Virulence Phenotypes of a Worldwide Collection of Puccinia triticina from Durum Wheat

ABSTRACT A total of 78 isolates of Puccinia triticina from durum wheat from Argentina, Chile, Ethiopia, France, Mexico, Spain and the United States and 10 representative isolates of P. triticina from common wheat from the United States were tested for virulence phenotypes on seedling plants of 35 near-isogenic lines of Thatcher wheat. Isolates with virulence on lines with leaf rust resistance genes Lr10, Lr14b, Lr20, Lr22a, Lr23, Lr33, Lr34, Lr41, and Lr44 represented the most frequent phenotype. Cluster analysis showed that P. triticina from durum wheat from South America, North America, and Europe had an average similarity in virulence of 90%, whereas isolates from Ethiopia were <70% similar to the other leaf rust isolates collected from durum wheat. Of the 11 isolates from Ethiopia, 7 were avirulent to Thatcher and all near-isogenic lines of Thatcher. The isolates from common wheat had an average similarity in virulence of 60% to all leaf rust isolates from durum wheat. P. triticina from durum wheat was avirulent to many Lr genes frequently found in common wheat. It is possible that P. triticina currently found on durum wheat worldwide had a single origin, and then spread to cultivated durum wheat in North America, South America, and Europe, whereas P. triticina from Ethiopia evolved on landraces of durum wheat genetically distinct from the cultivated durum lines grown in Europe and the Americas.     

Leaf Rust on Aegilops speltoides Caused by a New Forma Specialis of Puccinia triticina

ABSTRACT A leaf rust attacking Aegilops speltoides in its natural habitat is reported for the first time. It was found in two locations in northern and central Israel. The two collections from A. speltoides resemble wheat leaf rust, Puccinia triticina, in most spore dimensions, in the morphology of the substomatal vesicle of the urediniospore, and in DNA content in pycniospore nuclei. Similarly to P. triticina isolates from wheat, isolates taken from A. speltoides are compatible with Thalictrum speciosissimum as an aecial host and they are crossed easily with wheat leaf rust isolates. However, isolates from A. speltoides differ from wheat leaf rust in their telial host range. They are avirulent to cultivated wheat cultivars, but attack hundreds of A. speltoides accessions that were immune to wheat leaf rust. This distinct host preference justifies delineation of the newly found leaf rust as a forma specialis (f. sp. speltoides) within P. triticina.     

Genetic Variation and Virulence on Lr26 in Puccinia triticina

ABSTRACT The genetic relationships between isolates of Puccinia triticina virulent on wheat with the Lr26 resistance gene were studied. The diversity within and between isolates of P. triticina from Israel, Europe, and the United States was determined by virulence on near-isogenic Thatcher lines and by random amplified polymorphic DNA. According to the molecular markers, isolates that were virulent on Lr26 had diversity levels similar to those of Lr26 nonpathogenic isolates. Distances between subpopulations of isolates virulent and avirulent on Lr26 varied and were unrelated to the Lr26 virulence phenotype. Cluster analysis suggested four groups, three of which were closely associated with the geographical origin of the isolates-Israel, the United States, and Europe. All four groups included both Lr26 virulent and avirulent pathotypes. The results showed that Lr26 virulent rust pathotypes are as genetically dissimilar as the rest of the population. The cluster analysis showed that the rust population in Israel includes at least two different subpopulations, both of which contain Lr26 virulent and Lr26 avirulent isolates.     

Relationship Among Genes Conferring Partial Resistance to Leaf Rust (Puccinia triticina) in Wheat Lines CI 13227 and L-574-1

