Köln, Universiẗat, Diss., 2000.

Thèse (Ph. D.)--Université Laval, 2008. / Bibliogr.: f. 66-79. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.

Thèse (M.Sc.)--Université Laval, 1996. / Bibliogr.: f. 57-68. Publié aussi en version électronique.

Thèse (M.Sc.)--Université Laval, 2006. / Bibliogr.: f. [66]-73. Publié aussi en version électronique.

No description available.

Arbuscular mycorrhizal (AM) fungi have been living in association with land plants for at least 400 million years. Because they are obligate symbionts, the study of AM symbiosis has focused primarily on its plant host and progress in the molecular biology of AM fungi has been very slow. Using two different approaches, library screening and direct PCR-based assays, genetic information of AM fungi was compared across isolates and species. This allowed the study of novel DNA regions previously unexplored in AM fungi. The following species were investigated: Glomus intraradices, Glomus mosseae, Gigaspora margarita, Scutellospora calospora, Acaulospora scrobiculata and Entrophosphora colombiana. In the first approach, using in vitro grown G. intraradices, a DNA extraction protocol was developed for the construction of a partial genomic library. This library was screened for the presence of microsatellite-containing loci. PCR primers were designed based on five identified loci. Two of these loci were monomorphic for all isolates and species. The second approach used a combination of degenerate and specific primers for fungal chitin synthase genes to explore the variability of this gene family in AM fungi. A total of 21 AM sequences were isolated and sequenced, covering class I and II chitin synthases. RT-PCR with G. intraradices revealed differential expression of chitin synthases in spores and mycelium, as compared to mycorrhized roots. In addition, using primers designed from a highly conserved sequence for plant resistance genes, classical PCR and RT-PCR allowed the detection of a genomic sequence and its cDNA counterpart encoding a putative serine/lysine rich protein in G. intraradices. We have thus investigated genetic variability in AM fungi in functional genes as well as in repetitive DNA regions. Study of gene expression was also possible using in-vitro grown G. intraradices.

Two field studies were conducted to assess the potential benefit of arbuscular mycorrhizal (AM) inoculation of elite strawberry plants on plant multiplication, and fruit yield, under typical nursery conditions, in particular soils classified as excessively rich in P. To study plant productivity, five commercially in vitro propagated elite strawberry cultivars ('Chambly', 'Glooscap', 'Joliette', 'Kent', and 'Sweet Charlie') were not inoculated with AM fungi or were inoculated with either a single species (Glomus intraradices), or a mixture of species (G. intraradices, Glomus mosseae, and Glomus etunicatum). AM inoculation was found to impact strawberry plant productivity in a soil with excessive P levels. The AM fungi introduced into the field by inoculated mother plants established a mycelial network in the soil through colonization of the daughter plant roots, however, persistence of colonization was determined to below (<12% in inoculated plant roots). In soils excessively rich in P, individual crop inoculation may be the only option for management of the symbiosis, as the host and non-host rotation crops, planted prior to strawberry production, had no effect on plant productivity or soil mycorrhizal potential. / To study the impact of AM inoculation on fruit production, three commercially grown strawberry cultivars (Glooscap, Joliette, and Kent) were not inoculated with AM fungi or were inoculated with either G. intraradices or G. mosseae. AM fungi impacted the fruit yield, with all inoculated cultivars producing more fruit than noninoculated cultivars during the first harvest year. The percentage of root colonization could not be used to explain the differences in total fruit yield during the first harvest year, or the increase in total fruit yield the second harvest year. / We wished to examine the effects of various P treatments on C metabolism within the intraradical mycelia (IRM) of the fungus. Specific primers were developed for the Glomus intraradices glucose-6-phosphate dehydrogenase (G6PDH) gene. Real-time quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) was used to measure the gene expression of the G. intrarardices G6PDH gene in response to external P conditions of colonized transformed carrot roots. The results showed a significant down-regulation of G6PDH in the IRM of G. intraradices when cultures were grown in a high P (350 muM P) medium compared to those grown in the low P (35 muM P) medium. The down-regulation may suggest a reduction in the C flow from the host to the fungus. There was no effect on G6PDH expression following a two-hour incubation with additional P applications (No P, low P and high P).

