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Phytophthora cinnamomi and P. cactorum were detected in soil samples from a Vaccinium corymbosum stand in southern Germany. Both species were virulent in an underbark inoculation assay and have not been reported from highbush blueberry in Germany before. While P. cactorum is a widely distributed species in nurseries and (semi)natural habitats like forests, field reports of P. cinnamomi in Germany are rare due to its sensitivity to frost. Its occurrence in an outdoor blueberry stand indicates its potential to survive Central European winter periods that tend to be increasingly mild. Phytophthora cinnamomi was also found in the substrate of young V. corymbosum nursery plants, suggesting a high degree of contamination in commercial blueberry production and demonstrating the risk of spreading exotic invasive plant pathogens via planting of infested nursery stock.

Roots, collars and rhizosphere soils from diseased boxwood saplings (Buxus sempervirens) from German and Romanian nurseries were shown to be colonized by a Phytophthora species (P. taxon Buxus) closely resembling the recently described species P. himalsilva. After comparison of both taxa using morphological, phylogenetic and pathogenicity data the high similarity between P. taxon Buxus and P. himalsilva was confirmed. No differentiation was found regarding growth patterns, morphological characters and breeding behaviour. In pathogenicity tests with boxwood twigs, leaves and root collars, both the isolates from boxwood and P. himalsilva proved to be highly aggressive towards this host. Although some of the phylogenetic markers used showed some degree of differentiation, others did not provide evidence for a radiation of two taxa. While based on ITS, β-tubulin and ypt gene sequences P. taxon Buxus could not be clearly distinguished from P. himalsilva, the cox1 gene sequences did separate the strains from P. himalsilva and placed them more closely to P. citrophthora. Since P. himalsilva was reported to be a highly variable species, a definite decision on the taxonomic status of the isolates described here cannot be made yet. More importantly, our findings highlight the increasing importance of exotic pathogens causing plant diseases in commercially important plants, especially in nurseries. As the phylogenetic positioning of the box isolates indicated that they may belong to a group of species potentially endemic to Asia, the Phytophthora taxa involved in this disease might represent another important threat to European boxwoods with an exotic origin.

Rhizoctonia solani AG2-2IIIB is the causal agent of late crown and root rot in sugar beet. In a 4-year field study we analyzed the impact of different plant residue management systems of sugar beet and maize as well as of growing wheat (non-host) and different maize varieties on the soil inoculum density of R. solani. Sugar beet remains were either tilled or removed from the field; maize was then grown during the two following years and also tilled or removed. The soil inoculum potential of R. solani was studied using three different on- and off-site monitoring systems. A monthly assessment of root damage indices of maize and sugar beet and broad bean as an indicator plant was carried out. In addition, an indirect quantitative real-time PCR assay using quinoa seed baits was developed to analyze field soil samples for R. solani AG2-2 soil concentration at the end of each year. The results show that the non-host wheat as a pre-crop to sugar beet reduced the Rhizoctonia inoculum potential in the soil significantly. Additionally, the incorporation of host plant debris (sugar beet + maize) into the soil increased the Rhizoctonia soil inoculum potential and the incidence of sugar beet rot. Although the maize genotypes’ susceptibility to R. solani differed, their plant debris did not significantly influence growth and survival of R. solani in the soil. This work describes methods that allow elucidating the effect of agricultural practice on Rhizoctonia levels in the soil and on disease development in the field.

A set of isolates closely related to the reed pathogen Pythium phragmitis was found among Pythium strains obtained from reed ( Phragmites australis ) soil and plant samples in Germany and Switzerland. These isolates consistently differed from P. phragmitis at 6, 6 and 3 nucleotide positions in the rDNA internal transcribed spacer region, the β-tubulin, and the cytochrome oxidase II gene, respectively. They are formally described here as Pythium phragmiticola sp. nov. An analysis of phenotypic traits like oospore size, growth and aggressiveness to reed showed that P. phragmiticola is almost indiscernible from P. phragmitis , as most features assessed overlapped considerably between species. Phylogenetic analyses provided evidence that P. phragmiticola is the second parent of a previously described Pythium hybrid involving P. phragmitis . The alloploid status of the hybrid, and the parents' reproductive separation was confirmed by molecular evidence and the high ratios of aborted oospores. In natural environments there obviously are two species closely associated with reed, P. phragmitis and P. phragmiticola which are homothallic, but can outcross, resulting in sterile, vegetatively propagated interspecific hybrids. Driving forces leading to the radiation of these two species are unknown, but might be connected with divergent parasitic adaptation to different host tissues or species.

The term ‘girth scab’ describes a chronic disease of sugar beet roots (Beta vulgaris ssp. vulgaris) for which the causes still remain unclear. While pathogenicity of the oomycete Aphanomyces cochlioides to sugar beet has been known for a long time, most practical guides and other professional literature refer to actinobacteria as the causal agents. In this study, we try to provide some clarification of the aetiology of this disease by studying affected sugar beets from different regions in Bavaria, with a focus on the involvement of A. cochlioides and other soilborne oomycetes. In parallel, the samples were investigated for the presence of actinobacteria. A. cochlioides and several Pythium spp. were isolated from the samples in both 2010 and 2011, among these P. recalcitrans, P. intermedium and P. sylvaticum. In a soil infestation test, A. cochlioides in particular proved to be highly aggressive to young beet plants, causing severe symptoms of ‘girth scab’, and a significant biomass reduction. P. recalcitrans also caused mild scab, while the other species led to biomass reduction only. Bacteriological studies showed that Streptomyces spp. found on some samples were most likely non-pathogenic strains that were not primarily involved in the disease. Our results show that A. cochlioides rather than actinobacteria is most probably the causal agent of the ‘girth scab‘ disease. The wet weather conditions and the massive occurrence in 2010 make the contribution of this moisture-associated oomycete most plausible. The role of several Pythium spp. that caused similar symptoms remains to be clarified.

Since its first isolation from Salix roots in 1972, isolates of a sexually sterile Phytophthora species have been obtained frequently from wet or riparian habitats worldwide and have also been isolated from roots of Alnus and Prunus spp. Although originally assigned to Phytophthora gonapodyides on morphological grounds, it was recognized that these isolates, informally named P. taxon Salixsoil, might represent a separate lineage within ITS Clade 6. Based on phylogenetic analyses and comparisons of morphology, growth-temperature relationships and pathogenicity, this taxon is formally described here as Phytophthora lacustris sp. nov. Isolates of P. lacustris form a clearly resolved cluster in both ITS and mitochondrial cox1 phylogenies, basal to most other Clade 6 taxa. Phytophthora lacustris shares several unusual behavioural properties with other aquatic Clade 6 species, such as sexual sterility and tolerance of high temperatures, that have been suggested as adaptations to riparian conditions. It appears to be widespread in Europe and has also been detected in Australia, New Zealand and the USA. Itwas shown to be weakly or moderately aggressive on inoculation to Alnus, Prunus and Salix. The extent of P. lacustris’ activity as a saprotroph in plant debris in water and as an opportunistic pathogen in riparian habitats needs further investigation. Its pathogenic potential to cultivated fruit trees also deserves attention because P. lacustris has apparently been introduced into the nursery trade.

In recent years, Common ash (Fraxinus excelsior) throughout Europe has been severely impacted by a leaf and twig dieback caused by the hyphomycete Chalara fraxinea. The reasons for its current devastating outbreak, however, still remain unclear. Here, we report the presence of four Phytophthora taxa in declining ash stands in Poland and Denmark. Phytophthora cactorum, Phytophthora plurivora, Phytophthora taxon salixsoil and Phytophthora gonapodyides were isolated from rhizosphere soil samples and necrotic bark lesions on stems and roots of mature declining ash trees in four stands. The first three species proved to be aggressive to abscised roots, twigs and leaves of F. excelsior in inoculation experiments. Soil infestation tests also confirmed their pathogenicity towards fine and feeder roots of ash seedlings. Our results provide first evidence for an involvement of Phytophthora species as a contributing factor in current decline phenomena of F. excelsior across Europe. Specifically, they may act as a predisposing factor for trees subsequently infected by C. fraxinea. Phytophthora species from ash stands also proved to be aggressive towards a wide range of tree and shrub species commonly associated with F. excelsior in mixed stands. Although damage varied considerably depending on the Phytophthora species/isolate-host plant combination, these results show that many woody species may be a potential source for survival and inoculum build-up of soilborne Phytophthora spp. in ash stands and forest ecosystems in general.

Summary During and after prolonged periods of rainfall in late spring, blighted young twigs of European beech (Fagus sylvatica) were frequently observed in several beech stands in south-western and southern Germany. Long and short shoots of young understorey trees or lower branches up to 1.5 m above the soil level were affected. Symptoms also occurred regularly on twigs in heights up to 2 m and more above the ground. Necroses usually expanded within the current year’s tissue and often also reached into the previous year’s wood. Ponding rain water in the stands or along forest roads or open soil seemed to promote the disease. Of a total of 54 symptomatic twigs collected in four stands, 37 revealed Phytophthora isolates, of which 33 were P. plurivora and four were P. cambivora. Both species caused extensive lesions on beech twigs in laboratory pathogenicity tests. Patterns of the disease indicated that these pathogens, generally considered soilborne species, in most cases are transmitted from the soil to above-ground parts of the trees via rain splash. In larger heights, however, other vectors such as snails might be responsible for transmission. Although Phytophthora spp. are well known as causal agents of seedling blight as well as root and cambium rot and aerial bleeding cankers of mature beech, to our knowledge this is the first report of a twig blight in beech associated with soilborne Phytophthora spp. In particular in periods of high precipitation, this disease might pose an additional threat to Central European beech forests, especially endangering the success of artificial and natural regeneration of beech in affected stands.

