| Summary: | Environmental hazards and health problems due to the application of chemical pesticides in agricultural sectors incite huge public concerns. Therefore, one of the better solutions is through introduction of biological control means to manage the outbreaks of plant diseases. To date, only small numbers of beneficial microorganisms - belonging to the category of hyperparasitic or mycoparasitic fungi have proven to keep plants or protect crops from plant pathogen infection. The objective of this study was to characterize a group of <i>Fusarium</i>-associated melanosporaceous biotrophic mycoparasitic fungal isolates, which were identified and pre-selected by Dr. Vladimir Vujanovic and deposited in the Saskatchewan Microbial Collection and Database (SMCD). Particular objectives were to examine spore germination of a biotrophic mycoparasite, to test effects of this fungus on seed germinations, to study interactions between the mycoparasite and Fusarium hosts, and to investigate relationships between the mycoparasite-the <i>Fusarium</i> host-wheat root under controlled conditions in the university Phytotron facilities.<p>
Information related to this group of fungi is relatively limited. In order to characterize potential biotrophic mycoparasitic fungal isolate(s), molecular and microscopy methods were performed to accomplish taxonomical, phylogenetical and morphological studies. Since, spore germination is a very crucial stage in fungal life cycle and growth, ascospores (sexual spores) of the biotrophic mycoparasite were isolated from a fungal colony. These spores were inoculated on media supplemented with different <i>Fusarium</i>-filtrates or suspended in different <i>Fusarium</i>-filtrates to examine spore germination rates and growth patterns. Together with other mycoparasitic fungi, this biotrophic mycoparasite was inoculated on spring wheat seeds, to test effects of these fungal inoculants on seedlings growth using <i>in vitro</i> assays. Dual-culture, slide culture, and microscopy approaches were carried out to elucidate intimate and special relationship between the biotrophic mycoparasite and <i>Fusarium</i>-hosts. In order to study tritrophic interactions (biotrophic mycoparasite-<i>Fusarium</i> host-wheat root), spring wheat was grown in the phytotron with different treatments of fungal inoculations. Wheat roots were then subjected to genus-specific quantitative real-time PCR analyses.<p>
One melanosporaceous biotrophic mycoparasitic strain was identified as a new species in the genus <i>Sphaerodes</i>. This biotrophic mycoparasite was isolated from <i>Fusarium</i>-infected fields in Saskatchewan and Quebec, and named <i>Sphaerodes mycoparasitica</i>. Germination of <i>S. mycoparasitica</i> sexual spores was improved when treated with filtrates or extracellular extracts from the <i>Fusarium</i>-host as compared to <i>Fusarium</i>-non-host filtrates. No pathogenic effects on wheat seeds were observed when inoculated with <i>S. mycoparasitica</i>. Furthermore, seedlings growth was enhanced with this biotrophic mycoparasite compared to other mycoparasitic fungi. Later, this biotrophic mycoparasitic strain was found to establish biotrophic fusion and haustorial contact relations with <i>F. avenaceum, F. oxysporum</i>, and two F. graminearum chemotypes. Since, 3-Acetyldeoxynivalenol-producing <i>F. graminearum</i> is one of the most highly toxigenic and aggressive wheat pathogens in Saskatchewan and North America, therefore, this pathogen strain was chosen for tritrophic interaction study. Under controlled conditions in the phytotron, <i>S. mycoparasitica</i> improved seedlings growth when these were challenged with <i>F. graminearum</i> as compared to seedlings only inoculated with the <i>Fusarium</i> pathogen. In conclusion, S. mycoparasitica could be a potential candidate for biological control of <i>Fusarium</i> diseases in wheat.
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