No description available.

Les spores de Glomus intraradices nouvellement formées sont soumises à un processus de dormance intrinsèque, levé par un passage à 4°C d'un minimum de 14 jours. Des changements morphologiques apparaissent au cours de ce processus, tels que, sans les 14 jours minimaux au froid, les spores mises à germer meurent majoritairement ou forment des patrons de croissance particuliers, confinés autour de la spore, très ramifiés, et dépourvus d'hyphes principaux. En revanche, dès que les 14 jours de rigueur au froid sont respectés, le taux de mortalité des spores mises à germer diminue et des hyphes principaux s'individualisent et s'allongent sur plusieurs centimètres. L'examen des processus morphologiques dans la littérature a révélé que le principe dimorphique se rencontrait tout au long du cycle de croissance externe du champignon MA, les hyphes tantôt formant de fines ramifications, les ± FB ¿ (Fine-Branching), tantôt s'allongeant sous la forme d'hyphes principaux, les ± RH ¿ (Runner-Hyphae). En phase germinative, les FB semblent apparaître en situation de stress. En phase pré-symbiotique, les FB sont représentés essentiellement par des structures ± fan-like ¿, les RH apparaissant dans le cas des rares colonisations racinaires directes. En phase extraradicale, les RH caractérisent les gros hyphes structuraux à partir desquels se ramifient des FB. Une nouvelle approche quantitative a été développée pour évaluer la croissance des hyphes, basée sur la mesure des dimensions fractales (DF). Cette technique a été appliquée à quatre souches de champignons MA du genre Glomus cultivées in vitro, soumises à l'influence de différentes molécules stimulant ou inhibant la croissance. La technique s'avère particulièrement efficace pour mesurer les FB germinatifs et les hyphes extraradicaux. La méthode traditionnelle de Grid-Line intersect (GL) demeure utile pour mesurer la longueur des RH germinatifs.

Azoxystrobin (AZY), a systemic broad-spectrum fungicide, is applied on crops to control soil-borne pathogenic fungi. This study aimed to determine the effects of AZY on non-target plant species and Glomus intraradices Schenck & Smith, an arbuscular mycorrhizal fungus (AMF) associated with plants' roots. We hypothesized that AZY negatively affects AMF viability; and that, if the plants were dependent on this symbiosis, AZY exerts an indirect detrimental effect on plant growth. To test this, three mycotrophic (Phalaris arundinacea L., Solidago canadense L., Geum canadense Jacq.) and one non-mycotrophic (Chenopodium album L.) native plant species were subjected to five AZY doses with or without AMF. Plants were grown for 60 days in a greenhouse, in individual pots, (4 plants X 2 AMF X 5 AZY X 6 replicates), and mesocosms (1 mes. X 2 AMF X 5 AZY X 6 replicates), and harvested 30 days after spraying, and dry mass was taken. Fresh root samples were used for microscopic assessment of AMF colonization. The results from the individual pot experiment show that the effects of AZY on biomass varied across plant species. AZY led to a significant increase in shoot and root mass of P. arundinacea, and a decrease in shoot mass of AMF inoculated G. canadense. The presence of AMF resulted in a significant increase in root and shoot mass of P. arundinacea, and an increase in root mass of S. canadense and shoot mass of C. album. In the mesocosm experiment AZY did not have a significant effect on the measured parameters, although the presence of AMF significantly increased root, shoot, and total dry mass of G. canadense and P. arundinacea. Conversely, AMF significantly decreased shoot and total dry mass of S. canadense. The results suggest that both direct and indirect effects should be taken into account when assessing the impact of pesticides on non-target plant species.