Researchers partner to eliminate wilt disease as region’s potato yields decline

Scientists from Kenya, Uganda and Ethiopia in partnership with Egerton University in Kenya and Boku University in Vienna, Austria and the Uganda National Seed Potato producers Association have been working together to address the bacterial wilt problem.

The disease has seen potato yields in the region reduce to below 10 tonnes per hectare against a target of 30-35 tonnes per hectare in progressive countries.

The scientists have developed new technologies for potato production and conducted research with the aim of increasing crop productivity, quality and the incomes of small-scale potato farmers by improving soil fertility and soil health with a specific emphasis on bacterial wilt control in farm systems.

“There are many challenges to potato production, which include high disease pressure, lack of clean seed, receding soil fertility and poor crop management,” said Bruce Ochieng, a plant pathologist at the International Potato Centre, adding, “The most devastating disease to potato is the bacterial wilt.”

Bacterial wilt, caused by a microscopic bacteria Ralstonia solanacearum, is a global disease. However, it is devastating in East Africa because of lack of clean potato seeds, infected soils, and a lack of knowledge among farmers.

“The bacterial wilt pathogen infects soils and seeds and is easily transported from one farm to another,” said Phoebe Mwaniki from Egerton University in Kenya.

The bacterial wilt pathogen can cause losses of between 10 per cent and 80 per cent of crop yields depending on the amount of inoculum in the soil, temperature and humidity. The higher the inoculum, temperature and humidity, the more devastating the pathogen is to potato crops.

Bacterial wilt is a virus with no known remedy and managing the disease is the only way to achieve optimum potato production in the region.

“Many farmers plant potato all year round, not understanding that by doing that they are predisposing their land to increased risk of soil borne diseases such as bacterial wilt, as well as reducing the overall fertility of the soil,” said Elmar Schulte-Gerdemann. “Therefore, farmers need to know about crop rotation and land management,” he added.

Bacterial wilt thrives in soil for longer periods as long as there is a host plant to sustain it. It is more prevalent and devastating to potato plants and crops from the same family. “It is important to ensure that all volunteer crops are uprooted once a potato crop has been harvested to ensure they do not host the wilt-causing pathogens,” said Bruce Ochieng a plant pathologist.

Volunteer crops are usually remnant seeds left in the soil after harvesting and they grow in the subsequent season.

The wilt pathogen can also survive in plants without showing any symptom, which makes the disease unnoticeable to the naked eye, leading to its spread to other regions if proper care is not taken.

“This is why the bacterial oozing test is important for farmers,” said Mr Ochieng. Using this test, farmers can identify and diagnose infected plants by cutting the stem of a wilting plant and suspending it using a wire in clear water. If the plant is infected then bacterial ooze will come out of the cut stem into the clear water.

It is aisable to carefully uproot the infected crop and take it away from the field. The infected crop should also not be fed to livestock because it may end up back in the farm as manure. Scientists aise burning as the best solution.

Farmers are also aised to get seeds from authorised seed multipliers. The ministries of agriculture in their respective countries can assist in identifying clean seeds.

To properly reduce the inoculum density of bacterial wilt in the soil, farmers are aised to practise proper crop rotation, which involves growing other crops such as brassicas, legumes, cereals and fodder. “Rotating crops reduces the bacteria inoculum in the soil and doing this for four crop seasons (a two-year cycle)ompletely eradicates the pathogen from the soils,” said Ms Mwaniki.

At the Ethiopian Institute of Agricultural Research, scientists have been working on clean seed multiplication of improved varieties of potato and further developing biological control agents that are effective against the destructive pathogen.

This is done by introducing the wilt pathogen and a potential bio-control agent in the same culture plate.

According to Bekele Kassa, a plant pathologist at the Ethiopian Institute of Agricultural Research, the bio-control agents seem to suppress the wilt pathogen by up to 80 per cent.