Antioxidant response in arbuscular mycorrhizal fungi inoculated wetland plant under Cr stress.

Arbuscular mycorrhizal fungi (AMF) provide a positive effect on antioxidant mechanisms in terrestrial plants under heavy metal stress. This study investigated the effects of AMF on wetland plant (Iris wilsonii) growth and antioxidant response under Cr stress at different water depths. Results showed that AMF inoculated I. wilsonii had higher antioxidant response than non-inoculated controls, with shoot superoxide dismutase (SOD), root SOD, shoot peroxidase (POD), and root POD contents increased by 4.7-39.6%, 7.5-29.5%, 11.2-68.6%, 16.8-50.3%, respectively. Meanwhile, shoot (root) proline, malondialdehyde (MDA) and superoxide anion (O2.-) contents in the AMF inoculated I. wilsonii were 10.2-44.3% (2.8-37.2%), 11.5-35.4% (16.9-28.2), and 14.9-30.5% (-0.9-26.3%) lower than those in the non-inoculated controls, respectively. Besides, AMF improved the growth of I. wilsonii with biomass, height, chlorophyll, K, and P contents in the shoots increased by 10.5-32.5%, 17.4-44.9%, 4.7-37.7%, 12.0-30.7%, 13.5-20.6%, respectively. Moreover, the I. wilsonii tolerance to Cr stress was also enhanced under the water depth of 6-3 cm. Therefore, AMF play an important role in wetland plant growth and antioxidant response under Cr stress, and it can improve wetland plants' tolerance to Cr stress at fluctuating water depth.

Using microbial seed coating for improving cowpea productivity under a low-input agricultural system.

BACKGROUND: Plant-growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal (AM) fungi have the ability to enhance the growth, fitness, and quality of various agricultural crops, including cowpea. However, field trials confirming the benefits of microbes in large-scale applications using economically viable and efficient inoculation methods are still scarce. Microbial seed coating has a great potential for large-scale agriculture through the application of reduced amounts of PGPR and AM fungi inocula. Thus, in this study, the impact of seed coating with PGPR, Pseudomonas libanensis TR1 and AM fungus, Rhizophagus irregularis (single or multiple isolates) on grain yield and nutrient content of cowpea under low-input field conditions was evaluated. RESULTS: Seed coating with P. libanensis + multiple isolates of R. irregularis (coatPMR) resulted in significant increases in shoot dry weight (76%), and in the number of pods and seeds per plant (52% and 56%, respectively) and grain yield (56%), when compared with non-inoculated control plants. However, seed coating with P. libanensis + R. irregularis single-isolate (coatPR) did not influence cowpea grain yield. Grain lipid content was significantly higher (25%) in coatPMR plants in comparison with control. Higher soil organic matter and lower pH were observed in the coatPMR treatment. CONCLUSIONS: Our findings indicate that cowpea field productivity can be improved by seed coating with PGPR and multiple AM fungal isolates under low-input agricultural systems. © 2019 Society of Chemical Industry.

Abiotic contexts consistently influence mycorrhiza functioning independently of the composition of synthetic arbuscular mycorrhizal fungal communities.

The relationship between mycorrhiza functioning and composition of arbuscular mycorrhizal (AM) fungal communities is an important but experimentally still rather little explored topic. The main aim of this study was thus to link magnitude of plant benefits from AM symbiosis in different abiotic contexts with quantitative changes in AM fungal community composition. A synthetic AM fungal community inoculated to the model host plant Medicago truncatula was exposed to four different abiotic contexts, namely drought, elevated phosphorus availability, and shading, as compared to standard cultivation conditions, for two cultivation cycles. Growth and phosphorus uptake of the host plants was evaluated along with the quantitative composition of the synthetic AM fungal community. Abiotic context consistently influenced mycorrhiza functioning in terms of plant benefits, and the effects were clearly linked to the P requirement of non-inoculated control plants. In contrast, the abiotic context only had a small and transient effect on the quantitative AM fungal community composition. Our findings suggest no relationship between the degree of mutualism in AM symbiosis and the relative abundances of AM fungal species in communities in our simplified model system. The observed progressive dominance of one AM fungal species indicates an important role of different growth rates of AM fungal species for the establishment of AM fungal communities in simplified systems such as agroecosystems.