Summary 1. Leaf litter breakdown by shredders in the field is affected by leaf toughness, nutritional value and the presence of secondary compounds such as polyphenols. However, experiments involving the use of single fungal strains have not supported the assumption that leaf parameters determine food selection by shredders perhaps because of a failure to test for high consumption prior to isolation of fungal strains, overrepresentation of hyphomycetes or the potential effects of accompanying bacteria. In this study, we used bacteria-free, actively growing fungi and oomycetes isolated from conditioned leaf litter for which a shredder had already shown high consumption rates. 2. Black alder (Alnus glutinosa) leaf litter was exposed to the littoral zone of Lake Constance in autumn, and subsamples were analysed for leaf parameters and consumption by Gammarus roeselii under standard conditions at regular intervals. On dates with a high consumption rate of the exposed leaves, 14 single strains of fungi and oomycetes were isolated, freed of bacteria and grown on autoclaved leaves. 3. Six of eight measured leaf parameters of exposed leaves were significantly correlated with Gammarus consumption rates, with high colinearity among leaf parameters hampering the identification of causal relations between leaf parameters and feeding activity. 4. When single strains of fungi and oomycetes were grown on autoclaved leaf litter, toughness of colonised leaves was always lower than in the control and the content of protein, N and P were increased. There were pronounced strain-specific effects on leaf parameters. Consumption rates also differed significantly, with nine of fourteen isolates consumed at higher rates than controls and none proving to be a deterrent. Protein and polyphenol content were significantly correlated with consumption rates. Oomycete-colonised leaves were consumed at similar rates but were of lower food quality than fungi-colonised leaves. 5. We argue that direct strain-specific attractant or repellent effects of fungi and oomycetes on consumption by G. roeselii are not important. However, we found indirect strain-specific role operating via effects on leaf parameters.

Im Rahmen der hier dargestellten Untersuchungen zur Entwicklung eines Behandlungskonzeptes gegen Phytophthora ramorum-Befall in Rhododendron-Bestanden wurden verschiedene Pflanzenschutz-, Pflanzenstarkungs- und Dungemittel auf ihre Wirksamkeit gegen P. ramorum auf Rhododendron getestet. Die Versuche wurden an kunstlich infizierten, jungen Rhododendron-Pflanzen und abgetrennten Blattern mit folgenden Praparaten durchgefuhrt: Phosphit (Nutri-Phite® PK), Kupfer-Hydroxid (Cuprozin® flussig), Bacillus subtilis (Serenade®), Mykorrhiza, und ein Praparat auf Basis von ‚Effektiven Mikroorganismen‘ (EMa). Zwar konnte die Ubertragung des Erregers von infizierten auf gesunde Pflanzen durch die drei Wirkstoffe Phosphit, Cu-Hydroxid und B. subtilis verhindert werden, doch zeigte sich in allen weiteren Versuchen, dass nur Phosphit und Cu-Hydroxid tatsachlich signifikante Effekte auf die Befallsentwicklung hatten. Alle anderen Praparate, die auf antagonistischen und/oder wachstumsfordernden Mikroorganismen basieren, hatten keine signifikant praventive oder kurative Wirkung. B. subtilis wirkte sich dabei tendenziell eher symptomverstarkend aus, die ubrigen Praparate bewirkten eine leichte Verminderung des Befalls. Phosphit und Cu-Hydroxid dagegen konnten einen Befall nahezu komplett verhindern. In Freilandbestanden scheint somit der Einsatz des okologisch unbedenklichen, systemischen Phosphit-Praparates gegen Phytophthora-Befall an Rhododendron sinnvoll und angeraten. Im Zusammenspiel mit anderen unterstutzenden Masnahmen kann dies im Rahmen eines Behandlungskonzeptes die weitere Ausbreitung von P. ramorum verhindern oder zumindest verlangsamen.

