Bananas are Britain's most popular fruit

Did you know we collectively eat about 100 million bananas per week? The vast majority are one variety called Cavendish. In Leicester, we are fortunate that the city market, Asian and African shops sell many other banana varieties with a range of different sizes, flavours and textures.

> Have you eaten cooked bananas? What sort of dishes are they used in? How many meals a day could you design around bananas?

Bananas are all grown in the tropics or subtropics, mostly in developing countries, where many livelihoods are dependent on the trade. They are also a major staple food - in Uganda, people eat more than 500 gram per day of banana on average, with every meal. There are large banana importers active in the UK, and some supermarkets import directly from producers. The importers have huge ripening room complexes, each shipping 30 million bananas per week, where temperature is controlled to 0.5 degrees, and the gas ethylene is introduced to induce ripening a few days before the bananas are packed for shipment to shops. Careful demand prediction means very few bananas are wasted between import and people buying them. However, transport and storage needs a lot of care. Unlike many other perishable fruit and vegetables, there is little processing use for overripe or damaged bananas. In fact, the largest wastage in the packhouses is from the quality control bunches that are kept in case the shop customers have a complaint.

> What do you think would happen, over what timescale, when conditions are wrong for transport and storage of banana?

Bananas are under threat

The bananas we eat are the sterile fruit from the banana plant (Musa acuminata for the Cavendish variety). The structure of a banana plant is similar to a grass: with plants 10 meters or more high, bananas can be thought of as giant herbs.

> If a banana plant can be 10 meters tall, why is it not a banana tree?

> Why does the cultivated banana produce a fruit without seeds?

Like animals, bananas suffer from a range of bacterial, fungal and viral diseases, as well as attack from insects and nematodes. These diseases reduce production enormously, in some times meaning the whole crop is lost, after all the labour, cultivation, water, light and fertilizer that has been used. Typically the cost of crop protection chemicals and application is a third of the total production costs. Sometimes diseases can cause banana varieties to go extinct. Before the Cavendish variety became the most widely exported banana, there was the very popular variety Gros Michel, which went extinct in the 1950s. Now there is the threat that Cavendish may phase extinction too.

WATCH the video clip below where visitors to Kew Gardens discuss what bananas mean to them and what they think bananas will look like in 2050.

> If a television crew asked you the same question as in the clip, how would you answer? Would you smile? Do you think another fruit might replace banana as the most popular fruit in the UK?

Banana diseases and research at Leicester

The University of Leicester has a major research programme on bananas and close relatives, involving international partners from many tropical countries. The research includes funding from the UK international Official Development Assistance budget through the Global Challenges Research GCRF programme. Now WATCH the short clip below that explains the importance of this research fund and consider the following question:

> Why can research on banana in Leicester contribute to overseas development? Think about both results and capabilities.

A focus of the work in Leicester is measurement of the diversity of the genetic resources in banana and its wild relatives, and understanding ways this diversity can be exploited to improve crop production and sustainability, in particular giving genetic resistance to diseases. In the last few years, as well as measuring morphological traits, molecular DNA-based methods, like those pioneered in Leicester by Sir Alec Jeffreys, have been used to measure diversity in crops and look at the differences between varieties. The picture below shows gel electrophoresis and staining of DNA: each vertical lane has multiple bands amplified from the DNA of one plant.

> Can you find groups of lanes with similar, or even identical, banding patterns? What might a similarity indicate about the genetics of those plants?

Some diseases can be controlled by agronomy - the way the plants are grown. A bacteria, Xanthamonas, is spread from plant to plant on the machetes used to cut the fruit bunches, and can be controlled by dipping the knife into bleach between each plant. The banana bunchy top virus BBTV is spread by insects, but can be controlled by burning plants as soon as they show symptoms; in south India, you will often see piles of large young banana plants being burned next to villages. Another devastating fungal disease, black sigatoka, can be controlled by cutting of leaves at the first sign of infection and removing them or carefully placing upside down in the field. If they are placed the normal way, raindrops will splatter and spread the spores a long distance to other plants. Despite the control possible, it has proved difficult to introduce these protocols widely in the field, and these diseases are still spreading.

> Can you name a human disease caused by each of a bacteria, a virus and a fungus? Can you give ways to stop spread equivalent to those used for banana disease?  Hopefully not involving burning infected people.

Fusarium wilt or Panama disease is currently a particular problem, with a new race of the fungus now spreading from Asia to Africa and South America. It is very easily spread, and once in an area cannot be easily controlled.

Now READ the recent BBC news article below, to get a sense of the seriousness of the problem, and then consider another few questions.

> How does a disease spread around the world?

> What is biosecurity? If you have travelled through sea or airports, what biosecurity measures have you seen?

> What diseases present around the world are now or may soon threaten crops and plants in the wild environment in the UK? Do you think the UK needs to increase restrictions on import of plants that might be carrying diseases?

Cavendish, the major banana variety in worldwide trade is extremely susceptible to Fusarium wilt, and chemical control is not possible, so the disease threatens the bananas in our shops. However, some other varieties, mostly unsuitable for shipping, are very resistant. So we here in Leicester and other scientists around the world are looking at the genetic variation that may provide genes giving both good transportability and ripening properties along with disease resistance.

> What properties makes Cavendish banana so good for international trade? How might these differ from other varieties eaten locally?

Now WATCH the video clip below from one of our collaborators, Altus Viljoen in Stellenbosch, South Africa. He has been instrumental in developing Fusarium detection and quarantine measures in sub-Saharan Africa. His work stopped spread of the disease outside one plantation in Mozambique.

> How can you contain and control banana Fusarium wilt?

> Why are diseases a particular problem for subsistence and smallholder farmers?

More banana research at Leicester

The long-time orthodoxy was that no plants had virus sequences integrated in their genomes which could be triggered and later expressed to give an infection, like the human herpes or HIV retroviruses. With banana, the people in the Leicester group showed the first virus sequence integrated into the nuclear genome in plants, a pararetrovirus called Banana Streak Virus, firstly by showing homologous sequences to the virus along chromosomes, and then by sequencing the genome. Interestingly, the virus genome is fragmented in the nucleus and reconstructed to express the virus. The picture below shows how we were first able to show the presence of the virus in the chromosomes of a banana cultivar, using a technique called 'in situ hybridization' to a chromosome preparation. Before this work, it was thought that there were asymptomatic plants carrying the virus, or a reservoir of infection in the environment.

Now consider another few questions:

> Can antibiotics cure or control viruses in plants or animals?

> How are virus diseases transmitted between plants?

> Can you think what might induce the virus to be expressed from the nuclear genome?

Food Security is vital

Measuring and exploiting the diversity of crops and their wild relatives is a key approach to producing enough food for us to eat in a sustainable way. We can search for genes giving improved stress resistance to both biotic, disease-related, stresses, and to abiotic stresses such as temperature and water availability. Under climate change scenarios, crops may need to be selected to grow in different conditions. Finding genes for better crops with easier agronomy and lower crop protection inputs, and working out how to use them in productive agriculture, is requiring huge worldwide research effort. The improved varieties are valuable to subsistence farmers, smallholders and on commercial farms. With many partnerships, people in the University of Leicester are working on the major theme of Food Security and are playing a significant role in research underpinning agriculture for the future.

> What might be the direct and indirect effects of climate change on crop production?

Finally, if you are interested you may want to watch the 18 minute video below, which is a talk to a specialist audience about ways that crops can be 'climate-proofed' for the future.

Or alternatively, you may want to go and eat a Cavendish banana while you still can...