Narcissus mosaic virus (NMV) is a member of the genus Potexvirus (family Alphaflexiviridae). It was first described in Britain from Narcissus (family Amaryllidaceae) in 1966 (Brunt 1966). In 1989, the type isolate of NMV from The Netherlands was one of the first plant virus genomes to be fully sequenced (GenBank accession D13747) (Zuidema et al. 1989). Later, it was described from New Zealand (Clark and Guy 2000). In 2001 a partial genome sequence (AJ270988) from the Netherlands was released, and in 2003 another complete genome from New Zealand became available (AY225449). Most records of NMV are from narcissus, but it is recorded to naturally infect Nerine and Hippeastrum, both of which are also members of the family Amaryllidaceae (Koenig et al. 1973), Crocus (Iridaceae) (Miglino et al. 2005), Lilium (Liliaceae) (Bellardi et al. 1988), and it is recorded as transmissible to a number of experimental host plant species including Nicotiana benthamiana and N. clevelandii (Solanaceae), Chenopodium amaranticolor, C. quinoa, and Gomphrena globosa (Amaranthaceae) (Brunt et al. 1996; Zuidema et al. 1989).

Here we report the detection and sequencing of the complete genome of an isolate of NMV infecting Iris xiphium Desf. cv Telstar Blue (Spanish Iris, Dutch Iris) (Iridaceae) in Australia. An iris bulb was purchased in 2013 from a retail hardware store in Perth, Western Australia, and grown within an insect-free greenhouse. The leaves and spathe displayed mild streaking patterns resembling those of some virus infections. Leaf material from this plant was macerated in cold 0.1 M phosphate buffer (pH 7.0) and mixed with diatomaceous earth before manually applying the mixture to five seedling plants each of Nicotiana benthamiana (accession RA-4), N. umbratica (accession We-1), Chenopodium amaranticolor and Gomphrena globosa. The same number of plants were mock-inoculated with buffer and diatomaceous earth. Chlorotic local lesions appeared on inoculated leaves of five C. amaranticolor plants within 7 days of inoculation. On G. globosa, faint pink spots appeared on inoculated leaves of 3/5 plants inoculated after 12 days. Symptoms of systemic infection in five plants each of N. benthamiana and N. umbratica were mild mosaic and slight leaf distortion on uninoculated emerging leaves 12–21 days after inoculation. Mock-inoculated plants did not display these symptoms. Interestingly, Zhang et al. (Zhang et al. 2013) reported that N. benthamiana plants displayed very mild symptoms of systemic infection with a strain of NMV from New Zealand (12), whereas the Australian strain described here appears to induce somewhat stronger symptoms on this host.

Previously we used a high-throughput sequencing approach to identify isolates of Ornithogalum mosaic virus, Iris mild mosaic virus, and Japanese iris necrotic ring virus infecting Iris species in Australia (Wylie et al. 2012a, b), and in this case a similar procedure was followed. Briefly, total RNA was extracted from a symptomatic leaf of the same plant used to inoculate experimental host plants (above), and cDNA was synthesized using random primers before library preparation. High-throughput sequencing was done on a Roche GS Junior machine. Adaptor sequences were removed and sequence reads were edited where necessary before contigs were assembled de novo using CLC Genomics workbench software v6.0.1. Blastn and Blastx analysis revealed a sequence of 6,957 nucleotides (nt) that shared 97 % nt identity across its complete genome with those of the Dutch (6,955 nt) and New Zealand (6,956 nt) isolates of NMV, confirming its identity as an isolate of Narcissus mosaic virus. Mean length of sequence reads corresponding to the NMV genome was 451 nt, with a range of 200–801 nt (reads of less than 200 nt were eliminated from the analysis). Mean sequence coverage over the virus genome was 17-fold.

The new isolate was designated NMV-SW13-Iris. Like other NMV isolates, the NMV-SW13-Iris genome is predicted to encode a replicase with a mass calculated to be 184.8 kDa, a triple gene block involved in viral movement consisting of three proteins of 25.9 kDa, 12.8 kDa, and 11.1 kDa translated from overlapping reading frames, a coat protein (CP) of 24.4 kDa, and a protein of unknown function of 10.1 kDa expressed from within the CP gene in the +1 reading frame. The nucleotide sequence of the NMV-SW13-Iris genome was granted Genbank accession KF752593. Only one RNA virus, NMV, was detected in the symptomatic plant tested.

This virus was previously described infecting members of at least five monocotyledonous plant genera representing three families. Although NMV has been identified in Crocus, a genus in the family Iridaceae, the significance of this discovery is that NMV also naturally infects at least one species within its sister genus Iris. The presence of NMV in Australia has not previously been reported. This finding has implications for the production of healthy iris plants by the floriculture and horticulture industries, in addition to potential biosecurity implications for the international trade in iris bulbs and flowers. A range of viruses infects Iris, a genus that is generally clonally propagated through bulbs and tubers. Vegetatively propagated plants are susceptible to an accumulation of viruses over (vegetative) generations, and some species, such as garlic (Allium sativum), Hippeastrum and Narcissus species may be simultaneously infected with numerous viruses (Wylie et al. 2010, 2011; Wylie and Jones 2012). Thus, it will not be surprising if future studies of other species of Iris reveal the presence of NMV.