Pulses are an important component in crop rotations in the semiarid Brown soil zone of southern Saskatchewan, Canada. Besides their capability to fix nitrogen, pulse crops establish a strong symbiotic relationship with arbuscular mycorrhizal fungi (AMF), which have been shown to increase nutrient and water uptake through hyphal extensions in the soil. Incorporating strongly mycorrhizal crops in a rotation may increase inoculum levels in the soil and benefit the growth of a subsequent crop. The objective of this study was to determine if AMF potential and colonization of a durum crop is significantly affected by cropping history and to assess the impact of pulses in crop rotations on the abundance and diversity of AMF communities in the soil. In 2004 and 2005, soil, plant, and root samples were taken on Triticum turgidum L. (durum) with preceding crops of Pisum sativum L. (pea), Lens culinaris Medik (lentil), Cicer arietinum L. (chickpea), Brassica napus L. (canola) or Triticum turgidum L. (durum). Although there were few differences in soil N and P levels, previous crop had a significant effect (p<0.05) on durum yields in both years. A previous crop of pea was associated with the highest yields, while the durum monocultures were lowest. Arbuscular mycorrhizal potential and colonization were significantly affected (p<0.05) by cropping history, but not consistently as a result of inclusion of a pulse crop. Phospholipid and neutralipid fatty acids (PLFA/NLFA) were completed to analyse the relative abundance of AMF (C16:1ù5), saprophytic fungi (C18:2ù6), and bacteria in the soil. The effect of treatment on the abundance of AMF, saprotrophic fungi and bacteria were not significant (p<0.05), but the changes over time were. These results demonstrate that although previous crop may play a role in microbial community structure, it is not the only influencing factor.

Pulses are an important component in crop rotations in the semiarid Brown soil zone of southern Saskatchewan, Canada. Besides their capability to fix nitrogen, pulse crops establish a strong symbiotic relationship with arbuscular mycorrhizal fungi (AMF), which have been shown to increase nutrient and water uptake through hyphal extensions in the soil. Incorporating strongly mycorrhizal crops in a rotation may increase inoculum levels in the soil and benefit the growth of a subsequent crop. The objective of this study was to determine if AMF potential and colonization of a durum crop is significantly affected by cropping history and to assess the impact of pulses in crop rotations on the abundance and diversity of AMF communities in the soil. In 2004 and 2005, soil, plant, and root samples were taken on Triticum turgidum L. (durum) with preceding crops of Pisum sativum L. (pea), Lens culinaris Medik (lentil), Cicer arietinum L. (chickpea), Brassica napus L. (canola) or Triticum turgidum L. (durum). Although there were few differences in soil N and P levels, previous crop had a significant effect (p<0.05) on durum yields in both years. A previous crop of pea was associated with the highest yields, while the durum monocultures were lowest. Arbuscular mycorrhizal potential and colonization were significantly affected (p<0.05) by cropping history, but not consistently as a result of inclusion of a pulse crop. Phospholipid and neutralipid fatty acids (PLFA/NLFA) were completed to analyse the relative abundance of AMF (C16:1ù5), saprophytic fungi (C18:2ù6), and bacteria in the soil. The effect of treatment on the abundance of AMF, saprotrophic fungi and bacteria were not significant (p<0.05), but the changes over time were. These results demonstrate that although previous crop may play a role in microbial community structure, it is not the only influencing factor.