The interaction of microbial colonization with leaf litter breakdown by the shredder Gammarus roeselii was studied in the littoral of large Lake Constance. In a first step we studied selective feeding of gammarids on leaf litter from three different treatments. Littoral exposed, tap water exposed, and autoc1aved leaves were offered to G. roeselii in standard food-choice assays under laboratory conditions. We found highly selective feeding on littoral exposed leaf litter indicating that microbial conditioning is 'affecting the shredders feeding behaviour. Neither C, N, and P nor protein nor ergosterol content were positively correlated with the relative consumption rates of littoral exposed leaves. For a more detailed study of the microbial conditioning of the leaves oomycetes and fungi were iso­ lated from the littoral exposed leaves. Based on the sequence of internal transcribed spacer (ITS) regions of rDNA, we identified single strains of Fusarium sporotrichoides, Microdochium sp., Ascomycete sp., and Cylindrocladiella parva; two strains of Cylindrocarpon sp.; and three strains of Pythium sp. Subsequently, food choice assays were conducted using the isolated strains by offering autoclaved leaves and leaves colonized with a single strain. Three strains (c. parva, Cylindrocarpon sp. 94-2057 and Ascomycete sp.) were preferred by G. roeselii, while leaves with F. sporotrichoides were avoided. Leaves with each of the three oomycete isolates (Pythium sp.) were neither pre­ ferred nor rejected by G. roeselii. Our results suggest that the selective feeding behaviour of G. roeselii is affected by the relative abundance of specific fungal strains. Thus, whether microbial conditioning acts as a repellent or as an attractor for shredders depends on the microbial community on the leaves.

In a 3-year-study, we analysed the population dynamics of the reed pathogen Pythium phragmitis and other reed-associated oomycetes colonizing fresh and dried reed leaves in the littoral zone of a large lake. Oomycete communities derived from internal transcribed spacer clone libraries were clearly differentiated according to substrate and seasonal influences. In fresh leaves, diverse communities consisting of P. phragmitis and other reed-associated pathogens were generally dominant. Pythium phragmitis populations peaked in spring with the emergence of young reed shoots, and in autumn after extreme flooding events. In summer it decreased with falling water levels, changing water chemistry and rising temperatures. Another Pythium species was also highly abundant in fresh leaves throughout the year and might represent a new, as-yet uncultured reed pathogen. In dried leaves, reed pathogens were rarely detected, whereas saprophytic species occurred abundantly during all seasons. Saprophyte communities were less diverse, less temperature sensitive and independent of reed development. In general, our results provide evidence for the occurrence of highly specialized sets of reed-associated oomycetes in a natural reed ecosystem. Quantitative analyses (clone abundances and quantitative real-time PCR) revealed that the reed pathogen P. phragmitis is particularly affected by changing water levels, water chemistry and the stage of reed development.

[EN] An analysis of incidence of Phytophthora spp. in 732 European nurseries producing forest transplants, larger specimen trees, landscape plants and ornamentals, plus 2525 areas in which trees and shrubs were planted, is presented based on work conducted by 38 research groups in 23 European countries between 1972 and 2013. Forty-nine Phytophthora taxa were recorded in 670 nurseries (91.5%); within these nurseries, 1614 of 1992 nursery stands (81.0%) were infested, although most affected plants appeared healthy. In forest and landscape plantings, 56 Phytophthora taxa were recovered from 1667 of 2525 tested sites (66.0%). Affected plants frequently showed symptoms such as crown thinning, chlorosis and dieback caused by extensive fine root losses and/or collar rot. Many well-known highly damaging host¿Phytophthora combinations were frequently detected but 297 and 407 new Phytophthora¿host associations were also observed in nurseries and plantings, respectively. On average, 1.3 Phytophthora species/taxa per infested nursery stand and planting site were isolated. At least 47 of the 68 Phytophthora species/taxa detected in nurseries and plantings were exotic species several of which are considered well established in both nurseries and plantings in Europe. Seven known Phytophthora species/taxa were found for the first time in Europe, while 10 taxa had not been previously recorded from nurseries or plantings; in addition, 5 taxa were first detections on woody plant species. Seven Phytophthora taxa were previously unknown to science. The reasons for these failures of plant biosecurity in Europe, implications for forest and semi-natural ecosystems and possible ways to improve biosecurity are discused., The authors are grateful to all public and private owners of nurseries and plantings who contributed to this extensive study. T. Jung acknowledges the support by the Regione Autonoma della Sardegna, Visiting Professor Program at the University of Sassari, Italy. The authors also thank the COST Office and the European Council for providing the European COST Actions FP0801 (http://www.cost.eu/domains_actions/fps/Actions/FP0801) and FP 1002 (http://www.cost.eu/domains_actions/fps/Actions/FP1002), the EU projects FOR-THREATS and ISEFOR, and BiodivERsA project RESIPATH as platforms for stimulating discussions on the nursery pathway and possible management solutions.

