sion and concern in many hosta-growing groups. An article in May of this year, by Mike Bryan of the Michigan Department of Agriculture, reported their inspectors found hosta virus X in record-high numbers in sales lots. We have received several inquiries at the Plant Clinic, asking what symptoms to watch for, how to positively identify the virus, and how to control the disease. |
Plant viruses are grouped according to physical features, including presence of either DNA or RNA, number of nucleic acid strains, type of replication, and other features such as particle shape. Hosta virus X is categorized as a potexvirus. The symptoms of hosta virus X vary with the hosta cultivar, making it difficult to identify by symptoms alone in the field. Symptoms may include severe mosaic, chlorotic spotting, interveinal chlorosis, deformed growth, stunting, and necrotic tissue as leaves dry out. Color breaking may occur in flowers. A recent positive hosta virus X sample at the U of I Plant Clinic (confirmed by AGDIA ELISA) exhibited leaves that were thickened, slightly distorted, showing severe mosaic and some light spotting. Hosta virus X symptoms may be mild or severe, depending on the cultivar. Therefore, a plant could be infected but free of symptoms, thereby serving as a source of virus in the planting. In reports by Currier and Lockhart (researchers in Minnesota), systemic symptoms did not occur on new leaves for 4 to 5 weeks after inoculation.
There are other virus diseases reported on hosta, including tomato ringspot, impatiens necrotic spot, and arabis mosaic virus. Symptoms of many viruses are similar, and the specific disease cannot always be discerned by symptoms alone. Virus particles cannot be seen with a compound microscope nor cultured in a lab. Sometimes virus particles can be seen with an electron microscope used to observe infected plant sap. Positive identification can be attained by ELISA (enzyme linked immunosorbant assay) testing. Although ELISA tests can be done by many labs, the test requires having specific antibodies for each virus tested. When a hosta virus suspect is sent to a lab, specific virus tests or a screen can be requested. Screens include all the more common viruses for which antibodies are available. Screens are more expensive because they involve multiple tests done at once.
As hostas have grown in popularity, so have their reproduction and sales. Virus diseases such as hosta virus X can be spread mechanically through infected sap, so vegetative reproduction is an easy means of transmitting the virus. The virus is known to spread by vegetative propagation and infected sap, but there is no known insect vector. With more money in the hosta business, additional resources will be used on hosta virus research.
How do we manage this disease? First, do not purchase hosta cultivars that appear out of character for the cultivar. Do not propagate or share such oddities. Any virus-infected plants in the planting should be removed and destroyed. If you are splitting hostas or otherwise trimming plants, keep in mind that you could be transmitting a virus. Disinfect cutting tools between plants. Become familiar with hosta virus symptoms. Images of hosta virus X can be found at the Michigan State site, http://www.ipm.msu.edu/CAT05_land/L05-13-05hosta.htm, and the AGDIA site, http://www.agdia.com/cgi_bin/slideshow.cgi. You can also find more information on the Internet by searching under hosta virus X.