The nutrient exchange between plant and fungus is the key element of the arbuscular mycorrhizal (AM) symbiosis. The fungus improves the plant’s uptake of mineral nutrients, mainly phosphate, and water, while the plant provides the fungus with photosynthetically assimilated carbohydrates. Still, the knowledge about the mechanisms of the nutrient exchange between the symbiotic partners is very limited. Therefore, transport processes of both, the plant and the fungal partner, are investigated in this study. In order to enhance the understanding of the molecular basis underlying this tight interaction between the roots of Medicago truncatula and the AM fungus Rhizophagus irregularis, genes involved in transport processes of both symbiotic partners are analysed here. The AM-specific regulation and cell-specific expression of potential transporter genes of M. truncatula that were found to be specifically regulated in arbuscule-containing cells and in non-arbusculated cells of mycorrhizal roots was confirmed. A model for the carbon allocation in mycorrhizal roots is suggested, in which carbohydrates are mobilized in non-arbusculated cells and symplastically provided to the arbuscule-containing cells. New insights into the mechanisms of the carbohydrate allocation were gained by the analysis of hexose/H+ symporter MtHxt1 which is regulated in distinct cells of mycorrhizal roots. Metabolite profiling of leaves and roots of a knock-out mutant, hxt1, showed that it indeed does have an impact on the carbohydrate balance in the course of the symbiosis throughout the whole plant, and on the interaction with the fungal partner. The primary metabolite profile of M. truncatula was shown to be altered significantly in response to mycorrhizal colonization. Additionally, molecular mechanisms determining the progress of the interaction in the fungal partner of the AM symbiosis were investigated. The R. irregularis transcriptome in planta and in extraradical tissues gave new insight into genes that are differentially expressed in these two fungal tissues. Over 3200 fungal transcripts with a significantly altered expression level in laser capture microdissection-collected arbuscules compared to extraradical tissues were identified. Among them, six previously unknown specifically regulated potential transporter genes were found. These are likely to play a role in the nutrient exchange between plant and fungus. While the substrates of three potential MFS transporters are as yet unknown, two potential sugar transporters are might play a role in the carbohydrate flow towards the fungal partner. In summary, this study provides new insights into transport processes between plant and fungus in the course of the AM symbiosis, analysing M. truncatula on the transcript and metabolite level, and provides a dataset of the R. irregularis transcriptome in planta, providing a high amount of new information for future works. / In der arbuskulären Mykorrhiza (AM) Symbiose werden die Wurzeln fast aller Landpflanzen von Pilzen der Abteilung Glomeromycota besiedelt. Der Pilz erleichtert der Pflanze die Aufnahme von Mineralien, hauptsächlich Phosphat, und Wasser. Im Gegenzug versorgt die Pflanze ihn mit Photoassimilaten. Trotz der zentralen Bedeutung der Austauschmechanismen zwischen Pilz und Pflanze ist nur wenig darüber bekannt. Um die molekularen Grundlagen der Interaktion zwischen den Wurzeln der Leguminose Medicago truncatula und dem arbuskulären Mykorrhizapilz Rhizophagus irregularis besser zu verstehen, werden hier die Transportprozesse, die zwischen den Symbiosepartnern ablaufen, näher untersucht. Die zellspezifische Regulation der Transkription potentieller M. truncatula Transporter Gene in arbuskelhaltigen und nicht-arbuskelhaltigen Zellen mykorrhizierter Wurzeln wird bestätigt. Ein Modell zur möglichen Verteilung von Kohlenhydraten in mykorrhizierten Wurzeln, nach dem Zucker in nicht-arbuskelhaltigen Zellen mobilisiert und symplastisch an arbuskelhaltige Zellen abgegeben werden, wird vorgestellt. Die Analyse eines Mykorrhiza-induzierten Hexose/H+ Symporter Gens, MtHxt1, liefert neue Einsichten in die Mechanismen der Kohlenhydratverteilung in mykorrhizierten Pflanzen. Metabolitanalysen von Wurzeln und Blättern einer knock-out Mutante dieses Gens zeigen dessen Einfluss auf den Kohlenhydrathaushalt der ganzen Pflanze und auf die Interaktion mit dem Pilz. Die Metabolitzusammensetzung von M. truncatula wird durch die Mykorrhiza Symbiose signifikant beeinflusst. Darüber hinaus werden durch Transkriptomanalysen die molekularen Grundlagen der AM Symbiose auf der Seite des Pilzes analysiert. Arbuskeln wurden mittels Laser Capture Mikrodissektion direkt aus mykorrhizierten Wurzeln isoliert. Über 3200 pilzliche Transkripte weisen in diesen Arbuskeln im Vergleich zu extraradikalen Geweben ein deutlich verändertes Expressionslevel auf. Unter diesen Transkripten sind auch sechs zuvor unbekannte Gene, die für potentielle Transporter codieren und mit großer Wahrscheinlichkeit eine Rolle im Nährstoffaustausch zwischen Pilz und Pflanze spielen. Während die Substrate von drei potentiellen MFS Transportern noch unbekannt sind, spielen zwei potentiellen Zuckertransporter möglicherweise eine Rolle im Transport von Kohlenhydraten in Richtung des Pilzes. Zusammengefasst bietet diese Arbeit neue Einsichten in Transportprozesse zwischen Pilz und Pflanze im Laufe der AM Symbiose. M. truncatula Transkript- und Metabolitlevel werden analysiert und die Transkriptomanalyse von R. irregularis liefert einen umfassenden Datensatz mit einer großen Menge an Informationen zu der noch unzureichend erforschten pilzlichen Seite der Symbiose für folgende Arbeiten.

