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Banana bacterial wilt - refining the 'road map' for control

Approximately one third of Uganda's banana growing land is now affected by bacterial wilt (CABI Bioscience)
Approximately one third of Uganda's banana growing land is now affected by bacterial wilt
CABI Bioscience

Banana bacterial (Xanthomonas) wilt, first detected in Uganda in 2001, has since spread rapidly. Approximately one third of Uganda's banana growing land is now affected by the disease, which renders fruit inedible and ultimately kills the plant. The Ugandan government has been praised for its promptness in attempting to control the spread, but despite these efforts, and the encouraging success of control in some areas, the risk of further spread, both within and beyond Uganda, remains.

Strengthening and refining the control effort is now clearly essential, but how should this be done, where are the research priorities, and what action should be taken by Uganda's neighbours? In July this year an expert consultation of senior stakeholders from policy, research and disease control, was convened at the UK's Central Science Laboratory near York. They offered New Agriculturist their points of view on the current status of the disease and the ways forward for control.

The story so far - spread and impact

Within the last four years this disease has moved from Ethiopia into Uganda, into Congo, into Rwanda and into Tanzania. It is moving very fast and may soon cross into Kenya and into Burundi. Once this disease takes root in the Congo we will have a major problem because the infrastructure for management is really rudimentary in this country and it may be very difficult for us to handle this situation.
Eldad Karamura, regional coordinator for East and Southern Africa, International Network for Improvement of Banana and Plantain (INIBAP)

It is in the four districts of Kagera region but for the other parts of Tanzania, we have not done the complete survey: it might be there but it is not reported. But Kagera supplies bananas to some other areas including Uganda, Rwanda, Burundi and the DRC.
Mgenzi Byabachwezi, research officer, Agricultural Research and Development Institute-Maruka, Bukoba, Tanzania

For Uganda, it is estimated the disease caused losses of up to US$35 million in 2005, and it was projected that in 2006 we would lose up to US$100 million, that is in Uganda alone where the disease is established in about 30% of the banana growing region. If it manages to establish itself across the whole region we are talking about losses to the tune of a billion or beyond per year. And we know that in eastern Congo, in the region neighbouring Uganda, there are already big pockets of disease which are rapidly expanding.
Wilberforce Tushemereirwe, programme leader for banana research, NARO, Uganda

At farm level, many farmers have lost their fields and this has resulted in the reduction of food and income that they get from the bananas. Currently banana bacterial wilt is in 35 districts in Uganda, so millions of farmers have been affected.
Caroline Nankinga, co-ordinator, on-farm research, NARO, Uganda

Lessons learned...

Banana bacterial wilt lasts in the soil for less than three months (CABI Bioscience)
Banana bacterial wilt lasts in the soil for less than three months
CABI Bioscience

One of the reasons why we think the disease has spread so fast and so widely within Uganda is that it is spread by insects that visit banana flowers. As the insects visit the male buds of a diseased plant they can pick the bacteria up and move it onto the inflorescence of a healthy plant. Now the kayinja - exotic, brewing bananas - seem to be particularly susceptible to this route. In the highland banana types this mode of spread seems to be much less frequent, and it appears that a more common mode of spread is during leaf pruning. Inadvertently this practice is encouraging spread by moving infection from diseased plants to healthy plants on cutting knives.
Simon Eden-Green, consultant in plant pathology, UK

This is a disease that seems to not only affect bananas, it affects monocots. So looking at how it survives on other alternatives hosts is also important, because if we know it survives on say, maize, then controlling its spread from banana to maize will be of importance. That will also affect which crops should be used as alternatives to banana. You may be better off using root crops rather than cereals because there is that risk of re-infection with cereals.
Valentine Aritua, biotechnology research officer, NARO, Uganda

We have established that the disease lasts in the soil for less than three months so that if you destroyed this diseased garden, within 3-6 months the disease should disappear and you can get back to planting bananas.
Wilberforce Tushemereirwe, NARO, Uganda

The trouble with trade

Once a bunch is harvested and it is mature it can be moved long distances, up to 400 kilometres, and the issue is whether the disease can survive in the bunch. And therefore what can we do to address the issue with the marketers? Because we have been concentrating on farmers, on farmer fields and how it can be controlled, but the issue of the marketing of bananas as a source of infection has not been addressed.
Komayombi Bulegeya, Commissioner for Crop Protection, MAAIF, Uganda

Our biggest problem is this material - banana stalks and leaves - which has come from the fields to the banana collection centre. Many farmers see this material as a good provision of either mulching material or they use it to return minerals into the field. If this material has got the disease, this is one way the disease is actually spreading through traders back into the fields.
Okaasai Opolot, High Commissioner of Crop Production and Marketing, MAAIF, Uganda

