Mycorrhizal gateways: Advancing interpretations of fungal symbiosis in sugarcane agriculture

Anders Claassens

doi:10.25918/thesis.452

This thesis investigates the symbiotic relationships between sugarcane (Saccharum spp.) and arbuscular mycorrhizal (AM) fungi across diverse agricultural contexts. Through a comprehensive methodological approach combining microscopy, quantitative PCR, and DNA metabarcoding, the research provides novel insights into the ecological dynamics and functional significance of AM fungi in sugarcane cultivation systems. Initially, the research established optimised methodologies for detecting and quantifying AM fungi in sugarcane roots. Comparative analysis of sample preservation techniques demonstrated that oven-drying represents a robust alternative to liquid nitrogen for preserving AM fungal DNA in field-collected root samples, enabling high-quality molecular assessments in resource-limited contexts. Further investigations examined AM communities in both roots and soil, revealing striking differences in taxonomic composition that challenge the assumption that root colonisation directly reflects soil inoculum potential. The research demonstrates that sugarcane roots actively recruit specific AM taxa, functioning as "rhizosphere gatekeepers" through selection mechanisms that favour certain fungal partners. This selective process likely reflects host plant affinity for fungi that have been enriched through long-term sugarcane monocropping, creating non-random assemblages of AM fungi within roots. Experimental studies showed that soil abiotic factors significantly modulate AM fungal associations in sugarcane. Manipulation of soil moisture, phosphorus levels, and pH revealed differential impacts on both the extent of root colonisation and the composition of AM communities. Notably, reduced moisture conditions promoted increased colonisation and hyphal proliferation, while elevated phosphorus suppressed the formation of arbuscules and vesicles, indicating compromised symbiotic functionality. Subsequent research challenged conventional practices by demonstrating that commercial AM fungal inocula provided no substantial benefits compared to uninoculated controls with native AM communities. Despite varying propagule densities and species compositions, introduced inocula failed to enhance colonisation, alter community composition, or improve plant growth, indicating that native AM fungi possess superior adaptive traits for establishing functional symbioses with sugarcane. Collectively, this research advances our understanding of the selective mechanisms underlying AM symbioses in sugarcane and has important implications for sustainable agricultural practices. The findings suggest that management strategies should focus on optimising soil conditions to support native AM fungal communities rather than relying on commercial inoculation, with approaches tailored to specific sugarcane production environments and soil conditions.

Mycorrhizal gateways: Advancing interpretations of fungal symbiosis in sugarcane agriculture

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Mycorrhizal gateways: Advancing interpretations of fungal symbiosis in sugarcane agriculture

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