Soilborne wheat mosaic diseases: new viruses are being described
Soilborne wheat mosaic diseases can be caused by different viruses. The main viruses involved are soilborne wheat mosaic bymovirus and wheat spindle streak mosaic bymovirus (closely related or identical to wheat yellow mosaic bymovirus) which are transmitted by the soil-inhabiting fungus Polymyxa graminis and occur in many countries from various parts of the world.
In France, these two viruses are present, essentially in the south-east of Paris Basin, region Centre, Gard, and south of Brittany. Resistant wheat cultivars can be grown in infested areas, and so far no resistant-breaking strains have been observed. In 1999 in département of Aube, mosaic symptoms were observed on resistant cultivars (Triticum aestivum cvs. Sponsor, Charger). Electron microscopy revealed the presence of a virus, which is serologically distinct from soilborne wheat mosaic and wheat spindle streak mosaic bymoviruses. The field distribution of the disease suggested soil transmission, but so far, Polymyxa graminis was not detected in roots of infected plants. Virus vector nematodes were not found. This apparently new virus has tentatively been called Aubiane wheat mosaic virus.
The authors noted that other new wheat mosaic viruses are being found in other countries. They mentioned the occurrence of a virus called soilborne rye mosaic virus in Germany, which is transmitted by P. graminis and of a unnamed virus found in England. Concerning the latter, Clover et al. (1999) explained that an unknown disease of wheat has been observed on winter wheat (cv. Riband) in a crop in Bedfordshire in England, since 1995. A virus was found to be associated with diseased plants. It is morphologically similar to soilborne wheat mosaic bymovirus but serologically distinct. This new virus is seed-transmitted and its distribution pattern in the field suggested soil transmission but vectors are not known.
Finally, it can be recalled that a new soilborne virus has also been described in China and called wheat China mosaic virus (EPPO Alert List).
Sources
Clover, G.R.G; Hugo, S.A.; Harju, V.A.; Wright, D.M.; Henry, C.M. (1999) Preliminary investigations of an uncharacterized virus of winter wheat (Triticum aestivum L.) in England.
Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz, 106(3), 275-283 (abstract).
Hariri, D.; Fouchard, M.; Gelie, B.; Lapierre, H. (1999) Mosaïques sur blé: mise en évidence d'un nouveau virus.
Phytoma - La Défense des Végétaux, no. 519, 21-22.