Melanie Jones and Dan Durall aren't looking to the treetops for clues about the "wood wide web." They're looking to the soil at fungi that are crucial to renewing our forests.

Mokslinį tiriamąjį darbą “Mikorizės morfotipai paprastosios pušies želdiniuose” sudaro 52 puslapiai, iš jų 10 lentelių, 26 paveikslų, literatūros sąraše 72 šaltiniai. Išanalizuotas paprastosios pušies Labanoro provenencijos sodmenų vystymosi ir adaptyvumo ypatumai lauko daigyne ir želdiniuose. Įvertinta atskirų daigyno substratų (pušyno, ąžuolyno pakločių) įtaka sėjinukų (2+0) vystymuisi, adaptyvumui ir mikorizės išplitimui. Nustatyti minėtos provenencijos sodinukų (2+1) reakcijos į naujas augimo sąlygas atskirose želdavietėse (poligone, miško kirtavietėje, žemės ūkio naudmenose) ypatumai. Pateikti mikorizės kiekybinės ir kokybinės sudėties skirtumai atskiruose daigyno substratuose ir tirtose želdavietėse. Palygintos tradiciniu (morfotipavimo) ir molekuliniais (PCR-RFLP, sekvenavimas) metodais nustatytos mikorizės grybų rūšys. / The study from the research “The mycorrhizal morphotypes of Scots pine seedlings in response to different site” amounts to 52 pages, 10 tables, 26 figures and 72 refrences. The peculiarities of development and adaptivity of Scots pine seedlings from Labanoras provenance in bare-roots nursery and different site were analyzed. We hypothesized that soil with forest litter amendment would affect ectomycorrhizal community structure and growth and productivity characteristics of Scots pine seedlings in bare-roots nursery and in response to different site. In our experimental system, a layer of pine or oak litter was placed on the surface of the nursery bed soil in order to mimic natural litter cover. The influence of different nursery substrata (oak and pine litter) on development, adaptivity and mycorrhizal spread of seedlings (2+0) has been assessed. The peculiarities of seedlings (2+1) of mentioned provenance in response to new growth conditions in different site were found. The differences of qualitative and quantitative composition in nursery substrata and different site were investigated. Mycorrhizal fungi species were assessed by morphotyping and molecular methods (PCR-RFLP, sequence) identification. We have preliminary evidenced that changes to the supply of organic matter through litter manipulation may have wide-reaching effects on soil physical properties and soil chemistry and thus influence growth and survival Scots pine seedlings and their mycorrhizal communities... [to full text]

Les métaux lourds (ML) s’accumulent de plus en plus dans les sols à l’échelle mondiale, d’une part à cause des engrais minéraux et divers produits chimiques utilisés en agriculture intensive, et d’autre part à cause des activités industrielles. Toutes ces activités génèrent des déchets toxiques qui s’accumulent dans l’environnement. Les ML ne sont pas biodégradables et leur accumulation cause donc des problèmes de toxicité des sols et affecte la biodiversité des microorganismes qui y vivent. La fertilisation en azote (N) est une pratique courante en agriculture à grande échelle qui permet d’augmenter la fertilité des sols et la productivité des cultures. Cependant, son utilisation à long terme cause plusieurs effets néfastes pour l'environnement. Par exemple, elle augmente la quantité des ML dans les sols, les nappes phréatiques et les plantes. En outre, ces effets néfastes réduisent et changent considérablement la biodiversité des écosystèmes terrestres. La structure des communautés des champignons mycorhiziens à arbuscules (CMA) a été étudiée dans des sols contaminés par des ML issus de la fertilisation à long terme en N. Le rôle des différentes espèces de CMA dans l'absorption et la séquestration des ML a été aussi investigué. Dans une première expérience, la structure des communautés de CMA a été analysée à partir d’échantillons de sols de sites contaminés par des ML et de sites témoins non-contaminés. Nous avons constaté que la diversité des CMA indigènes a été plus faible dans les