Seed seekers bank on success

By Lesley Parker July 5, 2010
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Roughly a quarter of all the world’s plant species face the threat of extinction and scientists are working hard to preserve the future of our nation’s flora.

IT’S A RACE AGAINST time. One more really warm day and the little black prizes the seed chasers are hunting will have been ejected from the rare boronia. Gone for another year. As with many plants, there is only a small window of opportunity to find Boronia angustisepala seeds. Any seed gathered by the two collectors must have remained on the plant until mature enough to survive on its own, yet they must capture it before it’s scattered over the ground. One danger is that the seed will ripen too quickly for them to reach it in time. Another is that the sort of bushfire that ripped through this area five years earlier will wreck their plans.

Richard Johnstone and Graeme Errington have come to Gibraltar Range National Park, in northern New South Wales, with a shopping list of native seeds they hope to collect for storage at the NSW Seedbank, based at Mount Annan Botanic Garden in Sydney – and to send a copy sample to the Millennium Seed Bank (MSB) in England. From their four-wheel-drive packed with expedition gear – the four volumes of Flora of NSW alone weigh some 8 kg – Richard and Graeme head for a spot off the Dandahra Crags track.

They’d checked this location in spring based on research showing that they were likely to find B. angustisepala there. Sure enough, they’d found the boronia’s showy pink flowers and estimated the seeds would be ripe in mid-December. B. angustisepala’s tiny black seeds shoot out like bullets – the fruits forcibly squeeze them out – and can travel 1-2 m from the plant, far enough to be impossible to find once they have been dispersed.

“It would be lost – not to nature, but to us,” Richard says. “We line things up in the flowering period because they’re much easier to see. Then we go back and can see precisely where they are, even if the flowers are gone and they’ve become harder to spot.”

Armed with a GPS, Graeme and Richard spend an hour walking the track and scrambling up and around rocks and boulders to reach the site. They turn up many more of the boronia plants than they did in spring, including a large number of immature specimens. It shows the population is healthy and reproducing well. Invasive weeds such as Crofton and lantana, which are known elsewhere in the park, aren’t evident here.

The duo has arrived in the nick of time: Richard estimates the seeds would have popped within a few days. “Probably the next hot day,” he says. It’s relatively easy picking. Although the collectors have had to look hard to find the fruit, the walk hasn’t been arduous. It’s sunny and the small shrubs are little more than a metre high: no climbing or pruning poles required here.

However, because the plants don’t have many fruits, the pair takes as few as five and no more than 20 seed capsules off each of about 50 of the 70 or so plants present. That will probably mean about 100 seeds once the material is cleaned and sorted back at the NSW Seedbank – a reasonable, but not overly rich, collection.

At this stage, the collectors’ biggest enemy is rain. “It’s essential when you’re collecting seeds to keep them dry and cool,” Richard says. “If you get them wet, they prematurely age or they rot.” Soon the specimens are in a paper bag bearing the species’ name and the number RJ2717 – Richard Johnstone’s 2717th collection for the NSW Seedbank. At the end of the expedition, the paper bag is transported carefully to Mount Annan. Some seeds will be kept for study and others will travel 17,000 km to the other side of the globe.

Rescued from extinction

Since the late 1980s, the NSW Seedbank has collected seed from about 30 per cent of threatened plant species and nearly 40 per cent of known plant species in the State. Mount Annan is part of Sydney’s Botanic Gardens Trust (BGT), a cog in the huge global effort known as the Millennium Seed Bank Project (MSBP), based at Wakehurst Place, in southern England, to conserve the valuable genetic material held within wild plant seeds.

Seed banking involves collecting and storing seed from plants. It is both an insurance policy against extinction and a source of high-quality material for the restoration of habitats. It’s labour-intensive work but is cost effective – it is estimated an average of $5000 is needed to save a species from extinction. The NSW Seedbank received an injection of funds from the State Government in 1999 and a major boost from the MSB upon joining its program in 2003. More recently, HSBC Bank Australia became a major BGT supporter and part of its funding was directed to seed banking.

What’s learnt in the seed-banking process also aids the understanding and management of species in the wild. So far, MSB has banked seeds from 10 per cent of the world’s known wild plants, more than 24,000 species, including 12 now extinct in the wild. Its next target is to have saved seeds from 25 per cent of plant species by 2020. Roughly a quarter of all the world’s plant species face the threat of extinction, but twice that number could be at risk should the average planetary temperature rise 2-3°C, as climate change experts predict. Of Australia’s 25,000 species, 23 per cent are under threat.

“Our partnership with the Millennium Seed Bank means we can provide a lifeline for plants most at risk of extinction,” says Dr Tim Entwisle, the BGT’s executive director. “Our native flora is under threat from climate change, salinity, invasive weeds and landscape fragmentation, and seed banking is the kind of thing the Royal Botanic Gardens in Sydney has been doing for more than 190 years – right back to our first alliance with the Royal Botanic Gardens at Kew through Sir Joseph Banks.”