An unnamed ITS clade 6 Phytophthora was frequently isolated from rhizosphere soil of reed (Phragmites australis) growing on the littoral zone of Lake Constance. The isolates closely resembled P. gonapodyides, having internally proliferating, non-papillate sporangia, a rather high temperature optimum for growth (30 � C), and being sexually sterile. ITS sequence analysis revealed that they were identical to the as yet unnamed Phytophthora taxon Salixsoil, originally isolated from Salix roots in the UK and Alnus debris in Denmark. The taxon was readily isolated from permanently as well as occasionally flooded reed sites using standard baiting procedures, indicating a wide distribution in the Lake Constance littoral zone. In an in vitro leaf inoculation assay P. taxon Salixsoil proved to be more aggressive towards Salix alba than P. gonapodyides. The new taxon may be of significance as a root pathogen of woody plants in moist or flooded situations occurring in alluvial forest/plant communities. We propose that due to its close resemblance to P. gonapodyides the taxon might have passed unnoticed in the past, and possibly is much more widely distributed than previously recognised.

In several studies of oak decline in Europe, a semi-papillate homothallic Phytophthora taxon was consistently isolated, together with other Phytophthora species, from rhizosphere soil samples. It was also found associated with necrotic fine roots and stem necroses of Fagus sylvatica and Alnus glutinosa. Due to morphological and physiological similarities, the semi-papillate isolates were previously identified as P. syringae by various authors. The morphology, physiology and pathogenicity against fine roots of Quercus robur, Q. petraea and F. sylvatica, bark of A. glutinosa, leaves of Ilex aquifolium and apple fruits of this Phytophthora species are described and compared with those of related and similar Phytophthora species, namely P. ilicis, P. psychrophila, P. quercina, P. citricola and P. syringae. The phylogenetic placement on the basis of ITS and mtDNA sequence data was also examined. Isolates of this taxon produce colonies with stellate to rosaceous growth patterns and limited aerial mycelium on various agar media. Antheridia are predominantly paragynous. In water culture catenulate hyphal swellings and semi-papillate caducous sporangia, that are usually limoniform, ellipsoid or ovoid, are formed abundandly, mostly in lax or dense sympodia. This taxon is a moderately slow growing, low temperature species with optimum and maximum temperatures around 20 and 25 degrees C, respectively. Tested isolates are moderately aggressive to fine roots of oaks and beech, highly aggressive to holly leaves and apple fruits, and slightly pathogenic to alder bark. Thirteen tested isolates had an identical and distinct ITS sequence which was more similar to that of P. ilicis and P. psychrophila than any other known taxa. On the basis of their unique combination of morphological characters, colony growth patterns, cardinal temperatures for growth, growth rates, pathogenicity to oaks, beech, alder, apple and holly, their host range, and ITS and mtDNA sequences the semi-papillate caducous Phytophthora isolates from oaks, beech and alder are clearly separated from related and similar Phytophthora spp., and described as a new species, P. pseudosyringae sp. nov.

During a study on soilborne Pythiaceae in the Bavarian Alps, 3 isolates of a papillate Pythium species with aplerotic oospores were found in rhizosphere soil from a declining spruce stand. The isolates showed a unique combination of sporangial and gametangial characters, and could not be assigned to any known species of the genus. They were characterised by a relatively low growth rate, internally proliferating sporangia and extremely variable, monoclinous, sessile or shortly stalked antheridia. Direct germination of sporangia frequently occurred in water culture. Internal transcribed spacer (ITS) regions of the ribosomal DNA showed very low levels of similarity to those of all known species of Pythium. This paper describes the isolates as Pythium montanum sp. nov., gives details on its morphology and provides preliminary information on its pathogenicity. Additional molecular evidence for its status as a new species is also provided. Phylogenetic analyses with a set of Pythium spp. showed that P. montanum groups in a clade together with P. vexans, a species whose taxonomical status still remains unclear, and that is considered a ‘border species’ between Pythium and Phytophthora.

