Five viruses causing colour-breaking of tulip flowers were isolated from tulips and lilies. Tulip-breaking virus (TBV), tulip top-breaking virus (TTBV), tulip bandbreaking virus, Rembrandt tulip-breaking virus and lily mottle virus were all characterized as potyviruses by serology and potyvirus-specific PCR. Sequence analysis of amplified DNA fragments spanning a conserved area of the coat protein cistron ofpotyviruses was performed in order to classify the isolates as distinct viruses or strains. It appears that all tulip-breaking viruses are distinct viruses and TTBV was found to be strain-related to turnip mosaic virus.

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Potyviruses (genus Potyvirus, family Potyviridae) are transmitted by aphids in a non-persistent manner and cause significant losses in many crops including bulbous ornamentals. Host range, symptoms, physical and biochemical properties of many potyviruses in bulbous ornamentals are reported, but, especially for viruses infecting ornamentals of minor economical importance, sequence data are still lacking. We used molecular techniques for the identification, characterization and detection of these viruses. Leaf material of several ornamental crops showing viruslike symptoms were tested in indirect ELISA, using monoclonal antibodies specific for potyviruses. Generic potyvirus primers were used in an RT-PCR to amplify the 3' terminal region of these viruses. The fragments encode the viral coat protein (CP) gene and comprise the 3'-untranslated region (3'-UTR). Nucleotide sequences of the obtained fragments were determined and compared with potyvirus sequences present in the NCBI database using the BLAST algorithm. We have characterized