ABSTRACT This study describes the segregation of genes for resistance to the fungus Puccinia triticina in a cross between partially resistant wheat lines L-574-1 and CI 13227 with two and four genes for resistance, respectively. The objectives of this study were to use parental, F(1), F(2), and backcross populations to quantify maternal effects, degree of dominance, and transgressive segregation, and to determine whether CI 13227 and L-574-1 share any resistance genes for long latent period or small uredinia. In two experiments conducted in the greenhouse, the uppermost leaf of adult wheat plants was inoculated prior to heading with P. triticina. On days 6 to 21 after inoculation, the number of uredinia that erupted from the leaf surface was counted and used to calculate the mean latent period (MLP). The length and width of five arbitrarily selected uredinia were measured and used to calculate uredinium area. Midparent values, degree of dominance, and broad-sense heritability were calculated for MLP and uredinium area. For experiment A, MLP values for CI 13227, L-574-1, F(1), and F(2) generations were 12.2, 10.5, 10.2, and 10.6 days, respectively. For experiment B, MLP values for CI 13227, L-574-1, F(1), F(2), backcross to CI 13227, and backcross to L-574-1 were 12.3, 10.0, 10.6, 10.8, 11.1, and 10.0 days, respectively. The inheritance of long latent period was partially recessive, and no maternal effect was present (P = 0.62 to 0.87 for the comparison of means in reciprocal crosses). Broad-sense heritability for MLP ranged from 0.72 to 0.74, and there was transgressive segregation in the F(2) and backcross populations. Uredinia of the F(1) generation were slightly larger than uredinia for CI 13227. The inheritance of uredinium size was partially dominant, and no maternal effect was present (P = 0.5 to 0.63). Broad-sense heritability for uredinium area ranged from 0.36 to 0.73 and transgressive segregation was present in the F(2) and backcross populations. The results for MLP indicate that lines CI 13227 and L-574 likely share one gene for resistance (based on F(1) values) but not two genes (based on the presence of transgressive segregation). CI 13227 and L 574-1 appear to have at least one gene difference for uredinium area. The linear relationship between uredinium area regressed onto MLP was significant (P < 0.001) and r(2) values ranged from 0.14 to 0.26. These results indicate that the resistance in CI 13227 and L-574-1 could be combined to create wheat cultivars with greater partial resistance than that possessed by either parent based on MLP or uredinium size.     

Virulence of Puccinia triticina in Turkey and leaf rust resistance in Turkish wheat cultivars

Leaf rust caused by Puccinia triticina is a common disease on wheat in the coastal regions of Turkey. Collections of P. triticina from infected wheat leaves were obtained from the main wheat production zones of Turkey in 2009 and 2010. A total of 104 single uredinial isolates were tested for virulence on 20 lines of Thatcher wheat that differ for single leaf rust resistance genes. Forty-four different virulence phenotypes were identified over both years. Four phenotypes were found in both years. Phenotype FHPTQ found in 2009, with virulence to genes Lr2c, Lr3, Lr16, Lr26, Lr3ka, Lr17a, Lr30, LrB, Lr10, Lr14a, Lr18, Lr3bg, and Lr14b, was the most common phenotype at 15.4 % of the total isolates. Forty-three winter and spring wheat cultivars from Turkey were tested as seedlings with 13 different P. triticina virulence phenotypes from Canada, the US and Turkey. The infection types on the cultivars were compared with infection types on the Thatcher near isogenic lines to postulate the presence of seedling leaf rust resistance genes in the cultivars. Resistance genes Lr1, Lr3a, Lr10, Lr14a, Lr17a, Lr20, Lr23, and Lr26 were postulated to be present in the Turkish wheat cultivars. DNA of the wheat cultivars was tested with PCR markers to determine the presence of the adult plant resistance genes Lr34 and Lr37. Marker data indicated the presence of Lr34 in 20 cultivars and Lr37 in three cultivars. Field plot evaluations of the wheat cultivars indicated that no single Lr gene conditioned highly effective leaf rust resistance. Resistant cultivars varied for combinations of seedling and adult plant resistance genes.     