Not all seed is physically suited to banking, however, and there’s no point collecting and storing seed unless you can be sure it is living material and will survive long periods in storage. Many rainforest species, for example, don’t take well to the drying process, and overcoming such obstacles is one of the goals of the research. It’s also necessary to know how to break the seed’s dormancy and germinate it – something that’s not necessarily a simple case of ‘just add water’.

“For many years, we were concerned about seed banking because there was this concept of whether we had a gene bank or a gene morgue,” says Dr Cathy Offord, manager of horticultural research at the BGT. She says the knowledge and techniques built up during the past decade have “enabled us to be confident to say that we can successfully collect the majority of species that grow in NSW”. Still, some species continue to perplex. “There are still a lot of challenges,” she says. “We could spend several lifetimes even on just one or two species.”

Bag of tricks

At Mount Annan, seed technology officer Leahwyn Seed (yes, really) tips the contents of the paper bag into a brass sieve. She removes larger material, such as sticks and leaves, and looks for insects. “You’d be amazed how long insects can live in the drying room,” she says. Some seeds are already free of their casings, and the warmth of the room is causing others to pop, so it’s quickly back into the bag and off to the drying room.

After a couple of weeks, most of the seeds have worked themselves free and it’s time for further sieving and, if necessary, manual seed removal. B. angustisepala can be prised open with the fingers, but for other species Mount Annan uses techniques such as the ‘banksia barbecue’ – a blowtorch providing the heat necessary to get species such as banksias to release their seeds.

Separated from the waste material, the B. angustisepala seeds go into a jar and are returned to the drying room. The room is set at a cool 15°C and a dry 15 per cent humidity and the seed may remain in here for weeks, even months. The lower the moisture content (preferably just 7 per cent), the better they are able to survive long-term storage in the freezer.

Once drying is completed, some of the seeds are separated to test viability. Seed research officer Dr Amelia Martyn says boronias have some of the most difficult seeds to germinate. In research just published, Amelia and the Mount Annan team looked at 112 species in the Rutaceae family, of which boronias are part, and found that the presence of an embryo and endosperm – referred to as ‘seed fill’ – could vary from 0 to 100 per cent. “Not all seed that looks good to the eye is filled,” she says. “Even if you think you have 100 seeds in your hand, the seed fill might be as low as 20 or 30 seeds.”

And even that handful of seeds still might not be viable. “Sometimes things happen while the seed is still being formed and they don’t finish maturing,” she says. In her study, 80 per cent of seed collections had more than 25 per cent unhealthy seeds. Some had no viable seed at all. To check seed fill and viability, some of the B. angustisepala seeds are sliced in half and examined under the microscope. One seed had a small hole – a sign of insect predation. Another was crumbled inside, but a third was healthy: white and full. Seed viability can also be checked with a stain test, during which live tissue shows as pink.

Next, the seeds have a germination test. Amelia’s research shows that germination of boronia seeds can be significantly improved by using a combination of smoke water (water with smoke from burned vegetation bubbled through it) and the plant hormone gibberellic acid. (Applying these to seven different boronia species improved germination from 0-25 per cent to 27-100 per cent.) Ten B. angustisepala seeds are soaked for 24 hours in laboratory-made smoke water from Kings Park and Botanic Garden, in WA. The seeds are then placed on a plate of laboratory growth medium, known as agar, which incorporates gibberellic acid, and is placed into an incubator where the temperature is set to the equivalent of spring conditions in the Gibraltar Range.

Amelia says the results from other boronia suggest it may take from fifty to a couple of hundred days for germination. If the test is successful, the seedlings will be potted and nurtured in the Mount Annan nursery, possibly one day making it into the gardens’ display. Species that germinate well are also tested for seed longevity in an accelerated ageing test. Here, the seed is stored in an incubator at 45°C and 60 per cent humidity and monitored to see how long it survives under these harsh conditions. That allows a prediction of its likely survival in the MSB freezers – and of the time when a new collection may be needed.

Freeze frame

Before final packing, the seeds of each species are counted – by hand if it’s a small collection or by weight for larger lots. Some are separated for testing and the rest go into two vacuum-sealed foil packs: one for the NSW Seedbank to keep; the other, as a fail-safe, to be air-freighted to the MSB, with a pressed botanical specimen made by the collectors at the time they gathered the seed.

Mount Annan’s foil pack of B. angustisepala goes into a walk-in freezer set at -18°C, a temperature that will slow the seeds’ metabolic activity and prolong their lives. The seed from some species may survive just 10 years under these conditions; others – such as wattle seed – may have a life of 1000 or more years. In the meantime, the NSW Seedbank will move into a new phase.

“In this next phase we’d like to extend the genetic diversity in our collection,” says Peter Cuneo, BGT’s seedbank manager. So, rather than just collecting B. angustisepala from the Gibraltar Range, specimens might be collected from other places where it occurs. This diversity will be vital because seed banking is used for ecological restoration, Peter says. “Seed knowledge, I believe, is going to be quite critical over the next couple of decades.”

Source: Australian Geographic Issue 98 (April – June 2010)

From July to September 2010, the Australian Geographic Society is raising funds for the Save a Species Campaign run by the Botanic Gardens Trust.