Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

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

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.

In this study, we have demonstrated that inoculation of bean seeds with non-pathogenic binucleate Rhizoctonia (np-BNR) at sowing protected bean seedlings from infection of R. solani. Using quantitative real-time RT-PCR (QRT-PCR), transcript levels of defense genes encoding 1,3-beta-glucanase (GLUC), phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) in one-week old bean seedlings was monitored during np-BNR and R. solani interaction. The results revealed that protection effect of np-BNR correspond to a systemic suppression of these three defense genes' expression from significant higher level elicited by R. solani to the level of non-infected plants. This indicates that bio-protection by np-BNR isolates is not correlated to activation of these three defense genes' expression. Similar suppression was achieved for pre-colonization of bean seedlings with arbuscular mycorrhizal (AM) Glomus introradices on GLUC gene expression, although the AM fungus did not significantly reduce rot symptoms. Possible mechanisms implicated in down-regulation during plant-pathogen and np-BNR or AM interaction are discussed.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

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

A time course study was conducted to monitor disease development and expression of the defense-related genes phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), and hydroxyproline-rich glycoprotein (HRGP) in bean (Phaseolus vulgaris L.) plants colonized by the arbuscular mycorrhizal (AM) fungus Glomus intraradices , and post-infected with the soil-borne pathogen Rhizoctonia solani. Pre-colonization of bean plants by the AM fungus did not significantly reduce the severity of rot symptoms. RNA blot analysis revealed a systemic increase in transcript levels of the four defense-related genes in response to R. solani infection. On the other hand, pre-colonization of bean plants with G. intraradices elicited no change in PAL, CHS and CHI transcripts, but an increase of HRGP transcripts in leaves was detected. A differential and systemic alteration in the expression of all four defense genes was observed in AM beans post-infected with R. solani. Depending on the time after infection with R. solani and the tissue examined, varying responses from stimulation, suppression, to no change in transcript levels were detected.

The effect of the arbuscular mycorrhizal symbiosis at reducing the incidence of root diseases has received considerable attention. However, information on the role of mycorrhizae in reducing disease incidence of Fusarium root rot of beans (Phaseolus vulgaris), caused by the root pathogen Fusarium solani f. sp. phaseoli, is scarce. A study was undertaken to investigate how the arbuscular mycorrhizal fungus (AMF) Glomus intraradices affects disease development and population number of F. solani f. sp. phaseoli in the mycorhizosphere of bean plants growing in an experimental microcosm unit. This newly designed unit facilitated the spatial monitoring and quantification of both the symbiont and pathogen in different ecological soil regions of the mycorrhizosphere using compartmentation based on a physical segregation of roots, colonized or not by AMF (rhizosphere), AMF mycelium alone (mycosphere), or none (bulk soil). To study the interaction between both organisms, the experimental set-up consisted of a randomized complete block design using bean seedlings pre-colonized or not for 28 days by G. intraradices and infected or not for 6 days with F. solani f. sp. phaseoli. Monitoring of population number of the symbiont and the pathogen in bean plants and in the different mycorrhizosphere soil compartments was achieved with quantitative real-time PCR using specific molecular probes for each fungus, and with cultivation-dependant or morphological based methods. The results of this study indicated that non-mycorrhizal bean plants infected with the pathogen had typical root rot symptoms while infected plants that were pre-colonized by G. intraradices remained free of disease. The population number of F. solani f. sp. phaseoli was significantly reduced in the root system and in each of the mycorrhizosphere soil compartments of mycorrhizal infected plants. The mycorrhizosphere population of G. intraradices was not significantly modified, although the p

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

The aim of this diploma thesis was to determine the impact of mycorrhizal fungi on the growth parameters of model vegetable crops. As a model crops were selected Cucumber (Cucumis sativus L.) and Tomato ( Lycopersicon esculetnum Mill.). There were selected these three sorts of arbusko - mycorrhizal fungi to inoculate the medium were the crop seeds were sown: genus Glomus. Glomus claroideum BEG210, Glomus intraradices BEG140 a Glomus mosseae BEG95. The experiment that was conducted on this diploma thesis took place partially in the glasshouse as well as in the climate chamber, both in Horticulture Faculty in Lednice, Mendel University in Brno. The evaluation of treatment impacts was focused on the growth parameters such plant size, the width of the root collar and the leaf area of plants. Besides these parameters was also compared the plants 'weight. The results were statistically analyzed using STATISTICA 12 and are also included in the thesis. From the results we can conclude that the positive effect of mycorrhiza was reflected in both plant size and the weight of above-ground parts, which means an increase in fresh biomass. For these parameters, there were statistically significant differences in compare to control variation. Mycorrhizal treatment had also a positive effect on the growth of leaf area, and thus the photosynthetic apparatus of plants was increased. These results were supported by statistically significant differences compared to the control, as well. So this means that the mycorrhizal treatment has a very positive effect on plants.