Australian Stories: Plant Breeder Digby Growns

Australian Stories: Plant Breeder Digby Growns

I live a fortunate life. And part of that fortune is working here and plant breeding. I enjoy my job. There’s always something going on. I get to talk to people about it all the time. It’s a privilege really.  You know, a lot of people work their jobs and they could be really interesting, and they never get to tell their story and I get to tell my story a lot. People are probably like, oh, not him again!

Digby Growns is the Senior Plant Breeder at The Botanical Gardens and Parks, Western Australia.

His work at Kings Park focuses on the development of resilient plants that bring positive environmental effects into gardens, including providing habitat and a food source for urban fauna and important pollinators, reducing water and fertiliser use, and increasing pest and disease resistance – as well as making your garden look colourful and stunning!

Digby has worked with ETTO on developing Blue Mallee plants that yield higher amounts of oil. Higher yield results in a more sustainable farming practice as we maximise each plant. 

We chat to Digby about what it means to develop plants, the serendipitous blue kangaroo paw, the best tea tree plants in existence (hint: they are on ETTO’s farm), and what he grows in his backyard.

Digby with his favourite native, the Scarlet Featherflower

How did you get into plant breeding and development?

The story about how I got into horticulture is that, after school, I took off traveling. Back in those days air fares were so expensive, so you got on a plane, and you just left (with no return ticket)! I took off and I spent time in Greece, England, and South America. While I was in South America, I took the train in Peru to visit Machu Pichu. I had learnt a bit of Spanish by then and I was talking to this old guy in the seat next to me as we went past a grove of eucalyptus. They were huge eucalyptus, which I was really surprised at because of the altitude, and I said to him, “oh those trees are from Australia, where I’m from.” He refused to believe me. He said, “no, no, no, they’re Peruvian, we use them for wood and all these things”. It got stuck in my head how versatile plants are that you can take a tree from Australia and plant it in Peru and it does grow, it flourishes and does very well.

So, when I came back to Australia, there was a horticulture degree starting at Murdoch and I thought, oh well, I’m interested in plants I’ll do that. It’s been good since then.

I’ve been doing it for about 30 years. I did it at The Department of Agriculture for 12 years or so. There I was mostly working on wax flower hybridisation, mostly for the cut flower market. And then I came to Kings Park with a remit to build the plant development program here. I came in as one of the directors and then was offered to go full time into plant breeding and I took that opportunity and I’m loving it.

Flowering Eucalyptus variety in Kings Park

So, to confirm, Eucalyptus is native to Australia?

Yes, eucalyptus is native, they would have been transported there (to Peru). Apparently, they’ve been there for about 100 years. Eucalyptus varieties are grown all around the world now for a whole lot of different uses. It was more the fact he claimed them as Peruvian than anything. Basically, they were adopted and, in many respects, genetically they may in fact be Peruvian now because they would evolve and adapt to those conditions. And that’s the interesting thing about genetics, that can happen. You might bring those back to Australia now and they might not do well.

Eucalyptus are now causing problems in some places, like in California, because eucalyptus trees are so fire responsive and they burn incredibly hot because of the oil. They’re starting to take over their natural forests because when they catch fire, they kill the local forest which doesn’t regenerate well, but eucalyptus just comes back like hairs on a cat’s back.

Is that a problem here in Australia?

We’re fire adapted. It’s a problem for people if you’re in a place where they catch fire. But our environment here has adapted to it and it’s the way they regenerate.

You’ve done a bit of work for ETTO and the trees on our farms, tell us a bit about that.

It came about as I was sitting on the Tea Tree Advisory body which at the time was funding the breeding program for Tea Tree.

When I was asked for my advice on the breeding program at the ETTO farm, I said, well you know you’ve got the best Tea Tree plant that has ever existed growing on your place.

At the farm I did a random sampling project. I got a map and using random number generators I picked out 100 points, and on a 40°C day, it was horrendous, I went out and sampled each plant that I had randomly selected. Ten of those plants were above 4% oil which is double the normal amount.

Emu's wandering through ETTO Tea Tree Farm in New South Wales, Australia

We’ve seen the Tea Tree’s survive complete flooding on the farm, it’s quite amazing.

They’re a swamp plant so they are used to being underwater, they would have a root system with a high amount of air to allow them to keep functioning. They’re tough plants!

What about your work on the ETTO Blue Mallee farm?

The work on the Blue Mallee farm is looking into developing a plant that is much better yielding for oil per hectare. 

