THE BATTLE BENEATH TABLE MOUNTAIN

WITH ROOT ROT DEVASTATING ONE OF THE WORLD’S GREAT BOTANIC GARDENS, CHIEF SCIENTIST AND DIRECTOR SCIENCE, EDUCATION AND CONSERVATION PROFESSOR BRETT SUMMERELL TRAVELLED TO SOUTH AFRICA TO HELP IN THE FIGHT.

Back in 1999 at the 16th International Botanical Congress in St Louis, delegates were asked to vote on the world’s most important botanic gardens based on a range of factors, including the diversity of their living collections, science programs and visitor facilities. Among the elite group named was Kirstenbosch National Botanic Garden in Cape Town, South Africa.

More than 20 years later, it was still on my bucket list of botanic gardens to visit, so you can imagine how delighted I was to be invited to take part in a recent workshop at Kirstenbosch on botanic gardens biosecurity. The invitation came from the South African National Biodiversity Institute, the University of Pretoria and the International Plant Sentinel Network, which since 2014 has facilitated collaboration among institutes around the world to provide an early warning system of new and emerging pest and pathogen risks. A similar network was set up in Australia several years ago and it was hoped it could be a model for what might be achieved in South Africa.

Set at the foothills of Table Mountain, Kirstenbosch is one of South Africa’s 10 national botanic gardens. It has a strong focus on Indigenous flora (similar in a way to the Australian Botanic Garden Mount Annan), notably the flora of the fynbos region around Cape Town. The Garden is particularly known for its plants in the Proteaceae family –especially the spectacular species of

Protea, Leucadendron and Leucospermum found in the Cape region. It also boasts remarkable collections of cycads, restios and other South African favourites.

Unfortunately, areas of the Garden have been infested by the root rot pathogen, Phytophthora cinnamomi, which has particularly devastating effects on members of the Proteaceae family. It is estimated that over the past decade the diversity of Proteaceae species able to be grown in the Garden has dropped by half – problematic, given that visitors come specifically to see these plants.

The disease is having an enormous impact on the local endemic Silver Tree, Leucodendron argentea, found in the area around the Garden, and up to Table Mountain. This species is extremely sensitive to Phytophthora root rot and will start to show symptoms within a couple of weeks after the pathogen is introduced. Significant efforts are underway to develop techniques to manage the disease and protect the tree from its effects, with the use of potassium phosphonate (sold as AntiRot) showing strong promise as a control option that is safe and cost-effective.

Against this backdrop, the workshop was held at Kirstenbosch, with participants including horticultural and records staff from six botanic gardens across South Africa. Sessions were held on disease management and prevention in collections and the production nurseries, and attempts were made to trouble shoot issues and enhance techniques. While the initiative identified a number of options for improving practices, unfortunately a lack of resources may undermine what can ultimately be achieved.

At Kirstenbosch I was brought up to speed about the issue of illegal plant harvesting in southern African ecosystems. At the Garden they receive up to 6,000 plants per week that have been seized by authorities and need identifying, then cultivating in the nursery. This presumably is only the tip of the iceberg in terms of the number of plants that are actually removed for the black market. This is of course a huge impost for Kirstenbosch staff and one for which they receive no additional funding. Most of the species seized are succulents, highlighting the downside of the current popularity of these types of plants.

After the workshop I travelled to Pretoria and Johannesburg for presentations and discussions with students. While there I took the opportunity to inspect a number of trees affected by an insect known as the polyphagous shot hole borer. This tiny beetle bores holes into stems and limbs of a broad range of trees, creating a network of tunnels in the timber. Unfortunately, in cavities behind its mouth parts it carries a Fusarium fungus, which once introduced spreads and slowly kills the tree. Susceptible species include Box Elder (Acer negundo), plane trees (Platanus species), coral trees (Erythrina species) and figs (Ficus species including Moreton Bay Fig) – all of which are, of course, a huge component of Sydney’s tree population.

This beetle and fungus have recently been detected in a number of trees in

Perth – including some in Kings Park and Botanic Garden. This sparked a huge biosecurity operation that which resulted in the destruction of around 300 trees and raised awareness of this pest and pathogen. It was extremely useful to see first-hand the impact in South Africa and to understand the symptoms and necessary management of the problem. It is anticipated that over half of the tree population in Johannesburg could be killed over the next 10 years – involving the removal of millions of trees.

Sydney urban landscapes are heavily populated with many of these very susceptible species and the potential impact should it arrive (or perhaps, when it arrives) would dramatically alter our streets, urban parks and their amenity. In addition, the impact it might have on tree species in our native landscapes is unknown, making it essential that we undertake every effort to prevent its introduction.