Students help discover herbicidal properties of mānuka

All over the country, students in Years 5 to 13 have been collecting and testing samples of their local mānuka plants.

The project provided an opportunity for students to get involved with authentic research, while also supplying researchers with a wide variety of mānuka samples.

University of Otago Chemistry Outreach Programme Coordinator Dave Warren says the research was suitable for almost all students, as long as they had some basic measuring skills.

“There’s something in it for every level, it’s a real nature of science programme – how you do a science investigation, talk about the controls and what you’re doing. If you wanted to get into the chemistry and the biologies you can look at the biochemistry that’s taking place or the molecules involved, there’s always more stuff to it.”

Each participating school received research kits containing samples of an Australian mānuka strain called ‘copper glow’, which has a high concentration of the herbicidal chemical grandiflorone.

After collecting local mānuka, students took an extract from both leaf types using acetone.

Using the Australian mānuka as a positive control, they were required to grow lettuce seeds on filter papers treated with different solutions: water, acetone, copper glow extract and local mānuka extract.

Students also experimented with planting seeds in a tenth extraction of copper glow and local mānuka to see whether each leaf extract was also an effective herbicide at lower concentrations.

“After a week they look at the germination of the seeds, make observations like the colour of the leaves, the length of the stalk, the length of the leaves and the length of the roots. From these measurements they can work out whether their local mānuka has got high or low levels of this herbicide molecule,” says Dave.

“They also send in a sample for the Plant & Food guys to do a full analysis, to look at the whole chemical picture.”

The project was a joint initiative between the University of Otago and Plant & Food Research.

Although a full statistical analysis is yet to be completed, initial findings suggest mānuka around the country varies quite markedly. Researchers expected to find regional variations but are also seeing differences within each region.

Mānuka research at Musselborough Primary School

Years 3–6 students at Musselburgh Primary School who chose science as their elective session worked with Dave and his team of students from the University of Otago each Friday.

Musselburgh Primary School Deputy Principal Robin Taylor says he was interested in the opportunity to use locally sourced mānuka and work on an ongoing project with the university.

“It was also a great project as the students learned the scientific skills of accuracy, measuring, weighing, observation, prediction and hypothesis making,” he says.

“Our inquiry-based, school-wide project has been looking at our place in the world, our local community and our local environment – this research fitted in with that really well as a context for undertaking the research and the skills part of the lessons fit in beautifully with levels 2 and 3 of the Nature of Science strand of the curriculum as well as the Material World strand.”

 The learning outcomes for the students were based more on acquiring skills around investigating and scientific technique rather than the context, says Robin.

However, students were also able to discover the differences in composition between mānuka plants both locally, nationally and compared with Australian mānuka, and consider the possible application of local mānuka as a weedkiller.

Mānuka research at Whangaroa College

Located in the Far North, Whangaroa College has a significant proportion of students belonging to Ngāti Kahu and Ngāpuhi Riri.

Whangaroa College Head of Science Jinesh Joseph was looking for a way to connect his Year 11 science programme with Māori culture, in which mānuka plays an important role.

Last year his students studied mānuka and kawakawa to learn about the antibacterial properties of both plants – which are widely used in Rongoā Māori, a traditional Māori healing system – and to find out whether each extract could help cure wounds or aid with spider bites.

Jinesh saw an opportunity to extend this learning through the mānuka research project, which he also used as a practical investigation topic for his NCEA Level 1 science students.

“I thought this is a good way; we have a natural resource here for students to collect and find a way to extract the oils to use as a natural herbicide.”

His students discovered lettuce seeds planted in local mānuka samples did not germinate well, which showed that mānuka in the area had some herbicidal properties.

“From this the students found  it can be used as an organic herbicide , instead of a chemical herbicide,” says Jinesh.

“We noticed when we walked through the bush that underneath the mānuka plants you don’t see much vegetation because the oil is naturally oozing into the soil and that suppressed or oppressed the germination of the plants there.”

A science research topic which connected with his students’ culture made a big difference to their interest in science in general, says Jinesh.

“They were interested to do all these things because it had some chemistry in it; it had some biology in it, so it has those aspects to it but also that connected stream – it connected history with this tree. This plant has got so much importance to their lives.”