Metabolic potential of microorganisms associated with the halophyte Aster tripolium L. in saline soils

Increased soil salinization may be caused by a natural (e.g. climate change) and anthropogenic (e.g. improper fertilization and irrigation of agricultural land) factors. The submitted work assumes that microorganisms associated with plant halophytes have a unique metabolic properties that can stimulate plant growth under salt stress. The aim of the study was to determine the abundance and metabolic biodiversity of endophytic and rhizosphere microorganisms co-existing with Aster tripolium L. and compare them with the properties of soil microorganisms not affected by plant roots at a salty meadows in the vicinity of a soda factory (central Poland). In order to select halotolerant and halophilic microorganisms culture medium was enriched with various concentrations of NaCl (0, 100, 200, 400, 600 mM NaCl). Total metabolic activity of endophytic, rhizosphere and soil populations was measured to compare the community-level physiological profiles. Results of our study revealed that bacterial and fungal density increased in the following order: endophytes < soil < rhizosphere. Only the highest concentration (600 mM) of NaCl decreased the number of microorganisms. The highest total microbial metabolic activity was observed for the rhizosphere, while the activity of endophytes was higher compare to soil populations. To carbon sources which significantly differentiated zones belonged: D-lactose, 4-hydroxybenzoic acid and L-asparagine. The results are preliminary studies leading to the development of inoculum based on selected microbial halotolerant and halophilic strains which can be used in agriculture and/or recultivation of saline soils

Strigolactones as mediators between fungi and plants

A constantly changing environment is challenging for all organisms on Earth, especially for terrestrial plants, which face several environmental stresses despite their static way of life. In attempts to understand the mechanisms responsible for plant growth and development, scientists have recently focused on a small group of carotenoid derivatives called “strigolactones” (SLs), which are synthesized mostly in the roots in response to a variety of external factors. Strigolactones are compounds that define plant plasticity towards many environmental factors, including the establishment of mycorrhizal symbiosis under nutrient-deficient conditions. As exogenous signals, they can stimulate the branching of arbuscular mycorrhizal fungal (AMF) hyphae and as endogenous signals they adjust a plant architecture, including changes within the roots, allowing host plant and fungi to meet. SLs can also function as signaling molecules that allow colonization and establishment of the later stages of mutualistic symbioses between organisms such as AMF. SLs act on AMF metabolism by stimulating its mitochondrial respiration. Genes encoding enzymes crucial for SL biosynthesis – CCD7 and CCD8 – are also found in gymnosperm genomes, which encourages speculation that strigolactones may also be part of a host-plant and ectomycorrhizal fungi signaling pathway during the establishment of symbiosis. Nevertheless, SLs impact on ectomycorrhiza formation remain unknown. The broad spectrum of SL bioactivity has made these compounds valuable from an industrial perspective. In the future, SLs may be commercialized in plant protection products, biostimulants, or as substances used in genetic engineering to allow the creation of crops capable of growing under disadvantageous conditions

The Contribution of Endomycorrhiza to the Performance of Potato Virus Y-Infected Solanaceous Plants: Disease Alleviation or Exacerbation?

Solanaceae, comprising meaningful crops (as potato, tomato, pepper, eggplant, and tobacco), can benefit from a symbiosis with arbuscular mycorrhizal fungi (AMF), which improve plant fitness and support plant defense against pathogens. Currently, those crops are likely the most impacted by Potato virus Y (PVY). Unfortunately, the effects of AM symbiosis on the severity of disease induced by PVY in solanaceous crops remain uncertain, partly because the interplay between AMF and PVY is poorly characterized. To shed some light on this issue, available studies on interactions in tripartite association between the host plant, its fungal colonizer, and viral pathogen were analyzed and discussed. Although the best-documented PVY transmission pathway is aphid-dependent, PVY infections are also observed in the absence of insect vector. We hypothesize the existence of an additional pathway for virus transmission involving AMF, in which the common mycorrhizal network (CMN) may act as a potential bridge. Therefore, we reviewed (1) the significance of AM colonization for the course of disease, (2) the potential of AMF networks to act as vectors for PVY, and (3) the consequences for crop breeding and production of AM biofertilizers

Diversität von Ektomykorrhizapilzen unter Pioniervegetation auf einem küstennahen Regosol

Die natürliche Pioniervegetation auf küstennahen Regosolen in Norddeutschland umfasst mehrere Wirtspflanzen von Ektomykorrhizapilzen, wie z.B. Salix, Populus und Pinus spp.. Ektomykorrhizapilze können auf diesen stark erosionsgefährdeten Standorten durch die Ausbildung von abziehenden Hyphen bzw. Rhizomorphen zur Stabilisierung der Oberböden beitragen. In der vorliegenden Untersuchung wurde die Diversität von Ektomykorrhizen an Salweiden (Salix caprea) auf einem küstennahen Regosol in einem Zeitraum von zwei Jahren morphologisch-anatomisch beschrieben und die beteiligten Pilzpartner über die Sequenzierung der rDNA identifiziert. Es wurden 11 Arten aus 8 Gattungen von Asco- und Basidiomyceten nachgewiesen, deren Verbreitung einer zeitlichen Dynamik unterlag. Dunkel pigmentierte Tomentella spp. (Thelephoraceae) und kurz-Distanz Explorationstypen dominierten die Ektomykorrhizierung der Salweiden jedoch unabhängig vom Probenahmetermin

