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Melampsora epitea(Pucciniales, Basidiomycota) has been widely known as the main rust pathogen on willows, but its species boundary has been extremely confusing.Melampsora epiteawas often confused with several morphologically similar species, such asM. arctica, M. humilis, andM. epiphylla. Recent DNA-based studies using specimens from North America and Europe suggested thatM. epiteawas a complex of several phylogenetic species. In this study, we examined the species boundary ofM. epiteabased on rDNA phylogeny and the general mixed Yule coalescent (GMYC) model from 534 specimens. Twelve distinct species corresponding to 10 known species and 2 new species were recognized from East Asian specimens. We also evaluated the association of morphological characteristics, geographic origins, and host ranges with phylogenetic relationships. Our results revealed that several previously overlooked morphological characters in uredinial and telial stages were informative in delimitingM. epiteaand allied species. Two novel species,M. salicis-futuraeandM. salicis-triandrae, are described and compared with closely related species. A lectotype forM. epiteaand epitypes forM. epitea, M. epiphylla, andM. humilisare designated to stabilize the use of names. [ABSTRACT FROM PUBLISHER]

Rust fungi in the genus Melampsora usually cause disease on hosts in the Salicaceae. Identification of Melampsora species is often complicated due to few differences in spore morphology and little publicly available comparative sequence data. Weeping willow trees (primarily Salix babylonica and its hybrids) have been reported to be infected by 11 Melampsora species; however, most of these records are based on morphological characterization. New collections of rust fungi on weeping willows from the central USA were analysed using a combination of morphology, ITS and LSU r DNA sequencing, and host data to determine that they represent an undescribed rust fungus, Melampsora ferrinii sp. nov. Additional studies of herbarium material revealed that M. ferrinii has occasionally been collected but identified as M. epitea. In addition to North America, M. ferrinii is also present in South America and has been infecting weeping willows there since at least the 1990s. [ABSTRACT FROM AUTHOR]

In North America Melampsora rusts that parasitize willows (Salix species) have never been adequately studied and mostly have been referred to a collective species, Melampsora epitea (Kunze & Schm.) Thüm, of European origin. Even taxa that are nominally distinct from M. epitea, such as M. abieti-caprearum and M. paradoxa, currently are considered to be "races" of M. epitea. Within the range of our field surveys and collections in the Pacific Northwest and the Southwest only two species of Melampsora thus were expected: M. epitea (including its races) and M. ribesii-purpureae. In this study of Melampsora on 19 species of Salix in the western United States 14 phylogenetic species, or phylotypes, were apparent from nuclear rDNA sequencing of 140 collections or isolates. Our collections of the races of M. epitea, M. abieti-caprearum and M. epitea f. sp. tsugae belonged to one phylotype, termed lineage 'N'. Assuming that M. ribesii-purpureae represents one other phylotype, 12 phylotypes still are unaccounted for by current taxonomy. Moreover Eurasian M. ribesii-purpureae was not closely related to any of the phylotypes reported here. Even more problematic was the resistance of Eurasian species of Salix, including the type host of M. epitea, S. alba, to North American Melampsora, including phylotype 'N', in both the field and in inoculation experiments. These results suggest the need for the description of many new species of Melampsora on Salix in western North America. Additional analyses presented here might guide further research in this direction. [ABSTRACT FROM AUTHOR]

We report the discovery, characterization and validation of 118 single nucleotide polymorphisms (SNPs) for poplar leaf rust Melampsora medusae f. sp. deltoidae identified using a gene-targeted approach in an expressed sequence tag (EST) library. We developed a genotyping assay using the iPLEX™ primer extension method for two multiplex assays of 28 and 22 SNPs. [ABSTRACT FROM AUTHOR]

AFLP analysis was used to examine the genetic structure of the mycoparasite Sphaerellopsis filum on willow rust Melampsora larici-epitea using two sets of samples of a willow clone in a short-rotation coppice planting. The first set was collected from a plot (short strip) in 1998, 1999 and 2000 and the second from another plot (long strip) in 2000. In all, 228 S. filum isolates were typed, 139 AFLP loci scored and 54 AFLP genotypes identified. In the short strip, genotypes sampled in 1998 were no longer detected in subsequent years and genotype diversity fluctuated (0·25–0·68) over the years, indicating that migration had a major impact on the genotype structure. Two distinct groups (average Nei and Li's similarity coefficient between the groups = 0·047) were identified. The group B genotypes were sampled only in 2000. Within the groups, the average similarities were > 0·96. Both the index of association test and the parsimony tree length permutation test suggest that there was a significant clonality in group A while recombination cannot be ruled out in group B. Localized clusters of AFLP genotypes were detected using the software SaTScan that is based on the spatial scan statistic. Possible mechanisms involved in the spread of S. filum in willow coppice plantations are discussed. [ABSTRACT FROM AUTHOR]

