Graduation date: 1991

High bicarbonate (HCO3-) content and associated high pH of irrigation water is detrimental to plant growth. Sustain ableagricultural/horticultural production will increasingly have to rely on economically feasible and environmentally sound solutions to the problems associated with high levels of HCO3- in irrigation water. The ability of a mixed Glomus Tulasne & Tulasne species inoculum of arbuscular mycorrhizal fungi (AMF), Glomus ZAC-19 (containing Glomus albidum Walker & Rhodes, Glomus claroideum Schenck & Smith, and Glomus diaphanum Morton & Walker), to enhance plant tolerance to HCO3- was tested on the growth and nutrient uptake of Rosa multiflora Thunb. ex J. Murr. cv. Burr (rose). Arbuscular mycorrhizal colonized and non-inoculated (non-AMF) R. multiflora cv. Burr were treated with 0, 2.5, 5, and 10 mM HCO3-. Increasing HCO3- concentration and associated high pH reduced R. multiflora cv. Burr growth, nutrient uptake, and acid phosphatase activity (ACP), while increasing alkaline phosphatase activity (ALP). Inoculation with AMF enhanced plant tolerance to HCO3- as indicated by greater growth, nutrient uptake, leaf chlorophyll content, higher mycorrhizal inoculation effect (MIE), lower root iron reductase activity, and generally lower soluble and wall-bound ALP activity. While AMF colonization (arbuscules, vesicles, and hyphae formation) was reduced by increasing HCO3- concentration, colonization still occurred at high HCO3- concentration. At 2.5 mM HCO3-, AMF plant growth was comparable to plants at 0 mM HCO3-, further indicating the beneficial effect of AMF for alleviation of HCO3- plant stress.

In this thesis I investigated the mutualism between Kunzea ericoides (kanuka) and two groups of soil fungi, ectomycorrhizae (ECM) and arbuscular mycorrhizae (AMF). Mycorrhizal mutualisms, which are considered globally ubiquitous, are poorly understood over changing abiotic gradients. A field survey of K. ericoides assessed how the relationship with the soil fungi varieties altered over a hydrologic gradient. Arbuscular mycorrhizal colonisation was significantly improved by increasing rainfall levels and amount of surrounding kanuka, and negatively affected by increasing altitude. Ectomycorrhizal colonisation was not significantly affected by any measured variables and remained relatively constant across all circumstances, suggesting that it is the preferred fungal mutualist for this tree species. A glasshouse experiment was done to measure the effect of ECM inoculation on the growth and water usage of K. ericoides over varying moisture availability. The seedlings were planted in soil inoculated with both ECM and AMF (experimental) or AMF only (control) and then grown under varying levels of water stress. The experiment was replicated with two soil types, with soil from beneath adult manuka (Leptospermum scoparium) and soil from beneath adult kanuka (K. ericoides). ECM colonisation significantly increased as soil moisture decreased for both soil types. ECM inoculation also increased the root:shoot ratio, and drastically decreased water usage under drought conditions. There were some soil effects as the seedlings grown in manuka-soil achieving greater biomass than seedlings grown in kanuka-soil. This is possibly due to presence of pathogens or some type of legacy competition which the seedlings would experience growing near conspecifics. Overall, K. ericoides formed a dominant mutualism with ectomycorrhizae. These two both thrive in dry environmental conditions and have a suite of complementing abilities which possibly allow K. ericoides to expand it range into these dry habitat types. The increased benefit of these mutualisms at the hydrologic range limit of the species supports the importance of biotic interaction mediating environmental stress. Understanding the effects and response of mycorrhizal mutualisms are especially significant considering current climate change issues in New Zealand and worldwide.

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.

Arbuscular mycorrhizal (AM) fungi are an important component of agricultural ecosystems, and can directly influence the productivity of these systems. Unfortunately, conventional agricultural practices have been shown to adversely affect AM fungi. The use of more ecologically sustainable agricultural practices such as tree-based intercropping (TBI) may have the potential to reduce the negative impact of agricultural practices on AM fungi. The objectives of this thesis were to determine (1) if trees influence the structuring of AM fungal communities, (2) if TBI systems support a more diverse AM fungal community compared to conventional monocropping (CM) systems, and (3) if differences in AM fungal richness and composition between the two cropping systems have a functional effect on the growth of crops. Molecular analysis of the AM fungal community in the TBI system revealed 17 phylotypes that all belonged to the family Glomeraceae. Differences in richness and composition among the treatments indicated that trees had an effect on the structuring of AM fungal communities. Intercropping alleys adjacent to white ash and poplar tree rows had a significantly (P < 0.05) richer and different AM fungal community compared to intercropping alleys adjacent to Norway spruce tree rows. When comparing TBI and CM systems, AM fungal abundance was not significantly (P > 0.05) different between the two cropping systems. However, differences in both richness and community composition of AM fungi were observed between the two cropping systems. The TBI system had a significantly higher AM fungal richness and contained several taxa not found in the CM system. Controlled greenhouse experiments revealed that differences in AM fungal richness and community composition between the TBI and CM systems had no functional effect on the growth of three crops (i.e. barley, canola, and soybean). The similar growth response of crops to AM fungi from the two cropping systems may be due to the lack of functional complementarity among the AM fungi. Overall, the TBI system had a more diverse AM fungal community compared to the CM system and trees appear to be a significant factor in the structuring of these communities.