Nano Zero-Valent Iron Mediated Metal(loid) Uptake and Translocation by Arbuscular Mycorrhizal Symbioses.

Nano zero-valent iron (nZVI) has great potential in the remediation of metal(loid)-contaminated soils, but its efficiency in metal(loid) stabilization in the plant-microbe continuum is unclear. This study investigated nZVI-mediated metal(loid) behavior in the arbuscular mycorrhizal (AM) fungal-maize ( Zea mays L.) plant association. Plants with AM fungal inoculation were grown in metal(loid)- (mainly Zn and Pb) contaminated soils (Litavka River, Czech Republic) amended with/without 0.5% (w/w) nZVI. The results showed that nZVI decreased plant metal(loid) uptake but inhibited AM development and its function in metal(loid) stabilization in the rhizosphere. AM fungal inoculation alleviated the physiological stresses caused by nZVI and restrained nZVI efficiency in reducing plant metal(loid) uptake. Micro proton-induced X-ray emission (µ-PIXE) analysis revealed the sequestration of Zn (possibly through binding to thiols) by fungal structures in the roots and the precipitation of Pb and Cu in the mycorrhizal root rhizodermis (possibly by Fe compounds originated from nZVI). XRD analyses further indicated that Pb/Fe mineral transformations in the rhizosphere were influenced by AM and nZVI treatments. The study revealed the counteractive effects of AM and nZVI on plant metal(loid) uptake and uncovered details of metal(loid) behavior in the AM fungal-root-nZVI system, calling into question about nZVI implementation in mycorrhizospheric systems.

Plant growth promotion of Miscanthus × giganteus by endophytic bacteria and fungi on non-polluted and polluted soils.

Putative endophytes of Miscanthus × giganteus were isolated, and screened in the laboratory, greenhouse and field for their plant growth promoting properties in this host. Pantoea ananatis and Pseudomonas savastanoi were the predominant bacteria in leaves whereas other pseudomonads prevailed in roots. Almost all fungal endophytes belonged to the Pezizomycotina and most were isolated from roots; Fusarium oxysporum was most abundant, followed by the genera Periconia, Exophiala, Microdochium and Leptodontidium. All endophytic groups produced phytohormones and some bacteria also produced siderophores, solubilised P and exhibited ACC-deaminase activity in vitro. In subsequent pot experiments with pre-selected endophytes, several isolates including pseudomonads, Variovorax paradoxus, Verticillium leptobactrum, Halenospora sp. and Exophiala sp. enhanced Miscanthus growth in gamma-sterilised soil. These promising Miscanthus-derived isolates were tested either as single or mixed inocula along with a mixed bacterial inoculum originating from poplar. No significant effects of inocula were detected in a pot experiment in non-sterilised soil. On two marginal field sites the mixture of bacterial endophytes from poplar had a consistently negative effect on survival and growth of Miscanthus. Contrarily, mixtures consisting of bacteria or fungi originating from Miscanthus promoted growth of their host, especially on the heavy metals-polluted site. The combination of bacteria and fungi was inferior to the mixtures consisting of bacteria or fungi alone. Our observations indicate extensive potential of mixed bacterial and fungal endophytic inocula to promote establishment and yield of Miscanthus grown on marginal and polluted land and emphasise the necessity to test particular microbial-plant host combinations. Morphotypes of fungi isolates from Miscanthus × giganteus.

Real-time PCR quantification of arbuscular mycorrhizal fungi: does the use of nuclear or mitochondrial markers make a difference?

