What Do Carrots, Elephants and Forestry have in Common
By Melissa Wray
In the Kruger National Park
There is a team of scientists who would never dream of entering the Kruger National Park (KNP) without a goodly supply of fresh carrots to assist them in their research. The carrots are not used to get up close and personal with some hungry mammal, but are actually a cunning trap for unwary fungi destined to spend time having their DNA unravelled.
With the aid of carrot 'sandwiches' Jolanda Roux and her colleagues from the DST-NRF Centre for Tree Health Biotechnology (CTHB) based at the University of Pretoria have discovered a species of fungus in Kruger that is new to science.
There is a lot more to fungi than mushrooms, and the species that they have isolated infects wounds on trees and can potentially kill some tree species. For the last year the CTHB team has gone into Kruger and travelled around the Skukuza area hot on the heels of hungry elephants.
Fungi that hitch a ride on insects frequently infect trees that have been wounded by elephants. The insects might move on, but the fungi they leave behind start off a succession of different fungal organisms that utilise the wood exposed by the elephants' destructive tendencies. Fungi play an important role in decomposing ageing and dead trees and recycling the nutrients they contain.
This is the first research in 50 years that has been done on indigenous trees to find out what type of fungi occurs in the country naturally. Work has previously been done in exotic plantations, where fungal diseases can destroy the timber. One of the species that Jolanda and her team were searching for is well known for causing serious diseases in black wattle (Acacia mearnsii).
The carrots come into action when the team returns from their inspection of wounded trees in the veld. Magnifying lenses reveal if fungi is present in a wound, and small samples are taken back every day to makeshift labs, often in the team's bedrooms.
If too much time has past between the tree being wounded and the team arriving to take a sample, a multitude of fungal species will be present. In order to isolate only the fungi that infect fresh wounds, carrot sandwiches are made.
The wood sample is placed between two freshly cut pieces of carrot, the knife cut effectively creating a wound, and then the whole thing is wrapped up in masking tape for five to 10 days.
The desired fungi then infect the carrot pieces, and can be isolated onto growth medium in the laboratory and later tested to see if they cause disease in other trees. Once isolated, the DNA of the fungi can be sequenced. The CTHB has identified a new species of the fungal genus Ceratocystis in the park through its DNA profile.
A related species of this fungus can kill Combretum molle (velvet bushwillow) and Acacia caffra (common hook thorn) trees, as well as the black wattle. While working in Kruger, the team were also alerted to a massive fungal outbreak that occurred on Ziziphus mucronata (buffalo thorn,blinkblaarwag'n bietjie) near Orpen Gate.
The fungus was so widespread on the trees that it looked like snow had been falling in the area. The team identified the fungus, and are continuing to monitor the trees for signs of ill health. They also intend to monitor the wounded trees where they were able to isolate the new fungus, in order to see how pathogenic it is.
The team are hoping to determine which fungal species are indigenous to South Africa, and therefore less likely to cause massive indigenous tree die-offs if trees become infected. Exotic fungi are renowned all over the world for the destruction that they can cause to indigenous forests.
In America and Europe, an introduced fungus caused Dutch elm disease, which killed thousands of indigenous elms. Jolanda estimates that it can take up to 30 years before a country is aware of a dangerous introduced fungus. A knowledge of what species are indigenous can help identify foreign intruders and protect biodiversity.
The CTHB hope to expand their work in Kruger to find out as much as possible about indigenous fungi. They are also working on fungal diseases in a nature reserve in Gauteng and in other Southern African countries.