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In dahlia visual selection on tomato spotted wilt virus (TSWV) is only possible to a limited extent. The unequal distribution of the virus in various plant parts during the growing and storage period caused problems in the development of a reliable test protocol. A serological test on tubers appeared to be the best: the tubers have to be stored for at least 1 month at 9°C and samples have to consist of at least three roots per tuber. 40-90% of the cuttings from TSWV-infected dahlia tubers appeared to be infected. Symptoms of TSWV in both gladiolus and iris cannot be distinguished from those caused by Impatiens necrotic spot virus (INSV). In iris a third (putative) tospovirus was detected, which is called iris yellow spot virus. In progeny-plants from infected iris and gladiolus no tospoviruses were detected. In Hippeastrum, Amaryllis and Nerine TSWV was detected in symptom-bearing leaves and also in the tunics connected with these leaves, but less frequent in other parts of the bulbs. This might explain the curing of the main bulbs after some years and the limited transmission of TSWV to the daughter bulbs.

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 virus-like 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 some potyviruses previously accepted by the International Committee on Taxonomy of Viruses (ICTV), including Freesia mosaic virus (FreMV), Gloriosa stripe mosaic virus (GSMV), Hippeastrum mosaic virus (HiMV), Hyacinth mosaic virus (HyaMV), Iris mild mosaic virus (IMMV) and Nerine yellow stripe virus (NeYSV). Additionally, the identities of other potyviruses infecting ornamentals such as Anemone, Galtonia, Muscari, Ornithogalum, Allium, Stenomesson and Veltheimia have been determined. These viruses, however, have not yet been reported by the ICTV. The virus-specific sequence information generated in this research project can subsequently be used to develop PCR-based detection methods.

The coat protein (CP) genes and flanking regions of three alstroemeria-infecting cucumber mosaic virus isolates (CMV-ALS), denoted ALS-LBO, ALS-IPO, and ALS-NAK, were cloned and their nucleotide sequence determined and compared at both nucleic acid and deduced protein level with the published sequences of CMV RNA 3. The sequences of these isolates showed more than 95% nucleotide and peptide sequence homology to each other and to other members of subgroup II CMV. Strikingly, an additional sequence of 218 nt was found in the central region of the 3’-non-translated region (NTR) of RNA 3 of two out of three isolates. The additional sequence appeared to have arisen from RNAs 1 or 2. A subgroup-specific DIG-labeled probe has been developed from this additional sequence and applied to detect subgroup II CMV strains in dot blot hybridization and to differentiate the Alstroemeria isolates containing additional sequences in Northern blot hybridization.

Mixed infections of potyviruses and other viruses occur very frequently in Narcissus. Isolation and characterization of individual potyviruses from Narcissus has partially failed sofar, because other host plants have not been found. In the Netherlands, three different potyviruses from Narcissus were distinguished on the basis of symptomology, viz. narcissus yellow stripe virus, narcissus silver streak virus and narcissus late season yellows virus. We have applied general PCR on various Narcissus samples to identify these viruses at the molecular level and to establish their relationships by sequence analysis of parts of their coat protein cistrons. We conclude that at least three different potyviruses occur in Dutch stocks of Narcissus and that narcissus silver streak virus is identical to narcissus late season yellows virus. Of the other two potyviruses, one occurred in N. tazetta and is probably identical to the narcissus degeneration virus described in England. A third potyvirus was detected together with NLSYV in a sample with symptoms of 'yellow stripe'.

Detection of iris severe mosaic virus (ISMV) in ISMV-infected iris bulbs during storage, by either ELISA or electron microscopy has been problematic. We have applied different storage-temperature treatments and a cutting method as possible procedures to enhance ISMV detection in stored iris bulbs cv. Professor Blaauw. While at lifting ISMV could not be detected in the bulbs, gradually the virus became detectable in time when bulbs were stored at about 17°C. Better results were obtained when the cutting method was employed. Using ELISA, a 100 ␜core was obtained for infected bulbs that were cut 1 month prior to testing. The virus could be detected only in tissue adjacent to the cut surface. These results offer good prospects for the development of a reliable detection method for ISMV in iris bulbs.