Gene Action and Linkage of Avirulence Genes to DNA Markers in the Rust Fungus Puccinia graminis

ABSTRACT Two strains of the wheat stem rust fungus, Puccinia graminis f. sp. tritici, were crossed on barberry, and a single F(1) progeny strain was selfed. The parents, F(1), and 81 F(2) progeny were examined for virulence phenotypes on wheat differential cultivars carrying stem rust resistance (Sr) genes. For eight Sr differentials, phenotypic ratios are suggestive of single dominant avirulence genes AvrT6, AvrT8a, AvrT9a, AvrT10, AvrT21, AvrT28, AvrT30, and AvrTU. Avirulence on the Sr; (Sr 'fleck') differential showed phenotypic ratios of approximately 15:1, indicating epistatic interaction of two genes dominant for avirulence. Avirulence on Sr9d favored a 3:13 over a 1:3 ratio, possibly indicating two segregating genes-one dominant for avirulence and one dominant for avirulence inhibition. Linkage analysis of eight single dominant avirulence genes and 970 DNA markers identified DNA markers linked to each of these avirulence genes. The closest linkages between AvrT genes and DNA markers were between AvrT6 and the random amplified polymorphic DNA marker crl34-155 (6 centimorgans [cM]) AvrT8a and the amplified fragment length polymorphism marker eAC/mCT-197 (6 cM) and between AvrT9a and the amplified fragment length polymorphism marker eAC/mCT-184 (6 cM). AvrT10 and AvrTU are linked at distance of 9 cM.     

Effects of Brown Rust caused by Puccinia recondita on Wheat

Abstract

Plants of susceptible and resistant varieties were inoculated with the brown rust pathogen Puccinia recondita. Rust reduced the average plant height, weight of grain, volume of grain and yield of susceptible varieties compared with healthy controls. Two varieties, Lerma Rojo and E.871 were resistant and are recommended for use in further hybridisation work.     

Evaluation of Wheat Leaf Rust Resistance Genes in 10 Wheat Genotypes

Journal of Plant Diseases and Protection - Wheat leaf rust (Puccinia triticina) is one of the most important plant diseases in the world, and growing resistant cultivars is the most economical,...     

Simple Sequence Repeat Diversity of a Worldwide Collection of Puccinia triticina from Durum Wheat

ABSTRACT Isolates of Puccinia triticina collected from durum wheat from Argentina, Chile, Ethiopia, France, Mexico, Spain, and the United States were analyzed with 11 simple sequence repeat (SSR) markers in order to determine the genetic relationship among isolates. These isolates also were compared with P. triticina isolates from common wheat from North America, and an isolate collected from Aegilops speltoides from Israel, to determine genetic relationships among groups of P. triticina found on different telial hosts. The large majority of isolates from durum wheat were identical for SSR markers or had <8% genetic dissimilarity, except for isolates from Ethiopia, which had 55% dissimilarity with respect to the other durum isolates. Isolates from common wheat had >70% genetic dissimilarity from isolates from durum wheat, and the isolate from A. speltoides was >90% dissimilar from all isolates tested. Analysis of molecular variance tests showed significant levels (P = 0.001) of genetic differentiation among regions and among isolates within countries. Isolates of P. triticina from durum wheat from South America, North America, and Europe were closely related based on SSR genotypes, suggesting a recent common ancestor, whereas P. triticina from Ethiopia, common wheat, and A. speltoides each had distinct SSR genotypes, which suggested different origins.     

A Study on the Phylogeny of the Dyer's Woad Rust Fungus and Other Species of Puccinia from Crucifers

ABSTRACT The identity of a Puccinia species occurring on the introduced weed dyer's woad (Isatis tinctoria) was studied using sequences from the internal transcribed spacer of the nuclear ribosomal DNA. The relationship of this fungus to other Puccinia species occurring on the family Brassicaceae in Europe and North America was examined, and we tested the hypothesis that P. thlaspeos and P. monoica are correlated species. The data suggest that the Puccinia species from dyer's woad is closely related to the North American species P. consimilis and may be derived from an indigenous strain of P. consimilis that switched hosts. Thus, the Puccinia species from dyer's woad is probably native to North America and is unlikely to cause disease epidemics on indigenous plants if used as a biological control agent against dyer's woad. P. thlaspeos appears to be polyphyletic and, therefore, P. thlaspeos and P. monoica do not appear to be correlated species. Additional DNA sequence data will be needed to clarify further the phylogeny of Puccinia species on the family Brassicaceae.     

