Thesis
The manipulation of sex expression in Cannabis sativa L.
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2025
DOI:
https://doi.org/10.25918/thesis.546
Appears in Recent Southern Cross PhD Theses
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Abstract
Cannabis sativa is a multi-purpose dioecious crop grown for food, fibre and pharmaceuticals. Sex expression is key to C. sativa crop performance, with males or females being more attractive depending on the target end-use. Although regulated by an XX/XY sex chromosome system, C. sativa shows flexible sex expression, including monoecy and hermaphroditism. This variability presents a significant issue for producers, where unexpected changes in sex expression can cause losses in product yield and quality. This thesis aims to gain further insight into the regulation of sexual phenotypes and provide potential methods to manipulate and stabilise their expression.
The first experimental chapter (Chapter 3) compares and develops methods of chemically altering sexual phenotypes by applying a broad range of plant growth regulators influencing hormone families postulated to regulate plant sex expression. This showed that manipulation of ethylene pathway is key to modifying sex expression, and that gibberellin pathways steer resource allocation. The next two chapters (Chapters 4 and 5) use multi-omics techniques to explore the regulation of phenotypes of interest from Chapter 3. Chapter 4 revealed important changes in the expression of floral homeotic gene homologues in the male-to-female sex reversion instigated by promoting the ethylene pathway. While chapter 5 revealed that changes in sugar signalling and source/sink dynamics were fundamental to gibberellins' effects on reproductive resource allocation and harvest index, which are in turn linked to cannabinoid accumulation. Chapter 6 details the description and characterisation of a novel XY monoecious phenotype with potential breeding applications. Finally, Chapter 7 utilises Chapters 3 and 6 methods to ascertain the impact of inbreeding depression via single-seed-descent on fertility and provided a proof-of-concept example of stabilising sexual phenotypes in an F1-hybrid seed system. In doing so, this thesis provides novel industry-relevant techniques for the control of sexual phenotypes, as well as uncovering promising targets for future C. sativa variety improvement.
Details
- Title
- The manipulation of sex expression in Cannabis sativa L.
- Creators
- Lennard Garcia-de Heer
- Contributors
- Tobias Kretzschmar (Supervisor) - Southern Cross UniversityJos C Mieog (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- xvi, 234
- Identifiers
- 991013345139802368
- Copyright
- © Lennard Garcia-de Heer 2025
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis