柄锈菌Puccinia microsphincta为中国新记录种。提供了详细的形态描述和线条图。研究标本保存在赤峰学院菌物标本室(CFSZ)和中国科学院菌物标本馆(HMAS)。     

Rapid accumulation of trihydroxy oxylipins and resistance to the bean rust pathogen Uromyces fabae following wounding in Vicia faba

BACKGROUND AND AIMS: Insect damage to plants leads to wound-activated responses directed to healing of damaged tissues, as well as activation of defences to prevent further insect damage. Negative cross-talk exists between the jasmonic acid-based signalling system that is activated upon insect attack and the salicylic acid-based system frequently activated following pathogen infection. Thus, insect attack may compromise the ability of the plant to defend itself against pathogens and vice versa. However, insect herbivory and mechanical wounding have been shown to reduce fungal infections on some plants, although the underlying mechanisms remain to be defined. This work examines the effects of mechanical wounding on rust infection both locally and systemically in the broad bean, Vicia faba and follows changes in oxylipins in wounded leaves and unwounded leaves on wounded plants. METHODS: The lamina of first leaves was wounded by crushing with forceps, and first and second leaves were then inoculated, separately, with the rust Uromyces fabae at various times over a 24 h period. Wounded first leaves and unwounded second leaves were harvested at intervals over a 24 h period and used for analysis of oxylipin profiles. KEY RESULTS Mechanical wounding of first leaves of broad bean led to significantly reduced rust infection in the wounded first leaf as well as the unwounded second leaf. Increased resistance to infection was induced in plants inoculated with rust just 1 h after wounding and was accompanied by rapid and significant accumulation of jasmonic acid and two trihydroxy oxylipins in both wounded first leaves and unwounded second leaves. The two trihydroxy oxylipins were found to possess antifungal properties, reducing germination of rust spores. CONCLUSIONS: These results demonstrate the rapidity with which resistance to pathogen infection can be induced following wounding and provides a possible mechanism by which pathogen infection might be halted.     

Effect of gene Lr34 in the enhancement of resistance to leaf rust of wheat

Summary Leaf rust resistance gene Lr34 is present in many wheat cultivars throughout the world that have shown durable resistance to leaf rust. Fourteen pair-wise combinations of Lr34 and seedling leaf rust resistance genes were developed by intercrossing near isogenic Thatcher lines. In both seedling and adult plant tests homozygous paired combinations of specific resistance genes with Lr34 had enhanced resistance relative to either parent to different numbers of isolates that were avirulent to the additional resistance genes. The TcLr34, 18 line also expressed enhanced resistance to specific isolates virulent to Lr18 in seedling and adult plant stages. In rust nursery tests, homozygous lines were more resistant than either parent, if the additional leaf rust gene conditioned an effective of resistance when present singly. The ability of Lr34 to interact with other genes conditioning effective resistance may contribute to the durability of leaf rust resistance in cultivars with Lr34. Contribution 1453 Agriculture Canada     

Identification of a STS marker linked to the Aegilops speltoides-derived leaf rust resistance gene Lr28 in wheat

 A sequence-tagged-site (STS) marker is reported linked to Lr28, a leaf rust resistance gene in wheat. RAPD (random amplified polymorphic DNA) analysis of near-isogenic lines (NILs) of Lr28 in eight varietal backgrounds was carried out using random primers. Genomic DNA enriched for low-copy sequences was used for RAPD analysis to overcome the lack of reproducibility due to the highly repetitive DNA sequences present in wheat. Of 80 random primers tested on the enriched DNA, one RAPD marker distinguished the NILs and the donor parent from the susceptible recurrent parents. The additional band present in resistant lines was cloned, sequenced, and STS primers specific for Lr28 were designed. The STS marker (Indian patent pending: 380 Del98) was further confirmed by bulk segregation analysis of F₃ families. It was consistently present in the NILs, the resistant F₃ bulk and the resistant F₃ lines, but was absent in recurrent parents, the susceptible F₃ bulk and the susceptible F₃ lines. Received: 20 February 1998 / Accepted: 4 March 1998     