Bacterial and Fungal Endophytic Microbiomes of Salicornia europaea

We examined Salicornia europaea, a nonmycorrhizal halophyte associated with specific and unique endophytic bacteria and fungi. The microbial community structure was analyzed at two sites differing in salinization history (anthropogenic and naturally saline site), in contrasting seasons (spring and fall) and in two plant organs (shoots and roots) via 16S rRNA and internal transcribed spacer amplicon sequencing. We observed distinct communities at the two sites, and in shoots and roots, while the season was of no importance. The bacterial community was less diverse in shoot libraries than in roots, regardless of the site and season, whereas no significant differences were observed for the fungal community. Proteobacteria and Bacteroidetes dominated bacterial assemblages, and Ascomycetes were the most frequent fungi. A root core microbiome operational taxonomic unit belonging to the genus Marinimicrobium was identified. We detected a significant influence of the Salicornia bacterial community on the fungal one by means of cocorrespondence analysis. In addition, pathways and potential functions of the bacterial community in Salicornia europaea were inferred and discussed. We can conclude that bacterial and fungal microbiomes of S. europaea are determined by the origin of salinity at the sites. Bacterial communities seemed to influence fungal ones, but not the other way around, which takes us closer to understanding of interactions between the two microbial groups. In addition, the plant organs of the halophyte filter the microbial community composition

AMF species do matter: Rhizophagus irregularis and Funneliformis mosseae affect healthy and PVY-infected Solanum tuberosum L. in a different way

Arbuscular mycorrhizal fungi (AMF) were documented to positively influence plant growth and yield, which is extremely important for the production of many crops including potato. However, the nature of the interaction between arbuscular mycorrhiza and plant virus that share the same host is not well characterized. In this study, we examined the effect of different AMF, Rhizophagus irregularis and Funneliformis mosseae, on healthy and potato virus Y (PVY)-infected Solanum tuberosum L. The analyses conducted included the measurement of potato growth parameters, oxidative stress indicators, and photosynthetic capacity. Additionally, we evaluated both the development of AMF in plant roots and the virus level in mycorrhizal plants. We found that two AMF species colonized plant roots to varying degrees (ca. 38% for R. irregularis vs. 20% for F. mosseae). Rhizophagus irregularis had a more positive effect on potato growth parameters, causing a significant increase in the total fresh and dry weight of tubers, along with virus-challenged plants. Furthermore, this species lowered hydrogen peroxide levels in PVY-infected leaves and positively modulated the levels of nonenzymatic antioxidants, i.e., ascorbate and glutathione in leaves and roots. Finally, both fungal species contributed to reduced lipid peroxidation and alleviation of virus-induced oxidative damage in plant organs. We also confirmed an indirect interaction between AMF and PVY inhabiting the same host. The two AMF species seemed to have different abilities to colonize the roots of virus-infected hosts, as R. irregularis showed a stronger drop in mycorrhizal development in the presence of PVY. At the same time, arbuscular mycorrhiza exerted an effect on virus multiplication, causing increased PVY accumulation in plant leaves and a decreased concentration of virus in roots. In conclusion, the effect of AMF-plant interactions may differ depending on the genotypes of both symbiotic partners. Additionally, indirect AMF-PVY interactions occur in host plants, diminishing the establishment of arbuscular mycorrhiza while changing the distribution of viral particles in plants

Site-Effects Dominate the Plant Availability of Nutrients under Salix Species during the First Cutting Cycle

Fast-growing willows (Salix spp.) provide alternative sources of renewable energy generation, but need an adequate nutrient availability in the soil for high biomass production. In general, species mixtures can be more nutrient-efficient than pure cultures, but this is scarcely known for Salix spp. Therefore, this study evaluates the nutrient availability and P mobilization under two willow species, Salix dasyclados var. 'Loden' and S. schwerinii x viminalis var. 'Tora', grown as pure and mixed cultures at non-fertilized former arable sites in Germany (Stagnic Cambisol) and Sweden (Vertic Cambisol). The plant availability of potassium (K), magnesium (Mg) and phosphorus (P) and soil phosphatase activities in the topsoil were measured in spring of the year of planting (initial) and under 4 years-old stocks (one year after the first 3-year cutting cycle). The initial plant availability of the nutrients significantly differed between the sites and the two sampling dates at both sites. The plant availability of K and Mg was optimal to high at both sites and sampling dates, but rather low for P (after 4 years <= 5 mg P 100 g(-1) soil). The plant-available P and K content in soil significantly decreased within the 4 years of willow growth at both sites. The acid and alkaline phosphatase activity in the soil of the German site (Rostock) was significantly lower after 4 years of willow growth, but differed not significantly between the two sampling dates at the Swedish site (Uppsala). Higher activity of acid phosphatase compared to alkaline phosphatase was recorded in the soils at both test sites based on the site-specific soil pH (<7). The slight decrease of plant availability of P after 4 years of Salix growth in pure culture differed not significantly between the different species. Mixed growth did not decrease the plant availability of P within this period, although no significant difference in the biomass production of pure and mixed growth was observed. This was valid at both sites, and therefore, seems independent of the site-specific differences in soil and climate conditions. The general validity of the assumptions should be tested also for other species mixtures and soil conditions in the future before site-adapted growth designs can be recommended in biomass production of Salix

