A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>

Date: 11 March 2008
Source: The New Vision [edited]
<http://allafrica.com/stories/200803120062.html>

Virus lowers potato yields in Kabale

A rampant potato disease reported in Kabale district [Western Region] poses a danger to people's livelihood. Dr Andrew Kiggundu, a research officer at the National Agricultural Research Institute, Kawanda [KARI], says the virus affects the quality and quantity of the crop and research shows that almost all the potatoes grown in the area have the virus.

The current average potato production in Uganda stands at about 7 tonnes per hectare, compared with a possible yield of 30 to 40 tonnes per hectare, if well-managed. "Poor farmers have been planting virus infested potatoes, rapidly increasing the virus' multiplication," Kiggundu says. The crop is mainly grown in the districts of Kabale, Kisoro, Kanungu, Mbale, Sironko, and Kapchorwa.

The virus is spread by insect vectors and through human contact from plant to plant. The virus can also be transmitted from tuber plants from one season to another. Symptoms of the disease include curling of leaves, mosaic, retarded growth, and poor yields. However, a tissue culture laboratory to deal with the potato disease in the area has been developed at Kachwekano Zonal Agricultural Research and Development Institute in Kabale.

"Through the use of tissue culture, improved quality seed potato can be generated and provided to farmers as clean seed to improve yields, even under sub-optimal soil fertility and rain conditions," Kiggundu says.

[byline: Aidah Nanyonjo]

--
communicated by:
ProMED-mail
<promed@promedmail.org>

[Around 40 viruses have been reported to affect potato, and a number of them can be spread by insects, including aphids. In addition, since the crop is vegetatively propagated, many pathogens including viruses such as _Potato leafroll virus_, _Potato virus X_ and _Potato virus Y_, as well as _Potato spindle tuber viroid_ are disseminated in tubers. Some viruses, for example _Potato virus A_, may only have a minor effect on yield if they are the only infecting virus species and if a crop is newly infected in the field. If virus-infected seed tubers are used, however, the virus population will gradually build up during every crop cycle, both in number of co-infecting (possibly synergistic) virus species and in amounts of infectious units per species. This invariably leads to severely reduced plant vigour and a dramatic drop in yield.

The virus referred to above may be _Potato leafroll virus_ (PLRV; genus _Polerovirus_) which is a destructive pathogen causing symptoms similar to the ones described. It can also affect tubers and is transmitted by aphids as well as seed tubers. PLRV can also affect tomato and a number of weeds.  Different potato cultivars may show different levels of susceptibility to PLRV.

The important role that tubers play in virus and viroid spread is recognised by the strict requirements for certified seed potato production in many countries worldwide. Meristem tip tissue culture, often in conjunction with heat or cold treatments, has been used to obtain virus free material for plant propagation. Intra-cellular plant pathogens -- such as viruses and viroids -- spread from cell to cell and newly formed cells in the meristem will be invaded. If these cells can be removed before they are infected, clean cell lines can be obtained. However, it is vital to verify the pathogen status of the resulting lines since typically not all cultures will be pathogen free. For example, strains of _Potato spindle tuber viroid_ have been distributed widely in Russia with tissue culture lines that had not been successfully cleared of the viroid (see ProMED-Mail post no. 20070423.1323).

Maps
Uganda:
<http://unimaps.com/uganda/mainmap.gif> and <http://healthmap.org/promed?v=1.3,32.4,6>
Uganda districts:
<http://en.wikipedia.org/wiki/Districts_of_Uganda>
Pictures of potato virus symptoms via:
<http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Potatoes/Viruses/PotVirusPhotoList.htm> 

Links
Virus and viroid diseases of potato, factsheet:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_Potato.htm>
Information on potato viruses:
<http://www.hort.uconn.edu/Ipm/veg/htms/viruspot.htm>  and <http://www.ipm.ucdavis.edu/PMG/r607101411.html>
List of potato viruses and other pathogens:
<http://www.apsnet.org/online/common/names/potato.asp>
Taxonomy of all potato viruses via:
<http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/index.htm>
Virus elimination treatments:
<http://www.blackwell-synergy.com/doi/abs/10.1111/j.1364-3703.2007.00456.x>
KARI information:
<http://www.hridir.org/countries/uganda/PROVCOUN/national_agricultural_research_organisationnaro/
kawanda_agricultural_research_institute_kari/index.htm>
- Mod.DHA]