Over the past year, my colleagues and I have met with banana producers, importers, retailers, and researchers around the world. A picture is emerging of an industry facing multiple pressures, with important choices to be made to ensure environmental, social, and economic sustainability.

By Dan Bebber

Bananas, the UK’s favourite fruit, appear at first glance to be among our most reliable and resilient fresh produce – they are stocked in every supermarket on every day of the year and their price seldom varies by more than a few pence per kilo. But beneath this apparently smooth and steady supply lies a complex international supply network affected by extreme weather, plant disease, social and political shifts, and the looming threat of climate change. The reliability of banana availability to UK consumers, despite these diverse threats and the fact that only one variety of banana is internationally traded, makes the banana supply chain a fascinating system to study in the context of the resilience of food systems. Will producers and importers continue to adapt and respond to stresses posed by the likes of the dreaded Fusarium Wilt (also known as Panama Disease), or will the combined pressures of climate extremes, disease, and economic realities eventually break the system and require us to revolutionize our relationship with bananas?

The aim of the GFS-funded BananEx project (officially known as Securing the Future of the UK’s Favourite Fruit) is to analyse these various stresses, identify strengths and weaknesses in the system, and consider how the resilience of the banana supply chain might be strengthened in future. To some, the extreme monoculture and intensive production methods of the Cavendish export market signifies an inherently unstable system which must be radically altered and diversified for long term environmental, social and economic sustainability. To others, the economic upheaval caused by dramatic industry shifts is unthinkable, and technological advances must be applied to ensure that the production and supply of Cavendish bananas to consumers in Europe, North America and China continues undisturbed. As Tropical Race 4 of Fusarium Wilt continues its westward march towards the New World, hurricanes batter the Caribbean, and economies develop, the banana supply chain approaches a crossroads: will the status quo be maintained, or will a new route be taken?

BananEx is approaching this question from three sides. Firstly, we are investigating the influence of climate change and extreme weather events on production. The effects of extreme weather have been felt strongly in recent months, with simultaneous impacts of hurricanes and cold weather in several countries across Latin America and the Caribbean (LAC). At a recent BananEx meeting in London with representatives of the major UK importers and retailers, we learned that under normal circumstances the geographical range of suppliers ensures that extreme weather events that reduce availability from one country can be compensated by production in others. The diverse range of sources provides redundancy in the system, increasing resilience to climate shocks. But the past year has been different. Hurricanes Irma and Maria devastated production in the Caribbean, while bad weather affected production in Central America. Importers and retailers have struggled to meet demand, and have been forced to put under-ripened green bananas on supermarket shelves. The optimum colour for bananas is yellow with a hint of green. Too green and sales fall. Take a look at the bananas in your supermarket – the greener they are, the more stress the supply chain is under. BananEx is investigating the probabilities that such multiple weather stresses will occur, and whether climate change will increase or decrease their frequency.

Hurricane Irma (centre) over Cuba and Hispaniola, flanked by Tropical Storms Katia (left) and Jose (right) on 8th September 2017. Image: NASA/NOAA GOES Project.

To answer this question we need to model the relationship between banana production levels and weather, and to study past weather observations and future projections. This task is being undertaken by Dr. Varun Varma of Exeter University, a Research Fellow in the BananEx project. Unlike other major crops like wheat, rice and maize, whose climate relations have been intensively studied, bananas have received relatively little scientific attention. Dr. Varma has approached the issue from two directions. Firstly, from the ‘bottom up’, gathering available data on the responses of individual banana plants to temperature and moisture to develop a growth model that can then be scaled up to plantation level. While there are several pieces of information missing, this approach has revealed some little-known but potentially important processes. For example, shredding of banana leaves by wind and heavy rain can dramatically reduce their ability to photosynthesize – or, convert sunshine to banana fruit. This effect has important implications for the influence of storms and hurricanes on production, as it is not only blow-down of whole plants or flooding of their root systems that can cause yield losses. Secondly, the ‘top-down’ approach, which involves gathering all available information on productivity of bananas over time, at as fine a spatial scale as possible (for example, from the 315 Districts in India that grow bananas), and linking these data to local weather over the years. This analysis has revealed that several important banana-growing regions around the world have benefitted, and will likely continue to benefit, from global warming, as they are currently cooler than the optimum temperature for banana production. While we cannot reveal the findings in detail yet, prior to peer review, Dr. Dan Bebber will be presenting some of these data in his keynote address to the Acorbat 2018 conference in May. BananEx is also studying the impacts of extreme weather events such as hurricanes, focussing on the Dominican Republic which produces most of the organic bananas sold in the UK. With partners in the Dominican Republic, we are using satellite imagery to quantify the damage done to plantations, and how quickly production can recover following these devastating events.