豆科植物上单胞锈菌属—新变种和—中国新记录种（英文）

报道了豆科植物上单胞锈菌属1新变种和中国1新记录种。达乌里黄耆Astragalus dahuricus上的斑点单胞锈菌达乌里黄耆变种Uromyces punctatus var.dahuricus为新变种;山岩黄耆Hedysarum alpinum上的八岳山单胞锈菌Uromyces yatsugatakensis为中国新记录种。提供了详细的形态描述和线条图。研究标本保存在赤峰学院菌物标本室(CFSZ)和中国科学院菌物标本馆(HMAS)。     

中国菊科植物上的柄锈菌属一新种和一新记录(英文)

报道了中国菊科植物上柄锈菌属1新种和1新记录变种。拐轴鸦葱Scorzonera divaricata上的苏尼特柄锈菌Puccinia sonidensis为新种;猫儿菊Hypochaeris ciliata上的山柳菊柄锈菌猫儿菊变种Puccinia hieracii var.hypochaeridis为中国新记录。提供了详细的形态描述和线条图。研究标本保存在赤峰学院菌物标本室(CFSZ)和中国科学院菌物标本馆(HMAS)。     

Mapping and pyramiding of qualitative and quantitative resistance to stripe rust in barley

The identification and location of sources of genetic resistance to plant diseases are important contributions to the development of resistant varieties. The combination of different sources and types of resistance in the same genotype should assist in the development of durably resistant varieties. Using a doubled haploid (DH), mapping population of barley, we mapped a qualitative resistance gene (Rpsx) to barley stripe rust in the accession CI10587 (PI 243183) to the long arm of chromosome 1(7H). We combined the Rpsx gene, through a series of crosses, with three mapped and validated barley stripe rust resistance QTL alleles located on chromosomes 4(4H) (QTL4), 5(1H) (QTL5), and 7(5H) (QTL7). Three different barley DH populations were developed from these crosses, two combining Rpsx with QTL4 and QTL7, and the third combining Rpsx with QTL5. Disease severity testing in four environments and QTL mapping analyses confirmed the effects and locations of Rpsx, QTL4, and QTL5, thereby validating the original estimates of QTL location and effect. QTL alleles on chromosomes 4(4H) and 5(1H) were effective in decreasing disease severity in the absence of the resistance allele at Rpsx. Quantitative resistance effects were mainly additive, although magnitude interactions were detected. Our results indicate that combining qualitative and quantitative resistance in the same genotype is feasible. However, the durability of such resistance pyramids will require challenge from virulent isolates, which currently are not reported in North America.Communicated by J.W. SnapeOregon Agricultural Experiment Station paper No. 11953     

Comparative virulence phenotypes and molecular genotypes of Puccinia striiformis f. sp. tritici, the wheat stripe rust pathogen in China and the United States

Stripe rust (yellow rust) of wheat, caused by Puccinia striiformis f. sp. tritici, is one of the most important diseases in both China and the United States. The Chinese and US populations of the stripe rust fungus were compared for their virulence phenotypes on wheat cultivars used to differentiate races of the pathogen in China and the US and molecular genotypes using simple sequence repeat (SSR) markers. From 86 Chinese isolates, 54 races were identified based on reactions on the 17 Chinese differentials and 52 races were identified based on the 20 US differentials. The selected 51 US isolates, representing 50 races based on the US differentials, were identified as 41 races using the Chinese differentials. A total of 132 virulence phenotypes were identified from the 137 isolates based on reactions on both Chinese and US differentials. None of the isolates from the two countries had identical virulence phenotypes on both sets of differentials. From the 137 isolates, SSR markers identified 102 genotypes, of which 71 from China and 31 from the US. The virulence data clustered the 137 isolates into 20 virulence groups (VGs) and the marker data clustered the isolates into seven molecular groups (MGs). Virulence and SSR data had a low (r = 0.34), but significant (P = 0.01) correlation. Principal component analyses using either the virulence data or the SSR data separated the isolates into three groups: group a consisting of only Chinese isolates, group b consisting of both Chinese and US isolates and group c consisting of mostly US isolates. A neighbour-joining tree generated using the molecular data suggested that the P. striiformis f. sp. tritici populations of China and the US in general evolved independently.     