Investigations on root and crown status of spruce and beech were carried out on selected trees in the ‘Werdenfelser Land’ area (Bavarian Alps, Southern Germany). In addition, the association of fine root pathogens of the genera Phytophthora and Pythium with the trees’ rhizosphere was studied. In a variety of stands representing various site conditions, soil and root samples were taken from 12 spruce (Picea abies) pairs and eight beech (Fagus sylvatica) pairs. Each pair consisted of a healthy and a declining tree as indicated by crown transparency. The root status was characterized using a set of parameters, and correlations between crown and fine root status were observed. In spruce, most parameters decreased significantly with increasing crown transparency, whereas in beech, correlations were less pronounced. The total number of lateral roots per cm small root (diameter 2–5 mm) was significantly lower in both species for declining trees compared to healthy trees. Pythium spp. were isolated from 15 of 24 soil samples taken from under spruce, and from eight of 16 samples from under beech. Phytophthora citricola was found in two beech stands only. Among the isolated species, Pythium anandrum, Pythium inflatum and Pythium acrogynum were identified according to morphological features. After polymerase chain reaction-restriction fragment length polymorphism analysis, residual Pythium isolates were assigned to four different groups. No crown transparency-dependent differences in isolation frequency were found. In soil infestation tests, all species tested caused root damage on both young spruce and beech plants, with P. citricola being the most aggressive pathogen. Additionally, Pythium-infected beeches showed severe leaf chloroses and necroses. Due to their low isolation frequency, Phytophthora spp. are not considered to play a major role in the decline of spruce and beech in the investigated area. Pythium spp., however, were isolated frequently, showed pathogenicity towards the fine roots of spruce and beech, and are therefore considered to be at least contributing factors in the decline of Bavarian mountain forests. Etude comparee de l’etat des racines fines d’epiceas et de hetres, sains ou deperissants, dans les Alpes bavaroises, et presence d’especes de Phytophthora et de Pythium Les travaux sur l’etat des racines et du houppier de l’epicea et du hetre dans les Alpes bavaroises ont ete realises dans la region ‘Werdenfelser Land’ (sud de l’Allemagne). Les parasites racinaires des genres Phytophthora et Pythium associes a la rhizosphere des arbres ont egalement eteetudies. Dans un certain nombre de peuplements en conditions variees, des echantillons de sol et de racines ont ete preleves sur 12 couples d’epiceas et 8 couples de hetres. Chaque couple comprenait un arbre sain et un arbre deperissant, evalues d’apres la transparence du houppier. L’etat racinaire a ete caracterise en utilisant un ensemble de parametres, et des correlations entre l’etat des racines et celui du houppier ont ete obtenues. Chez l’epicea, la plupart des parametres diminuaient significativement quand la transparence augmentait; chez le hetre, les correlations etaient moins nettes. Le nombre total de racines laterales par cm de petite racine (diametre 2–5 mm) etait significativement plus faible chez les arbres deperissants des deux especes, que chez les arbres sains. Des Pythium spp. ont ete isoles chez 15 echantillons de sol parmi les 24 preleves sous epicea, et chez 8 sur 16 dans le cas du hetre. Phytophthora citricola n’a ete trouve que dans deux hetraies. Parmi les especes isolees, Pythium anandrum, P. inflatum et P. acrogynum ont ete identifies morphologiquement. Apres analyse PCR-RFLP, les autres isolats de Pythium ont ete repartis entre 4 groupes differents. Aucune difference liee a la transparence n’a ete trouvee pour la frequence d’isolement. Dans des tests d’infection par le sol, toutes les especes testees causaient des degâts racinaires a l’epicea et au hetre, P. citricolaetant le plus agressif. Les hetres infectes par Pythium ont presente d’importantes chloroses et necroses foliaires. A cause de leur faible taux d’isolement, on considere que les Phytophthora spp. ne jouent pas un role majeur dans le deperissement de l’epicea et du hetre, dans la zone etudiee. Cependant, les Pythium spp. ayant ete isoles frequemment et s’etant montres parasites vis-a-vis les racines fines de l’epicea et du hetre, ils doivent etre consideres au moins comme des facteurs qui contribuent au deperissement dans les forets de montagne de la Baviere. Vergleichende Untersuchungen zum Feinwurzelzustand von gesunden und kranken Fichten und Buchen in den Bayerischen Alpen sowie zum Vorkommen von Phytophthora- und Pythium-Arten An ausgesuchten Probebaumen im Werdenfelser Land wurde untersucht, ob ein Zusammenhang zwischen Kronen-und Feinwurzelzustand von Fichten und Buchen im Bayerischen Alpenraum besteht. Auch wurde gepruft, ob bodenburtige Wurzelpathogene aus den Gattungen Phytophthora und Pythium an den festgestellten Feinwurzelschaden beteiligt sind. Auf unterschiedlichen Standorten wurden von insgesamt 12 Fichten-und 8 Buchen-Baumpaaren, die unterschiedliche Kronenzustande reprasentierten, Boden-und Wurzelproben entnommen. Nach Charakterisierung des Wurzelzustandes mit Hilfe verschiedener Wurzelparameter liesen sich insbesondere bei der Fichte bei den meisten Parametern signifikant negative Korrelationen zum Verlichtungsgrad der Krone feststellen. Bei der Buche waren diese Zusammenhange weniger straff und nicht statistisch absicherbar. Bei dem Parameter “Seitenwurzeln pro cm Tragerwurzel” waren bei beiden Baumarten signifikante Unterschiede zwischen gesund erscheinenden und verlichteten Βaumen festzustellen. Bei Isolierversuchen konnten aus 15 von 24 unter Fichten, und aus 8 von 16 unter Buchen entnommenen Bodenproben Pythium-Arten isoliert werden, wahrend in nur 2 Bestanden an Buche Phytophthora citricola gefunden wurde. Isoliert wurden u.a. Pythium anandrum, P. inflatum und P. acrogynum. Die ubrigen Pythium-Isolate konnten morphologisch, sowie nach PCR-RFLPs in 4 Gruppen eingeteilt werden. Die Isolierrate zeigte keine Abhangigkeit vom Kronenzustand des jeweiligen Baumes. In Infektionsversuchen losten alle getesteten Arten Schaden am Wurzelsystem junger Fichten und Buchen aus, wobei sich P. citricola als am aggressivsten gegenuber beiden Baumarten erwies. Pythium-Arten losten auserdem deutliche Blattsymptome an den infizierten Buchen aus. In der Diskussion wird der Gattung Phytophthora trotz der Ergebnisse der Infektionsversuche aufgrund der geringen Isolierrate keine Bedeutung fur die Verlichtungserscheinungen in den untersuchten Waldern zugeschrieben. Pythium-Arten dagegen konnten, aufgrund der nachgewiesenen Aggressivitat und der hohen Isolierfrequenz, an den dort beobachteten Schaden beteiligt sein.