sols et les racines des plantes récoltées à partir de sites contaminés par rapport aux sites noncontaminés. Nous avons également constaté que la structure de la communauté d'AMF a été modifiée par la présence des ML dans les sols. Certains ribotypes des CMA ont été plus souvent associés aux sites contaminés, alors que d’autres ribotypes ont été associés aux sites non-contaminés. Cependant, certains ribotypes ont été observés aussi bien dans les sols pollués que non-pollués. Dans une deuxième expérience, les effets de la fertilisation organique et minérale (N) sur les différentes structures des communautés des CMA ont été étudiés. La variation de la structure de la communauté de CMA colonisant les racines a été analysée en fonction du type de fertilisation. Certains ribotypes de CMA étaient associés à la fertilisation organique et d'autres à la fertilisation minérale. En revanche, la fertilisation minérale a réduit le nombre de ribotypes de CMA alors que la fertilisation organique l’a augmenté. Dans cette expérience, j’ai démontré que le changement de structure des communautés de CMA colonisant des racines a eu un effet significatif sur la productivité des plantes. Dans une troisième expérience, le rôle de deux espèces de CMA (Glomus irregulare et G. mosseae) dans l'absorption du cadmium (Cd) par des plants de tournesol cultivés dans des sols amendés avec trois niveaux différents de Cd a été évalué. J’ai démontré que les deux espèces de CMA affectent différemment l’absorption ou la séquestration de ce ML par les plants de tournesol. Cette expérience a permis de mieux comprendre le rôle potentiel des CMA dans l'absorption des ML selon la concentration de cadmium dans le sol et les espèces de CMA. Mes recherches de doctorat démontrent donc que la fertilisation en N affecte la structure des communautés des CMA dans les racines et le sol. Le changement de structure de la communauté de CMA colonisant les racines affecte de manière significative la productivité des plantes. J’ai aussi démontré que, sous nos conditions expériemntales, l’espèce de CMA G. irregulare a été observée dans tous les sites (pollués et non-pollués), tandis que le G. mosseae n’a été observé en abondance que dans les sites contaminés. Par conséquent, j’ai étudié le rôle de ces deux espèces (G. irregulare et G. mosseae) dans l'absorption du Cd par le tournesol cultivé dans des sols amendés avec trois différents niveaux de Cd en serre. Les résultats indiquent que les espèces de CMA ont un potentiel différent pour atténuer la toxicité des ML dans les plantes hôtes, selon le niveau de concentration en Cd. En conclusion, mes travaux suggèrent que le G. irregulare est une espèce potentiellement importante pour la phytoextration du Cd, alors que le G. mosseae pourrait être une espèce appropriée pour phytostabilisation du Cd et du Zn. / Trace metals (TM) are continually world-wide added to soils through the intensive use of mineral fertilizers and agriculture chemicals, together with industrial and other activities generating toxic wastes. Problems associated with metal-contaminated soil exists because TM are not biodegradable. TM that accumulate in soils affect the biodiversity of soil microorganisms. Nitrogen (N) fertilization is a widespread practice to increase soil fertility and crop production. However, the long-term use of N fertilization causes many detrimental effects in the environment. The intensive use of N fertilization increase TM input in soils, and in extreme cases, N fertilization result in TM pollution of the surrounding soil and water and increase TM concentration in plant tissues. In addition, the long-term use of N fertilizers changes and declines the biodiversity of above and underground ecosystems. The community structure of arbuscular mycorrhizal fungi (AMF) was investigated in TM contaminated and long-term N fertilized soils. In addition, the role of different AMF species in TM uptake or sequestration was investigated. In the first experiment, AMF community structure was analyzed from