两系杂交小麦恢复系MR168抗条锈病基因遗传分析及分子标记定位

小麦条锈病是影响杂交小麦普及推广的重要因素。文章利用基因推导法和SSR分子标记技术,研究了温光型两系杂交小麦恢复系MR168的抗条锈性遗传规律及其控制基因染色体位置。结果表明,MR168对CY29、CY31、CY32、CY33等条锈菌生理小种表现高抗至免疫;对SY95-71/MR168杂交组合的正反交F1、BC1、F2和F3群体分单株接种鉴定显示,MR168对CY32号小种的抗性受1对显性核基因控制,该抗病基因来源于春小麦品种辽春10号。利用集群分离分析法(Bulked segregant analysis,BSA)和简单重复序列(Simple sequence repeat,SSR)分子标记分析抗病亲本MR168、感病亲本SY95-71及183个F2代单株,发现了与MR168抗条锈病基因连锁的5个微卫星标记Xgwm273、Xgwm18、Xbarc187、Xwmc269、Xwmc406,并将该基因初步定位在1BS着丝粒附近,暂命名为YrMR168;构建了包含YrMR168的SSR标记遗传图谱,距离YrMR168最近的两个微卫星位点是Xgwm18和Xbarc187,遗传距离分别为1.9 cM和2.4 cM,这两个微卫星标记可用于杂交小麦抗条锈病分子标记辅助育种。     

Identification and molecular tagging of a gene from PI 289824 conferring resistance to leaf rust (Puccinia triticina) in wheat

Host-plant resistance is the most economically viable and environmentally responsible method of control for Puccinia triticina, the causal agent of leaf rust in wheat (Triticum aestivum L.). The identification and utilization of new resistance sources is critical to the continued development of improved cultivars as shifts in pathogen races cause the effectiveness of widely deployed genes to be short lived. The objectives of this research were to identify and tag new leaf rust resistance genes. Forty landraces from Afghanistan and Iran were obtained from the National Plant Germplasm System and evaluated under field conditions at two locations in Texas. PI 289824, a landrace from Iran, was highly resistant under field infection. Further evaluation revealed that PI 289824 is highly resistant to a broad spectrum of leaf rust races, including the currently prevalent races of leaf rust in the Great Plains area of the USA. Eight F₁ plants, 176 F₂ individuals and 139 F_2:3 families of a cross between PI 289824 and T112 (susceptible) were evaluated for resistance to leaf rust at the seedling stage. Genetic analysis indicated resistance in PI 289824 is controlled by a single dominant gene. The AFLP analyses resulted in the identification of a marker (P39 M48-367) linked to resistance. The diagnostic AFLP band was sequenced and that sequence information was used to develop an STS marker (TXW₂₀₀) linked to the gene at a distance of 2.3 cM. The addition of microsatellite markers allowed the gene to be mapped to the short arm of Chromosome 5B. The only resistance gene to be assigned to Chr 5BS is Lr52. The Lr52 gene was reported to be 16.5 cM distal to Xgwm443 while the gene in PI 289824 mapped 16.7 cM proximal to Xgwm443. Allelism tests are needed to determine the relationship between the gene in PI 289824 and Lr52. If the reported map positions are correct, the gene in PI 289824 is unique.     

Characteristic expression of wheat PR5 gene in response to infection by the leaf rust pathogen,Puccinia triticina

TaLr35PR5 gene was obtained from the gDNA and cDNA of TcLr35 wheat. It was induced by Puccinia triticina, ABA and SA, but TaLr35PR5 was induced earlier and its expression level was higher in the incompatible interaction than that in the compatible interaction. In addition, the accumulations of TaLr35PR5 increased stably and showed significant peak challenged by P. triticina at different growth and development periods of TcLr35 wheat while it maintained similar level and changed little in mock inoculated. Western blottings were conducted to confirm that TaLr35PR5 be induced by P. triticina infection at the protein expression level. Similar to the expression patterns of TaLr35PR5 at RNA levels, the accumulations of TaLr35PR5 protein were weak in the seedling stage, then increased to the peak and kept constant levels at the mature stage which is consistent with the expression feature of Lr35 gene as an adult plant resistance gene.