Root colonization by arbuscular mycorrhizal fungi (AMF) can be quantified by different approaches. We compared two approaches that enable discrimination of specific AMF taxa and are therefore emerging as alternative to most commonly performed microscopic quantification of AMF in roots: quantitative real-time PCR (qPCR) using markers in nuclear ribosomal DNA (nrDNA) and mitochondrial ribosomal DNA (mtDNA). In a greenhouse experiment, Medicago truncatula was inoculated with four isolates belonging to different AMF species (Rhizophagus irregularis, Claroideoglomus claroideum, Gigaspora margarita and Funneliformis mosseae). The AMF were quantified in the root samples by qPCR targeted to both markers, microscopy and contents of AMF-specific phospholipid fatty acids (PLFA). Copy numbers of nrDNA and mtDNA were closely related within all isolates; however, the slopes and intercepts of the linear relationships significantly differed among the isolates. Across all isolates, a large proportion of variance in nrDNA copy numbers was explained by root colonization intensity or contents of AMF-specific PLFA, while variance in mtDNA copy numbers was mainly explained by differences among AMF isolates. We propose that the encountered inter-isolate differences in the ratios of mtDNA and nrDNA copy numbers reflect different physiological states of the isolates. Our results suggest that nrDNA is a more suitable marker region than mtDNA for the quantification of multiple AMF taxa as its copy numbers are better related to fungal biomass across taxa than are copy numbers of mtDNA.

Asymmetric response of root-associated fungal communities of an arbuscular mycorrhizal grass and an ectomycorrhizal tree to their coexistence in primary succession.

The arbuscular mycorrhizal (AM) grass Calamagrostis epigejos and predominantly ectomycorrhizal (EcM) tree Salix caprea co-occur at post-mining sites spontaneously colonized by vegetation. During succession, AM herbaceous vegetation is replaced by predominantly EcM woody species. To better understand the interaction of AM and EcM plants during vegetation transition, we studied the reciprocal effects of these species' coexistence on their root-associated fungi (RAF). We collected root and soil samples from three different microenvironments: stand of C. epigejos, under S. caprea canopy, and contact zone where roots of the two species interacted. RAF communities and mycorrhizal colonization were determined in sampled roots, and the soil was tested for EcM and AM inoculation potentials. Although the microenvironment significantly affected composition of the RAF communities in both plant species, the effect was greater in the case of C. epigejos RAF communities than in that of S. caprea RAF communities. The presence of S. caprea also significantly decreased AM fungal abundance in soil as well as AM colonization and richness of AM fungi in C. epigejos roots. Changes observed in the abundance and community composition of AM fungi might constitute an important factor in transition from AM-dominated to EcM-dominated vegetation during succession.

Increased protein content of chickpea (Cicer arietinum L.) inoculated with arbuscular mycorrhizal fungi and nitrogen-fixing bacteria under water deficit conditions.

BACKGROUND: Chickpea (Cicer arietinum L.) is a widely cropped pulse and an important source of proteins for humans. In Mediterranean regions it is predicted that drought will reduce soil moisture and become a major issue in agricultural practice. Nitrogen (N)-fixing bacteria and arbuscular mycorrhizal (AM) fungi have the potential to improve plant growth and drought tolerance. The aim of the study was to assess the effects of N-fixing bacteria and AM fungi on the growth, grain yield and protein content of chickpea under water deficit. RESULTS: Plants inoculated with Mesorhizobium mediterraneum or Rhizophagus irregularis without water deficit and inoculated with M. mediterraneum under moderate water deficit had significant increases in biomass. Inoculation with microbial symbionts brought no benefits to chickpea under severe water deficit. However, under moderate water deficit grain crude protein was increased by 13%, 17% and 22% in plants inoculated with M. mediterraneum, R. irregularis and M. mediterraneum + R. irregularis, respectively. CONCLUSION: Inoculation with N-fixing bacteria and AM fungi has the potential to benefit agricultural production of chickpea under water deficit conditions and to contribute to increased grain protein content. © 2017 Society of Chemical Industry.

Seed coating with arbuscular mycorrhizal fungi as an ecotechnologicalapproach for sustainable agricultural production of common wheat (Triticum aestivum L.).