In a 3-year-study, we analysed the population dynamics of the reed pathogen Pythium phragmitis and other reed-associated oomycetes colonizing fresh and dried reed leaves in the littoral zone of a large lake. Oomycete communities derived from internal transcribed spacer clone libraries were clearly differentiated according to substrate and seasonal influences. In fresh leaves, diverse communities consisting of P. phragmitis and other reed-associated pathogens were generally dominant. Pythium phragmitis populations peaked in spring with the emergence of young reed shoots, and in autumn after extreme flooding events. In summer it decreased with falling water levels, changing water chemistry and rising temperatures. Another Pythium species was also highly abundant in fresh leaves throughout the year and might represent a new, as-yet uncultured reed pathogen. In dried leaves, reed pathogens were rarely detected, whereas saprophytic species occurred abundantly during all seasons. Saprophyte communities were less diverse, less temperature sensitive and independent of reed development. In general, our results provide evidence for the occurrence of highly specialized sets of reed-associated oomycetes in a natural reed ecosystem. Quantitative analyses (clone abundances and quantitative real-time PCR) revealed that the reed pathogen P. phragmitis is particularly affected by changing water levels, water chemistry and the stage of reed development.

A comparison of oomycete diversity in reed stands (Phragmites australis) of Lake Constance, Germany, and maize fields close by provided evidence for the occurrence of natural hybridization between Pythium phragmitis, a newly described reed pathogen, and an as-yet unknownPythiumspecies closely related to P. phragmitis and P. arrhenomanes. Internal transcribed spacer and ß-tubulin sequences of a large set of Pythium isolates from reeds showed dimorphic signals at several positions, indicative of a mixture of characters of two parent species. Involvement of P. phragmitis in the putative hybrid species was confirmed after cloning and sequencing of ITS regions and ß-tubulin genes of the hybrid isolates. Mitochondrially inherited coxII gene sequences did not show dimorphic sites and suggested that the hybridization event was relatively ancient, or that other species might be involved. Intermediate habitat preferences, morphological characters and aggressiveness towards reeds and other grasses confirmed the suggestion that these isolates comprise a natural hybrid between two Pythium species.Pythium arrhenomanes, likely to be involved in the putative hybrid s evolution, wasrepeatedly isolated from maize fields adjacent to P. phragmitis-infested reed stands. The interface between natural habitats with established oomycete communities and agricultural fields with potentially introduced pathogens might constitute an evolutionary hot-spot giving rise to new species with as-yet unknown host ranges. As indicated by inoculation tests, the hybrid was significantly more pathogenic towards reed rhizomes thanP. phragmitis, which caused no damage to these organs. This is apparently the first report of the occurrence of natural hybridization in Pythium.

Coinciding with a population decline in the invasive spiny-cheek crayfish Orconectes limosus in Lake Constance. SW Germany, we found crayfish specimens with a fungus-like Aufwuchs which after DNA-isolation and sequencing was identified as consisting of a set of previously undescribed Saprolegnia species. This finding may have implications for the farming and conservation of native crayfish as well as for the lake's ecosystem. We propose that spiny-cheek crayfish might function as a disease vector for these potential pathogens.

