Fungal endophytes live inside plants without causing apparent symptoms of infection. All plant species surveyed thus far, including liverworts, mosses, seedless vascular plants, conifers, and angiosperms, harbor one or more endophytic fungi. Fungal endophytes can be divided into four groups including class 1, class 2, class 3 and class 4 endophytic fungi according to host range, colonization pattern, transmission, and ecological function. Class 2 fungal endophytes benefit their host by increasing environmental stress tolerance (i.e. water, temperature, salt) in a habitat-specific manner. In my study, class 2 fungal endophytes were studied from weedy plants growing in an environmentally stressed area: mine tailings from the Athabasca oil sands. This area is a vast hydrocarbon reserve in western Canada that supplies 10% of Canadian oil needs. Hydrocarbons are extracted from tar sands with hot water, alkali, and solvents. The tailing sands can later be remediated (by adding organic material and fertilizer) to establish new plant communities. Prior to remediation, tailing sands have extremely low content of organic carbon and available minerals, and are hydrophobic compared to unimpacted and remediated soils. Nevertheless, <i>Taraxacum</i> (dandelion) and <i>Sonchus</i> (sow-thistle) can colonize extracted tailing sands even prior to remediation. Preliminary results show that pioneer plants have similar fungal abundance as plants of unextracted treatments. Fungal endophytes were isolated from surface sterilized <i>Taraxacum</i> and <i>Sonchus</i> that had been growing upon unimpacted, remediated and extracted soil. Fungi isolated in this way included <i>Alternaria, Tricoderma, Fusarium</i> and an unidentified <i>Perithecial Ascomycote</i>. These endophytic fungi were used to inoculate tomato plants in a greenhouse trial to determine whether they confer stress tolerance to host plants, especially for drought and low mineral nutrition. Before exposing the tomato plants to environmental stresses, the specific endophytic fungal strains applied were successfully recovered from tomato plants originally inoculated with the same endophytic fungi. Although the other endophytic fungi turned out to be harmful to the tomato plants in the test, a <i>Trichoderma spp.</i> strain isolated from samples of extracted treatment appears to confer tolerance of tailing sands to the tomato plants. This <i>Trichoderma spp.</i> strain which we can call <i>TSTh20-1</i> was molecularly identified as <i>Trichoderma harzianum</i>. Despite an identification to species, all strains of <i>T. harzianum</i> are not necessarily identical regarding strain-specific attributes. Using similar techniques described here, it is possible to isolate and potentially use beneficial class 2 endophytic fungal strains for the remediation process in the Athabasca oil sands or to assist plant growth in other high stress environments.

Academic dissertation : Chemistry : Helsinki : 1998. / Textes et résumés en anglais. ISBN de la version électronique 951-38-5226-1. Pagination multiple pour les articles reproduits en annexe. ISSN de la version électronique : 1455-0849. Bibliogr. p. 56-72. Bibliogr. à la suite des articles.

Reproduction de : Thèse de doctorat : Pharmacie. Chimie analytique et écotoxicologie marine : Nantes : 2007. / Bibliogr.

Reproduction de : Thèse de doctorat : Pharmacie. Mycologie et mycochimie : Université de Nantes : 2007. / Bibliogr.

Sclerotinia sclerotiorum is a widespread plant pathogen that produces structures known as sclerotia. When sclerotia germinate they give rise to infective hyphae, myceliogenic germination, or they produce ascocarps, carpogenic germination. Biological control has usually targeted sclerotia or ascospores. The main objectives of the research presented herein were to observe the effect of a mycoparasite and fungus gnats (Bradysia coprophila) on the survival of sclerotia in vitro and in field conditions, and to study the enzymatic activity of the mycoparasite when in contact with sclerotia damaged by fungus gnats. / In this research several mycoparasites were evaluated for their efficacy to degrade sclerotia in soil. From these tests, an isolate of Trichoderma hamatum, TMCS 3 proved to be the most effective. Larvae of fungus gnats have also been reported to feed on sclerotia. When both organisms were combined in laboratory tests, fewer sclerotia survived than when the organisms acted alone. Sclerotia recovered from this treatment contained fewer viable cells when compared to sclerotia recovered from treatments with TMCS 3 or fungus gnats alone. The results obtained from field trials showed that TMCS 3 was effective at degrading sclerotia. Unfortunately environmental conditions were not always optimal for the establishment of high populations of fungus gnats. Few larvae were observed feeding on sclerotia and no significant differences were found among treatments. / Growth of TMCS 3 was studied using different carbon sources as substrates, including sclerotia of S. sclerotiorum. Biomass obtained from this latter treatment was significantly larger than on the other carbon sources tested. Enzymatic activity was also induced by the presence of sclerotia. In many cases, sclerotial exudates from mechanically damaged sclerotia or sclerotia damaged by larval feeding showed that the concentration of amino acids, carbohydrates, and electrolytes was increased as damage to the sclerotia has increased. Exudation of protein was not different when damaged and undamaged sclerotia were compared. Exudates from sclerotia with the melanized rind completely removed by fungus gnats feeding accelerated the germination of conidia of TMCS 3. These heavily damaged sclerotia also enhanced the growth of TMCS 3 when both organisms were grown together. However enzymatic (i.e. glucanase and chitinase) activity of TMCS 3 was not increased by the damage to the sclerotia. When damaged sclerotia were buried in soil infested with TMCS 3 they were degraded faster when the medulla of sclerotia was completely uncovered by larval feeding.

The biocontrol fungus Trichoderma virens is an avirulent symbiont with the ability to control plant disease by the production of antibiotic compounds, induction of plant resistance to pathogens, and mycoparasitism of other fungi. In this document, the analysis of a putative terpene biosynthesis gene cluster (vir cluster) in T. virens is described. The vir cluster contains genes coding for four putative cytochrome P450s, an oxidoreductase, MFS transporter, and a terpene cyclase. To determine the function of this cluster in secondary metabolism biosynthesis, a strain of T. virens with a deletion of the putative cyclase, vir4, was constructed. Deletion mutants were deficient in the synthesis of sesquiterpene volatiles and complementation of vir4 restored this loss in transformants, albeit at a lower level of production. An analysis of phenotypic characteristics between mutant and wild-type strains did not identify any differences when the strain interacted with other fungi, bacteria, or Arabidopsis seedlings. Paralogs of the gene encoding the elicitor SM1 were examined as genetic sources for potential elicitors to induce systemic resistance in plants. A search of the T. virens genome revealed the presence of three paralogs of sm1. One paralog, sm3, was found to be expressed when grown in association with plant roots and in still-culture. The Pichia pastoris protein expression system was used to generate sufficient quantities of SM3 to allow characterization of its function. The purified protein from the yeast system (picSM3) was shown to be glycosylated and to increase expression of a plant defense gene in maize seedlings. Mutant strains in which sm3 was either deleted or over-expressed were constructed to further explore the potential of sm3 as an elicitor of ISR. The differential production of SM1 and SM3 by these strains suggested that SM1 and SM3 may be co-regulated and native SM3 may be glycosylated. To further understand the role of a putative glycosylation site as a mechanism to prevent dimerization and subsequent elicitor activity, a point mutation was created in a sm1 deletion strain. Analysis of the behavior of the protein demonstrates that the putative glycosylation site is not involved in protein aggregation and deletion of this site does not prevent the protein from testing positive for glycosylation. We propose that SM1is not glycosylated but instead may interact with an oligosaccharide or other small molecule. However, the mechanism of dimerization in SM1 remains unknown.

Graduation date: 1992

Thesis (doctoral)--University of Helsinki, 2007. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (doctoral)--University of Helsinki, 2004. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.