The abundance of leaf rust (Melampsora sp.) was assessed on four willow clones in four experimental Estonian willow short-rotation forest plantations. Three plantations were established on poor mineral soil and one was constructed for wastewater purification. Clones 78183 and 81090 were most severely damaged in all four plantations, whereas clones 78021 and 78195 were fairly resistant to rust. In addition to clone type, the number of uredinia on leaves depended on plantation, sampling date, and fertilization. Infection increased significantly during the growing season, and the leaves collected from fertilized plants had more and larger rust pustules than those from unfertilized plants. Uredinia were smaller on older shoots and larger on younger shoots. [ABSTRACT FROM AUTHOR]

1 Host–pathogen interactions in isolated populations may result in the adaptation of pathogens to local hosts. However, results of earlier studies of local adaptation in plant–pathogen systems have been contradictory and it has been suggested that specific, species characteristics, for example distribution, dispersal and the degree of pathogen dependence on the host, are important for the outcome of host–pathogen interactions. In addition, the scale of the study may influence whether or not local adaptation is found. 2 We argue that local adaptation of the pathogen to the host can be expected in a system where: (i) the pathogen is host-specific with a short generation time compared with the host; (ii) populations are isolated, allowing localized evolution to occur; and (iii) the study is performed on a geographical scale exceeding the maximum dispersal range of the interacting species. 3 To test these predictions we examined the within- and among-population variation in resistance and virulence of the plant–pathogen system Salix triandra– Melampsora amygdalinae. The pathogen occurs throughout the whole distribution range of the host, and the area of interest consists of highly isolated, small natural populations. 4 Resistance and virulence differed both within and between populations and all clones showed a unique resistance pattern. We conclude that M. amygdalinae is locally adapted to the host S. triandra as all pathogen populations have a higher probability of infecting sympatric than allopatric hosts. Furthermore, high resistance in the host population was accompanied by a high virulence in the pathogen population, suggesting that high resistance levels in a host population may select for more virulent pathogen populations, or vice versa. 5 The nature of host–pathogen interactions differs among systems, and the dynamics of the interaction between S. triandra and M. amygdalinae is governed by characteristics that have resulted in the evolution of local adaptation. 6 Thus, when studying local adaptation of pathogens to their hosts it is important to consider the biology, as well as the scale of dispersal and spatial distribution of both host and pathogen. [ABSTRACT FROM AUTHOR]

We developed 15 microsatellite loci in the poplar rust fungus, Melampsora larici-populina, using two enrichment protocols. Polymorphism of each locus was assessed on a panel of 30 isolates, comprising three subpanels (world, regional and local scales). Thirteen loci were polymorphic with three to eight alleles detected. The 15 loci were also tested on five related Melampsora species, M. allii-populina, M. medusae f. sp. deltoidae, M. larici-tremulae, M. rostrupii and M. pinitorqua, and partial or global cross-amplification events were detected. [ABSTRACT FROM AUTHOR]

The 5' end of the large subunit (LSU) region and the entire internal transcribed spacer (ITS) region of ribosomal DNA were sequenced from 11 species or special forms of Melampsora on Salix, and three species on Populus. For all the species, except for M. larici-epitea and M. coleosporioides, the sequences in both the examined regions were identical within a species. Within M. larici-epitea, f. sp. larici-epitea typica and f. sp. larici-retusae shared the same sequences which slightly differed from that of f. sp. larici-daphnoides. In the LSU region, M. larici-epitea, M. capraearum and the stem-infecting form on S. viminalis shared the same sequence and the Far-Eastern species M. epiphylla differed from them only slightly (p distance 0.006), indicating that they may share a common ancestral lineage. M. amygdalinae and M. coleosporioides formed a distict group (bootstrap value 100% for combined ITS and LSU data). M. larici-epitea and M. ribesii-purpurea, both belonging to the M. epitea complex, appeared to be distinct. The molecular data also suggest that the differences in certain characteristics, such as the thickness of teliospore walls and host specificity, may have evolved relatively recently. [ABSTRACT FROM AUTHOR]

