Bananas are our favourite fruit: you can hear lots about them on BBC Radio 4 The Food Programme, produced by award-winning BBC producer Emma Weatherill and presented by Sheila Dillon, a University of Leicester graduate. A short version will be broadcast at 12.30pm today Sunday 8th August on BBC Radio 4 and the long version will be on Monday at 3.30pm on BBC Radio 4. You can listen to it via the iPlayer from this page. And from Monday afternoon you will be able to download a podcast of the programme from here (which might be useful for those of you living outside the UK.) In this piece, I will show some pictures of the things I talked about and amplify some of the points discussed.
As consumers in the UK, we are largely familiar with only one variety of banana – Cavendish. Can you imagine if we only knew about one model of one make of car? There are more than 1200 banana varieties known, each with its own distinctive flavour and texture. We also know about only one use, as a sweet dessert banana – this may be versatile as we eat them fresh, on toast, sliced in our cereal or in banana custard, but much of the world uses cooked bananas as a savoury starch instead of potato, or eats fried chips and even fermented beer. For the Radio programme, I was able to find six contrasting varieties of banana from Belgrave Road in Leicester, as well as different types of chips. The varieties shown and probably talked about in the programme include the ubiquitous Cavendish and the much smaller and fatter AAB Silk or Figue Pomme and smaller Prata (both very popular in West Africa and Brasil). These are more citrus and apple flavours, with some dry starchy mouthfeel in Silk as well. We also had three larger fruits of plantains: one was sweet enough to eat fresh, the others would be cooked or deep-fried, with the largest one being popular in West and Central Africa, Latin America, Brasil, India and Philippines. The medium sized one is and East Africa cooking banana, eaten as matoke, a steamed and mashed dish served with nearly every meal.
Bananas hold a world record: they are the world’s largest herbaceous plant, with many being 5 m or 15 feet tall. They are not trees since they do not have a trunk or produce wood – the stem (‘pseudo-stem’) is actually mostly made up of leaf bases, like a grass. After flowering and producing the fruit, which takes 9 to 12 months, the stem is cut back, and another side-sucker allowed to grow to produce the next generation. After 2 to 8 crops, the plants are replaced typically with new, disease free plants. We do occasionally see banana plants, and their close relatives Canna, as ornamentals, but the leaves have other uses as plates for food or as building materials. Wild bananas have seeds, but most of the cultivated types are sterile.
The Cavendish banana has a major threat in the farms where it is grown: it is highly susceptible to a relatively new race of Panama Disease, a Fusarium fungus, known as Tropical Race 4. Like human diseases, new plant diseases arise regularly and travel the world infecting vulnerable crops wherever they go. A decade ago, it looked like the disease was spreading rapidly. But in fact, Tropical Race 4 has fortunately not moved out of South-East Asia and Queensland, Australia. It spread at the end of last century from Taiwan, into the Philippines, Malaysia, Australia and Southern China. Since the fungus cannot be effectively controlled or eradicated using fungicides or soil fumigants, once infected these areas cannot grow Cavendish banana. Fortunately, the major commercial areas of Latin America, the Caribbean and West Africa that we depend on for the bananas in the UK have not apparently been infected. The control of the spread has happened because of recognition of the need for strict biosecurity – the publicity given to the devastating effect of the disease means that all farmers, smallholders and even scientists, are now well aware that they must not move plants, fruit, soil, equipment, shoes and clothing without great care.
Everyone in banana growing areas is also on the lookout for the disease, with contingency plans in place for eradication of banana growing when it is detected. Nevertheless, biosecurity is only extending the time until the infection spreads to current growing regions so we need to be ready – and the most effective approach is to have cultivars which are genetically resistant to the disease so no sprays are required.
There have also been changes in the agronomy – how bananas are grown – which reduce the spread of all diseases. Like many tropical crops, and indeed people!, bananas are very susceptible to a range of fungal, viral and bacterial diseases, as well as insects and nematodes. Agrochemicals typically represent a third of the production costs for banana, so improving the genetic resistances of varieties being grown, and changing or improving the agronomy (how the plants are grown) not only can reduce the spread of diseases but also cut the spray financial, health (particularly to the people carrying out the spraying) and environmental costs. Cutting out and burning diseased plants is the starting point for much disease control, and is practised more widely than ever, including with roadside feral plants that give disease reservoirs.
