In 2019/20 CABI and KEPHIS conducted an extensive survey on potato diseases most notably on blackleg, a “wilting disease” caused by a complex of bacteria, including Pectobacterium and Dickeya spp. This group of bacteria referred to as the “Erwinia complex” are spread by tuber, by water, insects, wind and rain. The full report of 157 pages was published in October 2021 and is available as PDF. This paper provides a summary of the survey report.


Why the survey?

Blackleg is a very common disease in all potato production regions in the World. It is known in nearly all countries as quality organism and has no a quarantine status. Kenya is an exception to this rule. The “Erwinia” bacteria causes the stems and tubers to rot, either in the field or under (poor) storage conditions. This results in lower quality and yields. When infected seed potatoes are distributed, the disease spread.  It is important to know if and to what extent the Erwinia complex is present in Kenya in order to control it and prevent it from further spreading.

 Is there a problem with potato yield levels in Kenya? Yes, there is!

FAO figures show that potato yields in Kenya have consistently declined from 21.2 tons/hectare in 2008 to 8.6 tons/hectare in 2018. Kenya potato yields are amongst the lowest in Africa. A disastrous decline for a country that wants to be food secure. Part of these low yields are caused by diseases such as bacterial wilt (bacterium Ralstonia solanacearum), late blight (fungus Phytophthora infestans), blackleg and by poor agricultural methods (e.g. lack of crop rotation) and poor storage facilities.

The purpose of the extensive survey is to assist KEPHIS in detection and identification of the different  “Erwinia” bacteria present and mapping the occurrence of blackleg in the country to ensure that seed regulations are aligned with determined risks. This will lead to increased awareness of the country’s disease status, better disease prioritization and increased investments in appropriate disease prevention and control. This will potentially improve disease management practices of authorities and players in the market drive, increased availability of quality seed, hence improving potato productivity, incomes and therefore food security.

The survey was very extensive!

The survey done focused in six main potato-producing counties: Elgeyo Marakwet, Meru, Nakuru, Narok, Nyandarua and Trans Nzoia. There was high suspicion of high blackleg disease pressure increasing the chance of finding this target disease in these six counties. Farmers selected by the counties to participate in the survey were 1,002 and nearly 3,000 samples of tubers.  Samples from the plant materials and soil were collected and taken for analysis at the KEPHIS laboratory. In addition to the collection of samples, a structured questionnaire shared among the farmers to understand better the farming systems potentially affected by blackleg. There will be a planned farm visit for sampling in November/December 2019. Laboratory analysis took the whole of 2020.

What were the results?

Samples of 290 found in Pectobacterium spp., which is equivalent to one in every ten samples. More specifically the survey found the following species: P. brasiliense, P. carotovorum, and P. wasabiae. In Kenya, these blackleg and soft rot causing species have been described in previous studies. Confirmed again was their presence. During this survey, one Pectobacterium species was found for the first time: P. atrocepticum. A newly found bacteria in Kenya is Dickeya solani causing blackleg as well. Two farms in Elgeyo Marakwet and in Narok found to have them. When CABI and KEPHIS returned to those farms to check their findings with new samples it turned out that 50% of those samples tested positive on Dickeya solani. Disturbing fact: one of the farmers was a “clean seed” producer.

Conclusion: one in every ten samples taken from six counties tested positive on Blackleg. This clearly shows that this bacterial disease is widely present in Kenya, as it is in other countries.

Is Blackleg Problem going to increase?

The report does not state where the various blackleg species are coming from and when they arrived in Kenya. There has been trading in potato and related crops in Kenya for decades and the bacteria could have entered from anywhere at any time. The report indicates the main reason for the distribution of the bacteria and the increased incidence is the informal seed trade.

More than 80% of the seed planted in the six counties was farm-saved from fellow farmers or acquired otherwise and definitely not certified. This is a good explanation why seed-borne diseases such as blackleg are increasing in Kenya threatening potato production. The over-reliance on the use of non-certified seed in Kenya as reported before is responsible for the spread of the dangerous (more prevalent) disease brown rot caused by the bacterium Ralstonia solanacearum.

The use of locally produced variety Shangi plays an important role in the distribution of the disease. 89.7% of the farmers sampled across the six counties grew this variety. Blackleg disease will dramatically increase with time if the infested seed keeps moving from farm to farm.

Blackleg will likely increase inadequate knowledge of disease management, weed control, inadequate capacity to undertake potato diseases diagnosis, poor knowledge of the availability of disease-free lands for seed multiplication and lack of crop rotation. I.e. continuous cultivation of land. Farmers find it hard to identify the disease and lack the knowledge of possible hosts of the bacteria (weeds as well as rotation crops). Very few participating farmers in the survey could identify blackleg. Potato is a key crop in the traditional production areas hence the land is continuously cultivated to grow the crop and this leads to a build-up of diseases.

Low usage of agro-inputs (such as pesticides, both organic, inorganic and biologicals), poor agricultural practices (such as abuse of crop rotation regimes) and poor storage facilities contribute to the observed high disease incidences.

Conclusion: Blackleg caused by a complex of “Erwinia” bacteria  including Pectobacterium ssp and Dickeya spp is very likely to increase in Kenya both in terms of distribution (informal seed trade) and  incidence (poor management practices). When left uncontrolled this trend will negatively affect the quality of potatoes and yield levels that are already amongst the lowest in the world. This trend is seriously threatening food security in the country.

 What is the Kenya potato sector going to do about it?

Government of Kenya, NPCK, Friends of potatoes and other partners must do something!



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