The exploitation of arbuscular mycorrhizal (AM) fungi has become of great interest in agriculture due to their potential roles in reducing the need for agrochemicals, while improving plant growth and nutrition. Nevertheless, the application of AM fungi by dispersing inocula in granular form to open agricultural fields is not feasible because nontargeted spreading of inocula over large surface areas results in high cost per plant. Seed coating has the potential to significantly reduce the amount of inoculum needed, resulting in cost reduction and increased efficiency. The aim of this study was to assess whether seed coating with AM fungal inoculum is a feasible delivery system for production of common wheat (Triticum aestivum L.). Wheat seeds were coated with inoculum of Rhizophagus irregularis BEG140 and grown under different fertilization conditions: (1) none, (2) partial, or (3) complete. Data indicated that mycorrhizal inoculation via seed coating significantly increased the dry weight of shoot and seed spikes of wheat associated with reduced fertilization. Assessment of nutritional status of wheat showed that plants inoculated with R. irregularis via seed coating displayed enhanced stem concentrations of potassium (K), sulfur (S), and zinc (Zn). There were no significant differences in root colonization between plants conventionally inoculated with R. irregularis in soil and those inoculated via seed coating. Seed coating with AM fungi may be as effective as conventional soil inoculation and may contribute to reduce the utilization of chemical fertilizers. The application of AM via seed coating is proposed as an ecotechnological approach for sustainable agricultural wheat production.

Arbuscular mycorrhizal fungi are an alternative to the application of chemical fertilizer in the production of the medicinal and aromatic plant Coriandrum sativum L.

The widespread use of agrochemicals is detrimental to the environment and may exert harmful effects on human health. The consumer demand for organic food plants has been increasing. There is thus a rising need for alternatives to agrochemicals that can foster sustainable plant production. The aim of this study was to evaluate the potential use of an arbuscular mycorrhizal (AM) fungus as an alternative to application of chemical fertilizer for improving growth performance of the medicinal and aromatic plant Coriandrum sativum. Plants were inoculated with the AM fungus Rhizophagus irregularis BEG163 and/or supplemented with a commercial chemical fertilizer (Plant Marvel, Nutriculture Bent Special) in agricultural soil. Plant growth, nutrition, and development of AM fungus were assessed. Plants inoculated with R. irregularis and those supplemented with chemical fertilizer displayed significantly improved growth performances when compared with controls. There were no significant differences in total fresh weight between plants inoculated with R. irregularis or those supplemented with chemical fertilizer. Leaf chlorophyll a + b (82%), shoot nitrogen (44%), phosphorus (254%), and potassium (27%) concentrations increased in plants inoculated with R. irregularis compared to controls. Application of chemical fertilizer inhibited root mycorrhizal colonization and the length of the extraradical mycelium of R. irregularis. Inoculation with R. irregularis was equally or more efficient than application of chemical fertilizer in promoting growth and nutrition of C. sativum. AM fungi may thus contribute to improve biologically based production of food plants and reduce the dependence on agrochemicals in agriculture.

Arbuscular mycorrhiza differentially affects synthesis of essential oils in coriander and dill.

Research on the role of arbuscular mycorrhizal fungi (AMF) in the synthesis of essential oils (EOs) by aromatic plants has seldom been conducted in field-relevant conditions, and then, only limited spectra of EO constituents have been analyzed. The effect was investigated of inoculation with AMF on the synthesis of a wide range of EO in two aromatic species, coriander (Coriandrum sativum) and dill (Anethum graveolens), in a garden experiment under outdoor conditions. Plants were grown in 4-l pots filled with soil, which was either γ-irradiated (eliminating native AMF) or left non-sterile (containing native AMF), and inoculated or not with an isolate of Rhizophagus irregularis. AMF inoculation significantly stimulated EO synthesis in both plant species. EO synthesis (total EO and several individual constituents) was increased in dill in all mycorrhizal treatments (containing native and/or inoculated AMF) compared to non-mycorrhizal plants. In contrast, EO concentrations in coriander (total EO and most constituents) were increased only in the treatment combining both inoculated and native AMF. A clear positive effect of AMF on EO synthesis was found for both aromatic plants, which was, however, specific for each plant species and modified by the pool of AMF present in the soil.

