PHYTO MEDIZIN Mitteilungen der Deutschen ... - Die DPG

The spread of Rice yellow mottle virus in irrigated rice crops
S Sarra 1,2 and D Peters 2; 1 Institut d’Economie Rurale, Projet Riz Irrigué, Niono, Mali;
,2 Laboratory of Virology, Wageningen University
Rice yellow mottle virus (RYMV), a sobemovirus, is endemic in Africa, south
of the Sahara, and occurs mainly in irrigated rice ecosystems. Infected plants
give yellow or orange discoloured rice leaves, a delay in plant growth and
reduced tillering. These symptoms result in lower yields, but early infected
plants give the highest losses as they fail to set fruit. RYMV is primarily
known as a beetle-transmitted virus. A scattered distribution of infected
plants and the occurrence of small infected spots might be the result of
RYMV spread by beetles. However, various infection patterns can with difficulty
be explained by beetle transmission. Small infected spots occur next to
field-wide spots (20 m or more in diameter). Completely infected crops are
found next to completely healthy crops. Infected plants can be found on untided-land
along roadsides, levees and at corners. Severe infections can occur
in parcels in which cows have been housed for the night in the contra-season.
These observations stimulated us to search for other mechanism by which
RYMV could spread in the field. Transplantation of seedbeds with a limited
infection resulted in a drastic increase of infected plants in the field. This
number increased again sharply 3 to 4 weeks after transplantation due to
wind-mediated leaf contact and root-released virus from infected plants as
shown in field and greenhouse experiments. Weeding, application of fertilizers
may also enhance the number of infected plants. Some infections are
caused by cows and donkeys occasionally fouraging on rice, and by grass rats
gnawing plant on tided land. Mowing an infected crop, and fouraging stubble
fields enhance the inoculum which can infect the next seedbed by virus released
from infected plants when plowed down and other mechanisms such
as beetles and rats. Some severe seeded infections can occur when frequented
by cows. The spread and epidemiology of RYMV as deduced from our results
will diagrammatically be presented.
Identification of viruses in ornamental Allium species and control strategies
KTK Pham, MEC Lemmers, PJ van Leeuwen, VP Bijman and AFLM Derks; Applied
Plant Research, section Flowerbulbs, Lisse
In Allium giganteum, the most important ornamental onion grown in the
Netherlands, a virus disease occurs showing symptoms of light green to yellow
stripes on the leaves, a smaller inflorescence and/or a twisted flower
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