Right now, you might be harbouring a killer: one so small it’s hidden in the sole of your hiking shoes. These tiny murderers won’t harm you in the short term, but they can be deadly for the plants that are crucial to food security and biodiversity conservation.
New research we conducted with our colleagues shows that some of these plant-killing microbes, known as Phytophthora, can be detected in urban areas before they get the chance to escape and spread into the natural environment. Phytophthora is a Greek word that best translates to “plant destroyer”. Species in this group are responsible for some of the worst plant disease epidemics in history. The Irish Potato Famine in the mid 1800s was caused by Phytophthora infestans, a species that still plagues tomato and potato fields around the world.
Another species, Phytophthora cinnamomi, is known as the “biological bulldozer” in Australia. It has affected thousands of plant species and is considered a top environmental threat. It also occurs in the Cape Floral Kingdom of southwestern South Africa, a hugely important biodiversity hot spot that encompasses the city of Cape Town. Thanks to citizen scientists engaged as pathogen hunters, we have also learned that other “plant destroyers” are present in the Cape Floral Kingdom.
Many professional staff members from botanical gardens, nature reserves and national parks have already contributed to the project’s findings in the natural areas surrounding Cape Town. Now we’re asking citizens to help look for plant destroyers in the city’s urban areas.
This study is important because our best chance of preventing a plant disease epidemic is to detect the species before it spreads into natural or agricultural environments. Humans – the very “carriers” who can spread dangerous microbes unthinkingly from their equipment and shoes – can instead become the first line of defence against a possible microscopic invasion.
Dangerous species on the move
Cape Citizen Science is a project supported by the DST-NRF Centre of Excellence in Tree Health Biotechnology, the Forestry and Agricultural Biotechnology Institute at the University of Pretoria, and Stellenbosch University.
It engages non-scientists in ecological and microbiological research. Currently the project facilitates research about the diversity and distribution of Phytophthora species in the Cape Floral Kingdom. The results provide baseline knowledge about the plant destroyers already present in natural areas. But we fear that other species, which have not yet “escaped”, may be hiding in urban areas.
We suspect most of these species are limited to the soil. That means they can’t “escape” unless the soil or infected plant tissues from the same area are moved. The worst case scenario would be the discovery of a wind-dispersed species such as Phytophthora ramorum – the organism that causes Sudden Oak Death in the US. Finding these kinds of species before they can be blown away is important.
Our research suggests that surveys in urban environments could lead to the detection of Phytophthora species before they escape into the natural environment. Preventing their escape or spread is critical for preventing the damage these “destroyers” can do in natural or agricultural settings.
This is why we’ve launched a new phase of Cape Citizen Science called “The Cape Town Hypothesis Test”. A hypothesis is an idea that can be tested scientifically. In this case, we hypothesise that there are different Phytophthora species in Cape Town’s urban areas than there are in the area on and around Table Mountain National Park, a world heritage site that’s a major part of the Cape Floral Kingdom.
Citizens participating in the project could be the first to discover a new introduction of a Phytophthora species in South Africa. Detecting such a species before it spreads to the natural environment is critical for protecting South Africa’s incredible biodiversity and preventing destruction from other potential “biological bulldozers”. If a different species is detected in the urban areas then local communities, researchers, stakeholders and officials can prevent the spread into natural areas.
From November 2017 until the end of February 2018 we’re seeking ordinary people’s help to test our hypothesis. This involves the collection of soil and fine roots from under sick plants in Cape Town’s urban areas. Instructions and examples of sick plants have been made available online. Samples will then be tested in a laboratory at Stellenbosch University for the presence of a Phytophthora species.
We have also designated 15 important areas to collect samples. A map of these areas is available on the website. Once a sample is submitted from one of those areas, the map areas will change colours and a GPS point will be added with the citizen’s name (if they wish). By sampling these areas, the study will ensure broad coverage of Cape Town’s urban areas.
Testing hypotheses is an important part of scientific research. The results of this study can be used to inform decisions to protect the natural areas surrounding the mother city. For example, finding a different species in the urban areas may be enough to justify boot cleaning stations at the base of the Table Mountain Aerial Cableway – a way to keep those tiny murderers from “hitch hiking” into natural and agricultural areas on our boots.