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Interaction between orchids and fungi belongs to little understood aspects of orchid biology. This thesis investigated an identity of mycorrhizal and other fungal symbionts of several European orchid species and also an influence of these fungal symbionts on ecology, distribution, and evolution of the studied orchid species. Diverse methodological approaches were used including in situ seed germination, culture-dependent and -independent techniques for fungal isolation and identification, molecular phylogenetics, stable isotope analyses, and transmission electron microscopy.

The Arbuscular mycorrhiza (AM) symbiosis is a mutual association formed by plant roots and soil fungi. Most vascular flowering plants have the ability to form AM associations, which show significant impact on ecosystem function and plant health. This association is based on the mutual exchange of nutrients between plant and fungus. Therefore, AM association leads to increased demands for photosynthesis. The main aim of this study was to investigate the pathway used by plants during AM to increase the photosynthetic performance. To achieve this aim, we used the model legume Medicago truncatula. We have found out that AM symbiosis develops in roots, where AM fungi colonize the roots, leading to better plant growth and more biomass. Furthermore, AM symbiosis increases chlorophyll content and photosynthetic electron transport rate in leaves. Based on these results we suggest that AM symbiosis increases both efficiency and capacity of photosynthetic apparatus in Medicago truncatula

Germination ecology of four Epipactis species (E. albensis, E. atrorubens, E. helleborine, E. purpurata) was studied. Habitat preferences of adult plants were analyzed using phytosociological relevés from the Czech Phytosociological Database. A field experiment was carried out to determine course of germination of Epipactis seeds sown in different habitat types. Relationship between ecological preferences and germination ecology, and spatial aspects of seed dispersal and seedling recruitment are discussed.

Μελετήθηκε η επίδραση μυκορριζών στην αύξηση φυτών αραβοσίτου, προκειμένου να επαληθευτεί ο ρόλος τους υπό συγκεκριμένες συνθήκες καλλιέργειας στην περιοχή του Ρίου Πατρών και η ενδεχόμενη ευεργετική τους δράση στην αύξηση των φυτών. Ως δείκτες αύξησης θεωρήθηκαν το μήκος και το νωπό βάρος του βλαστού των φυτών, το νωπό και ξηρό βάρος φύλλων, το νωπό και ξηρό βάρος ολόκληρου του φυτού, η φυλλική επιφάνεια και το νωπό βάρος της ρίζας. Μετά από στατιστική ανάλυση των αποτελεσμάτων διαπιστώθηκε ότι φυτά που είχαν εμβολιαστεί με μυκόρριζα υπερτερούσαν ως προς το ύψος, το νωπό βάρος των στελεχών και τη φυλλική επιφάνεια συγκρινόμενα με τα φυτά μάρτυρες. Αντίθετα, τα εμβολιασμένα με μυκόρριζα φυτά δεν παρουσίασαν στατιστικά σημαντικές διαφορές ως προς το νωπό βάρος της ρίζας, συγκρινόμενα με τα φυτά μάρτυρες. Αναφορικά με το νωπό βάρος των φύλλων διαπιστώθηκε ότι τα εμβολιασμένα με μυκόρριζα φυτά υπερτερούσαν συστηματικά των φυτών μαρτύρων, καίτοι οι διαφορές δεν ήταν στατιστικώς σημαντικές. Τέλος, όσον αφορά το ξηρό βάρος των στελεχών, φύλων και ρίζας οι διαφορές στις τιμές των φυτών μαρτύρων και εκείνων που είχαν εμβολιαστεί με μυκόρριζα δεν ήταν στατιστικά σημαντικές. Υπολογίζοντας τον σχετικό ρυθμό αύξησης των φυτών προέκυψε ότι για όλες τις μετρούμενες παραμέτρους ο δείκτης ήταν υψηλότερος για τα εμβολιασμένα με μυκόρριζα φυτά σε σχέση με τα φυτά μάρτυρες. Τα αποτελέσματα της παρούσας μελέτης υποδεικνύουν τη θετική επίδραση της μυκόρριζας στην αύξηση της βιομάζας των φυτών του αραβοσίτου στις συνθήκες περιβάλλοντος που επικρατούν στην περιοχή του Ρίου Πατρών. / -