Pythium species are economically significant soilborne plant pathogens with worldwide distribution, causing seedling damping-off or root rot diseases. Pythium phragmitis is a newly described pathogen of common reed (Phragmites australis), widespread in the reed-belt of Lake Constance, Germany. It is highly aggressive towards reed leaves and seedlings, but obviously does not affect roots. In the context of ‘reed decline’ phenomena, P. phragmitis infection of reed inundated during flooding events may be of particular significance. We could show that flooding itself is not necessarily detrimental for reed plants. In the presence of the pathogen, however, most submerged leaves and plants were killed within several weeks. Clipped plants did not show regrowth in the Pythium infested treatments. Significant losses in assimilating leaf area of reeds could, thus, be the result of Pythium infection rather than of flooding alone. Therefore, we suggest that the combination of extended flooding and the presence of P. phragmitis might considerably contribute to ‘reed decline’ at Lake Constance. In parallel, we could show that pathogenicity and spread of this species are considerably favoured by rising temperatures. Since an increase in average water temperature has been found for Lake Constance, we propose that P. phragmitis could be an important factor in the dieback of reed stands likely to be promoted by predicted climate change phenomena.

A non-papillate, slow-growing Phytophthora species, which could not be assigned to any existing taxon, was isolated from rhizosphere soil of a declining oak in Northeast France, and from the rhizosphere of Phragmites australis at Lake Constance in south-west Germany in 1998 and 2004, respectively. We describe this species, previously informally designated Phytophthora taxon ‘G’, as Phytophthora gallica sp. nov. Morphology, growth rates, and pathogenicity against cuttings of riparian tree species and leaves of reed are described and compared with those of morphologically and phylogenetically similar Phytophthora species. P. gallica produces colonies with limited aerial mycelium and variable growth patterns. Gametangia are not formed in single or mixed cultures with tester strains of known mating types. P. gallica produces globose and elongated irregular chlamydospores, of which a high proportion is abortive. In water culture irregular hyphal swellings and non-papillate persistent sporangia are formed abundantly. P. gallica is moderately aggressive to Alnus glutinosa and Fagus sylvatica, weakly aggressive to Quercus robur and Salix alba and non-pathogenic to Fraxinus excelsior and Phragmites australis. According to ITS and mtDNA sequence data P. gallica belongs to a distinct Phytophthora clade, with P. boehmeriae and P. kernoviae being the closest relatives. The origin of P. gallica and its ecological role in wet ecosystems remain unclear.

A description is given of Pythium litorale sp. nov., a new species from reed stands in Germany. Pythium litorale was among the most abundant species when the oomycete community of littoral soils of Lake Constance was studied. It was consistently isolated from flooded as well as from drier reed sites. The species is characterized by subglobose, papillate and internally proliferating sporangia, globose hyphal swellings, the absence of oogonia in single culture and a high optimum growth temperature. It proved to be nonpathogenic to Phragmites australis, the predominating plant in the investigated sites. Molecular analysis of ribosomal DNA internal transcribed spacer regions placed Pythium litorale in a clade together with its closest relatives Pythium megacarpum, Pythium boreale, Pythium montanum and Pythium carbonicum. The generic status of this basal clade in Pythium is currently under discussion, as it possibly represents a separate genus that is distinct from Pythium, and shares several characteristics with Phytophthora.

During a study on the occurrence and pathogenicity of oomycetes in the reed-belt (Phragmites australis) of Lake Constance (Germany), a new Pythium resembling the important cereal pathogen species complex P. arrhenomanes/P. graminicola was consistently isolated from necrotic mature reed leaves and reed rhizosphere samples. The new species proved to be significantly more aggressive towards reed leaves and seedlings in vitro than related species. It is characterised by filamentous, inflated sporangia and plerotic oospores with usually more than one antheridium. ITS and cox II sequence data indicate this new species shares a common ancestor with P. arrhenomanes, but the sequence differences are clearly consistent with a divergence of the two taxa and with P. phragmitis being a distinct species. ITS 1 and 2 of 15 isolates of the taxon consistently differed from P. arrhenomanes by 13 positions. Sequence analyses of the cox II gene confirmed the new species' phylogenetic position. This paper gives a formal description of the taxon as P. phragmitis sp. nov., providing information on morphology, ecology and pathogenicity in comparison to related species. As indicated by the close association to Phragmites australis, the high aggressiveness towards reed leaves and seedlings, and the abundance in the investigated stands, Pythium phragmitis might act as a reed pathogen of considerable importance, in particular under flooding situations.

The genus Phytophthora (Greek “plant destroyer”) includes many soilborne species which cause root and collar rot symptoms of herbaceous and woody plants including different forest trees. This review will focus on Phytophthora diseases of forest trees, as their significance has increased in recent years. Chlorosis, necrosis and wilt symptoms can be seen on leaves in the whole crown before the tree dies. However, death can take several years. All soil-borne Phytophthora species share a common infection cycle which is summarized in Fig. 1. Open image in new window Fig. 1. The infection cycle of soil-borne Phytophthora species