Comparing Chilean and Swedish rust populations: possible impact of long‐distance transport of Melampsora rust

As willow (Salix) cultivation grows globally, worldwide monitoring of pathotypes for Melampsora rust, the most serious disease in willow, becomes increasingly important. We compared the pathotype composition of the Melampsora rust population in Chile with that in Sweden and assessed inocula exchange for the rust between the continents. For pathotyping rust isolates, a willow differential was used (a standardized set of willow test clones) to obtain clone‐virulence patterns. These patterns were used to identify virulence components involved in determining which willow clones a given individual pathogen isolate (genotype) can successfully attack. Each virulence component detected earlier in Sweden's rust population was present in Chile's rust population. Using isoenzyme analysis to classify willow species in Chile, a low genetic variation of Salix viminalis (an introduced willow species) was found, compared with the endemic species Salix humboldtiana. Comparison of rust populations for the two countries supports the present hypothesis that intercontinental inocula exchange can be a significant determinant of local pathotype structure, and consequently can be important for willow‐resistance breeding.     

Growing clonal mixtures of willow to reduce effect of Melampsora epitea var. epitea

Rust (Melampsora epitea var. epitea) is the single most limiting factor in the production of biomass from short rotation coppice willow. The use of fungicides is unacceptable for economic, environmental and practical reasons. Consequently, clonal mixtures were investigated as an alternative disease control strategy. At one of two sites Salix × dasyclados, Salix burjatica ‘Korso', S. burjatica‘Germany’, Salix viminalis‘Bowles Hybrid’ and S. viminalis‘683’ were included in the clonal mix. At the second site six clones were used. These were as above with the exception of S. burjatica‘Korso’ and including, Salix × calodendron, Salix mollissima-undulata‘SQ83’. At both sites all clones were also planted in monoclonal stands. Throughout each growing season disease levels were recorded on individual clones, both in monoclonal stands and mixtures. Fungicide treatments were included to compare their effectiveness to mixtures in reducing disease impact. Growing willow in mixed clonal stands delayed the onset of disease, slowed its build up and resulted in lower disease levels at the end of the growing season. These reductions in disease impact contributed to the increased yields obtained from clonal mixtures and were generally comparable to those achieved with fungicides.     

Compatible and Incompatible Reactions of Melampsora Rust on Willow Leaves

Spore germination, growth and appresssoria formation for Melampsora willow rust were studied for compatible and incompatible hosts to elucidate penetration specificity and prehaustorial events in the infection process. Rust originating from Salix dasyclados was inoculated on a compatible (S. dasyclados) and an incompatible (Salix daphnoides) clone and, for comparison, on the non-host plants tomato, tobacco and poplar. The same experimental procedure was also carried out for rust originating from poplar. Rust development was followed for 5 days at 20 h intervals using a microscope with fluorescent equipment. The study showed that the Melampsora rust can develop on, and penetrate, the leaf regardless of whether the rust was inoculated on compatible or incompatible willow plants. However, the fungus was able to infect and reproduce itself only in compatible interactions. For willow rust in the prehaustorial stage, the study indicated that specific recognition mechanisms were unnecessary to start the infection process.     

Effect of plantation design on stem‐infecting form of rust in willow biomass coppice

Planting of genotype mixtures is a major strategy for the non‐chemical control of willow rust in short‐rotation coppice willows grown for biomass. In 1997 and 1998, the relative severity and spatiotemporal distribution of stem canker damage by Melampsora spp. on Salix viminalis `Bowles Hybrid' in a field trial containing monocultures and two design mixtures (random or regular) of three or five genotypes were assessed. Sphaerellopsis filum, a hyperparasite of Melampsora spp. was detected in all plots during the summer (1998) between the time of the two canker assessments. The percentage of rust pustules with this hyperparasite was initially greater in monoculture plantings than in mixtures in June, but by July, more than 92% of pustules were parasitized, irrespective of plantation design. The stem rust assessments showed that, in general, there were fewer cankers per stool in plots containing mixtures of willow genotypes compared with monoculture plantings. The distribution of rust cankers was different between monocultures and willow mixture designs, with differences between years for monocultures.     

