St Helena is famous for its unique habitats from the lush endemic cloud forests on the peaks to the dry and rocky coastal fringes. Many of the islands plants and invertebrates are found nowhere else on earth and their populations and diversity have been studied extensively since scientists arrived in the 1800s. However, despite this intensive interest in the larger organisms almost no attention has been given to the microorganisms.
The fungi and bacteria of the island have been isolated for just as long as the plants and insects and it is likely that they have undergone a similar evolution process along their own path, albeit on a microscopic scale. Many of these microbes have evolved to be pathogens of plants and invertebrates as well as those that colonise dead material.
As is commonly the case in addition to the local home-grown microbial species which evolved on the island, settlers have brought more familiar pathogens over on crop plants.
CABI’s Dr Rob Reeder and Dr Phil Taylor are currently compiling lists of the microbial diseases on the crop plants of the island. With the help of the staff at the St Helena Government’s Agricultural and Natural Resources Division (ANRD) they are surveying the island investigating which diseases are present on crop plants.
Whilst the diseases of crops are familiar to the team they are also investigating diseases on the endemic trees that are likely to have never been characterised or catalogued previously.
The endemic cabbage trees are about the size and shape of a magnolia tree, they share a similar branching structure and don’t have one long trunk typical of many trees. There are so few trees that the death of any individual is a serious setback and attempting to find a pattern in their demise is not easy.
The black cabbage trees, which belong to the same family as daises, seem to be particularly badly hit, sometimes they die within a few weeks of first showing symptoms whereas other will die over decades. This would indicate that there is more than one syndrome taking place.
The CABI team are working closely with the local agricultural officers of ANRD and part of their remit is to improve their diagnostic skills with regard pests and diseases of crops on the island. Staff at ANRD have been keen to learn the infield diagnostic techniques promoted by the CABI Plantwise programme. Field diagnoses may need to be confirmed by a more detailed investigation and a lab at ANRD has been equipped with money from the Darwin Plus award to enable more sophisticated analysis of diseased plants.
Whilst finding many of the common diseases on crops that the team expected to find there were also many that appear to be absent. “This is some of the cleanest coffee I have ever seen,” Dr Reeder remarked after visiting two local coffee plantations.
He added that the biosecurity team – led by Julie Balchin – are doing a good job; just last year coffee rust was identified on all the Hawain islands leaving St Helena as the only coffee growing region of the entire world that does not suffer from this disease. Similarly, the strict embargo on the importation of bananas appears to be paying dividends as the bananas of the island are free of disease.
In addition to the fungal plant pathogens mycologists have neglected other fungi and a member of the CABI team – Dr Norbert Maczey – is investigating the fungi that parasitize insects. Whilst being of interest in their own right these fungi have the potential to be used as biocontrol agents and many have yielded important medical drugs. Insects which have died due to fungal infection are being taken back to CABI for further investigation.
The final part of the Darwin Plus award is to engage with the local schools to promote the idea of a career in crop production. The team have spoken with the Biology teacher at the secondary school and there is the intention to set up trial plots with the aim of training pupils in the diagnosis of crop maladies.
This is the first visit by CABI scientists as part of the three-year project. Dr Taylor said, “Considerable progress has been made but there is a lot more work to do.”
The CABI team are working with scientists from the University of Birmingham who are using a molecular approach to investigate the dieback of the endemic trees.
Main image: Despite receiving no chemical sprays the coffee is clean in St Helena, Dr Rob Reeder is unable to find diseases in the coffee plantation (Credit: CABI).
St Helena’s endemic trees and insects are under threat, possibly due to introduced pathogens or changes to the range of endemic pathogens due to climate change. This project will survey and identify pathogens associated with tree death (including nursery-raised stock) and insect populations. Additionally, crop diseases will be surveyed and their management assessed. Methods developed through CABI’s Plantwise initiative will build capacity in diagnostics and management across all sectors, supporting growers, conservationists and foresters. This will prevent further deterioration of the endemic ecosystem, increase food production and reduce the necessity to import food.
Find out more from the project page ‘Managing the pathogens threatening St Helena’s biodiversity and food security.’
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