Our second consideration is the threat from plant diseases. The impact of heavy rains on Dominican Republic organic producers has been exacerbated by fungal diseases, particularly Black Sigatoka (Mycosphaerella fijiensis), that thrives in wet conditions following hurricanes and heavy rains. Black Sigatoka originated in Asia-Pacific, reaching Honduras in 1972. It has since spread inexorably across LAC, becoming the most important disease of bananas in the region. The BananEx project is using published estimates of fungal responses to moisture and temperature to investigate how the risk of Black Sigatoka outbreaks has changed over time, and what might happen in future. Similar analyses for coffee and wheat stem rust found that changes in the amount of water on the leaf surface, necessary for fungal growth, tend to be more important in determining disease risk than changes in temperature. However, much of the information on pathogen physiology is old or incomplete, and much more research is required to understand the relationship between weather and disease risk. On a recent visit to an organic plantation in Colombia, for example, we were informed that Black Sigatoka was rarely a problem due to the local dry microclimate, while surrounding farms experiencing more humid conditions relied on regular fungicide sprays to control the disease.

black sigatoka
Black Sigatoka, the most important banana disease in Latin America and the Caribbean. Image: D. Bebber

While Black Sigatoka remains the major disease threat to LAC plantations, the potential arrival of Tropical Race 4 (TR4) of Fusarium Wilt is most feared by producers and importers alike. TR4 was a dominant topic of discussion at the third UN FAO World Banana Forum conference, with an international Task Force established to disseminate best practice for biosecurity and control of the disease. As pointed out by those studying bananas in Africa and Asia, where a diverse range of varieties are grown, we must remember that TR4 is primarily an issue for Cavendish ‘AAA’ genotype bananas, while many other cultivars are immune or only partially affected. Much remains to be determined about the biology, ecology, and epidemiology of this pathogen. For example, the Philippines, the main Cavendish exporter in the Asia-Pacific region, has been affected by TR4 for many years, but appears to be maintaining productivity via a combination of management techniques and partially-resistant Cavendish clones. However, the precise details remain unclear, and more research is required on the Philippines story – for example, to what extent have plantations been moved to uninfected sites? In BananEx, Prof. Sarah Gurr and Prof. Gero Steinberg (University of Exeter) are investigating some of the fundamental cell biology of the disease causing fungus, Fusarium oxysporum f. sp. cubense, and testing novel antifungal compounds to help tackle the disease in infected plantations. Taking another approach, an international team has developed a genetically modified Cavendish clone that is resistant to TR4. Elsewhere, potentially resistant Cavendish clones developed by conventional breeding and selection are being tested in the field. An exciting new avenue for research is the application of biocontrol organisms against banana pests and diseases. Biocontrol refers to the application of microbes and other organisms to kill an unwanted pest, for example the use of predatory mites to control red spider mite in greenhouses. Dr. Dan Bebber and Prof. David Studholme (University of Exeter) are members of an international project, MUSA, funded by the EU Horizon 2020 programme. MUSA is developing and testing biocontrols for several banana pests and diseases, including TR4, and will work with biocontrol companies to commercialize any promising agents. In a related project, Dr. Bebber is working with the Eden Project in Cornwall to test the efficacy of companion planting by Chinese Leeks (Allium tuberosum) to control TR4, and how such companion plants might affect other soil fungi such as beneficial mycorrhizae, that help plants extract nutrients from soil. Thus, a variety of approaches are being developed to address the issue of TR4, and LAC producers are watching the outcomes of these research efforts with interest.


Given the almost certain arrival of TR4 in LAC, at some point both growers and consumers will be forced to make difficult decisions regarding the way in which bananas will be produced. Will the status quo of Cavendish production be maintained by application of novel fungicides and genetic engineering, or will a less intensive system that enhances soil antimicrobial action via mixed cropping, organic amendment and biocontrols take its place? As the economies of LAC countries develop and grow, farm workers will expect larger wages and better standards of living. Are we prepared to match these increasing costs with higher retail prices? The Fairtrade movement has shown that many consumers are prepared to pay more for bananas if social and environmental sustainability is enhanced. This brings us to the third approach in the BananEx project. Prof. Steve McCorriston and Dr. Annalisa Marini (Business School, University of Exeter) are working with our partners BananaLink, 3Keel and the FAO World Banana Forum to investigate the economics of the banana supply chain, and the way in which value is transmitted along it. This economic analysis will reveal how production shocks caused by climate and disease affect prices in the producer countries and their competitors, and how these shocks are propagated through to retailers and consumers. In the end, the structure of the entire industry will depend upon the price that we, as consumers, are willing to pay to keep bananas in our shopping basket. The industry will have to adapt to changing pressures – the direction of that change is, in large part, down to us.


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