Trio of PhD degrees for project's students
by Engela Duvenage, 14 December 2020
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Any investment in research and the creation of new knowledge is at its heart also an investment in the people who perform the studies, and who try to make sense of what they experience and find in the process. It is to this end that the
DSI/ARC Honeybush Project is proud of three doctoral students funded through the initiative who have all successfully completed their PhD studies in 2020. They are Dr Jenifer Koen (completed October 2020), Dr Brigitte du Preez (completed December 2020) and Ms Gugu Mabizela
(completed January 2021).
Dr Koen and Ms Mabizela both completed their PhD degrees in Horticulture from Tshwane University of Technology under supervision of Prof Retha Slabbert. Dr Koen already graduated in October 2020, while Ms Mabizela will do so next year. Dr du Preez graduated with a PhD in Food Science from Stellenbosch University in December 2020.
Honeybush propagation
Dr Koen, who is now set to work in Malaysia, took a close look at the characteristics of honeybush pollen, flowers and seeds, and ways in which the sexual propagation rates of this indigenous tea can be improved on a commercial scale.
"She has so far published two papers from her PhD, with another one expected soon," says her PhD supervisor, Dr Cecilia Bester of the ARC.
In response to warnings about ecological unsustainability, the honeybush industry is currently transitioning from a predominantly wild-harvested source model to one relying primarily on material produced via commercial farming. To this end, honeybush genotypes are needed with improved homogeneity, sensory qualities, productivity, vigour and resistance to such pest and disease conditions as may arise in massed plantings.
In support of existing honeybush breeding programmes, Dr Koen’s study therefore focused on issues around reproductive anatomy of honeybush flowers, sexual compatibility, dimorphic seed production and embryo rescue of various species.
In the wild, honeybush plants normally produce lots of seeds when pollination is left to insects. When humans become involved, as is the case in commercial farming enterprises, the process often falters.
“Pollinating by hand causes honeybush plants to be strangely reluctant to produce enough seeds,” explains Dr Koen.
Through her careful research into the structure of honeybush pollen, flowers and pods, Koen has highlighted a number of strategies that local breeding programmes can use to overcome this problem.
“Honeybush flowers have extremely delicate parts, and it is crucial to handle them carefully and to avoid damaging them. Timing is also important – the flowers need to be at their optimal ripeness,” she says.
She also found that it is possible to freeze honeybush pollen for around two years without its viability being affected. She further tested different sugar-based mediums on which pollen can be successfully germinated, as well as standard basal salt formulations to use in the handling of honeybush embryos contained in seeds.
Dr Koen also found that cross-compatibility between and within genotypes in a species varies, and that genotypes can be
partially self-compatible but at the same time incompatible with others. This was true for all three species investigated, and has significant implications for breeding programme strategies.
“This study provides practical recommendations with regards to the sexual propagation of select honeybush species and expands the platform of scientific research available to honeybush breeders,” she notes.
The influence of drought stress
Dr Koen and Dr Mabizela have both been studying honeybush since their master's degree years, and completed their PhD research at the ARC Infruitec-Nietvoorbij in Stellenbosch.
Ms Mabizela has been part of the honeybush breeding programme at ARC Infruitec-Nietvoorbij since 2012, where she worked under supervision of Dr Cecilia Bester and Prof Lizette Joubert.
Ms Mabizela's PhD research formed part of ongoing efforts to support the honeybush industry to identify species that are particularly drought tolerant yet still produce quality tea. It is generally accepted that the regions in which honeybush grows naturally are becoming drier and more extreme due to climate change. Drought stress can hamper plant production and survival – an increasing challenge to the fledgling industry.
In her research, she focused on
Cyclopia subternata and
Cyclopia genistoides. She took particular note of how the former, which is a self-seeder, responds to seasonal variation and drought stress.
Dr Mabizela used methods such as high pressure liquid chromatography (HPLC), sensory analysis and proteomic analysis to investigate samples in terms of their chemical and genetic response to drought stress and seasonality. It provided her with insights into how honeybush plants respond to different climatic conditions influences, and how it plays out in the phenolic content (such as beneficial antioxidant levels) and the sensory profile of the plants.
Based on the data, she identified that summer is the best season in which to harvest these species of honeybush, while also ensuring the best possible quality.
Dr Mabizela identified particular drought stress responsive proteins of
Cyclopia
subternata. She says that proteomic tools can be applied when trying to breed plants that are more water stress-tolerance, and when identifying protein encoding genes that can be selected to generate plants that produce maximal yields.
"To optimise the sensory attributes and health benefits of honeybush tea, we must make sure plants always produce enough phenolic compounds, but without impacting negatively on taste," she says.
Dr Mabizela is thankful that her research is benefiting the honeybush industry. On a personal level, she is appreciative of the relationships she has formed through the project, and for the new skills she has acquired. "Patience tops my list of skills I've developed," she admits.
Sensory tool
Dr Brigitte du Preez received a PhD in Food Science from Stellenbosch University (SU) for the work she had done on developing a quality grading system for honeybush tea.
Her research was conducted under guidance from Prof Lizette Joubert (ARC and SU) and Nina Muller and Dr Erika Moelich of the SU Department of Food Science.
Her efforts built on a broader research programme of ARC Infruitec-Nietvoorbij and SU that focuses on the development of a set of sensory tools to define, communicate and evaluate the sensory characteristics of honeybush that started in 2011.
She worked on a revised sensory lexicon for honeybush, a scorecard and a validated rapid method for assessment of sensory quality. A major improvement in the lexicon was the establishment of universally available and stable chemical-based reference standards that can be used by researchers, processors, and marketers alike. In the process, a more standardised sensory language for honeybush was created.
The tools have already been used to train a number of industry role players in the aromas associated with high and poor quality tea.
“The aim is to ensure that honeybush tea of a consistent quality reaches the consumer,” says Dr du Preez. “It was important to create a single standardised set of measures, captured in a scorecard, to evaluate the sensory quality of honeybush tea.”.
She is of the opinion that the toolbox will provide processors, blenders, packers and marketers with a standardised grading system so that all have the same concept of what defines honeybush tea quality. It will also allow them to evaluate it in a similar and consistent manner.