non-contaminated and TM contaminated sites. We found the diversity of native AMF was lower in soils and plant roots harvested from TM polluted soils than from unpolluted soils. We also found that the community structure of AMF was modified by TM contamination. Some AMF ribotypes were more often associated with TM contaminated sites, other ribotypes with uncontaminated sites, while still other ribotypes were found both in polluted and unpolluted soils. In the second experiment, the effect of different organic and mineral N fertilization on AMF community structure was investigated. Variation in root-colonizing AMF community structure was observed in both organic and mineral fertilization. Some AMF ribotypes were more affiliated to organic fertilization and other to mineral fertilization. In addition, mineral fertilization reduced AMF ribotypes number while organic fertilization increased AMF ribotypes number. In this experiment, it was demonstrated that change in root-colonizing AMF community structure had a significant effect on plant productivity. In the third experiment, the role of different AMF species (G. irregulare and G. mosseae) in TM uptake by sunflower plants grown in soil amended with three different Cd levels was evaluated. It was demonstrated that AMF species differentially affected TM uptake or sequestration by sunflower plants. This experiment supported a different effect of AMF in TM uptake based on Cd concentration in soil and the AMF species involved. Our research demonstrated that TM and N fertilization affected and shifted AMF community structure within roots and soils. It was shown that change in root-colonizing AMF community structure significantly affected plant productivity. In this study, it was showed that the AMF species G. irregulare was recorded in all uncontaminated sites while G. mosseae was the most abundant AMF species in TM contaminated sites. Therefore, the role of G. irregulare and G. mosseae in Cd uptake by sunflower plants grown in soils amended with three different Cd levels was investigated. The results indicated that AMF species mediate different mechanisms to alleviate TM toxicity in host plants, depending on AMF species and soil Cd level involved. We hypothesize that G. irregulare is a potentially important species for Cd phytoextration processes, while G. mosseae might be a suitable candidate for Cd and Zn phytostabilization processes.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Certain crop plants are susceptible to pathogens or unable to develop efficient microbial symbioses. These crops adversely impact soil biological quality with consequences on plant health and productivity of cropping systems. Chickpea is a rotational pulse crop with two types: kabuli and desi, and several cultivars. Cultivation of chickpea has inconsistent effects on soil microbial communities and subsequent wheat crops. I conducted field studies and used high throughput molecular analyses to explore the variations among chickpeas to identify cultivars developing fungal communities that are conducive to plant health and productivity. I also carried out greenhouse studies and used biochemical analyses to investigate the response of chickpea cultivars to arbuscular mycorrhizal (AM) fungi and non-AM fungal endophytes and identify the influence of root and root metabolites on the endophytic and pathogenic fungi. Cultivars and types of chickpeas and environmental conditions promoted different fungal communities in the root endosphere. Funneliformis and Claroideoglomus were the dominant AM fungal genera and Fusarium and Alternaria were the dominant non-AM fungal genera in the roots of chickpea. The roots of cultivars CDC Corrine, CDC Cory and CDC Anna hosted the most diverse fungal communities in contrast to CDC Alma and CDC Xena roots which hosted the least diverse communities. Plant response to AM and non-AM fungal endophytes varied with genotype and type of chickpea. The root symbiosis effectively promoted plant growth in CDC Cory, CDC Anna and CDC