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Disease recognition and control in DRC

Surveillance for plant diseases is erratic in DRC (Eric Boa)
Surveillance for plant diseases is erratic in DRC
Eric Boa

In a hotel room in the heart of Africa, two scientists peer intently at their latest collected samples of blackened roots and shrivelled leaves. Yesterday it was cocoa, today it's cinchona. They strongly believe that the culprit is Phytophthora. The symptoms match those of a known disease and, although laboratory confirmation is still required, there's enough evidence for these plant doctors to advise concerned plantation owners. Research may in time identify resistant varieties of cinchona but action is needed now.

Eric Boa and Paula Nash of the Global Plant Clinic (GPC) have recently returned from North Kivu, in the Democratic Republic of Congo where - at the invitation of Philip Betts of ESCO (an export company) - they spent three days examining plant diseases on cocoa, cinchona and papaya. Cinchona is originally from Peru, where for centuries locals used infusions of the (quinine) bark to control fevers. Cinchona seeds were smuggled out of the country during the 1600s to set up large plantations in Java, Indonesia. Occupation by the Japanese in the Second World War, however, resulted in a quinine shortage prompting the Allies to start plantations in Africa, including in North Kivu (previously part of the Belgian Congo).

Unknown diseases in cinchona and papaya

North Kivu is a major global exporter of cinchona bark and demand is remarkably buoyant, particularly from India. The trees are harvested on a seven-year cycle; the bark is stripped and the tree coppiced and left to grow undisturbed for a further seven years. But young trees - their roots blackened and with leaves curling up - are dying within the plantations. Records show the disease has been known for over 40 years yet, until recently, it has not been a major problem. "We're still in the dark about this disease," observes Boa, "but our role is to come to a quick solution based on the best available evidence. When we get better scientific information we will review our advice." Phytophthora diseases live in the soil and so farmers are told to uproot young plants and plant something else.

Cinchona nursery owner with an affected plant (Eric Boa)
Cinchona nursery owner with an affected plant
Eric Boa

Around Beni, North Kivu, papaya is grown as the source of papain - a milky latex which is extracted and exported as a digestive enzyme for the meat and brewing industries. There's a healthy demand from Europe and good rewards for the local economy. But papaya is susceptible to many diseases (from viruses to phytoplasmas), and in Beni a new disease is causing concern. Samples analysed at Rothamsted Research in the UK have yielded no answers. Professor Phil Jones believes that the causal agent is a virus but it's proving elusive. On a subsequent visit, the plant doctors will go prepared to extract suitable material for testing in their makeshift hotel laboratory, another pragmatic approach to providing plant health services to growers in challenging circumstances.

A lucky strike

Nash and Boa achieved greater success with perhaps the most serious disease they were asked to investigate: a cocoa wilt disease that was killing trees and causing understandable concern to local farmers - and to Philip Betts. 'Look at the number of motorcycles in Beni,' Philip remarked. 'That's a sure sign that agriculture is doing well, something that this disease threatens.' Back in the field, staining under the bark suggested Verticillium wilt - a soilborne fungus, which was later positively identified by GPC scientists at CABI Bioscience in the UK. Hassan Mohamed, a local farmer, explained that over 100 trees had died. He was perhaps not best pleased to learn that the wilt is difficult to control as the fungus can remain in the soil for many years. Quickly removing infected plants and limiting spread of soil offers some damage limitation. Avoiding cuts to stems when weeding with a panga, by using a temporary shield, is another suggestion but the only long-term solution will be to find resistant varieties.

A distant dream?

North Kivu is more remote than many regions, even in the DRC, but it is no different from many areas in Africa where ministries are weak and surveillance for plant diseases is erratic. Most countries can only dream about having a central reference point for receiving disease samples. After many years of civil war, DRC has yet to realise its potential wealth and, as the breadbasket of the country, North Kivu has much to offer. But whilst Philip Betts hopes that production of these vital export crops can be improved and even expanded, these efforts will be much hampered unless the diseases affecting these crops are better understood and managed.

It takes time and resources to train plant pathologists capable of the type of work that Boa and Nash have recently been undertaking. "But this is not a necessity," stresses Boa, "and it is far better to establish plant clinics and train plant doctors in field diagnosis techniques before we start worrying about longer term research." With these needs in mind, Boa and Nash plan to return to Kivu in early 2006 to run a training course and to develop disease factsheets that explain simply and directly what the farmers want to know.

Date published: September 2005

 

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