Abstract Using a leaf disc method, 19 isolates of the poplar rust, Melampsora larici-populina , and one isolate of M.?populnea from England were inoculated on to 25 poplar clones belonging to Populus nigra and P.?trichocarpa , and hybrids between P. deltoides and P. nigra , P. deltoides and P. trichocarpa , P.?tacamahaca and P.?trichocarpa , and P. alba and P. tremula . Disease was scored based on the pustule area and inoculum density. In terms of whether sporulating uredinia formed, the 19 isolates showed seven different patterns to the tested poplar clones. The majority of the rust isolates infected P. nigra P3090 and Vereecken, P.?nigra ?? P. deltoides Casale and Tasman, P. tacamahaca ?? trichocarpa 36 and Balsam Spire, and P.?trichocarpa Blom. Populus trichocarpa ?? P. deltoides 69039/4 was infected by only three isolates collected from southern England. No visible symptoms appeared on P. alba ?? P. tremula Tower and P.?trichcarpa? ? P. deltoides ?? P. deltoides 76028/5 in inoculations with M. larici-populina isolates. Populus alba? ?P.?tremula Tower was infected only by M. populnea . When M. larici-populina isolates were tested using AFLP, no differences were found either between isolates from different geographical regions or between those having narrow spectrum of virulence and those showing wide spectrum of virulence on the tested clones. The results suggest that the UK rust populations possess virulences which were found in races E1, E2, E3 and E4 in continental Europe and that rust having virulence patterns similar to race E4 has occurred in UK poplar plantations since 1996. [ABSTRACT FROM AUTHOR]

A total of 174Salix(willow) clones belonging to 57 species and 14 interspecific hybrids were inoculated with seven pathotypes ofMelampsora larici-epiteausing the leaf disc method. Infection types were scored based on the uredinial pustule area data and the inoculum density. A close correlation (R2 = 0·82) was found between the average pustule area and the average number of spores produced. Most of the willows were also assessed in the field for rust in 1999. Most willow clones belonging to the species native to western Europe were infected by the rust. In inoculation experiments, uredinia developed on 46S. viminalisclones, out of a total of 47. In the field, all theS. viminalisclones were infected by rust. Within the subgenusVetrix, eight out of the 17 willow species that originated from North and South America produced rust pustules in inoculation experiments. Of these,S. pellitawas most susceptible.Salix irrorataandS. lasiolepsisvar.bracelinaeproduced well developed pustules after inoculation but no rust infections were detected in the field. In both leaf disc tests and field assessments, no rust infections were found onS. candida,S. cordata,S. drummondiana,S. eriocephala,S. hookeriana,S. houghtonii,S. humilis,S. rigidavar.mackenzianaandS. syrticola. Of 12 species of subgenusVetrixnative to northeast Asia and Japan, onlyS. kochianawas susceptible both in inoculation tests and in the field.Salix rossicaproduced no symptoms in leaf disc tests but showed low levels of infection in the field. The maximum infection type scores in leaf disc tests were highly significantly correlated with field disease severity scores (Spearman rank correlation coefficient was 0·76,P < 1 × 10−10). [ABSTRACT FROM AUTHOR]

Current taxonomy places all rust fungi that occur on willow (Salix spp.) in North America in one species complex, Melampsora epitea Thüm. Characteristics of M. epitea isolates from the Canadian arctic were compared to M. epitea isolates from temperate regions of North America. Sequences from internal transcribed spacer (ITS) regions of rDNA were obtained from urediniospores from rust-infected Salix leaves collected in the Canadian arctic and in Minnesota and compared. Phylogenetic analysis of nuclear ribosomal ITS regions indicated that arctic M. epitea samples were divergent from temperate M. epitea isolates, perhaps in part because all rusts examined diverged according to host species. Four urediniospore characteristics were examined: area, circularity (shape factor), major axis length and spine density. Statistically significant (P < 0.05) differences were observed for spine density among all host species except S. nigra and D. bebbiana. However major axis length differed between these species. These results represent the first evidence that arctic and temperate Melampsora species on Salix hosts in North America have evolved distinct molecular and morphological characters. [ABSTRACT FROM AUTHOR]

The article analyzes the inheritance of resistance to Melampsora on Salix viminalis, the variation in resistance over space and time, and rust infection rate in relation to the geographic origin of the host. Four series of experiments located in south-central and southernmost Sweden were used for the analysis. The analysis showed that there was considerable additive genetic variation for rust resistance, that the results have low repeatability over space and time, and that the material from southernmost Sweden was most sensitive to the rusts occurring in South Sweden.

Three isolates of Cladosporium tenuissimum were prepared by culturing a field isolate of this organism separately on three races of Melampsora larici-populina. In a subsequent experiment, the production of uredinia by these three races on three cultivars of Populus X euramericana was usually lowest in the presence of the isolate of C. tenuissimum which had been cultured on the particular race. This apparent adaptation of the isolates of the hyperparasite to particular races of the rust, i. e. "physiologic specialisation" in the relationship, is confirmed by the significant race x C. tenuissimum isolate term in the ANOVA. [ABSTRACT FROM AUTHOR]

Infection types were assessed when four cultivars of Populus deltoides Marsh, were inoculated with six races of Melampsora medusae Thüm, and incubated in combinations of light intensity (100, 500 and 1000 μEm-2s-1) and temperature ( 15 and 25 °C). Resistance in the cultivars was always at a maximum when the race/cultivar complexes were incubated in the high light intensity (1000 μEm-2s-1)/high temperature (25°C) regime. Increasing light intensity was generally associated with reduced infection type in the cultivars; the reduction was more pronounced in an incubation temperature of 25 than 15 °C. The potential epidemiological significance of the results is discussed. [ABSTRACT FROM AUTHOR]