Abstract Plants have evolved various adaptive strategies for balancing the benefits and costs of having a high affinity for resources, plasticity of growth allocation and mycorrhizal symbiosis. The relative growth rates of mycorrhizal and non-mycorrhizal plants were modelled for stable and variable nutrient availability. Mycorrhizal plants had higher growth rates at low and non-mycorrhizal plants at high nutrient availability. Variation in nutrient availability reduced the growth rate of mycorrhizal plants due to a high affinity for nutrients. However, mycorrhizal plants may be able to buffer against external fluctuations and therefore experience less environmental variation than non-mycorrhizal plants. Non-mycorrhizal plants may even benefit from variation. The optimal allocation of growth between shoot and roots depends on the availability of energy and nutrients. The optimisation model predicted that the requirement for phenotypic plasticity of shoot/root allocation is greatest in environments with low resource availability. Plants with a high affinity for resources required more plasticity in order to tolerate variation than plants with a low affinity. The model predicted a trade-off between the ability to deplete resources and the ability to tolerate resource fluctuations. Changes in the availability and ratio of resources lead to changes in the structure and composition of vegetation during primary succession. The field study of the forested phases of the land uplift island Hailuoto showed a successional change in the vegetation from the dominance of bryophytes and deciduous dwarf shrubs to dominance by lichens and evergreen dwarf shrubs. The humus layer became thinner and the availability of nutrients declined, while the C/N ratio of soil organic matter increased during succession indicating a decline in the quality of organic matter. The increased soil respiration rate indicates a successional increase in the energetic costs of decomposing organic matter. Nutrients mediate both direct and indirect trophic interactions. Indirect interactions of nutrient cycling are not explicit in continuous time models. A transformation to a discrete time model was shown to make the indirect interactions explicit as transition probabilities and allowed their dynamic contribution to be evaluated with an elasticity analysis. The importance of indirect interactions was greater in tundra than temperate forest and increased with the rate of nutrient cycling.

Sexual reproduction is an important process amongst eukaryotic organisms, with one function being to maintain genetic variation. The idea that complex eukaryotic species can persist for millions of years in the absence of sex defies fundamental evolutionary dogma, yet a group of organisms known as ancient asexuals were thought to have evolved clonally under deep evolutionary time. Prominent among these are the arbuscular mycorrhizal fungi (AMF), which are obligate plant symbionts that colonize the root cells of plants and extend their hyphae into the soil assisting the plant in acquiring key nutrients. Unlike most eukaryotes, AMF cells are multinucleate with thousands of nuclei moving through a continuous cytoplasm. Genomic analyses have identified a putative mating-type (MAT) locus within the nuclear genomes of model AMF Rhizophagus irregularis, a region that in other fungi dictates the process of sexual reproduction. Additional findings demonstrated that AMF strains carry one of two nuclear organizations. They can be either homokaryotic (AMF homokaryons), where all nuclei within the cytoplasm are virtually identical, or heterokaryotic (AMF dikaryons), where two MAT-locus variants co-exist within the cytoplasm. Despite a lack of observable traits indicative of sex, this homo/heterokaryotic dichotomy is reminiscent of the nuclear organization of sexual fungi. My research aims to build on these findings to investigate the actual role of the MAT-locus in driving AMF reproduction. To address this, I build my thesis into three main chapters. The first chapter reviews our current understanding of AMF genetics and what drives genome evolution in these organisms. The second chapter establishes a relatively easy, inexpensive, and reproducible approach to genotype known MAT variants of R. irregularis in natural and experimental conditions. The last chapter uses experimental crossings between strains to assess cytoplasmic compatibility and nuclear exchange. I demonstrate that dikaryotic spore progenies can be formed after co-culturing two distinct AMF homokaryotic strains. Further analyses of various genomic regions also reveal possible recombination in homokaryotic spore progenies from co-cultures. Overall, this research provides new experimental insights into the origin of genetic diversity in AMF. These findings open avenues to produce genetically new AMF strains in the lab using conventional crossing procedures and provide a glimpse of the mechanisms that generate AMF genetic diversity in the field.

Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts that colonize the roots of the majority of vascular land plants. These fungi have a unique nuclear organization, in which thousands of nuclei co-exist among an unsegmented fungal body. In individual strains these nuclei can all be genetically similar (homokaryotic) or be derived from two distinct parents (dikaryotic). In other fungal groups the presence of two distinct nuclei in one cell (fungal dikaryons) can change their fitness, function, and symbiotic relationship; begging the question, what impact does the presence of two parental genotypes have on the arbuscular mycorrhizal symbiosis? I am investigating this by measuring the mycorrhizal response (MR) of potato cultivars with different degrees of domestication using representative AMF homokaryons (4) and AMF dikaryons (4). I found that the genetic organization (dikaryotic vs homokaryotic) and domestication status of the host (modern vs old) are both significant factors in the mycorrhizal response of host plants. Specifically, biomass is significantly greater when inoculated with homokaryotic AMF compared to dikaryotic AMF. Dikaryotic strains have low arbuscule colonization in modern cultivars and higher in old, although there are not significant differences in other fungal responses between homokaryotic and dikaryotic AMF. Furthermore, nutrient uptake (N and P) is greater in old cultivars than modern cultivars, although the root:shoot ratio is lower in old cultivars. Analyses of single spores using digital droplet PCR (ddPCR) confirm that nucleotype ratio of dikaryotic spores shifts depending on the host identity. This research provides novel insights into the role of AMF genetic organization in the mycorrhizal symbiosis in greenhouse conditions. In particular, this work shows that the presence of two distinct nucleotypes results in the fungi being more readily adaptable to the host leading to a more stable MR and a potentially selfish strategy, when in symbiosis with potato cultivars.

Thesis (M. Sc.(Agronomy)) -- University of Limpopo, 2017. / Cleome gynandra is increasingly becoming an important strategy for achieving food and nutrition security among rural households in many developing countries. Root-knot (Meloidogyne species) nematodes, with limited nematode management strategies, limit the successful production of this vegetable crop. Nemafric-BL and Nemarioc-AL phytonematicides are separately being developed in South Africa for sustainable crop production systems. However, the two products have not been simultaneously tested for managing the notorious Meloidogyne species and absorption of phosphorus, with a combination of Vesicular arbuscular mycorrhiza (VAM). The objective of this study therefore was to determine the interactive effects of VAM and each of the two phytonematicides on nutrient content, growth of C. gynandra. A 2 × 2 × 2 factorial experiment, with the first, second and third factors being VAM (V), nematode (N) and Nemafric-BL phytonematicide (P). The eight treatments included (1) untreated control (V0N0P0), (2) nematodes alone (V0N1P0), (3) VAM alone (V1N0P0) (4) Nemarioc-AL phytonematicide alone (V0N0P1), (5) V1N1P0, (6) V0N1P1, (7) V1N0P1 and (8) V1N1P1, were laid out in a randomised complete block design, with ten replications. The same layout experiment was done for the Nemarioc-AL phytonematicide trial which had a similar layout. Seedlings were irrigated with 250 ml chloride-free tapwater every other day for 56 days. Multifeed and NPK (2:3:2(22) fertilisers were applied at transplanting. The second order interaction (V1N1P1), was highly significant (P ≤ 0.01) for plant height contributing 54% in TTV (Total Treatment Variation) of the variable. Among the main factors (N, P and V), only nematode had highly significant effects on stem diameter. All interactions of VAM, nematode and Nemarioc-AL phytonematicide and main factors each had no significant effect on Cleome. The second order (V1N1P1) and the first order interaction (V1N1P1) did not have significant effects on the three nutrient elements except for the first order interaction (V1N0P1) which was significant on foliar Zn contributing 42% in TTV of the variable. Also nematode had highly significant effect on foliar K and significant effect on foliar Zn contributing 49 and 31% in TTV of the respective variables. Using the two-way table, VAM and Nemafric-BL phytonematicide each increased foliar Zn by 27% and 29%, respectively. The second and first order interactions of VAM, N and Nemarioc-AL phytonematicide and the main factors did not have significant effect on foliar K, Fe and Zn. The second order interaction of VAM, nematode and Nemafric-BL phytonematicide had significant effects on gall rating, contributing 2% in TTV of the variable. VAM, nematode and Nemarioc-AL phytonematicide showed that the second and first order interaction except for V1N0P1 interaction on gall rating, were not significant for nematode variables. The V1N0P1 interaction contributed 20% in TTV of gall rating. Using a two-way table, VAM and phytonematicide each increased root galls by 7% and 74%, respectively. Combined, VAM and phytonematicide reduced root galls by 64%. The innovative products interacted together and that Nemafric-BL and Nemarioc-AL phytonematicides and VAM alone could be used in managing nematodes. / National Research Foundation, Agricultural Research Council-Universities Collaboration Centre