Evidence of the Ability of Microsatellite Method to Distinguish Cannabis Strains with High Cannabinoid Content.

Introduction: Cannabis is a plant with high potential for use in several sectors of the industry; however, it is also a controversial crop due to its tetrahydrocannabinol (THC) content. Moreover, the plant has a rather unclarified classification. Traditionally, two types of Cannabis have been distinguished, hemp as a source of fiber and low THC content, and marijuana with high THC levels, which is used as a drug. With the increasing use of CBD strains and wide range of commercially used THC strains, it is becoming paramount to be able to develop an easy and reliable method for Cannabis strain differentiation. The use of simple sequence repeat markers, or microsatellites, seems to be an applicable choice. Materials and Methods: In this study, 52 strains of Cannabis with variable cannabinoid content were collected from growers from different geographical regions and analyzed using 17 different microsatellite markers. For more precise differentiation, five strains were selected and a higher number of individuals of each were analyzed. Results: Fragment analysis and cluster analysis showed that when one to three individual plants per strain were analyzed, the method was able to classify these samples into distinguishable groups with similar gene structure. They also revealed that when a larger sample set was used (10 individual plants per strain), highly specific strain clusters could be fully discriminated. Conclusion: Our study involved the highest number of cannabinoid-rich strains up to now and showed that the microsatellite method can be used to reliably differentiate Cannabis strains and show their relationships.

Effects of inoculum additions in the presence of a preestablished arbuscular mycorrhizal fungal community.

Communities of arbuscular mycorrhizal fungi (AMF) are crucial for promoting plant productivity in most terrestrial systems, including anthropogenically managed ecosystems. Application of AMF inocula has therefore become a widespread practice. It is, however, pertinent to understand the mechanisms that govern AMF community composition and their performance in order to design successful manipulations. Here we assess whether the composition and plant growth-promotional effects of a synthetic AMF community can be altered by inoculum additions of the isolates forming the community. This was determined by following the effects of three AMF isolates, each inoculated in two propagule densities into a preestablished AMF community. Fungal abundance in roots and plant growth were evaluated in three sequential harvests. We found a transient positive response in AMF abundance to the intraspecific inoculation only in the competitively weakest isolate. The other two isolates responded negatively to intra- and interspecific inoculations, and in some cases plant growth was also reduced. Our results suggest that increasing the AMF density may lead to increased competition among fungi and a trade-off with their ability to promote plant productivity. This is a key ecological aspect to consider when introducing AMF into soils.

Enhanced production of select phytocannabinoids in medical Cannabis cultivars using microbial consortia.

The root microbiome of medical cannabis plants has been largely unexplored due to past legal restrictions in many countries. Microbes that live on and within the tissue of Cannabis sativa L. similar to other plants, provide advantages such as stimulating plant growth, helping it absorb minerals, providing protection against pathogen attacks, and influencing the production of secondary metabolites. To gain insight into the microbial communities of C. sativa cultivars with different tetrahydrocannabinol (THC) and cannabidiol (CBD) profiles, a greenhouse trial was carried out with and without inoculants added to the growth substrate. Illumina MiSeq metabarcoding was used to analyze the root and rhizosphere microbiomes of the five cultivars. Plant biomass production showed higher levels in three of five cultivars inoculated with the arbuscular mycorrhizal fungus Rhizophagus irregularis and microbial suspension. The blossom dry weight of the cultivar THE was greater when inoculated with R. irregularis and microbial suspension than with no inoculation. Increasing plant biomass and blossom dry weight are two important parameters for producing cannabis for medical applications. In mature Cannabis, 12 phytocannabinoid compounds varied among cultivars and were affected by inoculants. Significant differences (p ≤ 0.01) in concentrations of cannabidivarinic acid (CBDVA), cannabidivarin (CBDV), cannabigerol (CBG), cannabidiol (CBD), and cannabigerolic acid (CBGA) were observed in all Cannabis cultivars when amended with F, K1, and K2 inoculants. We found microbes that were shared among cultivars. For example, Terrimicrobium sp., Actinoplanes sp., and Trichoderma reesei were shared by the cultivars ECC-EUS-THE, CCL-ECC, and EUS-THE, respectively. Actinoplanes sp. is a known species that produces phosphatase enzymes, while Trichoderma reesei is a fungal train that produces cellulase and contributes to organic matter mineralization. However, the role of Terrimicrobium sp. as an anaerobic bacterium remains unknown. This study demonstrated that the use of inoculants had an impact on the production of phytocannabinoids in five Cannabis cultivars. These inoculants could have useful applications for optimizing cannabis cultivation practices and increasing the production of phytocannabinoids.