Uredospores of Melampsora larici-populina and Melampsora allii-populina show some reactions in common physical factors. In both species germination requires high relative humidity and darkness has adverse effects. For other characters, differences appear in their behavior. The optimum temperature for germination is 13°C for M. larici-populina but 16°C for M allii-populina. M. larici-populina uredospores germinate more slowly but their germ tubes grow faster. Above 16°C, germination of M. laricipopulnaa spores is reduced and temperatures above 30°C induce a delay in subsequent germination. However, their germination capacity is less affected by heavy and long frosts as compared with M. allii populina.

Melampsora medusae Thüm. and M. larici-populina Kleb. are the most popular conifer rusts, that have been found in Australia. M. medusae and M. larici-populina differ in the size, shape and wall echinulation of the urediniospores, in the apical wall thickness of their uredinial paraphyses, in the position of the telia on the host leaf, and in their host range. M. medusae has the widest host range, but it occurs mainly on Populus deltoides clones and hybrids. M. larici populina occurs mainly on P. nigra var. italica.

Eighteen isolates of the rust fungus Melampsora from different locations in England were tested for pathogenicity to a large range of willow clones (Salix spp.) in experiments involving inoculation of leaf discs. Seventeen of the isolates were of leaf-infecting M. epitea var. epitea, 16 of which represented forms which alternated on Larix and one of which alternated on Ribes. The remaining isolate was of uncertain identity. Two experiments were carried out. In the first exp>eriment, 24 willow clones consisting of 20 Salix species and interspecific hybrids were inoculated with eight isolates from clones of S. viminalis. In the other experiment, 77 clones from 57 species or hybrids were inoculated with 10 isolates from several Salix spp. The M. epitea var. epitea isolates from S. viminalis clones were all similarly pathogenic, whilst most of the other isolates expressed distinct host specificity. Eight distinct pathotypes were recognized within M. epitea var. epitea. All except one of these alternated on Larix and could be assigned to three formae speciales which had been reported previously in Europe: four pathotypes to f.sp. larici-epitea typica, two to f.sp. larici-retusae, and one to f.sp. tarici-daphnoides. The Ribes-alternating pathotype of M. epitea var. epitea infected only S. purpurea. Nine differential willow hosts are proposed as reference clones to distinguish between the larch-alternating pathotypes, the Ribes-alternating rust and the ‘stem-infecting’ form. The extent of pathogenic variation encountered amongst sexually reproducing rusts suggests that more pathotypes probably exist and will arise in future in response to selection given by long-term clonal willow plantings. [ABSTRACT FROM AUTHOR]

Disease severity, based on six parameters (time from inoculation to flecking and eruption of uredinia, uredinial density and the amounts of urediniospores produced), was assessed on leaf discs cut from four cultivars of Populus spp. raised with either a long ( 15 h) or a short (10 h) photoperiod. The discs were inoculated with race 4 of Melampsora medusae and subsequently incubated with either a long (15 h) or a short (10 h) photoperiod. While disease severity, based on most parameters, was lower in discs from the continuing long photoperiod (15 h pre-and 15 h post-inoculation) than from the continuing short photoperiod (10 h pre- and 10 h post- inoculation), maximum seventy was developed by discs given a combination of a short pre- and a long post-inoculation photoperiod. The relative contribution of the cultivar, the pre- and the post-inoculation photoperiod and their second- and third-order interactions to variation in disease severity depended on the parameter employed to assess severity. The parameters used are elements of disease monocycles and their possible significance in modelling epidemics is discussed. [ABSTRACT FROM AUTHOR]

Melampsora species and their hybrids are obligate parasites of Populus and Salix species worldwide. The increasing interest in Populus and Salix for biomass and fibre production necessitates genetic markers for population studies of Melampsora spp. Libraries enriched for simple sequence repeats were used to develop five microsatellite markers for Melampsora medusae and Melampsora larici-populina. The variation detected by these markers will be valuable for phylogenetic and population genetic studies, substantiate putative hybrids, and deployment of resistant poplar clones. [ABSTRACT FROM AUTHOR]

The article presents information on melampsora euphorbiae, a new disease found on Euphorbia rigidain in Turkey. Euphorbia rigida occurs widely in Turkey and is a weed of gardens and uncultivated areas. Symptoms include the drying of leaves before normal flowering season. It occurred mostly on the lower surface of leaves and on stems. Melampsora euphorbiae has clear potential as biological control agent against other Euphorbia species. The rust disease poses more of a threat to the horticultural trade of E. rigidain at present.