Collaborating to save a rare — and smelly — plant

McMaster and the Toronto Zoo have collaborated on the first-ever preservation protocol to pollinate Amorphophallus titanum — more familiarly known as the titan arum, or corpse flower, so named because of its characteristic odour of rotting meat.

The zoo’s curatorial gardener, Paul Gellatly, contacted McMaster biology professor Susan Dudley after hearing of the news that Arthur, one of Mac’s corpse flowers, would be blooming. Corpse flower don’t bloom regularly, so this was a rare occasion.

But what did the zoo want with Arthur?

The Toronto Zoo’s first-ever corpse flower, Pablo Pee-yew-caso, had bloomed several years ahead of schedule in September 2018, at which point the zoo’s reproductive sciences team collected and froze its pollen.

The pollen was stored in various ways to determine the best method for maintaining its viability following long-term storage. One portion was frozen and stored at -80C, while another was cryogenically preserved in liquid nitrogen. This was done in the hopes of preserving genetics and pollinating future Amorphophallus titanum blooms in the collection.

The zoo transported Pablo’s frozen pollen to McMaster University and was invited to conduct viability testing on Arthur to determine if cryogenics can provide a viable long-term storage solution.

Both McMaster and the zoo recognized the odds for cross-pollination were slim and that the window of opportunity was narrow, but the teams worked quickly to navigate the time-sensitive situation — made particularly urgent because the corpse flower’s bloom only lasts a few days at most. Grown from seed, it can take six to 10 years for a plant to produce its first flower, after which it can take several more years for it to bloom again.

One of the reasons it takes so long between blooms is that the titan arum produces one of the largest flowering structures in the entire world. The pale central “tower” of the inflorescence, known botanically as a spadix, is typically two metres tall. This is wrapped in a single large spathe – a modified leaf that looks like a big bell – shaped petal. To match the corpse flower’s aroma, this spathe has a dark red, ridged interior, which looks just like a piece of exposed flesh.

Flies and beetles attracted by the plant’s strong odour crawl down the spathe to the base of the spadix, where the small flowers that produce pollen and seeds grow, enabling pollination. Since these pollinators tend to be nocturnal by nature, the blooms usually open in the late afternoon and then begin to wilt by the next morning: a lot of effort for a short window of opportunity.

The titan arum is unique not only because of how infrequently it blooms, and because of how little time it has to be pollinated by only three species of beetle. Native to the Indonesian island of Sumatra, the plant is related to peace and calla lilies — but this species relies on carrion beetles and flies for pollination, which it attracts with an aroma that resembles rotting meat. It’s been called the plant kingdom’s worst odour.

Like much of Sumatra’s wildlife, including Sumatran orangutans and Sumatran tigers, the titan arum is threatened by habitat loss. Not only is space an issue, but as forests decline, so do hornbills, which are the corpse plant’s primary seed distributor. Through advances in horticultural techniques, the intricacies of breeding the corpse flower are slowly being uncovered, allowing institutions like zoos and universities to maintain them in managed care as insurance against a crash in their wild population.

This includes cross-pollination — but because the plant blooms infrequently, the odds that two plants in the same collection will bloom simultaneously are quite low. This means that cross-pollination is virtually impossible. As well, there is no recorded attempt of pollen preservation for this species, which means a protocol, or method for cross-pollinating, does not exist.

The Toronto Zoo’s reproductive sciences team developed a protocol from scratch using various plant science methods and examples, including orchids, to create a brand-new scientific protocol. To do this, Arthur’s female inflorescence was divided into a grid and the zoo was able to attempt cross-pollination with Pablo’s pollen in four different treatment groups.

“This entire family of flowers has never been stored before, and therefore this particular cross-pollination has not been attempted,” says Dr. Gabriela Mastromonaco, manager of reproductive sciences for the Toronto Zoo. “This is the first step in developing a first-ever preservation protocol for the Amorphophallus titanum and we look forward to continuing to research the best options for long term storage of genetic plant material.”

At this time it can be confirmed that Arthur has accepted Pablo’s pollen in all four different treatment groups, meaning the developed protocols provided some protection of the pollen during freezing. More time is still required to see if pollination has occurred, thereby confirming that Pablo’s pollen was viable. The final outcome is expected to be determined within another couple of weeks.

“The sheer presence of these blooms is remarkable and something that continues to fascinate the wider public.  This extreme form of plant reproduction is certainly a way of getting people engaged with the natural world and collaborations of this kind are important for conservation efforts,” says Dudley. “We are taking good care of Arthur and hoping for the best.”