Genetics of field resistance to Melampsora in Salix viminalis

The inheritance of resistance to Melampsora. spp. on Salix viminalis, the variation in resistance over space and time, and rust infection rate in relation to the geographic origin of the host was studied. The analysis showed that there was considerable additive genetic variation for rust resistance, that the results did not have high repeatability over space and time, and that the material from southernmost Sweden was most sensitive to the rusts occurring in south Sweden.     

Rust severity in bioenergy willow plantations treated with additional nutrients

A 3‐year field study was carried out to determine the effect of wastewater irrigation and previous differences in mineral fertilization on the occurrence of willow leaf rust (Melampsora epitea). The experiment was conducted in two energy forest plantations: one designed for wastewater purification and the other as a mineral fertilization experiment. The severity of leaf rust on different clones and sites with different treatments was assessed by counting the number of uredinia per leaf unit area. Generally, plants irrigated with wastewater consistently had more leaf rust, irrespective of the study years or willow clones. Previous mineral fertilization had mixed effects on different clones 2 years after the last application. Three years after the last fertilizer application, however, no impact of the treatment on rust disease development was detected. In general, the rust levels differed from year to year probably due to climate. In this study, no correlation was detected between shoot age and rust severity, whereas climate and treatments strongly influenced leaf rust levels on some willow clones.     

Variation in leaf phenolics of field‐cultivated willow (Salix myrsinifolia) clones in relation to occurrence of Melampsora rust

Concentrations of potential antifungal phenolics in field‐cultivated willow (Salix myrsinifolia) clones were analysed during three growing seasons, and correlated to the occurrence of Melampsora rust. Consistent relationships between phenolics and rust were not found across the experimental years. There was significant clonal and temporal variation in phenolic content and rust frequency. Levels of some phenolics varied considerably within a sequence of four full‐grown leaves, but the variation in rust occurrence within the same leaf sequence was nonsignificant. The results suggest that the possible association between willow phenolics and rusts is not straightforward, and emphasize the importance of long‐term studies to investigate the chemical basis of willow rust interactions.     

Variation in Melampsoridium resistance among European white-birch clones grown in different fertilization treatments

Resistance of 2-year-old plantlets of seven European white birch, Betula pendula, clones to birch rust, Melampsoridium betulinum, was studied in field experiments and in a leaf-disc bioassay. In addition, rust resistance of plantlets growing in a nursery under three fertilization treatments was tested. The birch clones clearly varied in their levels of resistance. One of the clones was consistently the most resistant, and two were very susceptible. Plantlets growing in the lowest fertility treatment were the most resistant. Clone × fertilization interaction was small. The plantlets grown in the lowest fertilization treatment, in particular, deviated from the other treatments. Generally good rust-resistance correlations were obtained between different experiments. The leaf-disc bioassay was an effective way of determining the field rust resistance of birch clones. The possibility of trade-offs between rust resistance and tree growth is discussed.     

Inter‐ and intraspecific variation and genotype × site interaction in Salix Alba L., S. Dasyclados Wimm. and S. viminalis L.

Three test series were planted on sites selected for their contrasting properties to study the genotype × site interaction. Various clones of Salix alba (8 clones in the 1980 series), S. dasyclados (8 clones in 1982 series) and S. viminalis (6, 9, 13 clones in the various series) were included. Growth capacity, survival and infection by rust fungi were analysed. Interspecific variation was seen at some of the sites in the 1982 series but it was pronounced in the 1980 series where 5. viminalis outgrew 5. alba at all sites. Intraspecific variation could be seen for growth capacity, survival and rust resistance. A genotype × site interaction was detected for all variables studied. Some of the interaction, especially at the species level, can be explained by the variation in susceptibility to rust fungi and preference for soil types. In the breeding work with Salix the genotype × site interaction must be considered.     

The distribution of Phratora vulgatissima (Coleoptera: Chrysomelidae) on cultivated willows in Britain and Ireland

Insect samples were collected from the canopy of 24 willow short rotation coppice (SRC) sites on farmland in Britain and Ireland in 1995. The blue willow beetle Phratora (= Phyllodecta) vulgatissima (L.) (Coleoptera: Chrysomelidae), previously identified as the main defoliating pest of this crop, was recorded from 13 of these at varying levels of abundance. Data describing aspects of the environment at each site were also collected. These data were used to create potential explanatory variables for a regression analysis of beetle abundance. This analysis indicated that P. vulgatissima were most likely to occur and were more abundant at older willow sites on clay soils and at sites that bad certain free-living willow species growing nearby. Within sites, most willow clones sampled contained P. vulgatissima, although two, Salix burjatica‘Germany’ (‘Aquatica Gigantea’) and Salix mollissima‘Q83’ (Salix triandra × Salix viminalis), were avoided. Chrysomelid pest avoidance and clonal resistance could form part of an integrated pest management strategy for SRC crops.     

