April 26, 2006
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes, May 2006 [edited] <http://www.apsnet.org/pd/searchnotes/2006/PD-90-0683B.asp>

First report of rice yellow mottle virus in rice in Uganda
A Pinel-Galzi, D Fargette, Institut de Recherche pour le Developpement, BP 64501, 34394 Montpellier cedex 5, France; R Hull, John Innes Centre, Norwich NR4 7UH, United Kingdom. Plant Dis 2006; 90: 683, published online
as DOI: 10.1094/PD-90-0683B. Accepted for publication 7 Feb 2006.

Rice yellow mottle virus (RYMV) of the genus _Sobemovirus_ is a major biotic constraint to rice production in Africa. First reported in Kenya in 1966, RYMV was later found in most countries in Africa where rice (_Oryza
sativa_) is grown (2). During July 2000, plants with leaf yellowing and mottling symptoms were observed in Uganda in a subsistence rice field north east of Lake Victoria, close to the Nile River. RYMV was detected by using
enzyme-linked immunosorbent assay with polyclonal RYMV antisera (1) in the 4 samples collected. Discriminant monoclonal antibodies revealed that the samples contained RYMV serotype 4, a serotype found in eastern Africa
(Madagascar, Kenya, and Tanzania) (2). The 720-nt long coat protein gene of 2 isolates was amplified by reverse transcriptase-polymerase chain reaction and sequenced (1).

The 2 Ugandan isolates had 99 per cent nt sequence identity (EMBL Accession Nos. AM114523 and AM114524). They belonged to a monophyletic group (97 per cent nt identity) containing isolates from eastern Kenya and northern Tanzania (close to the Lake Victoria). These form a sister group (93 per cent identity) of isolates from Lake Malawi Region in western Tanzania and are more distantly related (88 per cent identity) to the basal strains from eastern Tanzania (2).

Isolation of the Lake Victoria Region from the rest of the Tanzania by distance, physical barriers, and patchy rice cultivation explains the specificity of the strain. Year-round growth of wild and cultivated rice around the lake ensures host continuity in time and space, which facilitates spread that accounts for the homogeneity of the isolates of this area. Knowledge of the presence of RYMV in Uganda is important, since rice cultivation is intensified in this country and is planned in neighboring southern Sudan.

References:
1. A Pinel, et al. Arch Virol 2000; 145: 1621.
2. O Traore, et al. Mol Ecol 2005; 14: 2097.

--
ProMED-mail
<promed@promedmail.org>

[The crop plant rice, _Oryza sativa_, develops symptoms of the disease yellow mottle when infected by the virus rice yellow mottle virus (genus: _Sobemovirus_, RYMV). Symptoms include stunting, reduced tillering, mottling and yellowish streaking of the leaves, delayed flowering or incomplete emergence of the panicles and, in extreme cases, death of plants. The disease is a major constraint to rice production in Africa. RYMV was 1st reported in Kenya in 1966 and later found in most countries in Africa where rice is grown. RYMV is transmitted mechanically and by chrysomelid beetles but not by seed (a property of some _Sobemoviruses_). _Chaetocnema pulla Chapuis_ is thought to be an important vector of the disease in Tanzania. Much of the spread may not be due to transmission by beetles but rather by mechanical inoculation. Very few rice varieties are resistant to RYMV. The highest level of resistance was provided by a cultivar of _Oryza sativa indica_, "Gigante," and a few cultivars of _Oryza glaberrima_ series Tog. These varieties showed a natural high resistance characterized by a low virus titre and the absence of symptoms.

In this 1st report of RYMV in Uganda, 4 samples were collected from symptomatic plants growing in a subsistence rice field north east of Lake Victoria, close to the Nile River, in 2000. The samples contained RYMV serotype 4, a serotype found in eastern Africa (Madagascar, Kenya, and Tanzania). It differs from (88 per cent identity) the basal strains from eastern Tanzania.

Rice is a relatively new crop in Uganda. It was introduced on a large scale in the 1960s and is now widely grown in many parts of the country, especially in the eastern and northern regions. To meet the increasing demand for rice, Uganda imports about USD 100 million worth of rice every year. The presence of RYMV will not be good news for those making efforts to increase rice production in Uganda, including expansions into the upland areas.

Map: Uganda: <http://go.hrw.com/atlas/norm_htm/uganda.htm>
Pictures:
<http://www.dgpc.org/ressources_humaines/images_fiches_equipes/riz_rymv.jpg>
Links:
<http://agrifor.ac.uk/browse/cabi/433fa073ba77ab13ce8a14a2367a8cb9.html>
<http://www.warda.org/publications/AR2000/F3.pdf>
<http://image.fs.uidaho.edu/vide/descr697.htm>
<http://www.iita.org/info/virology/pdf_files/1-17.pdf>
<http://library.wur.nl/wda/dissertations/dis3747.pdf>
<http://www.usaid.gov/stories/uganda/fp_uganda_rice.html>
<http://www.warda.org/newsletter/no percent205/nericas percent20flying.htm>
<http://www.warda.org/publications/brochure/uganda.pdf> - Mod.JAD]
 

[see also in the archive:
2001
---
Rice yellow mottle virus, rice - Africa (Central) 20010806.1857]