Characterisation of bacterial symbionts in selected drought-tolerant legumes for biofertilisers development for use in Namibia
| dc.contributor.author | Mataranyika, Paidamoyo Natasha | |
| dc.date.accessioned | 2023-11-08T07:01:32Z | |
| dc.date.available | 2023-11-08T07:01:32Z | |
| dc.date.issued | 2023 | |
| dc.description | A dissertation submitted in fulfilment of the requirements for the degree of doctor of philosophy in microbiology | en_US |
| dc.description.abstract | Namibia is a semi-arid country with approximately 1% of arable land. Crop cultivation is profoundly challenged by nutrient-poor sandy soils combined with low water retention. To meet the increasing food demand, farmers resort to applying synthetic fertilisers and pesticides despite their environmental consequences. However, there is increasing evidence that arid or semi-arid plant microbiomes offer an unexploited reservoir that is pivotal to plant health, growth, and development. Plant growth promoting bacteria (PGPB) are of increased interest as they offer sustainable alternatives to environmentally unfriendly and unsustainable chemical fertilisers. The present study aimed to isolate, identify, and characterise plant-associated bacteria from five drought-tolerant legumes grown in Namibia. Identification was done using 16S rRNA sequencing and bioinformatics. Plant growth-promoting (PGP) abilities were characterised based on exopolysaccharide production, antifungal activity, indole acetic acid production, phosphate solubilization, siderophore production, and bacterial nitrogen fixation. Using 16S Illumina metagenomic sequencing, this study characterised the plant microbiomes of the nodules, roots, rhizosphere, and seeds. Isolates identified from the roots and rhizosphere were from the Proteobacteria (72%), Actinomycetota (15%), Bacteroidetes (5%) and Firmicutes (8%) phyla and included known plant growth-promoting species such as Stenotrophomonas pavanii, Streptomyces murinus, and Enterobacter cloacae. Nodule endophytes were mostly from the phylum Firmicutes (88%). The identified genera include Bacillus, Priestia, Paenibacillus, Gottfriedia, Neobacillus, Lysinibacillus, Fictibacillus, and Brevibacillus. Characterisation found that rhizobacteria expressed more plant growth promoting traits compared to root endophytes. Siderophore production was observed iii in most root endophytes and rhizobacteria. The following isolates, CRhi10, CRhi15, MBRhi17, HR5, RMBRhi4, RMBRhi1 and IPCRhi7 from the legume root endospheres and rhizospheres showed the most potential as plant growth promoters. A total of 34 nodule endophytes tested positive for at least one plant growth-promoting trait. Isolates MB1, MB3.1, H14, M25-11, M8-16.1 and M8-16.2 showed the most potential as plant-growth promoters. CRhi15 (S. maltophilia), HR5 (E. mori), H14 (P. aryabhattai), M25-11 (L. boronitolerans), and M8-16.1 (Bacillus sp.) were selected and assessed for their ability to induce drought tolerance on Vigna unguiculata seeds in potted trials. The inoculants were also combined and assessed in a consortium. Drought tolerance was observed to be highest with S. maltophilia (CRhi15), Bacillus sp. (M8-16.1) and E. mori (HR5). The average root length under drought stress was 37.5 cm, 51.8 cm, and 33.7 cm respectively while the average shoot length was 63.1 cm, 80.6 cm, and 75.3 cm. Microbiome analysis of the root, rhizosphere and seed microbiomes found important plant growth-promoting genera. These include Bacillus, Mesorhizobium, Pseudomonas, and Bradyrhizobium. The nodule microbiome was predominantly Bradyrhizobium. The relative abundance of the nitrogen-fixing Bradyrhizobium genus was determined in four drought-tolerant legume species- Vigna aconitifolia (mothbean), V. unguiculata (cowpea), Lablab purpureus (dolichos), and Macrotyloma uniflorum (horsegram). Both culture-dependent and independent methods revealed that these PGP bacteria can promote plant growth under drought, nutrient and biotic stress conditions. Therefore, S. maltophilia (CRhi15), Bacillus sp. (M8-16.1) and E. mori (HR5) may be further explored in field trials in efforts to develop commercial biofertilisers | en_US |
| dc.identifier.uri | http://hdl.handle.net/11070/3760 | |
| dc.language.iso | en | en_US |
| dc.publisher | University of Namibia | en_US |
| dc.subject | Commercial biofertilisers | en_US |
| dc.subject | Namibia | en_US |
| dc.subject | Crop cultivation | en_US |
| dc.subject | semi-arid plant | en_US |
| dc.subject | Bacterial symbionts | en_US |
| dc.subject | Drought tolerant legumes | en_US |
| dc.title | Characterisation of bacterial symbionts in selected drought-tolerant legumes for biofertilisers development for use in Namibia | en_US |
| dc.type | Thesis | en_US |