I’m also working on clonal propagation, so doing it from cuttings. Doing a cutting is basically replicating the same plant. But eucalyptus are not usually grown from cuttings, it’s quite hard to do so they are usually all seed grown.

But there is always genetic variation, so every now and then, you’ll get one that will strike from a cutting. Part of what I’m doing is finding those plants and finding the ones that grow from cuttings and that also have high yield and then trialling them.

We are finding ones that regenerate from cuttings. Commercial yields for Eucalyptus polybractea are currently about 1.8%, which equates to about 3% on average for leaf oil. We have plants that are about 5% leaf oil. Our research is to develop plants and systems that make these genetics (plant genes) commercially viable. 

Is the Blue Mallee its own variety or a hybrid?

In the original collection they suspected there was another eucalyptus involved and they actually collected some hybrids, so there may be hybrids in the Blue Mallee. For our work on the Blue Mallee we are not doing hybrids with other species because there is enough variation within the species for us to breed from.

Back in the day when CALM was still around (Department of Conservation & Land Management in Western Australia) they had an oil mallee breeding program. It was part of the shelter belt planting program, which they thought would help farmers get a second income. It didn’t work very well because transporting all that material to a distillery is time consuming and expensive. But they did a lot of breeding of oil mallees during this time!

Hold a Blue Mallee leaf up to the light and you can see the oil inside the leaf

Does Blue Mallee Eucalyptus (Eucalyptus polybractea) Oil have benefits over the Eucalyptus globulus oil variety?

Yes, because the oil quality of the Blue Mallee is better. With globulus, generally, they only get to about 60% cineole, so the extracted oil gets rectified. Whereas the Blue Mallee is at 80% already so it doesn’t have to go through that extra process. Yields are better with the Blue Mallee, it smells better too.

The interesting thing with Blue Mallee is the oil from one plant will smell slightly different to the oil from another Blue Mallee. If you’ve got a reasonably good nose palette you can pick the subtle difference. 

Editors note. ETTO’s organic chemist, Pete Stransky, explains the process of “rectifying:”

Eucalyptus globulus oil is steam extracted in an identical way as we do with Eucalyptus polybractea (Blue Mallee). However, globulus’ 1,8-cineole content is normally between 50 and 60% whereas polybractea is around 85% cineole. The international standards all require that commercially traded eucalyptus oils have a minimum content of 1,8-cineole of 70%. Therefore, steam extracted globulus oil must be “rectified” to get its cineole content above 70%.

Rectification involves a “low” temperature vacuum distillation of the oil that preferentially removes some of the lower boiling components (including pinene and sabinene) and thereby increases the concentration (to at least 70%) of the remaining cineole.

It is fair to say that because of the rectification process, the globulus derived eucalyptus oil is not a genuine reflection of the globulus oil composition as it is found in nature. Whereas ETTO Eucalyptus polybractea (Blue Mallee) oil is of a composition as found in the leaves of the blue mallee source. The final globulus oil is not as natural as blue mallee oil.

Kings Park Breeding Program, outside the greenhouse

When breeding plants in the Conservation & Research program, what is the focus, is it environmental or decorative?

The environment drives our program. As far as I’m aware we’re the only environmental based ornamental plant breeding program on the planet. I could be wrong! 

Because we’re an environmental agency it is really about the benefit to the environment. We want resilient plants and resilient landscapes, more habitat for native fauna, less water use, and less need for fertilisers and chemicals on the garden. 

The thing with gardening is you can have a plant that does all that but isn’t attractive. People won’t put it in their garden unless it looks nice, even if it has all those great benefits. So, we aim to have the pretty and the spectacular on top of the environmental benefits to get people to put them into their ground and get those environmental benefits delivered without them even knowing. It’s our sneaky way of saving the world.

In the lab at the Conservation Centre, Kings Park 

How do you go about it?

We pick out the plants in the family that seem to be more resistance to pests and droughts etc. And then we cross them and over generations we eventually get plants that are more resilient and more resistant to disease.

What is your home garden like?

I have got about a 700sqm block, so my wife owns the back yard and I own the front yard. She grows exotic plants, all various plants, and I grow Australian natives. I’ve got kangaroo paws, grevilleas, waxes, and I like to experiment so I like testing cuttings and seeing if I can grow plants from that. Usually, they die.

Does your native front garden use less water than your wife’s’ backyard?

Well, there is a bit of lawn in the front, so probably not.  I’m in the process of negotiating getting rid of the lawn and then maybe the front yard would use less water.

