PRO/PL> East African cassava mosaic virus, UG var. - Burundi

EAST AFRICAN CASSAVA MOSAIC VIRUS, UG VARIANT - BURUNDI
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Date: 7 Nov 2003
From: ProMED-mail<[EMAIL PROTECTED]>
Source: British Soc. Plant Pathol., New Disease Reports, Vol. 8 [edited]


1st evidence for the spread of East African cassava mosaic virus -- Uganda 
(EACMV-UG) and the pandemic of severe cassava mosaic disease to Burundi

S. Bigirimana <[EMAIL PROTECTED]> (Institut des Sciences 
Agronomiques du Burundi, Gitega, Burundi); P. Barumbanze (as for 
isabu-getega); R. Obonyo (International Institute of Tropical Agriculture, 
Eastern and Southern Africa Regional Centre, Kampala, Uganda); J.P. Legg 
(as for Obonyo); and J.P Legg (Natural Resources Institute, Chatham 
Maritime, UK). Accepted for publication 27 Oct 2003.

Cassava mosaic disease (CMD) is the most important constraint to cassava 
(_Manihot esculenta_) production in Africa. Since the 1990s, the importance 
of the disease has been greatly increased by the spread through East and 
Central Africa of a pandemic of unusually severe CMD (Legg, 1999), 
associated with the recombinant begomovirus, East African cassava mosaic 
virus -- Uganda (EACMV-UG) (Zhou et al., 1997).

Following reports of the spread of EACMV-UG to Rwanda (Legg et al., 2001), 
it became apparent that Burundi, to the south, was also threatened.

A survey of cassava plantings in Burundi was conducted in May/June 2003 to 
assess the status of CMD and to identify begomoviruses present. 53 fields 
were sampled in 10 of the country's 16 regions and CMD-diseased leaf 
samples collected in each field for virus diagnosis. Assessments were made 
of CMD incidence, severity (using the standard 1-5 scale), infection type 
(either cutting or whitefly-borne) and abundance of the whitefly vector, 
_Bemisia tabaci_ (Bt).

Viruses were diagnosed from leaf samples using both specific primer PCR 
(Zhou et al., 1997) and restriction digestion with EcoRV and MluI of near 
full-length DNA-A fragments amplified using universal begomovirus primers 
(Briddon & Markham, 1994).

EACMV-UG, ACMV, EACMV and mixed ACMV?UG infections were identified from 17, 
34, 1 and 3 sites, respectively. EACMV-UG occurred at all sites in the 
north-eastern regions of Muyinga and Kirundo was present at some sites in 
northern Gitega, Ngozi, Karuzi, Kayanza, Ruyigi and northern Rutana, but 
was not recorded from southern Gitega, southern Rutana, Muramvya or Bujumbura.

The EACMV-UG affected regions of Muyingo and Kirundo were distinct from the 
others in having higher CMD incidence (79 vs. 42 percent), a greater 
proportion of whitefly-borne to cutting-borne infection (1.9 vs. 0.6), more 
severe symptoms (4.17 vs. 3.26) and a greater abundance of Bt (4.9 vs. 
1.0). This data set provides clear evidence for the rapid spread of severe 
EACMV-UG associated CMD in the north-eastern regions of Kirundo and 
Muyinga. The occurrence of EACMV-UG at sites in northern, central, and 
eastern Burundi also suggests that similar changes in CMD epidemiology are 
likely to occur here in the near future.

These results represent the first report of the expansion of the African 
CMD pandemic into Burundi.

References

Briddon RW, Markham PG, 1994. Universal primers for the PCR amplification 
of dicot-infecting geminiviruses. Molecular Biotechnology 1, 202-5.

Legg JP, 1999. Emergence, spread and strategies for controlling the 
pandemic of cassava mosaic virus disease in east and central Africa. Crop 
Protection 18, 627-37.

Legg JP, Okao-Okuja G, Mayala R, Muhinyuza J-B, 2001. Spread into Rwanda of 
the severe cassava mosaic virus disease pandemic and associated Uganda 
variant of East African cassava mosaic virus (EACMV-Ug). Plant Pathology 
50, 796.

Zhou X, Liu Y, Calvert L, Munoz C, Otim-Nape GW, Robinson DJ, Harrison BD. 
1997. Evidence that DNA-A of a geminivirus associated with severe cassava 
mosaic disease in Uganda has arisen by interspecific recombination. Journal 
of General Virology 78, 2101-2111.

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ProMED-mail
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[It was just a matter of time before CMD would be reported from Burundi. 
The most likely means of spread of EACMV-UG into Burundi would be via 
viruliferous whiteflies (_Bemisia tabaci_) and movement of infected cassava 
cuttings. CMD continues to spread. Research by scientists at the Centro 
Internacional de Agricultura Tropical (CIAT) in Colombia has resulted in 
the development and deployment of microsatellites or simple sequence repeat 
(SSR) markers which facilitate resistance breeding. SSR markers have been 
successfully applied in tagging cassava genome loci involved in resistance 
to CMD.

Additional references:
<http://www.ciat.cgiar.org/pgr/cassava.htm>
<http://www.ciat.cgiar.org/pgr/cassava.htm>
- Mod.DH]

[see also:
East African cassava mosaic Zanzibar virus - Kenya 20030408.0859
2002
----
Cassava mosaic virus, Ugandan variant - Nigeria 20021207.6003
Cassava mosaic disease - East & Central Africa (02) 20020927.5416
Cassava mosaic disease - East & Central Africa 20020915.5321
2001
----
Cassava diseases - Kenya 20011117.2829
East African cassava mosaic virus - West Africa 20010814.1920
East African cassava mosaic begomovirus 20010523.1003]
.........................dh/pg/mpp

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