It possible that traders are bringing in residues from diseased banana plants such as dried banana leaves which are often used as packing materials. The discarded fruit stalks might also be a source on infection if the bunches have been infected in the field without showing symptoms.
Simon Eden-Green, UK

The issue of the marketing of bananas as a source of infection has not been addressed (CABI Bioscience)
The issue of the marketing of bananas as a source of infection has not been addressed
CABI Bioscience

There is a practice where our farmers sell the bananas in the field, on the plant, and it is the trader who harvests the bunches. If the trader has initially gone into another field where there is the disease, he comes with his tool into this field which does not have the disease and he uses this contaminated implement to harvest the banana, this is another route where the disease can actually be introduced into the farmers' fields.
Okaasai Opolot, MAAIF, Uganda

It seems to be apparent that with the banana beer that is being transported in jerry cans, they use this banana male bud to cover it, so that is why it jumped from Uganda over the lake to Tanzania. Because the disease is close to Kenya but it has never gone to Kenya and one asks why. It seems to be because there is little trade in beer between Uganda and Kenya but there is a higher trade in beer between Uganda and Tanzania and Rwanda.
Valentine Aritua, NARO, Uganda

Refining the control strategy

At the regional level the main priority is to develop specific transboundary policies that allow these countries to cooperate and exchange information so that the efforts in one country can reinforce those in the neighbouring country. And we also need detection methods such as PCR. This is a biochemical tool that is used to detect the disease, so that you can check the material that is crossing borders. However, what has been intriguing me is the idea of identifying high risk areas, because the region is massive, we cannot have resources to go everywhere we need to identify these high risk areas quantitatively and try to focus on them.
Eldad Karamura, INIBAP

We have managed to mobilise the affected farmers to work communally in preventing and controlling the disease. Success stories of control have been registered in many parts of the country and many farmers have rehabilitated their plantations or eradicated the disease. However you still find some people reluctant to implement the control measures and these gardens harbour disease inoculum in the area. There is a strong need to facilitate community leaders and extension to enable them reach farmers at community level and trigger action that can make farmers implement the control measures already known.
Caroline Nankinga, NARO, Uganda

One approach is educating the farmers on the need not to allow the traders to go and harvest bananas in their field using the trader implements. In the case of the materials which are brought into the collection centre and they return into the fields, if these materials can be decomposed for sometime, so it is not fresh materials which are returned into the fields it is manure which is returned to the field, we are confident the disease would cease to be transmitted.
Okaasai Opolot, MAAIF, Uganda

There has been some ambiguity in terms of what is an outbreak zone, a frontline, endemic or pest free zone, and how we might target a response that is appropriate to those levels of disease. Clearly different messages need to be given to the public as relates to those zones and the risks presented by this disease, so that the response is appropriate.
Julian Smith, International Development team leader, Central Science Laboratory, UK

Encouraging the growers to form associations would make it simpler to implement the control measures. The traders would be dealing with an organised group; if a group has been providing infected materials, the traders could easily change and deal with a group that had managed to control the disease. By peer pressure, the group which does not have a market for their bananas will look for information to make sure they actually control the disease.
Okaasai Opolot, MAAIF, Uganda

Where next for research?

Strengthening and refining the control effort is clearly essential (CABI Bioscience)
Strengthening and refining the control effort is clearly essential
CABI Bioscience

We want to try and begin with clean planting material. We want to develop, to identify those materials that are tolerant to the disease and multiply them massively. And with this in mind we need this type of support in the areas of identification of clean planting material, multiplying them and disseminating to those who need them badly.
Eldad Karamura, INIBAP

We need to know a lot more about the major sources of infection for these plants, whether it comes from residues or remains from banana fruits that are being transported into the area, or stalks or leaves: the ways by which the pathogen is being spread into the highland banana population, and what we can do to reduce the likelihood that it occurs.
Simon Eden-Green, UK

Some easy-to-use disease identification kits have been developed for bacteria in other crops and I think if these were developed for bacterial wilt of bananas they would also go a long way in helping us to control the disease, because you need to be able to detect it with precision to be able to destroy it.
Wilberforce Tushemereirwe, NARO, Uganda

We need to have good detection methods. We have an organisation in Kenya which regulates cross-border trade in terms of plant material, so they need to be given the tools to help them in their work.
Kinyua Murimi, Research officer, Kenya Agricultural Research Institute, Kenya

One of the major unknowns at the moment which needs to be addressed is for those farmers that are affected by banana Xanthomonas wilt, and who are probably likely to have to live with it for the medium maybe the long term, is how those farmers cope with living with it. Whether there are different crops to be recommended; if they have to remove their banana, how long before they can plant again; these sort of knowledge gaps aren't really clear to us, and those are some of the areas where the major issues reside now.
Julian Smith, Central Science Laboratory, UK

Date published: September 2006

 

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