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Source: International Potato Centre (CIP) [edited]
First documented in Uganda in 1958, bacterial wilt [BW] is widespread, limiting yields and degrading seed [tuber] quality. But little is known about the extent of the disease and the type of pathogen strains involved. BW is not always apparent: the harvest can look healthy, but will not be fit as seed [tubers]. "There has been no monitoring and documentation of BW in Uganda," said Kalpana Sharma, CIP. Many African countries do not have measures in place to prevent its spread [and] do not have certified seed systems.

[CIP] conducted a nationwide survey to chart the prevalence and spread of BW, as well as the type of pathogens present. The results confirmed that the disease was moving primarily through seed [tubers]. BW was present in 73% of ware potato farms and 50% of seed potato farms. The disease has moved from eastern and western regions to the northern region where potatoes have been more recently introduced.

"We have provided evidence about the types, presence and movement of BW, researchers and policy makers can use this to develop appropriate management strategies within [a] seed [tuber] regulatory framework," [said] Sharma. The completed study is being compared with the findings of a similar study in Ethiopia, Kenya and Rwanda. The next steps will be to scale this up into other countries, such as Tanzania and Malawi, to generate a BW regional map for improved collaboration across national borders.
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[Brown rot (also called bacterial wilt) of potato is caused by _Ralstonia solanacearum_ race 3 (biovar 2, adapted to cooler temperatures) or race 1 (prevalent in warmer areas). Yield losses are mostly caused by tuber rotting. The pathogen also causes bacterial wilt of tomato, a major disease of the crop, and it can also affect other solanaceous crops.

The bacteria are spread by mechanical means (including insect activities), contaminated equipment, infected plant material (including seed potatoes), soil and water. They can survive in soil on plant debris or roots of hosts. Some solanaceous weeds and unharvested potato plants may serve as pathogen reservoirs. Disease management is difficult, relying mostly on exclusion from new areas. Some cultural methods (such as crop rotation), control of pathogen reservoirs and phytosanitary measures (soil fumigation) may be used. Biological control is being investigated. Potato cultivars with levels of genetic resistance are available for certain growing conditions.

The source paper (see link below) reports that the strains identified in Uganda belonged to three phylotypes. Members of one of these was identified as playing an important epidemiological role, being disseminated via latently infected seed tubers.

Members of the _R. solanacearum_ species complex affect more than 200 plant species including many important crops. The various races and biovars are active under different climatic conditions and in different hosts.

Africa (overview):

Potato brown rot symptoms:,,, and
Bacterial wilt symptoms on tomato plants: and

Original publication for the story above:
Information on brown rot of potato:,, (with pictures),, and
Information on bacterial wilt of tomato: and
_R. solanacearum_, pathogen and disease information: (with pictures),,,,, and
Rs races and biovars: (overview) and (tomato and other Solanaceae)
Description and taxonomy of _R. solanacearum_:
- Mod.DHA]

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