New pest threatens potato production in Kenya

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Kenya has been invaded by a new potato pest that threatens to cut production by more than 80 per cent unless urgent measures are taken to control it. The pest has been identified in a few countries in North and West Africa, and in Europe, North and South America.

In these countries, it is strictly controlled through quarantines. It is the first time the pest is being reported in East Africa.

Pest is resistant to pesticides

Potatoes and soil samples taken from several sites in Nyandarua County, and tested in Kenya and Germany have confirmed the presence of potato cyst nematode (Globodera rostochiensis or G. rostochiensis). The region produces more than 40 per cent of the potatoes produced in Kenya.

Persistent in soil

There is no pesticide chemical or biological that is known to control the pest. The only control measure is to stop potato production in infested farms for up to 7 years. The pest, however, can remain in the soil for more than 30 years. The potato pest may spread fast to other parts of the country because more than 90 per cent of potato growers in the country buy seed from neighbours. Many farmers in Nyandarua county also sell potato seeds to farmers in other parts of the country, increasing the possibility of rapid spread of the pest to other potato growing areas.

Potato imports to blame

Scientists at KALRO have in past lodged complaints after discovering that some varieties of potato seed had been imported into the country without stringent checks by the Kenya Plant Health Inspection Service (KEPHIS), read TOF No.106 March 2014. The infected seeds have the potential to introduce new diseases and pests into the country.

What farmers need to know about new potato pest

Nematodes are slender worms that the naked eye cannot see unless when placed against a light. They are usually one millimetre in length and are cylindrical (long and round like an earthworm). Although potato cyst nematodes are indigenous to Peru and other regions with low temperatures in Europe, where potatoes have been cultivated for thousands of years, the pest has been confined to particular regions where it is prevented from spreading through quarantines. This has left many potato growing areas in the affected countries free of the nematodes.

In Africa, potato cyst nematodes have been reported in Northern African countries including Algeria, Egypt, Libya, Tunisia and Morocco (under quarantines). Other countries where the pest has been reported are Sierra Leone and South Africa where they are also controlled.

Potato imports responsible for spread of pest

Kenya can only produce 2 per cent of the required certified potato seed, limited to this following the grabbing of land meant for research and potato seed multiplication, among other challenges. Scientists at the Kenya Agricultural and Livestock Research Organisation (KALRO) have noted with concern that some varieties of potato seed had been imported into the country without stringent checks by the Kenya Plant Health Inspection Service (KEPHIS). These have the potential to introduce new diseases and pests into the country (read TOF No. 106, March 2014). Any seed variety imported into Kenya has to undergo screening and quarantine protocols. This is meant to ensure the seeds do not introduce diseases and pests that could affect potato production.

How can farmers identify potato cyst nematodes?

It is not easy for farmers to identify potato cyst nematodes infestation in their potato crop. This is because potato cyst nematodes are very small in size and thus not easily visible to the naked eye. Infested potatoes show the same symptoms caused by other diseases and pests such as stunted growth, yellow or wilted leaves. The potato plant may develop tiny tubers and sometimes no tubers at all.

How can farmers control potato cyst nematodes?

Potato cyst nematodes are among a species of harmful nematodes that specifically target potatoes and other crops in the potato family such as tomatoes, pepper, eggplant, and black nightshade. So far there is no known chemical or biological pesticide that controls potato cyst nematodes. In countries where the pest has been identified, the most effective measure has been to ensure that no potatoes from the affected areas are transported or sold in the market both for food or as seeds (this restriction by the government or local authorities is called a quarantine).

Farmers in areas where the pest is found are not allowed to grow potatoes but are instead encouraged to grow other crops that do not belong to the potato family. Other measures that farmers can take to keep the pest from their farms include:

• Using certified potato seed at all times in their farms and not seeds bought from neighbours or those from unknown sources.

• Using quality declared seed from known potato seed growers.

• All farms where the potato cyst nematode is identified should not be planted with potatoes for up to 7 years. Potato cyst nematodes can remain in the soil for up to 30 years; land remaining free of potatoes for seven years has less infestation of the nematodes.

• Farmers are also encouraged to practice crop rotation at all times to reduce the population of potato cyst nematodes in their farms.

• Affected land can also be left to remain fallow for 7 years, if possible. This is, however, a challenge in Kenya because land sizes are very small and farmers need the land to grow other food crops.

• Potato varieties resistant to potato cyst nematodes can be developed. This needs years of study for research institutions to identify and get certification for resistant varieties.

How was the potato cyst nematode discovered?

Between August and October 2014, potatoes and soil samples were taken from several sites in Nyandarua County and tested in Kenya and Germany. Scientists have confirmed the presence of potato cyst nematode (Globodera rostochiensis or G. rostochiensis) in most areas in the county. James Maina Mwangi, currently an assistant lecturer at Department of Biological Sciences at Chuka University, was sampling farmers’ fields in Nyandarua County in the search for nematodes that affect cabbages for his MSc. thesis, when he came across cysts that resembled those of Heterodera species.

As a follow up, he went back and sampled both cabbage and potato farms and extracted more cysts.

“It was then that I consulted my supervisor whereupon we did a detailed molecular analysis (in Kenyatta University Laboratories and DNA sequencing by Inqaba Biotech in South Africa). We discovered that the species we were handling was Globodera rostochiensis. To confirm our findings, we sent the samples to our colleague in Bonn, Germany,’ he says.

The results of the external analysis confirmed that it was indeed Globodera rostochiensis or potato cyst nematode that had been discovered. Mwangi presented a paper on the same at Kenyatta University on December 3, 2014. Potato cyst nematodes were found in all the areas that were sampled in Ndaragwa, Ol joro orok, Ndundori, Ol Kalou, North and South Kinangop. Farmers in the affected areas said they had sourced their potato seeds from other growers in different parts of Nyandarua county.

Although the potato cyst nematode is mainly found in Europe and a few African countries where it has been confined (quarantined) to prevent its spread, farmers in the country are surprised at the discovery of the new potato pest in Kenya: “The maize disease (Maize Lethal Necrosis) has destroyed our maize crop last season. I did not harvest anything because my maize crop wilted before it could form the cobs.

Now the potatoes are also affected by the new pest. We do not know what to grow next because these are the two main crops we grow here for food and sale,” says Shadrack Thiongo,a farmer from Mirangine, Tumaini in Nyandarua.

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