Detection of infectious Brome mosaic virus in irrigation ditches and draining strands in Poland

Environmental waters, e.g. rivers, lakes and irrigation water, are a good source of many plant viruses. The pathogens can infect plants getting through damaged root hairs or small wounds that appear during plant growth. First results demonstrated common incidence of Tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV) in water samples collected from irrigation ditches and drainage canals surrounding fields in Southern Greater Poland. Principal objective of this work was to examine if environmental water might be the source of viruses infective to cereals. The investigation was focused on mechanically transmitted pathogens. Virus identification was performed by biological, electron microscopic, serological and molecular methods. Preliminary assays demonstrated Brome mosaic virus (BMV) infections in symptomatic plants inoculated with 9 out of the 17 tested concentrated water samples. The final identification was confirmed by molecular methods for selected isolates named: BMV-Ch1, -DBS, -N, -R and -S. Partial coding sequences of polymerase 1a (RNA1) and 2a (RNA2) and complete nucleotide sequence of coat protein (CP) gene (RNA3) of each BMV isolate were determined and compared with corresponding sequences of other known BMV isolates. Results confirmed the highest amino acid sequence homology in the fragment of polymerase 2a (99.2% – 100%) and the most divergence in CP (96.2% - 100%). This is the first report on the detection of an infective cereal virus in aqueous environment.