Clonal response in Salix to Melampsora rusts in short rotation coppice plantations

The appearance of Melampsora spp. rust on a range of Salix spp. clones used for short rotation coppice was recorded. The progress of the disease and its subsequent effect on leaf fall was also recorded. Rust pustules from all the clones described were examined using the Stereoscan Elec-tron Microscope. This revealed no differences in uredospore architecture which could be consis-tently related to host.     

Genetic relationships among genetically distinct forms of Melampsora larici‐epitea and related species based on AFLP data

Amplified Fragment Length Polymorphism (AFLP) was used to study genetic relationship among leaf rust fungi (Melampsora spp.) occurring on Salix species in short‐rotation coppice. Special interest was paid to a newly identified rust fungus found on S. viminalis in southern Sweden, morphologically similar to M. larici‐epitea but with a distinct DNA profile. Genetic distances among 40 Melampsora isolates collected from S. viminalis, S. dasyclados, S. viminalis x dasyclados, S. daphnoides, S. acutifolia and M. larici‐populina were calculated based on 101 AFLP markers. Neighbour‐joining analysis revealed the presence of six clusters, which corresponded exactly to predefined groups, namely three formae speciales of M. larici‐epitea, a stem‐infecting form of Melampsora on S. viminalis, the newly identified Melampsora on S. viminalis and a group consisting of two isolates from the poplar rust M. larici‐populina. All six clusters were well supported by bootstrap analysis (84 to 100% support). The newly identified Melampsora on S. viminalis was indicated to be genetically separated from M. larici‐epitea as well as from the stem‐infecting form of Melampsora.     

Interactions between Melamspora larici‐epitea pathotypes and the mycoparasite Sphaerellopsis filum from willow rusts

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.     

Short rotation coppice willow in Northern Ireland since 1973: development of the use of mixtures in the control of foliar rust (Melampsora spp.)

A review is given of the use of clonal mixtures in the development of disease control strategies in short rotation coppice willow in Northern Ireland. Salix burjatica‘Korso’ had been grown successfully for over 10 years when, in 1985, Melampsora epitea var. epitea caused serious problems. Although fungicides were effective, their use was not practical for environmental and economic reasons. Therefore, in 1987 large scale field experiments were initiated to investigate the use of clonal mixtures as a disease control strategy. Increased yields were consistently recorded from mixed stands when compared to either the mean yield of component clones or the individual yields of any of the component clones grown in monoculture. Part of this increased yield was due to a reduction in the impact of rust disease. Investigations are currently being conducted on the effect of number of clones within a mixture, the best clones to use and the optimum planting density. It is essential that there is a range of susceptibilities to M. epitea var. epitea pathotypes within the components of the mixture.     

川东北地区杨树与柳树锈病发生与病理学观察

杨树和柳树均属于杨柳科植物,两者在经济林及绿化行道树上的运用越来越广泛。锈病在杨树和柳树高栽植密度苗圃地和成片用材林的发生极为严重。本研究比较杨树和柳树锈病的发病症状、流行特点及病原菌特征,为该病的防治提供理论和实际指导依据。以川东北地区4区(县)(南充市高坪区和西充县,广安市前锋区和武胜县)患发锈病的杨树和柳树为研究对象,采用流行病学调查和显微观察技术等方法。杨树锈病和柳树锈病大都侵害叶和幼苗,引起树叶早期脱落,幼苗枯萎。但杨树锈病的病原菌为锈菌科栅锈菌属松杨栅锈菌(Melampsora larici-populins),柳树锈病的病原菌为锈菌科栅锈菌属拟鞘锈栅锈菌(Melampsora coleosporioides Diet.)。杨树锈病和柳树锈病虽有共同的发病特征,但在为害症状、病原类型和发生规律方面均有很大的不同。建议在防治时根据寄主的不同选择针对性强的防治方法。     