Frontier and stimulated nitrogen fixation in CDC Corrine. Cultivars of chickpea responded differently to dual inoculation of the AM and non-AM fungal endophytes. Co-inoculation with AM and non-AM fungal endophytes had additive effects on CDC Corrine, CDC Anna and CDC Cory but non-AM fungal endophytes reduced the positive effect of AM fungi in Amit and CDC Vanguard. Desi chickpea appeared to form more efficient symbioses with soil fungal resources than kabuli chickpea. Protein(s) up-regulated in the mycorrhizal roots of the desi chickpea CDC Anna suppressed the growth of the fungal endophytes Trichoderma harzianum and Geomyces vinaceus and of the pathogens Fusarium oxysporum and Rhizoctonia sp. The formation of AM symbiosis decreased the production of root bioactive metabolites soluble in 25% methanol. Some of the root metabolites stimulated the growth of Trichoderma harzianum and Geomyces vinaceus, and a few inhibited Rhizoctonia sp. and Fusarium oxysporum. A few metabolites with contrasting effects on the different fungal species were detected. The non-protein phytochemicals had selective effects on the endophytes and pathogens whereas the antifungal proteins of mycorrhizal roots were non-selective. Overall the study reveals a "genotype effect" of chickpea on the soil microbiota suggesting the possibility to improve the performance of this crop through the selection of genotypes improving the communities of root associated fungi, by associating and responding to beneficial fungi and repressing the pathogens.

No description available.

South Africa is the world's second largest exporter of fresh citrus and is ranked 14th in citrus production. Fungal pathogens such as Phytophthora and Pythium cause economic losses as a result of root rot and brown rot. Mycorrhizal fungi are specialized members of the fungal community forming a mutualistic relationship with plant roots. Mycorrhizal fungal structures are known to associate with other soil microorganisms and these may contribute to improved plant growth. A diverse group of bacteria that interact with the mycorrhizal fungi are known as Mycorrhizal Helper Bacteria (MHB). The aim of this study was to investigate the role of arbuscular mycorrhiza and associated bacteria isolated from spores and determine whether they had any plant growth promoting potential. A total of 19 bacteria were isolated from arbuscular mycorrhizal spores and were molecularly identified as belonging to several Bacillus, Micrococcus, Onchrobactrum and Staphylococcus sp. All bacterial isolates were tested for plant growth promotion abilities. One Bacillus isolate was able to solubilise phosphate. Four isolates Micrococcus sp, Micrococcus leteus, Ochrobacterum sp and Ochrobacterum antropi were able to produce Indole Acetic Acid and three isolates showed potential to reduce growth of Phytophthora nicotianae, P. citrocola and P. citrophthora in in vitro plate cultures. Further tests using culture supernatants of the Bacillus sp, Micrococcus sp and Bacillus cereus confirmed their ability to inhibit or reduce growth of the three Phytophthora species in a 96 well bioassay. Bacillus sp and Bacillus cereus were able to inhibit Phytophthora spp by 95 to 100 % and Micrococcus spp was able to decrease pathogen growth by 60 to 94 %. These bacterial isolates were further evaluated for plant growth promoting abilities on citrus rough lemon seedlings alone or in combination with arbuscular mycorrhizal inoculum. Bacterial and mycorrhizal inoculants influence the increase in shoot and root biomass. Bacillus cereus in combination with mycorrhizal inoculum significantly increased seedling shoot to root ratio while root biomass was significantly increased with mycorrhizal inoculation. Due to the short duration of the trial mycorrhizal colonisation could not be assessed. It is evident that selected combinations of bacteria and mycorrhizal fungi could promote citrus seedling growth and potentially improve seedling health. Further studies under nursery conditions are recommended.