Intraradical dynamics of two coexisting isolates of the arbuscular mycorrhizal fungus Glomus intraradices sensu lato as estimated by real-time PCR of mitochondrial DNA.

Real-time PCR in nuclear ribosomal DNA (nrDNA) is becoming a well-established tool for the quantification of arbuscular mycorrhizal (AM) fungi, but this genomic region does not allow the specific amplification of closely related genotypes. The large subunit of mitochondrial DNA (mtDNA) has a higher-resolution power, but mtDNA-based quantification has not been previously explored in AM fungi. We applied real-time PCR assays targeting the large subunit of mtDNA to monitor the DNA dynamics of two isolates of Glomus intraradices sensu lato coexisting in the roots of medic (Medicago sativa). The mtDNA-based quantification was compared to quantification in nrDNA. The ratio of copy numbers determined by the nrDNA- and mtDNA-based assays consistently differed between the two isolates. Within an isolate, copy numbers of the nuclear and the mitochondrial genes were closely correlated. The two quantification approaches revealed similar trends in the dynamics of both isolates, depending on whether they were inoculated alone or together. After 12 weeks of cultivation, competition between the two isolates was observed as a decrease in the mtDNA copy numbers of one of them. The coexistence of two closely related isolates, which cannot be discriminated by nrDNA-based assays, was thus identified as a factor influencing the dynamics of AM fungal DNA in roots. Taken together, the results of this study show that real-time PCR assays targeted to the large subunit of mtDNA may become useful tools for the study of coexisting AM fungi.

Long-term tracing of Rhizophagus irregularis isolate BEG140 inoculated on Phalaris arundinacea in a coal mine spoil bank, using mitochondrial large subunit rDNA markers.

During the last decade, the application of arbuscular mycorrhizal fungi (AMF) as bioenhancers has increased significantly. However, until now, it has been difficult to verify the inoculation success in terms of fungal symbiont establishment in roots of inoculated plants because specific fungal strains could not be detected within colonized roots. Using mitochondrial large subunit ribosomal DNA, we show that Rhizophagus irregularis (formerly known as Glomus intraradices) isolate BEG140 consists of two different haplotypes. We developed nested PCR assays to specifically trace each of the two haplotypes in the roots of Phalaris arundinacea from a field experiment in a spoil bank of a former coal mine, where BEG140 was used as inoculant. We revealed that despite the relatively high diversity of native R. irregularis strains, R. irregularis BEG140 survived and proliferated successfully in the field experiment and was found significantly more often in the inoculated than control plots. This work is the first one to show tracing of an inoculated AMF isolate in the roots of target plants and to verify its survival and propagation in the field. These results will have implications for basic research on the ecology of AMF at the intraspecific level as well as for commercial users of mycorrhizal inoculation.

Dual inoculation with mycorrhizal and saprotrophic fungi applicable in sustainable cultivation improves the yield and nutritive value of onion.

