Jan Nechwatal

Phytophthora pseudosyringae sp. nov., a new species causing root and collar rot of deciduous tree species in Europe

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.

Diversity, host, and habitat specificity of oomycete communities in declining reed stands (Phragmites australis) of a large freshwater lake

We studied the diversity of oomycetes in a declining reed belt (Phragmites australis) of Lake Constance, Germany, using conventional baiting with specific reed and standard oak baits, accompanied by molecular techniques. Apart from an Aphanomyces sp. and a Phytophthora sp., baiting from reed rhizosphere samples from flooded, as well as drier, littoral sites revealed only Pythium spp. A total of 67 oomycete isolates was classified according to PCR-RFLP banding patterns and ITS sequencing, and 18 different sequence types could be separated. The majority of these seemed previously unknown species, as indicated by the degree of similarity to those deposited in nucleotide databases. Species communities in both flooded and drier habitats or both reed and oak baits clearly differed from one another, and only few species occurred in both dry and flooded sites, or in both oak and reed baits. A frequently occurring group of related Pythium species appeared to be specifically associated with reed, and these were the only species that proved pathogenic towards this host in vitro. Our study proved that unexplored natural ecosystems harbour diverse communities of oomycete species with specific habitat and host preferences within close-by, but ecologically contrasting, sites. Among the species isolated, those associated with the predominating plant might accumulate and thus may be reed pathogens of considerable importance.

Flooding events and rising water temperatures increase the significance of the reed pathogen Pythium phragmitis as a contributing factor in the decline of Phragmites australis

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.

Pythium montanum sp. nov., a new species from a spruce stand in the Bavarian Alps

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.

Host plant development, water level and water parameters shape Phragmites australis‐associated oomycete communities and determine reed pathogen dynamics in a large lake

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.

New Insights in the Genus Phytophthora and Current Diseases These Pathogens Cause in Their Ecosystem

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

Quantitative methods for assessment of the impact of different crops on the inoculum density of Rhizoctonia solani AG2-2IIIB in soil

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.

Potential suitability of various leaf treatment products as copper substitutes for the control of late blight (Phytophthora infestans) in organic potato farming

In organic potato production, late blight caused by Phytophthora infestans can cause severe losses in potato yield and quality. Currently, it can only be effectively controlled by the use of copper fungicides in some countries. In the course of a project aiming at the reduction of copper usage, potential copper-free products against late blight for organic farming were identified. Laboratory, greenhouse, and field tests were performed with a selection of commercial and non-commercial copper-free preparations as potential substitutes for copper. Data from lab tests with detached leaves are now available for more than 20 alternative products, some of which had efficiencies close to that of the copper fungicide control, including some degree of post-infectional effects. Climate chamber tests with whole potted plants confirmed these results for the most promising preparations, with almost no damage occurring on the treated plants. Data from field tests were less compelling but still highlighted some late blight reducing potential for some of the alternative products, in particular chitosan, a liquorice and a horsetail test product, and a copper fertilizer. In the future, these might possibly be used for applications mixed or alternating with copper, and thus might allow a further reduction in the use of copper fungicides in organic potato production.

Studien zur Bekämpfung von Phytophthora ramorum an Rhododendron im Rahmen der Entwicklung eines Behandlungskonzeptes für Park- und Gartenanlagen@@@Studies on the Control of Phytophthora ramorum on Rhododendron for the Development of Management Strategies in Parks and Gardens