Life-cycles and ecology of willow beetles on Salix viminalis in England

The life-cycles of three willow beetle pests, Phratora (= Phyllodecta) vulgatissima, Phratora (=Phyllodeeta) vitellinae and Galerucella lineola (Coleoptera, Chrysomelidae), were investigated during 1994–95 in a plantation of short-rotation coppiced willows (Salix viminalis cv. Bowles Hybrid) at Long Ashton, Bristol, UK. The P. vulgatissima had one generation during the year. Overwintered adults emerged from hibernation in April and after a short feeding period, copulation and egg-laying occurred. Larval stages were found from May–July. The new generation of adult beetles appeared in July–August and fed for a while before hibernating. Hibernating adults were found in hedgerows around the site and in the plantation on willow stools and ground vegetation. Dispersal of adult beetles between feeding and overwintering sites appeared to be fairly localized. Hence, crop management strategies that reduce the potential for overwintering in and around plantations may help to minimize spring re-invasion and damage. Although based on limited observations, the biology of P. vitellinae and G. lineola appeared similar to that of P. vulgatissima. However, there is evidence in the literature that both these species, unlike the latter, can have a partial second generation in some years. The potential effect of insect herbivory on the growth and biomass yield of S. viminalis cv. Bowles Hybrid was investigated experimentally by artificial hand-defoliation of pot-grown plants. Yield losses were strongly correlated with the amount and time of defoliation. Results indicated that even slight or moderate damage by insect herbivores could have a significant impact on the biomass productivity of coppiced willows.     

The significance of rotation periods for mycorrhiza formation in Short Rotation Coppice

Rotation periods control not only the above-ground growth but also the assimilate transfer to the root systems in Short Rotation Coppice (SRC). Since assimilates are needed for the nutrient supply of associated mycorrhizal fungi, their control by rotation period length seems most probable. One poplar (Populus nigra × maximowiczii cv. Max 4) and one willow clone (Salix viminalis clone 78–101) cultivated as SRC were investigated on their ectomycorrhiza formation in response to 15 years of continuous different rotation periods (three and six years) at the same test site in Northern Germany. On the poplar clone the frequency of ectomycorrhizae was significantly lower in 6-year than in 3-year rotation. On the willow clone frequency of ectomycorrhizae was not significantly affected, but the portion of dead fine roots was significantly higher in the 6-year than in the 3-year rotation in autumn. In both rotation systems, the frequency of ectomycorrhizal (EM) colonisation was significantly higher in autumn than in spring. Five EM morphotypes were found on the poplar and seven on the willow clone. EM morphotypes which were common on both clones were formed with two fungal partners of the Pezizales (Geopora cervina, Tuber rufum), one of the Agaricales (Laccaria sp.) and one of the Thelephorales (Thelephoraceae). In spring G. cervina constituted the largest part of all observed EM morphotypes on P. nigra × maximowiczii and S. viminalis. The results indicated a selective promotion of EM formation of some Pezizales (Tuber and Peziza spp.) and some Agaricales (Laccaria spp.) due to shorter rotations, and a selective promotion of other Agaricales (Inocybe sp.) and Boletales (Scleroderma spp.) due to longer rotations. This might allow selective manipulation of the mycorrhizal diversity by the selection of the rotation system. A future challenge will be to select which mycorrhizal diversity might be more advantageous for the vitality and biomass production of poplar and willow clones.     

Effect of Betula pendula clone and leaf age on Melampsoridium betulinum rust infection in a field trial

Ten 5‐year‐old Betula pendula clones were studied for their rust resistance in the field. The trees were treated by inoculating 10 leaves on a shoot with Melampsoridium betulinum urediniospore suspension or spraying the control leaves with water. The birch clones differed significantly in their resistance to M. betulinum leaf rust fungus and the clones also varied in their responses to the local rust strain and the inoculated rust strains. However, natural rust infections and inoculation treatment were positively correlated. The older leaves had fewer infections than the younger ones on the tip of the shoot in the control trees, but in the inoculation treatment no significant correlation was found between the leaf ages and rust infection. The factors behind the different leaf susceptibilities are discussed.     

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.     

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.