There have been other changes in how banana are grown in the last few years: most commercial banana plants are now produced in sterile tissue culture, and hence are disease-free, rather than the previous situation of growing from suckers which may carry disease from the parent. A particularly dramatic change has been in southern India, the world’s largest banana producer but almost entirely for the national market and not export. There, disease-free tissue culture plants are now available widely for smallholders as well as commercial growers, including from Women’s Cooperatives set up with assistance from one of our partners in India, Professor Asha Nair.
These are much needed because of a virus disease called bunchy top. Commercially, in parts of India, a new way of growing bananas has been introduced where they are now being grown over one or two years only in rotation with rice, while previously banana were grown continuously in plantations.
Disease diagnosis and understanding the DNA of both the Tropical Race 4 and the banana has improved rapidly since 2010. There are many races of the Panama disease, and until recently you needed to test a disease isolate by the infection of different banana varieties to determine the pathogen race – expensive, difficult and running the risk of spreading the disease. Basically the testing would need to be in a greenhouse, even in temperate areas such as Leicester where there is no risk of spreading to plantations. Now, enough is known about the pathogens that the DNA sequences can be examined directly, and that will tell which race is present. This ability is ensuring that Tropical Race 4 is diagnosed much more efficiently and quickly, so that better control by stopping banana production and movement in the area can be adopted.
Another important development in banana research is the sequencing of the whole genome of the crop which we completed last year in an international collaboration led by Agenlique D’Hont from CIRAD, France. This is now enabling us to learn about all the disease resistant genes that are present in the banana, and their diversity. Some banana varieties are resistant to the tropical race 4, but these have undesirable properties including ripening too fast, fruits falling from bunches, thin and easily bruised skin, as well as poor yield or undesirable flavour. We are now identifying the genes involved in disease resistance that will enable directed breeding using local landraces and tropical varieties, to ensure the future of bananas in our supermarkets.
Our work in Leicester is laboratory-based, with many different ways to look at the DNA, sequence and compare different varieties and wild plants, isolate genes, and look at the chromosomes, their evolution and behaviour in species and hybrids. We work with partners in banana growing countries. Thus we extract and study the DNA and grow the plants to look at chromosomes and cells, but rely on breeding material, germplasm and field assessments from others. They will be making crosses and growing the plants in the field to study agronomic characters, which together we can link to genes and the ancestral genomes giving rise to the cultivars. In Leicester, with no risk to local banana farms, we are fortunate in being able to work with plants from all over the world, and have the potential to screen for pathogen resistance in suitable contained greenhouses. Academic labs like ours will aim to publish all the results and they are freely available to anybody to use. We work with researchers throughout the tropics in banana growing areas, and aim to characterize and help develop their varieties, identify genes and devise crossing programmes. Any germplasm/varieties/gene we made or found would also be freely available, but would need considerable testing before going into production. Germplasm is distributed free to end-users through an international centre, based in Belgium, called the Bioversity International Transit Centre, and they are funded by agricultural development grants from many countries (particularly the Belgian government). Germplasm from some national and commercial organization is restricted in distribution, so we would follow any rules about its use, although we prefer to research with publicly available material where results and material will remain public.
British bananas are imported from the tropics, primarily the Caribbean, but other parts of South America too. There are four major companies involved: Fyffres, Del Monte, Dole and Chiquita. The global export banana trade was worth about $USD13 billion in 2011 (so a bit under ten billion pounds). Less than 20% of bananas are traded internationally though, and the local markets account for a similar amount: another c. £10 billion pounds (so a total of a little under the amount of Council Tax in the UK). With UK banana consumption averaging more than 2 per person per week or 13.8kg per year, we spend well over half a billion pounds on bananas each year.
We enjoy eating Cavendish bananas, but would certainly like to have more flavours and textures easily available in our supermarkets.
This can be done, but we would need to get used to the new types, which will differ considerably in how they are used. There is an enormous infrastructure of ships and ripening houses for transporting Cavendish with minimal wastage of the fruit and little energy use for ship-transport and storage: the infrastructure associated with Cavendish bananas is worth about 5 billion pounds ($USD8 billion). The properties of each variety of banana is unique: different bananas need different transport and ripening conditions, but we enjoy them all!
Thanks to Professors Rony Swennen and Asha Nair for help with identification of the banana varieties I bought in Leicester, where there are many Asian and Caribbean shops. I am grateful to colleagues at Bioversity – Gus Molina, Dietmar Stoian and Stephan Weise – for additional information about both the banana market and TR4, along with an industry source. All photos CC-By-SA – Pat Heslop-Harrison.