Wrażliwość odmian jarych i ozimych rzepaku na metale ciężkie i bakterie glebowe

Sprawdzono wpływ metali ciężkich (cynk, kadm, miedź, ołów) oraz bakterii ryzosferowych na wzrost siewek Brassica napus L. Przeanalizowano trzy odmiany rzepaku: dwie jare – Belinda i Clipper oraz jedną ozimą – Kronos. Wykazano, że porównywane odmiany charakteryzowały się zróżnicowaną wrażliwością na obecność metali ciężkich w środowisku. Najbardziej wrażliwa na metale ciężkie była odmiana ozima Kronos, natomiast najmniej – odmiana Clipper. Wszystkie analizowane szczepy ryzobakterii: Bacillus sp., Bacteroidetes bacterium, Flavobacterium sp., Luteibactor rhizovicina, Pseudomonas fluorescens, Serratia entomophila i Variovorax sp. sty-mulowały wzrost siewek, zwłaszcza korzeni, odmian jarych rzepaku, zaś hamowały w przypadku odmiany ozimej. Szczepy Bacteroidetes bacterium i Bacillus sp. najsilniej stymulowały wzrost siewek odmiany Kronos, a Flavobacterium sp. siewek odmiany Belinda w obecności miedzi, cynku i kadmu. Większość badanych bakterii ułatwiała rozwój siewek odmiany Clipper w środowisku zanieczyszczonym jonami cynku i ołowiu.We have examined the impact of heavy metals (zinc, cadmium, copper, lead) and rhizobacteria on the growth of seedlings of Brassica napus L. We analyzed three varieties of rape: two spring – Belinda and Clipper and one winter – Kronos. It was shown that the varieties possess different sensitivity to heavy metals in the environment. The most sensitive to heavy metals was Kronos winter variety, and the least – Clipper. All analyzed rhizobacteria strains: Bacillus sp, Bacteroidetes bacterium, Flavobacterium sp., Luteibactor rhizovicina, Pseudomonas fluorescens, Serratia entomophila and Variovorax sp. stimulated the growth of seedlings, especially their roots, of spring rape varieties, but inhibited in case of winter variety. Bacteroidetes bacterium and Bacillus sp. strains mostly stimulated the growth of winter cultivar, and Flavobacterium sp. of Belinda variety in the presence of copper, zinc and cadmium. Almost all studied bacteria promoted growth of Clipper seedlings in the environment polluted by zinc and lead

Interactive physiological response of potato (Solanum tuberosum L.) plants to fungal colonization and Potato virus Y (PVY) infection

Potato plants can be colonized by various viruses and by symbiotic, saprophytic and pathogenic fungi. However, the significance of interactions of viral infection and fungal colonization is hardly known. This work presents a model experiment in which the influence of three different types of fungal associations on the growth and physiology of the potato variety Pirol was tested individually or in combination with infection by PVY. It was hypothesized that simultaneous viral and fungal infections increase the biotic stress of the host plant, but mutualistic plant-fungal associations can mask the impact of viral infection. In the present study, a symbiotic arbsucular mycorrhizal fungus, Glomus intraradices, significantly stimulated the growth of plants infected with PVY. In contrast, two saprophytic Trichoderma spp. strains either did not influence or even inhibited the growth of PVY-infected plants. Also, inoculation of PVY-infected potato plants with a pathogenic strain of Colletotrichum coccodes did not inhibit the plant growth. Growth of the PVY-free potato plants was not promoted by the symbiotic fungus, whereas T. viride, T. harzianum and C. coccodes had an evident inhibitory effect. The strongest growth inhibition and highest concentration of H2O2, as an indicator of biotic stress, was observed in PVY-free potato plants inoculated with T. harzianum and C. coccodes strains. Surprisingly, ultrastructural analysis of PVY-infected plant roots colonized by G. intraradices showed virus-like structures in the arbuscules. This pointed to the possibility of mycorrhizal-mediated transmission of virus particles and has to be further examined by testing with immunoassays and real transmission to uninfected plants. In conclusion, although mycorrhiza formation might decrease the impact of PVY infection on plants, a possible role of mycorrhizal fungi as virus vectors is discussed