Arbuscular mycorrhizal fungi (AMF) are widespread soil dwelling microorganisms that associate with plant hosts. AMF receive carbon from the host as a result of the mutualism, while the plant’s ability to acquire nutrients is enhanced by AMF. Additionally, AMF benefit their host in the form of pathogen protection. While it is known that increased AMF species richness positively correlates with aboveground plant productivity, the relationship between AMF diversity and pathogen protection is not well understood. In a growth chamber study, the plant host Leucanthemum vulgare, a non-native plant species in North America, was introduced to all combinations of three AMF species either in the presence or absence of the plant root pathogen Rhizoctonia solani. In the presence of the pathogen, the plant host increased its dependence on the AMF symbiosis. However, the richest AMF species assemblage did not provide the greatest pathogen protection. Understanding how diverse groups of AMF protect plants from pathogen attack provides insight into how plant communities are formed and structured. / NSERC

No description available.

There has been little research into the compatibility of commonly utilized apple rootstocks and VA-fungal types, and even less research regarding the effects of herbicides used in orchards, on the VAM symbiosis of apple trees. Studies demonstrated that early inoculation of young apple plants, prior to transplanting, results in healthy and vigorous plants with better growth and nutrition than uninoculated plants. We studied the efficiency of VA-fungal species and isolates on young apple rootstocks, produced by in vitro propagation. Mycorrhizal inoculation promoted plant growth, dry mass production and leaf P concentration. Mycorrhizal efficiency was associated with larger external hyphal network but showed no relation with the internal colonization. Despite the high P-fertility of the soil used, growth enhancement due to mycorrhizal inoculation was attributed to an improved P nutrition. / In a second experiment, the effect of herbicides currently used in orchards was tested on the mycorrhizal symbiosis. Paraquat, simazine and dichlobenil were applied to soil with mycorrhizal and non-mycorrhizal apple plants. Mycorrhizae increased herbicide toxicity in apple, as demonstrated by the greatly increased plant mortality. While both paraquat and simazine decreased spore germination in vitro, none of the herbicide treatments affected root colonization in soil. Effects on the photosynthetic rate, measured after herbicide application, indicated a physiological interaction between mycorrhizal colonization and dichlobenil, involved in the toxic response of apple plants.

It may be possible to tailor crop management to encourage diverse soil microbial communities and beneficial microorganisms, and produce high quality food products. Studies were carried out in 2005-2007 to evaluate the impact of spring wheat (Triticum aestivum L.) cultivar choice and crop polycultures on soil microbial communities in organic and conventional systems, and subsequent wheat quality. Five wheat cultivars were grown organically and conventionally to evaluate grain breadmaking quality and micronutrient content and their impact on the soil microbial community. Organic grain yields were roughly half of conventional yields, but quality levels were all acceptable for Canadian Western Hard Red Spring wheat. Measured soil (0-15 cm) microbial profiles (by phospholipid fatty acid analysis) differed between the two management systems, and amongst cultivars in the conventional system. The most recent cultivar in the study, AC Superb, exhibited the highest levels of fungi suggesting that breeding efforts in conventionally managed environments may have resulted in cultivating mycorrhizal dependence in that environment. In general, many of the studied grain micronutrients were greater in the organically grown wheat system, possibly due in part to decreased grain yield and smaller grain size. Maximizing grain micronutrient content through wheat cultivar choice was dependent on management system. The presence of fungi biomarkers appears to have improved uptake of Mn and Cu. Monocultures and polycultures of common annual crops were grown organically and conventionally in 2006-2007. Intercrops exhibited an ability to overyield in an organic system, largely through weed suppression, but intercrops also overyielded in a conventional system where weeds were controlled through herbicides. As intercrop complexity decreased, the instances of improved weed suppression declined. Management systems and wheat cultivars can alter the composition of the soil microbial community. Annual crop polycultures did not alter soil microbial communities in this study, but showed evidence of agronomic benefits in both organic and conventional systems. / Plant Science

Bibliography: leaves 153-185. / [ix], 200, [29] leaves, [6] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Vesicular-arbuscular (VA) mycorrhiza formation is a complex process which is under the genetic control of both plant and fungus. This project aims to develop a model infection system in Hordeum vulgare L. (barley) suitable for molecular analysis; to identify host plant genes differentially expressed during the early stages of the infection process; and to screen a mutant barley population for phenotypes which form abnormal mycorrhizas. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1995