A new species of Melampsora rust on Salix elbursensis from Iran

A rust fungus was found causing stem cankers on 1‐ to 5‐year‐old stems of Salix elbursensis in the north west of Iran. The rust also forms uredinia on leaves and flowers of the host willow. Light and scanning electron microscopy revealed that the new rust is morphologically distinct from several Melampsora species occurring on the willows taxonomically close to S. elbursensis, but indistinguishable from Melampsora larici‐epitea. Examination of the internal transcribed spacer (ITS) region of the ribosomal DNA suggested that the rust fungus is phylogenetically close to Melampsora allii‐populina and Melampsora pruinosae on Populus spp. Based on both the morphological characteristics and the ITS sequence data, the rust is described as a new species –Melampsora iranica sp. nov.     

Melampsora and Marssonina pathogens of poplars and willows in New Zealand

New Zealand has hosted three Melampsora species attacking poplars (Populus spp.), namely, Melampsora larici-populina, Melampsora medusae and for a single season, Melampsora medusae-populina, a unique interspecific hybrid. The predominant species, M. larici-populina, over-winters via larch and each year new races appear causing defoliation of previously rust-resistant cultivars. Melampsora medusae also occurs in some seasons following over-wintering on certain hosts or by aerial transport from Australia. Willows (Salix spp.) host four Melampsora species, Melampsora coleosporioides, Melampsora epitea var. epitea and two unidentified species attacking Salix viminalis and Salix daphnoides/Salix incana× open pollinated hybrids, respectively. The host range and pathogenicity of these species have remained static as no breakdown in host resistance has been observed. The anthracnose fungi, Marssonina brunnea and Marssonina castagnei on poplar, and Marssonina salicicola on tree willows occur throughout New Zealand. All three species can cause severe defoliation of susceptible cultivars in moist districts where annual rainfall exceeds 1000 mm. Although all form abundant microconidia during autumn, the Drepanopeziza states have never been observed in New Zealand. During an unusually wet summer (199–93), a new strain of Marssonina salicicoa appeared which defoliated the previously resistant cultivar, salix matsudana × salix alba cv. 1002 The importance of monitoring the morphological (conidial dimensions, DNA fingerprints) and physiological (host range and pathogenicity) attributes of local populations of Melampsora and Marssonina species is discussed.     

The Status of Melampsora pinitorqua Rostr. in Italy1

Present knowledge of host range and distribution of Melampsora pinitorqua Rostr. in Italy is reported. Melampsora larici-tremulae, which occurs at high altitude in the Apennines and the Alps and infects only larch, can infects pine also in artificial conditions.     

Physiologie in vitro des basidiospores de Melampsora pinitorqua Conséquences pour la compréhension des infections

Physiology of in vitro germination of Melampsora pinitorqua Rostr. basidiospores; consequences for the understanding of the infection process. The in vitro germination of Melampsora pinitorqua Rostr. basidiospores is affected by several environmental factors: temperature, moisture, and by host substances: shoot diffusates, epicuticular waxes, terpenes. The failure of basidiospore spraying inoculations and the possible resistance factors of pines are discussed in view of the results obtained.     

A review of exapted resistance to diseases of Populus

The cultivation of hybrid poplar in the Pacific North-west (PNW) has expanded in the last 15 years. Native Populus trichocarpa is susceptible to many pests and fungal pathogens but its interspecific hybrids were largely disease-free until 1991 when Melampsora medusae f. sp. deltoidae first appeared in the region. Genetic analyses of resistance in the PNW, and elsewhere, reveal a pattern whereby genes for resistance are inherited in interspecific hybrids from the exotic, noncoevolved Populus parent. With some pathogen/poplar hybrid combinations, this resistance segregates in the F₁ generation, but with others, only in the F₂. Such exapted resistance is now known to occur in P. trichocarpa (versus the exotic, eastern North American rust species, M. medusae f. sp. deltoidae), in Populus deltoides (versus the Eurasian rust, Melampsora larici-populina, the PNW population of Septoria populicola, and an undescribed PNW eriophyid mite), and in Populus maximowiczii (versus Melampsora occidentalis, and the PNW populations of Venturia populina, S. populicola, and Linospora tetraspora).     

Morphology and ultrastructure of uredospores of Melampsora larici-populina Kleb1

The morphology and infrastructure is compared for uredospores of Melampsora larici-populina Kleb., collected from the leaves of Populus nigra and P. trichocarpa. Though the spores differed in pigmentation it was not possible to show significant differences in their morphology and ultrastructure.     

Ecophysiologie du stade urédien de Melampsora larici-populina Kleb. et de M. allii-populina Kleb.

Ecophysiology of the uredial states of Melampsora larici-populina Kleb. and M. allii-populina Kleb . Reactions of M. larici-populina and M. allii-populina urédiospores for germination and germ tubes growth to humidity, light and temperature are compared. Differences between the two species suggest that M. allii-populina is more thermophilic.     

Germination of Melampsora larici-populina uredospores on poplar leaves1

Using an electron scanning microscope the germination of Melampsora larici-populina ure dospores was observed on the lower leaf surfaces of a susceptible poplar clone Populus trichocarpa and a resistant one P. בSerotina de Poitou’. The observations were made from a few hours to more then a day after placing the uredospores on the leaf surfaces.     