ZusammenfassungIm Rahmen der hier dargestellten Untersuchungen zur Entwicklung eines Behandlungskonzeptes gegen Phytophthora ramorum-Befall in Rhododendron-Beständen wurden verschiedene Pflanzenschutz-, Pflanzenstärkungs- und Düngemittel auf ihre Wirksamkeit gegen P. ramorum auf Rhododendron getestet. Die Versuche wurden an künstlich infizierten, jungen Rhododendron-Pflanzen und abgetrennten Blättern mit folgenden Präparaten durchgeführt: Phosphit (Nutri-Phite® PK), Kupfer-Hydroxid (Cuprozin® flüssig), Bacillus subtilis (Serenade®), Mykorrhiza, und ein Präparat auf Basis von ‚Effektiven Mikroorganismen‘ (EMa). Zwar konnte die Übertragung 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 tatsächlich signifikante Effekte auf die Befallsentwicklung hatten. Alle anderen Präparate, die auf antagonistischen und/oder wachstumsfördernden Mikroorganismen basieren, hatten keine signifikant präventive oder kurative Wirkung. B. subtilis wirkte sich dabei tendenziell eher symptomverstärkend aus, die übrigen Präparate bewirkten eine leichte Verminderung des Befalls. Phosphit und Cu-Hydroxid dagegen konnten einen Befall nahezu komplett verhindern. In Freilandbeständen scheint somit der Einsatz des ökologisch unbedenklichen, systemischen Phosphit-Präparates gegen Phytophthora-Befall an Rhododendron sinnvoll und angeraten. Im Zusammenspiel mit anderen unterstützenden Maßnahmen kann dies im Rahmen eines Behandlungskonzeptes die weitere Ausbreitung von P. ramorum verhindern oder zumindest verlangsamen.AbstractIn this study dealing with the development of management strategies for P. ramorum in Rhododendron stands several plant protection and fertilizer products were tested for their suitability to control this pathogen on Rhododendron. Tests were conducted on young potted plants and abscised leaves, using the following products: phosphite (Nutri-Phite® PK), copper hydroxide (Cuprozin® liquid), Bacillus subtilis (Serenade®), a mycorrhizal preparation, and a product based on ‘effective microorganisms’ (EMa). Although transmission of the pathogen from infected to healthy plants was successfully inhibited by phosphite, Cu hydroxide and B. subtilis, subsequent tests showed that only phosphite and Cu hydroxide had a significant effect on disease development. All other preparations based on antagonistic or growth promoting microorganisms had no preventive or curative effect. While B. subtilis tended to increase disease symptoms, the remaining products caused a slight reduction of disease severity only. In contrast, phosphite and Cu hydroxide almost completely inhibited infection by P. ramorum. Therefore, in field situations, the use of the ecologically safe, systemic phosphite against P. ramorum in Rhododendron stands appears to be reasonable and advisable. Along with other supporting measures within the framework of a management strategy, this will allow to prevent or slow down further spread of the disease.

Studien zur Bekämpfung von Phytophthora ramorum an Rhododendron im Rahmen der Entwicklung eines Behandlungskonzeptes für Park- und Gartenanlagen

ZusammenfassungIm Rahmen der hier dargestellten Untersuchungen zur Entwicklung eines Behandlungskonzeptes gegen Phytophthora ramorum-Befall in Rhododendron-Beständen wurden verschiedene Pflanzenschutz-, Pflanzenstärkungs- und Düngemittel auf ihre Wirksamkeit gegen P. ramorum auf Rhododendron getestet. Die Versuche wurden an künstlich infizierten, jungen Rhododendron-Pflanzen und abgetrennten Blättern mit folgenden Präparaten durchgeführt: Phosphit (Nutri-Phite® PK), Kupfer-Hydroxid (Cuprozin® flüssig), Bacillus subtilis (Serenade®), Mykorrhiza, und ein Präparat auf Basis von ‚Effektiven Mikroorganismen‘ (EMa). Zwar konnte die Übertragung 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 tatsächlich signifikante Effekte auf die Befallsentwicklung hatten. Alle anderen Präparate, die auf antagonistischen und/oder wachstumsfördernden Mikroorganismen basieren, hatten keine signifikant präventive oder kurative Wirkung. B. subtilis wirkte sich dabei tendenziell eher symptomverstärkend aus, die übrigen Präparate bewirkten eine leichte Verminderung des Befalls. Phosphit und Cu-Hydroxid dagegen konnten einen Befall nahezu komplett verhindern. In Freilandbeständen scheint somit der Einsatz des ökologisch unbedenklichen, systemischen Phosphit-Präparates gegen Phytophthora-Befall an Rhododendron sinnvoll und angeraten. Im Zusammenspiel mit anderen unterstützenden Maßnahmen kann dies im Rahmen eines Behandlungskonzeptes die weitere Ausbreitung von P. ramorum verhindern oder zumindest verlangsamen.AbstractIn this study dealing with the development of management strategies for P. ramorum in Rhododendron stands several plant protection and fertilizer products were tested for their suitability to control this pathogen on Rhododendron. Tests were conducted on young potted plants and abscised leaves, using the following products: phosphite (Nutri-Phite® PK), copper hydroxide (Cuprozin® liquid), Bacillus subtilis (Serenade®), a mycorrhizal preparation, and a product based on ‘effective microorganisms’ (EMa). Although transmission of the pathogen from infected to healthy plants was successfully inhibited by phosphite, Cu hydroxide and B. subtilis, subsequent tests showed that only phosphite and Cu hydroxide had a significant effect on disease development. All other preparations based on antagonistic or growth promoting microorganisms had no preventive or curative effect. While B. subtilis tended to increase disease symptoms, the remaining products caused a slight reduction of disease severity only. In contrast, phosphite and Cu hydroxide almost completely inhibited infection by P. ramorum. Therefore, in field situations, the use of the ecologically safe, systemic phosphite against P. ramorum in Rhododendron stands appears to be reasonable and advisable. Along with other supporting measures within the framework of a management strategy, this will allow to prevent or slow down further spread of the disease.