I agree with getting rid of the lawn and planting more plants to eat from, attract pollinators and be more sustainable.

Geraldton Wax flowers in Kings Park

The wax project took about 12 years, in general are breeding programs that long?

Well, the Pink Lady apple took 25 years to produce, so yeah, if I do a pollination today, on average it’s about seven years before it’s commercially released, and another two or three to establish it in the market. You have to play the long game and it’s probably why we work on so many different plants at once, so there is always something happening. If I knew back then what I know about waxes now, I probably wouldn’t have started because it’s really hard!

Things like kangaroo paws are a bit faster. The eucalyptus, even longer.

What inspired the colour variations on the kangaroo paws?

Serendipity. Pretty much it. I was breeding for disease tolerance. We used a process called recurrent selection, so you take a population of plants, and they have a range of disease tolerances, and you select the two or three that are the best and you cross them. You keep doing that so over about four or five generations you generally get a lot of plants that are quite tolerant.

I selected a purple variant of the red and green kangaroo paw and a species called viridis (latin for green). The green one was tolerant of rust and the purple one was tolerant of the disease ink spot. So, I crossed them thinking some of these plants are going to be resistant to both and they were. Then I selfed (editor’s note: ‘selfed’ is a term used to describe self-pollination where the pollen is transferred from the stigma of one flower to that of another) those to try and drive that divide even more and then once I selfed it, one plant come up that bluey teal colour. I was blown away I couldn’t believe it! Unfortunately, that plant was highly susceptible to disease. I repeated the cross and eventually, six years later, we got one that was blue and pretty tolerant as well. 

"Masquerade"The Blue Kangaroo Paw developed by Kings Park & Botanic Gardens

Is it true blue is the rarest colour in nature? 

Yes, it is. The interesting thing about the blue kangaroo paw, is it is the only blue that has come through in a group of plants where there has been no blue before. We don’t know where that came from or why they’re blue. We’re currently doing a research program looking at what the blue is and how it gets delivered.

In Kangaroo paws, pinks, reds, yellows, and green are all naturally occurring. Purple does occur naturally as a mutation of the red and green.

How do you stay passionate over such a long game?

There’s lots of things happening all the time, not just one plant. And plus, I get to work in Kings Park! Every morning, I drive down that amazing drive and I never take it for granted. I live a fortunate life. And part of that fortune is working here and plant breeding. I enjoy my job. There’s always something going on. I get to talk to people about it all the time. It’s a privilege really.  You know, a lot of people work their jobs and they could be really interesting, and they never get to tell their story and I get to tell my story a lot. People are probably like, oh, not him again!

Digby in the Greenhouse at Kings Park

It was never going to be an office job was it, you were always going to be working out in nature?

No, no. If I’m in front of my computer or meetings I get twitchy. I’ve got to get out. I can’t do it. My brain is always coming up with these crazy ideas and every now and again one of them comes off. Which is lucky!

How does nature nourish you?

Big time.  I don’t go bush as much as I used to, but when I do it is nourishing. And feeds your soul. I get the same in Kings Park, just going for a walk in the park delivers that too. Being out in the nursery delivers that. I’m lucky I get that connection with nature every day to varying degrees.

You would agree it was good planning that they kept this land in the middle of the Perth city as bushland?

It was a bit of a mistake. Initially it was planned to be an English park, lots of lawns and roses. But they ran out of money. So, a lot of bushland got left. By the time they were talking about doing more, people loved it, loved the natural area. Particularly the wildflower society in the 1950s [which] was mostly women from wealthy families who had a lot of influence, so when there was talk of putting swimming pools and houses in, the ladies from the wildflower society put their foot down and said, it’s not happening! It’s fantastic that we have what we do today.

Wildflower Festival Kings Park, 2023

Do you have a favourite native plant?

It varies from day to day but it’s the Scarlet Featherflower (Verticordia grandis) for a whole range of reason! It flowers all year round, it is scarlet, and I love red (I’m into my colours), it’s  also a naturally occurring tetraploid! A tetraploid is a plant that has double the number of chromosomes than a normal plant. For example, humans are diploids, you can’t really change your number of chromosomes and stay healthy, but in the plant world you can. It’s an adaptive thing for plants. Some of the plants that thrive in the harsher environments are tetraploids. We make tetraploids ourselves in our laboratory as a way of restoring fertility in wide crosses. The featherflower is a bit of an inspirational plant for me, but also looks fantastic. It’s hard to grow, it’s one of those plants that’s best seen in nature as it doesn’t always look the best in gardens.


Back to blog