Life cycle of Melampsora larici‐epitea on short‐rotation cultures of Salix burjatica

The host alternation of Melampsora larici‐epitea occurring on Salix burjatica in experimental short‐rotation cultures in Finland was studied by inoculation tests. Larix sibirica was tested as the most probable alternate host. It was inoculated with rust basidiospores, and the life cycle of the pathogen was succesfully completed by inoculating the willow with aeciospores developed on larch needles.     

Physiologic specialisation in the hyperparasitism of races of Melampsora larici-populina by isolates of Cladosporium tenuissimum

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. et. “physiologic specialisation” in the relationship, is confirmed by the significant race x C. tenuissimum isolate term in the ANOVA.     

Infection of Populus alba var. hickeliana by Melampsora medusae Thüm.

The first record of infection of Populus alba var. hickeliana by the American rust, Melampsora medusae Thum. is reported. The morphology of uredospores of rust on P. alba is compared with that of other Melampsora spp. infecting white poplars. The implications of these observations for the widespread establishment in the future of white × black hybrid poplars are discussed.     

Effect of Cladosporium aecidiicola Thum. on the viability of urediniospores of Melampsora medusae Thum. in storage

The viability of urediniospores of Melampsora medusae decreased markedly when stored in mixture with the conidia of Cladosporium aecidiicola. The rate of decrease was more rapid in samples stored at 16°C with high concentration of Cladosporium (ratio of urediniospores to conidia 10:1 by weight) than at ?12°C and low concentration (20:1 by weight).     

Temperature sensitivity of qualitative race-cultivar interactions in Melampsora medusae Thüm. and Populus species

Six mono-uredospore isolates (races) of Melampsora medusae Thiim. produced qualitatively distinct reactions, in vitro, when incubated at 15 °C on leaf disks of certain cultivars of Populus deltoides Marsh. The infection types in some race-cultivar combinations were very temperature sensitive with less distinct reactions when incubated at 20 or 25°C. The significance of differential race-cultivar-temperature interaction in the epidemiology of M. medusae is discussed.     

Variability in pathogenicity of Melampsora allii-populina expressed on poplar cultivars

A collection of 42 isolates of Melampsora allii-populina was established. Fourteen isolates were collected from various poplar cultivars over several French localities and 28 isolates from the alternate hosts (Allium spp., Arum spp. and Muscari comosum) obtained from nature or after inoculation. These isolates were inoculated in the laboratory on a large range of poplar cultivars belonging to several species. No isolate proved pathogenic on all cultivars and many qualitative interactions were observed between isolates and cultivars. This is the first evidence for the existence of physiological races within this fungus. No link was found between pathogenicity on poplar and on the alternate hosts. Among the inoculated cultivars, at least three were susceptible to all isolates (Beaupre, Candicans and Robusta), whereas the following showed qualitative reactions to the inoculated isolates: Altichiero, Carpaccio, Cima, Fritzi Pauley, I 154, Isieres, Luisa Avanzo, NL 2842, Rap and Spijk. Race-specific resistance to M. allii-populina (i.e. resistance to some races of the pathogen, but not to the others) has been found in two North American species (Populus deltoides and Populus trichocarpa) which have never coevolved with this fungus. The results are discussed in comparison with Melampsora larici-populina.     

Epicuticular waxes and Melampsora pinitorqua Rostr. pre-infection behaviour on maritime pine shoots

Pre-infection behaviour of Melampsora pinitorqua basidiospores on maritime pine shoots was studied in scanning electron microscopy. An evolution of epicuticular wax fine structure during shoot growth was observed. The germination pattern of basidiospores was shown to be related to the wax structure.     

Trials of Italian Pines for susceptibility to Melampsora pinitorqua Rostr.1

The susceptibility of different pine species of Italian origins to Melampsora pinitorqua was determined in natural and artificial environments on seedlings, varying in age from 1–2 months and older. Seedlings differed significantly in their susceptibility depending on species and age. Decreasing degrees of infection and varying localization of infections according to the stage of development were observed in the very young seedlings of Pinus pinea.     

Effect of Melampsora medusae leaf rust infection on yield of hybrid poplars in the north-central United States

Melampsora medusae Thuem. is a hazard to cultivation and fiber production of hybrid poplars grown under short rotations, particularly when the alternate host is present. This rust can be controlled with biweekly fungicide applications but resistant clones are the best method of control.     

Parasitism of uredospores of Melampsora larici-populina Kleb. by Cladosporium sp.

Conidia of Cladosporium sp. are frequently present in large numbers in collections of uredospores of Melampsora larici-populina made in the field at Canberra in late autumn. The presence of these conidia considerably reduces the viability of the uredospores and consequently infection of leaves of Populus nigra var. italica under controlled conditions. Lysis of germinated and ungerminated uredospores under experimental conditions by the mycelium of Cladosporium sp. has been demonstrated. The potential for control of leaf rust of poplar by hyperparasitism is discussed.     

Two pathogenic races of Melampsora larici-populina in north-western Europe

Three collections of Melampsora larici-populina Kleb. originating from Belgium, France and the Netherlands were compared for their pathogenicity on eleven poplar clones. Qualitative type reactions suggest the existence of two pathogenic races designated E1 and E2. E2 is able to infect some clones previously considered to be resistant.     

Germination of teleutospores of Melampsora pinitorqua Rostr.1

The germination ability of teleutospores of Melampsora pinitorqua Rostr. overwintered in different situations and under different types of soil cover was studied. The germination period is affected by local environmental conditions. The intensity of germination of teleutospores overwintered in the underbrush is much lower than that of teleutospores overwintered On uncovered soil.