Knowledge Resource Center for Ecological Environment in Arid Area
| Diversity of Frankia associated with Morella species of the Cape floristic region of Southern Africa | |
| Wilcox;Dale Adrian | |
| 出版年 | 2016 |
| 学位授予单位 | University of the Western Cape |
| 英文摘要 | Philosophiae Doctor - PhD Frankia is one of two partners in the globally distributed N2-fixing actinorhizal symbiosis between this filamentous soil-dwelling actinomycete and almost 300 species of host plants from eight diverse angiosperm families. The actinorhizal symbiosis is a major contributor to nitrogen reservoirs in terrestrial ecosystems, and allows actinorhizal plants to perform the role of pioneers in newly formed and nitrogen-poor soils. Frankia are differentiated into four main host-infection groups (1: Alnus/Comptonia/Myrica-infective, 2: Rosaceae/Datisca/Coriaria-infective, 3: Elaeagnaceae/Gymnostoma-infective and 4: Casuarina-infective), and there is a large degree of phylogenetic clustering within these HIGs. Of these host lineages, species from the genus Morella, from the family Myricaceae, are notable as they have the ability to establish effective partnerships with Frankia from more than one host-infection group. Africa houses 16 of the world’s 33 currently accepted Morella species, and Morella is the continents only genus containing endemic actinorhizal species. Despite this, the diversity of Frankia in symbiosis with African Morella has never been explored. To address this lack of knowledge I investigated Frankia in root nodules of six Morella species from the Cape flora of Southern Africa, as well as in rhizosphere soils from selected hosts. Partial nif H gene fragments recovered from 202 root nodules yielded 26 unique sequences, which phylogenetic analysis assigned to Frankia Cluster I (the Alnus host infection group) and Frankia Cluster III (the Elaeagnus host infection group)1. Nineteen nif H sequences were assigned to three sub-clusters within Frankia Cluster III (CC-3, CC-4 and CC-5), and the remaining seven sequences to two sub-clusters within Cluster I (CC-1 and CC-2), one of which (CC-1) is novel to the current study. Identical sequences were recovered from nodules collected at geographically distant locations, suggesting a cosmopolitan distribution within the region for some subgroups from both clusters, but more localized distribution (or tighter host-specificity) for others. Soil pH correlated with strain presence in nodules, with Cluster I sequences being associated with hosts growing in acidic soils exclusively. Furthermore, three Morella species from the Cape flora of southern Africa are promiscuous in their natural habitats, with host infection group influenced by habitat edaphic conditions. In order to explore the correlation between soil characteristics and Frankia presence in nodules, nif H soil libraries were created from selected host rhizospheres. While Cluster III sequences from these libraries corresponded closely to sequences found in nodules from the same sites, the dominant Cape Cluster I group (CC-1) was absent from all six libraries, even when present in nodules recovered from the same soils. Whether this was due to low abundance of -but strong selection for- these strains by hosts under particular conditions, or due to the absence in soil of hyphal forms of these strains could not be determined. Cluster III strains are known to be better able to persist saprophytically than their relatives from other host-infection groups. A second group of Cluster I strains, detected at only one sampling site, was present in that site's corresponding soil library. An Alnus-infective subgroup, cluster AI, which has been detected in soils collected on five continents, was also detected in the of the Cape soil libraries but never in nodules, raising questions as to this group’s ability to persist in soil in the absence of known suitable hosts. Ten Frankia strains representing all three of the numerically dominant subgroups (CC-1, CC-3 and CC-4, found in 186 of 202 root nodules) were isolated from four Morella species. These isolates represent six of the most abundant unique nodular nif H sequences found in the field survey, and display morphological and cultural characteristics typical of Fra |
| 英文关键词 | Frankia Morella Southern Africa Actinorhizal symbiosis Actinorrhizal plants Myricaceae |
| 语种 | 英语 |
| URL | http://hdl.handle.net/11394/5346 |
| 来源机构 | University of the Western Cape |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/250292 |
| 推荐引用方式 GB/T 7714 | Wilcox;Dale Adrian. Diversity of Frankia associated with Morella species of the Cape floristic region of Southern Africa[D]. University of the Western Cape,2016. |
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