HVX Update: August 2007
by Cynthia Wilhoite, VP Genus Hosta, Indianapolis, Indiana
The American Hosta Society is proud to announce it has successfully completed the initial phase of the Hosta Virus X (HVX) research project. We have raised the first installment of $20,000 and signed an agreement with the University of Minnesota for the two-year project. Presently our plants are being grown in the University greenhouse, with testing to start shortly.
The research project was designed to discover, in an empirical manner, what we do not know about HVX. To do that, we needed a basis of understanding about what we do know about HVX. The American Hosta Society and Dr. Benham E.L. Lockhart, who is heading up the research, agreed upon the following tenets about what we know and what we need to know.
What we know:
• No chemical treatment is successful.
• HVX is spread by non-lethal contact and damage to epidermal cells.
• It is spread by hands, tools and machinery during garden operations.
• It is spread by propagation of infected stock.
• It is not spread by insects, nematodes, seed or pollen.
• HVX must invade a plant cell to multiply.
• Disease management must come through managing transmission.
What we need to know:
• How long can leaves be asymptomatic while the virus is present? (We will test over the two-year period of the study.)
• Can HVX survive the tissue-culture process?
• Which tissue-culture labs are testing for the virus?
• How long does the virus remain viable outside the host cell, on tools, hands and machines?
• Can the virus remain viable in soil with the host removed, and for how long?
• Can the virus be spread by root-to-root contact?
• What are appropriate cleaning methods for gardeners and greenhouses?
The project was designed around these tenets. More updates will follow in future issues of the Journal.
The American Hosta Society is both pleased and proud to announce a research project to address hosta gardener’s questions about Hosta Virus X. This research project is designed to provide empirical data useful for us as hosta gardeners. Many hosta gardeners have major concerns about Hosta Virus X. This study is intended to clarify methods of transmission and understand the dynamics of Hosta Virus X spread, so that we may protect our plants and gardens. We will be reporting back the results of this study both in The Journal and on our website as they become available.
Our research project is organized around the goal of providing empirically derived information to answer the questions that many of us have about HVX. The objectives leading to this goal are divided into primary and secondary categories. Primary objectives will be:
- a. Can HVX spread from infected to healthy hostas in any of the following ways?
- On tools (e.g. pruning or cutting tools)
- On sap-contaminated hands
- From residual infected plant material in soil
- By root contact
- If HVX can be spread by any of these means, how long does the virus remain infective on contaminated tools, in soil, on hands ET?
- If HVX can be spread by any of these means, and if the virus retains infectivity, then what are the most practical cost-effective and safest methods of decontamination?
Secondary objectives will be:
- Are all HVX isolates transmissible?
- How variable is HVX?
- Is transmission of HVX related to the amount of virus present in the source plant?
- What is the most sensitive and reliable method for the detection of HVX?
The experimental approach chosen for this project is designed to provide simple and straightforward answers to each research question listed above. The details of the experiments are as follows:
- Propagation of HVX to be used as a virus source. The virus isolate will be obtained from the Hosta clausa ‘Normalis’ and will be maintained in H. ‘Honeybells’ by mechanical transmission.
- Question: Can HVX be transmitted during normal cultivation?
To determine this, experiments will be done to determine if HVX can be transmitted by mechanical contact on tools, fingers, plant debris in soil, or root contact. In each experiment twenty healthy plants of H. ‘Honeybells’ will be used. After exposure, plants will be grown in the greenhouse for up to one year and will be observed for disease symptoms and tested for presence of HVX by ELISA and RT-PCR.
- Question: If HVX can be spread during normal cultivation practices, how long does the virus remain infective on tools and in soil?
To determine this, healthy test plants of H. ‘Honeybells’ will be exposed to contaminated tools and soil at different periods.
- Question: If HVX remains infective on contaminated tools or in soil, what practical measures can be used to eliminate it?
To determine this treatment with commonly available viricidal agents such as detergent, trisodium phosphate, detergent plus sodium hydroxide (caustic soda) etc. will be tested for efficacy in eliminating viral infectivity.
- Question: Is HVX transmission dose dependent?
Because the concentration of HVX can vary widely between hosta varieties experiments will be done to determine whether the rate of virus transmission by mechanical contact differs significantly according to virus concentration in the source plant.
- Question: Are all HVX isolates transmissible?
This question arises from the observation that two viruses present in hostas, Arabis mosaic virus (ArMV) and Cucumber mosaic virus (CMV) cannot be transmitted by mechanical inoculation from the plants in which they occur. Experiments will be done to determine if a similar phenomenon might occur in the case of some HVX isolates.
- Question: Is HVX variable?
Experiments will be done to determine whether serological or genomic (nucleotide sequence) differences exist among isolates of HVX. Such differences will have a significant impact on virus detection.
- Question: What is the most sensitive and reliable method for detection of HVX.
This question is especially relevant to future attempts to eliminate HVX from hosta cultivars using in vitro propagation (tissue culture) techniques. It will be important to have assay methods capable of detecting subliminal levels of virus infection at early stages of growth following tissue culture.
The principal investigator for our research project will be Dr. Benham E. Lockhart, Professor, Department of Plant Pathology, University of Minnesota. Dr. Lockhart will be assisted by graduate student Grace Anderson. (See biographies for both.) We expect the completion of this project within two calendar years. We anticipate that the primary objectives will be completed with by the middle of year two and those outcomes will dictate the course that the secondary objectives will be completed. We will continue to update our readers both in future additions of the Journal and on our website, hosta.org
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