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Title: Detection of mixed virus population in freesea plants with necrotic disease

item VAIRA, ANNA MARIA - National Research Council - Italy
item VALLINO, MARTA - National Research Council - Italy
item LENZI, RICCARDO - National Research Council - Italy
item MASENGA, VERA - National Research Council - Italy
item LISA, VITTORIA - National Research Council - Italy
item CONSTATINI, ANTONIO - National Research Council - Italy
item SALVI, DAVIDE - Studio Ferrari Salvi
item CARRA, ANDREA - National Research Council - Italy
item Hammond, John

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2014
Publication Date: 2/17/2015
Citation: Vaira, A., Vallino, M., Lenzi, R., Masenga, V., Lisa, V., Constatini, A., Salvi, D., Carra, A., Hammond, J. 2015. Detection of mixed virus population in freesea plants with necrotic disease. Acta Horticulturae. 1072:173-178.

Interpretive Summary: A disease causing brown necrotic spotting and streaking on leaves of freesia grown commercially for flower production has been known for at least forty years. The causal agent of ‘Freesia leaf necrosis’ disease is presumed to be one or more viruses, transmitted by a soil-borne fungal vector, but the specific virus or combination of viruses has not been definitively identified. Freesia plants showing symptoms of ‘Freesia leaf necrosis’ were collected from commercial nurseries in Liguria, northern Italy, and groups of plants subjected to analysis for the presence of viruses. An ophiovirus previously identified as Freesia sneak virus was detected in all groups of plants showing leaf necrosis. Electron microscopy of partial purifications from freesia leaves revealed the presence of four types of virus-like particles, consistent with a) the ophivirus Freesia sneak virus; b) a potyvirus; c) a varicosavirus; and d) a tenuivirus-like particle. Serological testing of virus preparations from freesia with an antiserum raised against a soil-borne tenuivirus-like agent (recently described in Japan, from tulips affected by tulip streak disease) revealed reaction with an approximately 30 kilodalton protein related to a similarly-sized protein of the Japanese Tulip streak virus, indicating the presence of a related virus in freesia with ‘Freesia leaf necrosis’. Detection of this previously unknown virus in freesia will facilitate further work to identify the causal agents of ‘Freesia leaf necrosis’ and future control of this disease, to the benefit of plant pathologists and plant disease clinics. An ability to detect and exclude infected plants from bulb propagation will eventually benefit freesia growers by making it possible to select healthy growing material for flower production.

Technical Abstract: Necrotic disorder of freesia (Freesia refracta hyb., Family Iridaceae) was first described in The Netherlands before 1970. In subsequent years, the disorder was widely reported in other European countries and more recently also in the United States and in New Zealand. The presence of the Ophiovirus Freesia sneak virus (FreSV) has been widely associated with the necrotic disease but some uncertainty remains. Freesia leaves showing necrotic disease were used to purify Ophiovirus and the product obtained was analyzed. Several differently shaped virus particles were visualized by TEM, and a new virus-like agent with a ca. 30kDa coat protein was detected by western blotting. Previously uncharacterized viruses, possibly transmitted by the same vector, might also play a role in the disease, at least in mixed infections, thereby complicating the search for the necrotic disease causal agent.