43个中国小麦品种(系)抗叶锈性研究

 选用12个墨西哥叶锈菌生理小种对43个中国小麦品种(系)所携带的抗叶锈病基因进行了推导,在25个品种(系)中推导出6个抗叶锈基因Lr1,Lr10,Lr13,Lr14a,Lr16和Lr26,9个品种(系)对本试验所使有的12个叶锈菌生理小种都表现感病反应,另有9个品种(系)携带未知的抗叶锈基因。在墨西哥2个地点进行的田间成株期抗叶锈性试验表明,12个品种(系)表现慢叶锈性,在将来的抗病育种中有一定的应用价值。     

Preinoculation Effects of Light Quantity on Infection Efficiency of Puccinia striiformis and P. triticina on Wheat Seedlings

ABSTRACT In a previous study under controlled conditions, a model was developed to predict the infection efficiency for the wheat leaf and stripe rust fungi based on temperature and dew period during the 24 h after inoculation. The two pathogens differed in their maximum infection efficiency under controlled conditions for temperature and dew period, the infection efficiency was 12 times greater for Puccinia triticina than for P. striiformis. In the present study, the model was validated by field results to predict P. triticina infection efficiency as a function of temperature and dew period only. However, this model failed to predict infection efficiency caused by P. striiformis in the field. The model was adapted to include the effects of light quantity on infection efficiency. Wheat seedlings, grown in climate-controlled rooms and exposed to various regimes of light duration and intensity for 24 h in either field or controlled conditions, were inoculated and incubated in climate-controlled rooms under optimal dew and temperature conditions. Quantity of natural or artificial light (light intensity x duration) received by the plants prior to inoculation enhanced infection efficiency of wheat seedlings inoculated by P. striiformis. Infection efficiency increased from 0.4 to 36% depending on the light quantity according to a Richards' function. For stripe rust, three environmental variables, preinoculation light quantity received by the plants, postinoculation temperature, and postinoculation dew period, were used for fitting a model for infection efficiency measured in the field.     

Genetic Differentiation of Puccinia triticina Populations in Central Asia and the Caucasus

ABSTRACT Isolates of Puccinia triticina collected from common wheat in the Central Asia countries of Kazakhstan, Uzbekistan, Tajikistan, and Kyrgyzstan and the Caucasus countries of Azerbaijan, Georgia, and Armenia were tested for virulence to 20 isolines of Thatcher wheat with different leaf rust resistance genes and molecular genotype at 23 simple sequence repeat (SSR) loci. After clone correction within each country, 99 isolates were analyzed for measures of population diversity, variation at single SSR loci, and for genetic differentiation of virulence phenotypes and SSR genotypes. Isolates from Central Asia and the Caucasus were also compared with 16 P. triticina isolates collected from common wheat in North America that were representative of the virulence and molecular variation in this region and two isolates collected from durum wheat in France and the United States. Populations from the Caucasus, Uzbekistan, Tajikistan, and Kyrgyzstan were not significantly (P > 0.05) differentiated for SSR variation with F(st) and R(st) statistics. Populations from the Caucasus, Uzbekistan, Tajikistan, and Kyrgyzstan were significantly (P < 0.05) differentiated from the populations in South and North Kazakhstan for SSR variation. All populations from Central Asia and the Caucasus were significantly differentiated from the North American isolates and isolates from durum wheat for SSR variation and virulence phenotypes. There was a correlation between virulence phenotype and SSR genotype among individual isolates and at the population level. Mountain barriers may account for the differentiation of P. triticina geographic populations in Central Asia and the Caucasus.     

