Search

Summary 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. [ABSTRACT FROM AUTHOR]

Five pathotypes of the willow rust Melamspora larici-epitea were inoculated with 12 isolates of Sphaerellopsis filum derived from Melampsora species/forms occurring on willows. On average, 20.5% uredinial pustules produced S. filum pycnidia and rust spore production was reduced by 38.4% on leaf discs inoculated with S. filum. Some rust isolates were more readily infected by S. filum than others while some S. filum isolates caused higher levels of infections than other S. filum isolates. In general, the suppressive effects of these S. filum isolates on rust spore production were similar on the majority of rust pathotypes tested. There appeared to be a positive link between the rust pustule area and the rate of infection by S. filum. Sphaerellopsis filum inoculum densities were positively correlated with the reduction in rust spore production but not with the number of rust pustules. Implications from the results were discussed in relation to the deployment of S. filum in biological control of willow rust in willow mixture plantations which harbour more diverse rust pathotypes compared with monocultures. [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]

Six Salix clones and four Melampsora larici-epitea isolates were used in two leaf-disc inoculation experiments to determine whether disease severity was affected by the presence of both virulent and avirulent rust genotypes. In the first experiment, an equal amount of urediniospores of a virulent isolate and an avirulent isolate was applied simultaneously using four levels of spore suspension. In the second, the willows were inoculated with one isolate first and then, after 3 days, with another using two spore concentrations. In the first experiment, overall rust spore production was reduced by 48.6% in inoculations with mixed inocula compared with that in the inoculations with single virulent isolates. In the second experiment, 20 of the 36 combinations involving pre-inoculations with avirulent isolates showed significant reduction in spore production. The suppressive effects on rust sporulation were more obvious at the higher inoculum densities and on the clones S. × calodendron and S. × mollissima‘Q83’. [ABSTRACT FROM AUTHOR]

The association between willow (Salix) and rust (Melampsora) is highly specific. Willows named Salix burjatica, S. dasyclados (S. × dasyclados) and S. × calodendron are important in renewable-energy plantations in the UK and western Europe. There has been much controversy over their origin, species status and nomenclature. It has been suggested that they have originated from hybridization between. S. caprea, S. viminalis and S. cinerea. In the present work, 59 willow clones were investigated through morphological examination and detached leaf inoculation using willow differentials, for their association, in southwest England, with M. capraearum and three pathotypes of Melampsora epitea (Me-A, B and C). M. capraearum was found on all clones of S. caprea and its hybrids with S. aurita; Me-A on all S. viminalis clones; Me-B on wild S. cinerea, S. × calodendron, S. × dasyclados'De Biardii 445' and S. 'Spaethii'; Me-C on all S. burjatica clones and most S. × dasyclados clones. Both M. caprearum and Me-A infected all S. × sericans (S. caprea × viminalis) clones and S. × dasyclados'LA041/03'. We suggest that S. × dasyclados'LA041/03' should be treated as S. × sericans (S. caprea × S. viminalis); S. burjatica, S. dasyclados and S. × dasyclados as synonyms; S. × dasyclados 'De Biardii 445' as S. × calodendron 'De Biardii 445'; and S. 'Spaethii' as S. × calodendron 'Spaethii'. [ABSTRACT FROM AUTHOR]

This article focuses on inoculation of seedlings of young pine at their cotyledon stage with aecipores of Peridermium pini. Over 200 seedlings of pine were misted with distilled water and then dusted with dry spores. Apart from 10% of the inoculated seedlings that showed discolorations on the cotyledons 2 weeks after inoculation, no distinct symptoms were observed among the inoculated seedlings at 6 months. The samples of 20 seedlings were sectioned and examined from seed sources after 6 months, many contained well-developed intercellular mycelina and haustoria.

In 1987 axenic cultures were obtained from Peridermium pini aeciospore samples obtained from Scots pine (Pinus sylvestris) in Morayshire, north-east Scotland and Thetford Forest District, East Anglia. The former typically had an ill-defined margin and a fluffy appearance; the latter a distinct margin and a mucilaginous appearance. A further test in 1988 with six additional aeciospore samples from both Morayshire and Thetford gave similar results. These differences accord well with other evidence for a distinction between the forms of Peridermium pini in the two areas based on germ-tube cytology and morphology, and on the establishment of cultures from single aeciospores. In some cultures from both spore sources, the distinction in colony morphology was largely obscured after a few months by the development of sectors of fast-growing mycelium. [ABSTRACT FROM AUTHOR]

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]

For the first time with a rust fungus, continuously growing axenic cultures have been obtained from singk spores. This was achieved with acciosporc sources of the pine stem rust Peridermium pini (Pers.) Lév. from Thetford Forest, East Anglia, but not with sources from north-cast Scotland. Approximately 30% of the single spores of two East Anglian sources out of the three tested developed into transferable and subeulturable colonies on modified Harvey & Grasham's medium. [ABSTRACT FROM AUTHOR]