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Combating cassava brown streak virus

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Farmers have been warned to brace-up and build capacity towards containing the invasion of the ravaging Cassava Brown Streak Virus Disease (CBSD).

CBSD, a major virus affecting cassava, is considered as a damaging disease of the tropical plants. It is currently ravaging countries in the East Africa region. It is considered the biggest threat to food security in coastal East Africa and around the eastern lakes.

Currently found in the Democratic Republic of Congo, it was first discovered in Tanzania, and has spread to other coastal areas of East Africa, from Kenya to Mozambique.

Unlike symptoms induced by majority of plant viruses, those of CBSD in cassava normally affect mature or nearly mature leaves but not expanding, immature leaves.

The virus consists of a characteristic yellow or necrotic vein banding, which may enlarge and coalesce to form comparatively large, yellow patches. Tuberous root symptoms may also be present: these consist of dark-brown necrotic areas within the tuber and reduction in root size; lesions in roots can result in post-harvest spoilage of the crop.

Experts say leaf and/or stem symptoms can occur without the development of tuber symptoms. The symptoms of the disease vary greatly with variety and environmental conditions, making diagnosis difficult, particularly when plants are infected both with CBSD and cassava mosaic disease.

Seeing the threat the disease poses, in 2015, the West African Virus Epidemiology (WAVE) project, to be undertaken by Covenant University and two other institutions was initiated.

The $3m project, funded by Bill and Melinda Gates Foundation, was aimed at increasing productivity and sustainability of root and tuber crops, and to also tackle the cassava viruses combating cassava plantation in Nigeria and six other West African countries.

Nigeria is the largest producer of cassava in the world, with about 50 million metric tons yearly from a cultivated area of about 3.7 million ha. It accounts for up to 20 per cent of the world cultivation, about 34 per cent of Africa’s and about 46 per cent of West Africa’s.

The national average yield of cassava is estimated at about 13.63 mt per ha, as against potential yield of up to 40 metric tons per ha.

Due to the importance of the country as a major player in the cassava cultivation, more needs to be done to stop the disease from spreading to Nigeria.

The WAVE Coordinator for Covenant University, Dr. Angela Eni, who sees the disease as a major threat, told The Guardian that though efforts have been intensified to keep it at bay, by securing borders of affected countries, she added that there is need for partnership to curb tuber crop diseases, through surveillance and monitoring.

“Nigeria as a country needs to look holistically at the problem. We need to build up the capacity to ensure that it doesn’t come into Nigeria.

“The CBSV is already in DR Congo but we don’t want it to get here, which is why we are making some pre-emptive efforts, and we want to provide adequate information to key policymakers.”

She noted that aside what they have put in place to forestall its invasion; government and other stakeholders should engage partners to brainstorm on how to solve the problem.

Aside the efforts already put in place, findings showed that a basic approach to prevent the disease should be the use of virus-free planting material. Experts claimed that with CBSD, it is always very difficult to select virus-free material because the symptoms of infection can be vague and indistinct.

A tuber research expert, Inioluwa Jacob, who claimed that the disease can be prevented if proper attention is given to planting materials imported into the country, said such step is necessary as there is a considerable traffic in plant material within and sometimes between countries and inevitably CBSVs are disseminated in this way.

“Effective means of detection are now available and being utilised. It is likely that considerable improvement could be made in the present unsatisfactory situation by selecting cuttings for propagation only from plants that have been inspected during growth and also at harvest and found to be free of leaf, stem and root symptoms.

“There are also advantages in farmers selecting propagating material only from unaffected plants at the time they collect cuttings. Unfortunately, however, farmers are not familiar with the whole range of CBSD symptoms, and cuttings may be collected at times when the source plants are almost leafless or severely affected by the cassava green mite (Mononychellus tanajoa), cassava mealybug (Phenacoccus manihoti), leaf spot or bacterial blight,” he said.


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