Genetic differentiation of the wheat leaf rust fungus Puccinia triticina in Europe

The objective of this study was to determine whether genetically differentiated groups of Puccinia triticina are present in Europe. In total, 133 isolates of P. triticina collected from western Europe, central Europe and Turkey were tested for virulence on 20 lines of wheat with single leaf rust resistance genes, and for molecular genotypes with 23 simple sequence repeat (SSR) markers. After removal of isolates with identical virulence and SSR genotype within countries, 121 isolates were retained for further analysis. Isolates were grouped based on SSR genotypes using a Bayesian approach and a genetic distance method. Both methods optimally placed the isolates into eight European (EU) groups of P. triticina SSR genotypes. Seven of the groups had virulence characteristics of isolates collected from common hexaploid wheat, and one of the groups had virulence characteristics of isolates from tetraploid durum wheat. There was a significant correlation between the SSR genotypes and virulence phenotypes of the isolates. All EU groups had observed values of heterozygosity greater than expected and significant fixation values, which indicated the clonal reproduction of urediniospores in the overall population. Linkage disequilibria for SSR genotypes were high across the entire population and within countries. The overall values of R_ST and F_ST were lower when isolates were grouped by country, which indicated the migration of isolates within Europe. The European population of P. triticina had higher levels of genetic differentiation compared to other continental populations.     

国际上小麦叶锈菌生理小种鉴别寄主及其小种命名方法

由于地理生态条件、叶锈菌群体结构、研究历史和研究方法等的差异,不同国家和地区采用相应的小麦叶锈菌鉴别寄主和小种命名方法。美洲、中国、欧洲、埃及、南非等国家和地区均采用以Thatcher为遗传背景的分别含有Lr1、Lr2 a、Lr2 c、Lr3、Lr9、Lr16、Lr24、Lr26、Lr3 ka、Lr11、Lr17和Lr30基因的近等基因系或单基因系作为小麦叶锈菌鉴别寄主,但附加的辅助鉴别品种不尽相同;澳大拉西亚和印度的鉴别寄主自成体系。这种格局不利于国家间研究结果的对比和交流。因此,建立一套国际通用鉴别体系实属当务之急。     

Wheat Leaf Rust Uredospore Production on Adult Plants: Influence of Leaf Nitrogen Content and Septoria tritici Blotch

ABSTRACT Leaf rust uredospore production and lesion size were measured on flag leaves of adult wheat plants in a glasshouse for different lesion densities. We estimated the spore weight produced per square centimeter of infected leaf, per lesion, and per unit of sporulating area. Three levels of fertilization were applied to the plants to obtain different nitrogen content for the inoculated leaves. In a fourth treatment, we evaluated the effect of Septoria tritici blotch on leaf rust uredospore production. The nitrogen and carbon content of the spores was unaffected or marginally affected by lesion density, host leaf nitrogen content, or the presence of Mycosphaerella graminicola on the same leaf. In leaves with a low-nitrogen content, spore production per lesion was reduced, but lesion size was unaffected. A threshold effect of leaf nitrogen content in spore production was however, evident, since production was similar in the medium- and high-fertilizer treatments. In leaves inoculated with M. graminicola and Puccinia triticina, the rust lesions were smaller and produced fewer spores. The relationships among rust lesion density, lesion size, and uredospore production were fitted to a model. We determined that the density effect on spore production resulted mainly from a reduction in lesion size, the spore production per unit of sporulating surface being largely independent of lesion density. These results are consistent with those obtained previously on wheat seedlings. The main difference was that the sporulation period lasted longer in adult leaves.     

小麦叶锈菌越夏与气象因子相关性初步分析

小麦叶锈病是一种严重威胁小麦安全生产、依靠气流传播的真菌病害,近年来发生呈逐年加重趋势。为明确气象因子对小麦叶锈菌越夏的影响,本研究通过对全国698个气象站点7月-8月最热10 d的日均温和平均日最高气温进行回归分析,对7月-8月0 cm平均地温、平均风速、平均降水量、平均日照时数和平均相对湿度进行空间插值,提取了93个小麦叶锈菌越夏调查点的气象数据,再与调查点小麦叶锈菌能否越夏进行相关性分析,结果显示小麦叶锈菌越夏与7月-8月最热10 d日均温和最热10 d平均日最高气温之间存在极显著相关性(P<0.01),与其他气象因子相关性不显著(P> 0.05),结果为小麦叶锈病的越夏区划奠定了基础。