Banana crops (Musa spp.) contribute significantly to the economy and food security of Asian, African, and South and Central American nations (Banana Link 2023; FAO 2023). Their production is constrained by multiple abiotic and biotic factors (e.g. drought, nutrient limitation and diseases) some of which lack effective solutions. Banana plants host microbial communities that strongly influence their health and nutrition. These organisms may provide novel solutions to production constraints, but their management is challenging, at least in part, because most of the taxa present differ over space and time. Despite this, a small number of ‘core’ taxa are almost always associated with their host irrespective of when and where the community is characterised (Lay et al. 2018; Simonin et al. 2020). These organisms represent logical targets as they are thought to disproportionately contribute to host function. Once these taxa are identified, researchers can investigate different management approaches that best manipulate core microbiomes to improve plant performance and overall health. Recently, Birt et al. (2022, 2023) determined that the core microbiome of Musa spp. in Australia comprises 36 bacterial and 21 fungal taxa. In this thesis, I determined whether the core microbiome of banana in other countries comprises the same taxa. I then investigated whether nutrient management can be used to influence the frequencies of core taxa.While Birt et al. (2022) demonstrated that the 36-core bacterial OTUs were present in datasets from 22 other studies of banana microbiomes globally, they did not investigate whether these OTUs would qualify as core taxa in those studies. Consequently, in Chapters 2 and 3, I used phylogenetic marker gene sequencing to characterise the core microbiome of banana (Pisang Awak, ABB) across 24 sites in six countries (Australia, Laos, Malaysia, Philippines, Uganda and South Africa) and three continents. Candidate core taxa were identified based on abundance and prevalence thresholds and then ranked by the number of sites in which they were consider core. This yielded internationally relevant lists of core bacterial and fungal taxa, that contained many of the core taxa identified by Birt et al. (2022, 2023).In Chapter 4, I investigated whether phosphorus (P) addition to field-grown bananas influenced microbial diversity and function using phylogenetic marker gene sequencing and enzyme assays. Pairwise sequence comparisons, revealed that the bulk soil and roots of the plants harboured 31/36 and 18/21 of the core bacterial and fungal OTUs reported by Birt et al. (2022, 2023). P addition did not significantly influence the alpha or beta diversity of bacterial or fungal communities, or the frequencies of core taxa. In contrast, P addition was associated with significant increases in the activities of alpha-glucosidase, chitinase, arylsulphatase, and acid phosphatase. This indicates that P application to banana soils may stimulate microbial activity but is not likely to be a useful lever to manage microbial diversity or the frequencies of core taxa.Overall, this thesis indicates that P addition is not likely to be a useful lever to manage the core microbiome of banana, but does provide an expansion of the core microbiome across multiple nations. The multinational core taxa lists detail the most persistent symbionts of one of the world’s most important crops and will help to prioritise future research. For example, it could help to direct international isolation efforts to build biobanks of globally relevant core taxa. The availability of these isolates would facilitate more detailed study into the functioning and ecological preferences of core isolates and help inform the design of microbiome management approaches thereby expediting the pathway for impact from microbiome research to end user benefit.