The aim of this paper was to test the use of dual microbial inoculation with mycorrhizal and saprotrophic fungi in onion cultivation to enhance yield while maintaining or improving the nutritional quality of onion bulbs. Treatments were two-factorial: (1) arbuscular mycorrhizal fungi (AMF): the mix corresponding to fungal part of commercial product Symbivit (Glomus etunicatum, G. microaggregatum, G. intraradices, G. claroideum, G. mosseae, and G. geosporum) (M1) or the single-fungus inoculum of G. intraradices BEG140 (M2) and (2) bark chips preinoculated with saprotrophic fungi (mix of Gymnopilus sp., Agrocybe praecox, and Marasmius androsaceus) (S). The growth response of onion was the highest for the M1 mix treatment, reaching nearly 100% increase in bulb fresh weight. The effectiveness of dual inoculation was proved by more than 50% increase. We observed a strong correlation (r = 0.83) between the growth response of onion bulbs and AM colonization. All inoculation treatments but the single-fungus one enhanced significantly the total antioxidant capacity of bulb biomass, was the highest values being found for M1, S + M1, and S + M2. We observed some induced enhancement of the contents of mineral elements in bulb tissue (Mg and K contents for the M2 and M2, S, and S + M2 treatments, resp.).

Establishing a quality management framework for commercial inoculants containing arbuscular mycorrhizal fungi.

Microbial inoculants containing arbuscular mycorrhizal (AM) fungi are potential tools in increasing the sustainability of our food production systems. Given the demand for sustainable agriculture, the production of such inoculants has potential economic value and has resulted in a variety of commercial inoculants currently being advertised. However, their use is limited by inconsistent product efficacy and lack of consumer confidence. Here, we propose a framework that can be used to assess the quality and reliability of AM inoculants. First, we set out a range of basic quality criteria which are required to achieve reliable inoculants. This is followed by a standardized bioassay which can be used to test inoculum viability and efficacy under controlled conditions. Implementation of these measurements would contribute to the adoption of AM inoculants by producers with the potential to increase sustainability in food production systems.

Effect of clone selection, nitrogen supply, leaf damage and mycorrhizal fungi on stilbene and emodin production in knotweed.

BACKGROUND: Fallopia japonica and its hybrid, F. xbohemica, due to their fast spread, are famous as nature threats rather than blessings. Their fast growth rate, height, coverage, efficient nutrient translocation between tillers and organs and high phenolic production, may be perceived either as dangerous or beneficial features that bring about the elimination of native species or a life-supporting source. To the best of our knowledge, there have not been any studies aimed at increasing the targeted production of medically desired compounds by these remarkable plants. We designed a two-year pot experiment to determine the extent to which stilbene (resveratrol, piceatannol, resveratrolosid, piceid and astringins) and emodin contents of F. japonica, F. sachalinensis and two selected F. xbohemica clones are affected by soil nitrogen (N) supply, leaf damage and mycorrhizal inoculation. RESULTS: 1) Knotweeds are able to grow on substrates with extremely low nitrogen content and have a high efficiency of N translocation. The fast-spreading hybrid clones store less N in their rhizomes than the parental species. 2) The highest concentrations of stilbenes were found in the belowground biomass of F. japonica. However, because of the high belowground biomass of one clone of F. xbohemica, this hybrid produced more stilbenes per plant than F. japonica. 3) Leaf damage increased the resveratrol and emodin contents in the belowground biomass of the non-inoculated knotweed plants. 4) Although knotweed is supposed to be a non-mycorrhizal species, its roots are able to host the fungi. Inoculation with mycorrhizal fungi resulted in up to 2% root colonisation. 5) Both leaf damage and inoculation with mycorrhizal fungi elicited an increase of the piceid (resveratrol-glucoside) content in the belowground biomass of F. japonica. However, the mycorrhizal fungi only elicited this response in the absence of leaf damage. Because the leaf damage suppressed the effect of the root fungi, the effect of leaf damage prevailed over the effect of the mycorrhizal fungi on the piceid content in the belowground biomass. CONCLUSIONS: Two widely spread knotweed species, F. japonica and F. xbohemica, are promising sources of compounds that may have a positive impact on human health. The content of some of the target compounds in the plant tissues can be significantly altered by the cultivation conditions including stress imposed on the plants, inoculation with mycorrhizal fungi and selection of the appropriate plant clone.