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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.

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.

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 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 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.